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Darwin and Modern Science
by A.C. Seward
September, 1999 [Etext #1909]
Project Gutenberg Etext Darwin and Modern Science, by A C Seward
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DARWIN AND MODERN SCIENCE
ESSAYS IN COMMEMORATION OF THE CENTENARY OF THE BIRTH OF CHARLES DARWIN AND
OF THE FIFTIETH ANNIVERSARY OF THE PUBLICATION OF "THE ORIGIN OF SPECIES"
BY
A.C. SEWARD
"My success as a man of science, whatever this may have amounted to, has
been determined, as far as I can judge, by complex and diversified mental
qualities and conditions. Of these, the most important have been--the love
of science--unbounded patience in long reflecting over any subject--
industry in observing and collecting facts--and a fair share of invention
as well as of common sense. With such moderate abilities as I possess, it
is truly surprising that I should have influenced to a considerable extent
the belief of scientific men on some important points."
Autobiography (1881); "The Life and Letters of Charles Darwin", Vol. 1.
page 107.
PREFACE
At the suggestion of the Cambridge Philosophical Society, the Syndics of
the University Press decided in March, 1908, to arrange for the publication
of a series of Essays in commemoration of the Centenary of the birth of
Charles Darwin and of the Fiftieth anniversary of the publication of "The
Origin of Species". The preliminary arrangements were made by a committee
consisting of the following representatives of the Council of the
Philosophical Society and of the Press Syndicate: Dr H.K. Anderson, Prof.
Bateson, Mr Francis Darwin, Dr Hobson, Dr Marr, Prof. Sedgwick, Mr David
Sharp, Mr Shipley, Prof. Sorley, Prof. Seward. In the course of the
preparation of the volume, the original scheme and list of authors have
been modified: a few of those invited to contribute essays were, for
various reasons, unable to do so, and some alterations have been made in
the titles of articles. For the selection of authors and for the choice of
subjects, the committee are mainly responsible, but for such share of the
work in the preparation of the volume as usually falls to the lot of an
editor I accept full responsibility.
Authors were asked to address themselves primarily to the educated layman
rather than to the expert. It was hoped that the publication of the essays
would serve the double purpose of illustrating the far-reaching influence
of Darwin's work on the progress of knowledge and the present attitude of
original investigators and thinkers towards the views embodied in Darwin's
works.
In regard to the interpretation of a passage in "The Origin of Species"
quoted by Hugo de Vries, it seemed advisable to add an editorial footnote;
but, with this exception, I have not felt it necessary to record any
opinion on views stated in the essays.
In reading the essays in proof I have availed myself freely of the willing
assistance of several Cambridge friends, among whom I wish more especially
to thank Mr Francis Darwin for the active interest he has taken in the
preparation of the volume. Mrs J.A. Thomson kindly undertook the
translation of the essays by Prof. Weismann and Prof. Schwalbe; Mrs James
Ward was good enough to assist me by translating Prof. Bougle's article on
Sociology, and to Mr McCabe I am indebted for the translation of the essay
by Prof. Haeckel. For the translation of the botanical articles by Prof.
Goebel, Prof. Klebs and Prof. Strasburger, I am responsible; in the
revision of the translation of Prof. Strasburger's essay Madame Errera of
Brussels rendered valuable help. Mr Wright, the Secretary of the Press
Syndicate, and Mr Waller, the Assistant Secretary, have cordially
cooperated with me in my editorial work; nor can I omit to thank the
readers of the University Press for keeping watchful eyes on my
shortcomings in the correction of proofs.
The two portraits of Darwin are reproduced by permission of Messrs Maull
and Fox and Messrs Elliott and Fry. The photogravure of the study at Down
is reproduced from an etching by Mr Axel Haig, lent by Mr Francis Darwin;
the coloured plate illustrating Prof. Weismann's essay was originally
published by him in his "Vortrage uber Descendenztheorie" which afterwards
appeared (1904) in English under the title "The Evolution Theory". Copies
of this plate were supplied by Messrs Fischer of Jena.
The Syndics of the University Press have agreed, in the event of this
volume being a financial success, to hand over the profits to a University
fund for the endowment of biological research.
It is clearly impossible to express adequately in a single volume of Essays
the influence of Darwin's contributions to knowledge on the subsequent
progress of scientific inquiry. As Huxley said in 1885: "Whatever be the
ultimate verdict of posterity upon this or that opinion which Mr Darwin has
propounded; whatever adumbrations or anticipations of his doctrines may be
found in the writings of his predecessors; the broad fact remains that,
since the publication and by reason of the publication of "The Origin of
Species" the fundamental conceptions and the aims of the students of living
Nature have been completely changed...But the impulse thus given to
scientific thought rapidly spread beyond the ordinarily recognised limits
of Biology. Psychology, Ethics, Cosmology were stirred to their
foundations, and 'The Origin of Species' proved itself to be the fixed
point which the general doctrine needed in order to move the world."
In the contributions to this Memorial Volume, some of the authors have more
especially concerned themselves with the results achieved by Darwin's own
work, while others pass in review the progress of research on lines which,
though unknown or but little followed in his day, are the direct outcome of
his work.
The divergence of views among biologists in regard to the origin of species
and as to the most promising directions in which to seek for truth is
illustrated by the different opinions of contributors. Whether Darwin's
views on the modus operandi of evolutionary forces receive further
confirmation in the future, or whether they are materially modified, in no
way affects the truth of the statement that, by employing his life "in
adding a little to Natural Science," he revolutionised the world of
thought. Darwin wrote in 1872 to Alfred Russel Wallace: "How grand is the
onward rush of science: it is enough to console us for the many errors
which we have committed, and for our efforts being overlaid and forgotten
in the mass of new facts and new views which are daily turning up." In the
onward rush, it is easy for students convinced of the correctness of their
own views and equally convinced of the falsity of those of their fellow-
workers to forget the lessons of Darwin's life. In his autobiographical
sketch, he tells us, "I have steadily endeavoured to keep my mind free so
as to give up any hypothesis, however much beloved...as soon as facts are
shown to be opposed to it." Writing to Mr J. Scott, he says, "It is a
golden rule, which I try to follow, to put every fact which is opposed to
one's preconceived opinion in the strongest light. Absolute accuracy is
the hardest merit to attain, and the highest merit. Any deviation is
ruin."
He acted strictly in accordance with his determination expressed in a
letter to Lyell in 1844, "I shall keep out of controversy, and just give my
own facts." As was said of another son of Cambridge, Sir George Stokes,
"He would no more have thought of disputing about priority, or the
authorship of an idea, than of writing a report for a company promoter."
Darwin's life affords a striking confirmation of the truth of Hazlitt's
aphorism, "Where the pursuit of truth has been the habitual study of any
man's life, the love of truth will be his ruling passion." Great as was
the intellect of Darwin, his character, as Huxley wrote, was even nobler
than his intellect.
A.C. SEWARD.
Botany School, Cambridge,
March 20, 1909.
CONTENTS
I. INTRODUCTORY LETTER TO THE EDITOR from SIR JOSEPH DALTON HOOKER, O.M.
II. DARWIN'S PREDECESSORS:
J. ARTHUR THOMSON, Professor of Natural History in the University of
Aberdeen.
III. THE SELECTION THEORY:
AUGUST WEISMANN, Professor of Zoology in the University of Freiburg
(Baden).
IV. VARIATION:
HUGO DE VRIES, Professor of Botany in the University of Amsterdam.
V. HEREDITY AND VARIATION IN MODERN LIGHTS:
W. BATESON, Professor of Biology in the University of Cambridge.
VI. THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY:
EDUARD STRASBURGER, Professor of Botany in the University of Bonn.
VII. "THE DESCENT OF MAN":
G. SCHWALBE, Professor of Anatomy in the University of Strassburg.
VIII. CHARLES DARWIN AS AN ANTHROPOLOGIST:
ERNST HAECKEL, Professor of Zoology in the University of Jena.
IX. SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN:
J.G. FRAZER, Fellow of Trinity College, Cambridge.
X. THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY:
- SEDGWICK, Professor of Zoology and Comparative Anatomy in the
University of Cambridge.
XI. THE PALAEONTOLOGICAL RECORD. I. ANIMALS:
W.B. SCOTT, Professor of Geology in the University of Princeton.
XII. THE PALAEONTOLOGICAL RECORD. II. PLANTS:
D.H. SCOTT, President of the Linnean Society of London.
XIII. THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS:
GEORG KLEBS, Professor of Botany in the University of Heidelberg.
XIV. EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS:
JACQUES LOEB, Professor of Physiology in the University of California.
XV. THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE:
E.B. POULTON, Hope Professor of Zoology in the University of Oxford.
XVI. GEOGRAPHICAL DISTRIBUTION OF PLANTS:
SIR WILLIAM THISELTON-DYER.
XVII. GEOGRAPHICAL DISTRIBUTION OF ANIMALS:
HANS GADOW, Strickland Curator and Lecturer on Zoology in the University
of Cambridge.
XVIII. DARWIN AND GEOLOGY:
J.W. JUDD.
XIX. DARWIN'S WORK ON THE MOVEMENTS OF PLANTS:
FRANCIS DARWIN.
XX. THE BIOLOGY OF FLOWERS:
K. GOEBEL, Professor of Botany in the University of Munich.
XXI. MENTAL FACTORS IN EVOLUTION:
C. LLOYD MORGAN, Professor of Psychology at University College, Bristol.
XXII. THE INFLUENCE OF THE CONCEPTION OF EVOLUTION ON MODERN PHILOSOPHY:
H. HOFFDING, Professor of Philosophy in the University of Copenhagen.
XXIII. DARWINISM AND SOCIOLOGY:
C. BOUGLE, Professor of Social Philosophy in the University of Toulouse,
and Deputy-Professor at the Sorbonne, Paris.
XXIV. THE INFLUENCE OF DARWIN UPON RELIGIOUS THOUGHT:
REV. P.N. WAGGETT.
XXV. THE INFLUENCE OF DARWINISM ON THE STUDY OF RELIGIONS:
JANE ELLEN HARRISON, Staff-Lecturer and sometime Fellow of Newnham
College, Cambridge.
XXVI. EVOLUTION AND THE SCIENCE OF LANGUAGE:
P. GILES, Reader in Comparative Philology in the University of Cambridge.
XXVII. DARWINISM AND HISTORY:
J.B. BURY, Regius Professor of Modern History in the University of
Cambridge.
XXVIII. THE GENESIS OF DOUBLE STARS:
SIR GEORGE DARWIN, Plumian Professor of Astronomy and Experimental
Philosophy in the University of Cambridge.
XXIX. THE EVOLUTION OF MATTER:
W.C.D. WHETHAM, Fellow of Trinity College, Cambridge.
INDEX.
DATES OF THE PUBLICATION Of CHARLES DARWIN'S BOOKS AND OF THE PRINCIPAL
EVENTS IN HIS LIFE
1809:
Charles Darwin born at Shrewsbury, February 12.
1817:
"At 8 1/2 years old I went to Mr Case's school." (A day-school at
Shrewsbury kept by the Rev G. Case, Minister of the Unitarian Chapel.)
1818:
"I was at school at Shrewsbury under a great scholar, Dr Butler; I learnt
absolutely nothing, except by amusing myself by reading and experimenting
in Chemistry."
1825:
"As I was doing no good at school, my father wisely took me away at a
rather earlier age than usual, and sent me (Oct. 1825) to Edinburgh
University with my brother, where I stayed for two years."
1828:
Began residence at Christ's College, Cambridge.
"I went to Cambridge early in the year 1828, and soon became acquainted
with Professor Henslow...Nothing could be more simple, cordial and
unpretending than the encouragement which he afforded to all young
naturalists."
"During the three years which I spent at Cambridge my time was wasted, as
far as the academical studies were concerned, as completely as at Edinburgh
and at school."
"In order to pass the B.A. Examination, it was...necessary to get up
Paley's 'Evidences of Christianity,' and his 'Moral Philosophy'...The
careful study of these works, without attempting to learn any part by rote,
was the only part of the academical course which...was of the least use to
me in the education of my mind."
1831:
Passed the examination for the B.A. degree in January and kept the
following terms.
"I gained a good place among the oi polloi or crowd of men who do not go in
for honours."
"I am very busy,...and see a great deal of Henslow, whom I do not know
whether I love or respect most."
Dec. 27. "Sailed from England on our circumnavigation," in H.M.S.
"Beagle", a barque of 235 tons carrying 6 guns, under Capt. FitzRoy.
"There is indeed a tide in the affairs of men."
1836:
Oct. 4. "Reached Shrewsbury after absence of 5 years and 2 days."
"You cannot imagine how gloriously delightful my first visit was at home;
it was worth the banishment."
Dec. 13. Went to live at Cambridge (Fitzwilliam Street).
"The only evil I found in Cambridge was its being too pleasant."
1837:
"On my return home (in the 'Beagle') in the autumn of 1836 I immediately
began to prepare my journal for publication, and then saw how many facts
indicated the common descent of species...In July (1837) I opened my first
note-book for facts in relation to the Origin of Species, about which I had
long reflected, and never ceased working for the next twenty years...Had
been greatly struck from about the month of previous March on character of
South American fossils, and species on Galapagos Archipelago. These facts
(especially latter), origin of all my views."
"On March 7, 1837 I took lodgings in (36) Great Marlborough Street in
London, and remained there for nearly two years, until I was married."
1838:
"In October, that is fifteen months after I had begun my systematic
enquiry, I happened to read for amusement 'Malthus on Population,' and
being well prepared to appreciate the struggle for existence which
everywhere goes on from long-continued observation of the habits of animals
and plants, it at once struck me that under these circumstances favourable
variations would tend to be preserved, and unfavourable ones to be
destroyed. The result of this would be the formation of new species. Here
then I had at last got a theory by which to work; but I was so anxious to
avoid prejudice, that I determined not for some time to write even the
briefest sketch of it."
1839:
Married at Maer (Staffordshire) to his first cousin Emma Wedgwood, daughter
of Josiah Wedgwood.
"I marvel at my good fortune that she, so infinitely my superior in every
single moral quality, consented to be my wife. She has been my wise
adviser and cheerful comforter throughout life, which without her would
have been during a very long period a miserable one from ill-health. She
has earned the love of every soul near her" (Autobiography).
Dec. 31. "Entered 12 Upper Gower street" (now 110 Gower street, London).
"There never was so good a house for me, and I devoutly trust you (his
future wife) will approve of it equally. The little garden is worth its
weight in gold."
Published "Journal and Researches", being Vol. III. of the "Narrative of
the Surveying Voyage of H.M.S. 'Adventure' and 'Beagle'"...
Publication of the "Zoology of the Voyage of H.M.S. 'Beagle'", Part II.,
"Mammalia", by G.R. Waterhouse, with a "Notice of their habits and ranges",
by Charles Darwin.
1840:
Contributed Geological Introduction to Part I. ("Fossil Mammalia") of the
"Zoology of the Voyage of H.M.S. 'Beagle'" by Richard Owen.
1842:
"In June 1842 I first allowed myself the satisfaction of writing a very
brief abstract of my (species) theory in pencil in 35 pages; and this was
enlarged during the summer of 1844 into one of 230 pages, which I had
fairly copied out and still (1876) possess." (The first draft of "The
Origin of Species", edited by Mr Francis Darwin, will be published this
year (1909) by the Syndics of the Cambridge University Press.)
Sept. 14. Settled at the village of Down in Kent.
"I think I was never in a more perfectly quiet country."
Publication of "The Structure and Distribution of Coral Reefs"; being Part
I. of the "Geology of the Voyage of the Beagle".
1844:
Publication of "Geological Observations on the Volcanic Islands visited
during the Voyage of H.M.S. 'Beagle'"; being Part II. of the "Geology of
the Voyage of the 'Beagle'".
"I think much more highly of my book on Volcanic Islands since Mr Judd, by
far the best judge on the subject in England, has, as I hear, learnt much
from it." (Autobiography, 1876.)
1845:
Publication of the "Journal of Researches" as a separate book.
1846:
Publication of "Geological Observations on South America"; being Part III.
of the "Geology of the Voyage of the 'Beagle'".
1851:
Publication of a "Monograph of the Fossil Lepadidae" and of a "Monograph of
the sub-class Cirripedia".
"I fear the study of the Cirripedia will ever remain 'wholly unapplied,'
and yet I feel that such study is better than castle-building."
1854:
Publication of Monographs of the Balanidae and Verrucidae.
"I worked steadily on this subject for...eight years, and ultimately
published two thick volumes, describing all the known living species, and
two thin quartos on the extinct species...My work was of considerable use
to me, when I had to discuss in the "Origin of Species" the principles of a
natural classification. Nevertheless, I doubt whether the work was worth
the consumption of so much time."
"From September 1854 I devoted my whole time to arranging my huge pile of
notes, to observing, and to experimenting in relation to the transmutation
of species."
1856:
"Early in 1856 Lyell advised me to write out my views pretty fully, and I
began at once to do so on a scale three or four times as extensive as that
which was afterwards followed in my 'Origin of Species'."
1858:
Joint paper by Charles Darwin and Alfred Russel Wallace "On the Tendency of
Species to form Varieties; and on the perpetuation of Varieties and Species
by Natural Means of Selection," communicated to the Linnean Society by Sir
Charles Lyell and Sir Joseph Hooker.
"I was at first very unwilling to consent (to the communication of his MS.
to the Society) as I thought Mr Wallace might consider my doing so
unjustifiable, for I did not then know how generous and noble was his
disposition."
"July 20 to Aug. 12 at Sandown (Isle of Wight) began abstract of Species
book."
1859:
Nov. 24. Publication of "The Origin of Species" (1250 copies).
"Oh, good heavens, the relief to my head and body to banish the whole
subject from my mind!...But, alas, how frequent, how almost universal it is
in an author to persuade himself of the truth of his own dogmas. My only
hope is that I certainly see many difficulties of gigantic stature."
1860:
Publication of the second edition of the "Origin" (3000 copies).
Publication of a "Naturalist's Voyage".
1861:
Publication of the third edition of the "Origin" (2000 copies).
"I am going to write a little book...on Orchids, and to-day I hate them
worse than everything."
1862:
Publication of the book "On the various contrivances by which Orchids are
fertilised by Insects".
1865:
Read paper before the Linnean Society "On the Movements and Habits of
Climbing plants". (Published as a book in 1875.)
1866:
Publication of the fourth edition of the "Origin" (1250 copies).
1868:
"I have sent the MS. of my big book, and horridly, disgustingly big it will
be, to the printers."
Publication of the "Variation of Animals and Plants under Domestication".
"About my book, I will give you (Sir Joseph Hooker) a bit of advice. Skip
the whole of Vol. I, except the last chapter, (and that need only be
skimmed), and skip largely in the 2nd volume; and then you will say it is a
very good book."
"Towards the end of the work I give my well-abused hypothesis of
Pangenesis. An unverified hypothesis is of little or no value; but if
anyone should hereafter be led to make observations by which some such
hypothesis could be established, I shall have done good service, as an
astonishing number of isolated facts can be thus connected together and
rendered intelligible."
1869:
Publication of the fifth edition of the "Origin".
1871:
Publication of "The Descent of Man".
"Although in the 'Origin of Species' the derivation of any particular
species is never discussed, yet I thought it best, in order that no
honourable man should accuse me of concealing my views, to add that by the
work 'light would be thrown on the origin of man and his history'."
1872:
Publication of the sixth edition of the "Origin".
Publication of "The Expression of the Emotions in Man and Animals".
1874:
Publication of the second edition of "The Descent of Man".
"The new edition of the "Descent" has turned out an awful job. It took me
ten days merely to glance over letters and reviews with criticisms and new
facts. It is a devil of a job."
Publication of the second edition of "The Structure and Distribution of
Coral Reefs".
1875:
Publication of "Insectivorous Plants".
"I begin to think that every one who publishes a book is a fool."
Publication of the second edition of "Variation in Animals and Plants".
Publication of "The Movements and Habits of Climbing Plants" as a separate
book.
1876:
Wrote Autobiographical Sketch ("Life and Letters", Vol. I., Chap II.).
Publication of "The Effects of Cross and Self fertilisation".
"I now (1881) believe, however,...that I ought to have insisted more
strongly than I did on the many adaptations for self-fertilisation."
Publication of the second edition of "Observations on Volcanic Islands".
1877:
Publication of "The Different Forms of Flowers on Plants of the same
species".
"I do not suppose that I shall publish any more books...I cannot endure
being idle, but heaven knows whether I am capable of any more good work."
Publication of the second edition of the Orchid book.
1878:
Publication of the second edition of "The Effects of Cross and Self
fertilisation".
1879:
Publication of an English translation of Ernst Krause's "Erasmus Darwin",
with a notice by Charles Darwin. "I am EXTREMELY glad that you approve of
the little 'Life' of our Grandfather, for I have been repenting that I ever
undertook it, as the work was quite beyond my tether." (To Mr Francis
Galton, Nov. 14, 1879.)
1880:
Publication of "The Power of Movement in Plants".
"It has always pleased me to exalt plants in the scale of organised
beings."
Publication of the second edition of "The Different Forms of Flowers".
1881:
Wrote a continuation of the Autobiography.
Publication of "The Formation of Vegetable Mould, through the Action of
Worms".
"It is the completion of a short paper read before the Geological Society
more than forty years ago, and has revived old geological thoughts...As far
as I can judge it will be a curious little book."
1882:
Charles Darwin died at Down, April 19, and was buried in Westminster Abbey,
April 26, in the north aisle of the Nave a few feet from the grave of Sir
Isaac Newton.
"As for myself, I believe that I have acted rightly in steadily following
and devoting my life to Science. I feel no remorse from having committed
any great sin, but have often and often regretted that I have not done more
direct good to my fellow creatures."
The quotations in the above Epitome are taken from the Autobiography and
published Letters:--
"The Life and Letters of Charles Darwin", including an Autobiographical
Chapter. Edited by his son, Francis Darwin, 3 Vols., London, 1887.
"Charles Darwin": His life told in an Autobiographical Chapter, and in a
selected series of his published Letters. Edited by his son, Francis
Darwin, London, 1902.
"More Letters of Charles Darwin". A record of his work in a series of
hitherto unpublished Letters. Edited by Francis Darwin and A.C. Seward, 2
Vols., London, 1903.
I. INTRODUCTORY LETTER
FROM SIR JOSEPH DALTON HOOKER,
O.M., G.C.S.I., C.B., M.D., D.C.L., LL.D., F.R.S., ETC.
The Camp,
near Sunningdale,
January 15, 1909.
Dear Professor Seward,
The publication of a Series of Essays in Commemoration of the century of
the birth of Charles Darwin and of the fiftieth anniversary of the
publication of "The Origin of Species" is assuredly welcome and is a
subject of congratulation to all students of Science.
These Essays on the progress of Science and Philosophy as affected by
Darwin's labours have been written by men known for their ability to
discuss the problems which he so successfully worked to solve. They cannot
but prove to be of enduring value, whether for the information of the
general reader or as guides to investigators occupied with problems similar
to those which engaged the attention of Darwin.
The essayists have been fortunate in having for reference the five
published volumes of Charles Darwin's Life and Correspondence. For there
is set forth in his own words the inception in his mind of the problems,
geological, zoological and botanical, hypothetical and theoretical, which
he set himself to solve and the steps by which he proceeded to investigate
them with the view of correlating the phenomena of life with the evolution
of living things. In his letters he expressed himself in language so lucid
and so little burthened with technical terms that they may be regarded as
models for those who were asked to address themselves primarily to the
educated reader rather than to the expert.
I may add that by no one can the perusal of the Essays be more vividly
appreciated than by the writer of these lines. It was my privilege for
forty years to possess the intimate friendship of Charles Darwin and to be
his companion during many of his working hours in Study, Laboratory, and
Garden. I was the recipient of letters from him, relating mainly to the
progress of his researches, the copies of which (the originals are now in
the possession of his family) cover upwards of a thousand pages of
foolscap, each page containing, on an average, three hundred words.
That the editorship of these Essays has been entrusted to a Cambridge
Professor of Botany must be gratifying to all concerned in their production
and in their perusal, recalling as it does the fact that Charles Darwin's
instructor in scientific methods was his lifelong friend the late Rev. J.S.
Henslow at that time Professor of Botany in the University. It was owing
to his recommendation that his pupil was appointed Naturalist to H.M.S.
"Beagle", a service which Darwin himself regarded as marking the dawn of
his scientific career.
Very sincerely yours,
J.D. HOOKER.
II. DARWIN'S PREDECESSORS.
By J. ARTHUR THOMSON.
Professor of Natural History in the University of Aberdeen.
In seeking to discover Darwin's relation to his predecessors it is useful
to distinguish the various services which he rendered to the theory of
organic evolution.
(I) As everyone knows, the general idea of the Doctrine of Descent is that
the plants and animals of the present-day are the lineal descendants of
ancestors on the whole somewhat simpler, that these again are descended
from yet simpler forms, and so on backwards towards the literal "Protozoa"
and "Protophyta" about which we unfortunately know nothing. Now no one
supposes that Darwin originated this idea, which in rudiment at least is as
old as Aristotle. What Darwin did was to make it current intellectual
coin. He gave it a form that commended itself to the scientific and public
intelligence of the day, and he won wide-spread conviction by showing with
consummate skill that it was an effective formula to work with, a key which
no lock refused. In a scholarly, critical, and pre-eminently fair-minded
way, admitting difficulties and removing them, foreseeing objections and
forestalling them, he showed that the doctrine of descent supplied a modal
interpretation of how our present-day fauna and flora have come to be.
(II) In the second place, Darwin applied the evolution-idea to particular
problems, such as the descent of man, and showed what a powerful organon it
is, introducing order into masses of uncorrelated facts, interpreting
enigmas both of structure and function, both bodily and mental, and, best
of all, stimulating and guiding further investigation. But here again it
cannot be claimed that Darwin was original. The problem of the descent or
ascent of man, and other particular cases of evolution, had attracted not a
few naturalists before Darwin's day, though no one (except Herbert Spencer
in the psychological domain (1855)) had come near him in precision and
thoroughness of inquiry.
(III) In the third place, Darwin contributed largely to a knowledge of the
factors in the evolution-process, especially by his analysis of what occurs
in the case of domestic animals and cultivated plants, and by his
elaboration of the theory of Natural Selection, which Alfred Russel Wallace
independently stated at the same time, and of which there had been a few
previous suggestions of a more or less vague description. It was here that
Darwin's originality was greatest, for he revealed to naturalists the many
different forms--often very subtle--which natural selection takes, and with
the insight of a disciplined scientific imagination he realised what a
mighty engine of progress it has been and is.
(IV) As an epoch-marking contribution, not only to Aetiology but to
Natural History in the widest sense, we rank the picture which Darwin gave
to the world of the web of life, that is to say, of the inter-relations and
linkages in Nature. For the Biology of the individual--if that be not a
contradiction in terms--no idea is more fundamental than that of the
correlation of organs, but Darwin's most characteristic contribution was
not less fundamental,--it was the idea of the correlation of organisms.
This, again, was not novel; we find it in the works of naturalist like
Christian Conrad Sprengel, Gilbert White, and Alexander von Humboldt, but
the realisation of its full import was distinctively Darwinian.
AS REGARDS THE GENERAL IDEA OF ORGANIC EVOLUTION.
While it is true, as Prof. H.F. Osborn puts it, that "'Before and after
Darwin' will always be the ante et post urbem conditam of biological
history," it is also true that the general idea of organic evolution is
very ancient. In his admirable sketch "From the Greeks to Darwin"
("Columbia University Biological Series", Vol. I. New York and London,
1894. We must acknowledge our great indebtness to this fine piece of
work.), Prof. Osborn has shown that several of the ancient philosophers
looked upon Nature as a gradual development and as still in process of
change. In the suggestions of Empedocles, to take the best instance, there
were "four sparks of truth,--first, that the development of life was a
gradual process; second, that plants were evolved before animals; third,
that imperfect forms were gradually replaced (not succeeded) by perfect
forms; fourth, that the natural cause of the production of perfect forms
was the extinction of the imperfect." (Op. cit. page 41.) But the
fundamental idea of one stage giving origin to another was absent. As the
blue Aegean teemed with treasures of beauty and threw many upon its shores,
so did Nature produce like a fertile artist what had to be rejected as well
as what was able to survive, but the idea of one species emerging out of
another was not yet conceived.
Aristotle's views of Nature (See G.J. Romanes, "Aristotle as a Naturalist",
"Contemporary Review", Vol. LIX. page 275, 1891; G. Pouchet "La Biologie
Aristotelique", Paris, 1885; E. Zeller, "A History of Greek Philosophy",
London, 1881, and "Ueber die griechischen Vorganger Darwin's", "Abhandl.
Berlin Akad." 1878, pages 111-124.) seem to have been more definitely
evolutionist than those of his predecessors, in this sense, at least, that
he recognised not only an ascending scale, but a genetic series from polyp
to man and an age-long movement towards perfection. "It is due to the
resistance of matter to form that Nature can only rise by degrees from
lower to higher types." "Nature produces those things which, being
continually moved by a certain principle contained in themselves, arrive at
a certain end."
To discern the outcrop of evolution-doctrine in the long interval between
Aristotle and Bacon seems to be very difficult, and some of the instances
that have been cited strike one as forced. Epicurus and Lucretius, often
called poets of evolution, both pictured animals as arising directly out of
the earth, very much as Milton's lion long afterwards pawed its way out.
Even when we come to Bruno who wrote that "to the sound of the harp of the
Universal Apollo (the World Spirit), the lower organisms are called by
stages to higher, and the lower stages are connected by intermediate forms
with the higher," there is great room, as Prof. Osborn points out (op. cit.
page 81.), for difference of opinion as to how far he was an evolutionist
in our sense of the term.
The awakening of natural science in the sixteenth century brought the
possibility of a concrete evolution theory nearer, and in the early
seventeenth century we find evidences of a new spirit--in the embryology of
Harvey and the classifications of Ray. Besides sober naturalists there
were speculative dreamers in the sixteenth and seventeenth centuries who
had at least got beyond static formulae, but, as Professor Osborn points
out (op. cit. page 87.), "it is a very striking fact, that the basis of our
modern methods of studying the Evolution problem was established not by the
early naturalists nor by the speculative writers, but by the Philosophers."
He refers to Bacon, Descartes, Leibnitz, Hume, Kant, Lessing, Herder, and
Schelling. "They alone were upon the main track of modern thought. It is
evident that they were groping in the dark for a working theory of the
Evolution of life, and it is remarkable that they clearly perceived from
the outset that the point to which observation should be directed was not
the past but the present mutability of species, and further, that this
mutability was simply the variation of individuals on an extended scale."
Bacon seems to have been one of the first to think definitely about the
mutability of species, and he was far ahead of his age in his suggestion of
what we now call a Station of Experimental Evolution. Leibnitz discusses
in so many words how the species of animals may be changed and how
intermediate species may once have linked those that now seem
discontinuous. "All natural orders of beings present but a single
chain"..."All advances by degrees in Nature, and nothing by leaps."
Similar evolutionist statements are to be found in the works of the other
"philosophers," to whom Prof. Osborn refers, who were, indeed, more
scientific than the naturalists of their day. It must be borne in mind
that the general idea of organic evolution--that the present is the child
of the past--is in great part just the idea of human history projected upon
the natural world, differentiated by the qualification that the continuous
"Becoming" has been wrought out by forces inherent in the organisms
themselves and in their environment.
A reference to Kant (See Brock, "Die Stellung Kant's zur
Deszendenztheorie," "Biol. Centralbl." VIII. 1889, pages 641-648. Fritz
Schultze, "Kant und Darwin", Jena, 1875.) should come in historical order
after Buffon, with whose writings he was acquainted, but he seems, along
with Herder and Schelling, to be best regarded as the culmination of the
evolutionist philosophers--of those at least who interested themselves in
scientific problems. In a famous passage he speaks of "the agreement of so
many kinds of animals in a certain common plan of structure"...an "analogy
of forms" which "strengthens the supposition that they have an actual
blood-relationship, due to derivation from a common parent." He speaks of
"the great Family of creatures, for as a Family we must conceive it, if the
above-mentioned continuous and connected relationship has a real
foundation." Prof. Osborn alludes to the scientific caution which led
Kant, biology being what it was, to refuse to entertain the hope "that a
Newton may one day arise even to make the production of a blade of grass
comprehensible, according to natural laws ordained by no intention." As
Prof. Haeckel finely observes, Darwin rose up as Kant's Newton. (Mr Alfred
Russel Wallace writes: "We claim for Darwin that he is the Newton of
natural history, and that, just so surely as that the discovery and
demonstration by Newton of the law of gravitation established order in
place of chaos and laid a sure foundation for all future study of the
starry heavens, so surely has Darwin, by his discovery of the law of
natural selection and his demonstration of the great principle of the
preservation of useful variations in the struggle for life, not only thrown
a flood of light on the process of development of the whole organic world,
but also established a firm foundation for all future study of nature"
("Darwinism", London, 1889, page 9). See also Prof. Karl Pearson's
"Grammar of Science" (2nd edition), London, 1900, page 32. See Osborn, op.
cit. Page 100.))
The scientific renaissance brought a wealth of fresh impressions and some
freedom from the tyranny of tradition, and the twofold stimulus stirred the
speculative activity of a great variety of men from old Claude Duret of
Moulins, of whose weird transformism (1609) Dr Henry de Varigny
("Experimental Evolution". London, 1892. Chap. 1. page 14.) gives us a
glimpse, to Lorenz Oken (1799-1851) whose writings are such mixtures of
sense and nonsense that some regard him as a far-seeing prophet and others
as a fatuous follower of intellectual will-o'-the-wisps. Similarly, for De
Maillet, Maupertuis, Diderot, Bonnet, and others, we must agree with
Professor Osborn that they were not actually in the main Evolution
movement. Some have been included in the roll of honour on very slender
evidence, Robinet for instance, whose evolutionism seems to us extremely
dubious. (See J. Arthur Thomson, "The Science of Life". London, 1899.
Chap. XVI. "Evolution of Evolution Theory".)
The first naturalist to give a broad and concrete expression to the
evolutionist doctrine of descent was Buffon (1707-1788), but it is
interesting to recall the fact that his contemporary Linnaeus (1707-1778),
protagonist of the counter-doctrine of the fixity of species (See Carus
Sterne (Ernest Krause), "Die allgemeine Weltanschauung in ihrer
historischen Entwickelung". Stuttgart, 1889. Chapter entitled
"Bestandigkeit oder Veranderlichkeit der Naturwesen".), went the length of
admitting (in 1762) that new species might arise by intercrossing.
Buffon's position among the pioneers of the evolution-doctrine is weakened
by his habit of vacillating between his own conclusions and the orthodoxy
of the Sorbonne, but there is no doubt that he had a firm grasp of the
general idea of "l'enchainement des etres."
Erasmus Darwin (1731-1802), probably influenced by Buffon, was another firm
evolutionist, and the outline of his argument in the "Zoonomia" ("Zoonomia,
or the Laws of Organic Life", 2 vols. London, 1794; Osborn op. cit. page
145.) might serve in part at least to-day. "When we revolve in our minds
the metamorphoses of animals, as from the tadpole to the frog; secondly,
the changes produced by artificial cultivation, as in the breeds of horses,
dogs, and sheep; thirdly, the changes produced by conditions of climate and
of season, as in the sheep of warm climates being covered with hair instead
of wool, and the hares and partridges of northern climates becoming white
in winter: when, further, we observe the changes of structure produced by
habit, as seen especially in men of different occupations; or the changes
produced by artificial mutilation and prenatal influences, as in the
crossing of species and production of monsters; fourth, when we observe the
essential unity of plan in all warm-blooded animals,--we are led to
conclude that they have been alike produced from a similar living
filament"..."From thus meditating upon the minute portion of time in which
many of the above changes have been produced, would it be too bold to
imagine, in the great length of time since the earth began to exist,
perhaps millions of years before the commencement of the history of
mankind, that all warm-blooded animals have arisen from one living
filament?"..."This idea of the gradual generation of all things seems to
have been as familiar to the ancient philosophers as to the modern ones,
and to have given rise to the beautiful hieroglyphic figure of the proton
oon, or first great egg, produced by night, that is, whose origin is
involved in obscurity, and animated by Eros, that is, by Divine Love; from
whence proceeded all things which exist."
Lamarck (1744-1829) seems to have become an evolutionist independently of
Erasmus Darwin's influence, though the parallelism between them is
striking. He probably owed something to Buffon, but he developed his
theory along a different line. Whatever view be held in regard to that
theory there is no doubt that Lamarck was a thorough-going evolutionist.
Professor Haeckel speaks of the "Philosophie Zoologique" as "the first
connected and thoroughly logical exposition of the theory of descent."
(See Alpheus S. Packard, "Lamarck, the Founder of Evolution, His Life and
Work, with Translations of his writings on Organic Evolution". London,
1901.)
Besides the three old masters, as we may call them, Buffon, Erasmus Darwin,
and Lamarck, there were other quite convinced pre-Darwinian evolutionists.
The historian of the theory of descent must take account of Treviranus
whose "Biology or Philosophy of Animate Nature" is full of evolutionary
suggestions; of Etienne Geoffroy St Hilaire, who in 1830, before the French
Academy of Sciences, fought with Cuvier, the fellow-worker of his youth, an
intellectual duel on the question of descent; of Goethe, one of the
founders of morphology and the greatest poet of Evolution--who, in his
eighty-first year, heard the tidings of Geoffroy St Hilaire's defeat with
an interest which transcended the political anxieties of the time; and of
many others who had gained with more or less confidence and clearness a new
outlook on Nature. It will be remembered that Darwin refers to thirty-four
more or less evolutionist authors in his Historical Sketch, and the list
might be added to. Especially when we come near to 1858 do the numbers
increase, and one of the most remarkable, as also most independent
champions of the evolution-idea before that date was Herbert Spencer, who
not only marshalled the arguments in a very forcible way in 1852, but
applied the formula in detail in his "Principles of Psychology" in 1855.
(See Edward Clodd, "Pioneers of Evolution", London, page 161, 1897.)
It is right and proper that we should shake ourselves free from all
creationist appreciations of Darwin, and that we should recognise the
services of pre-Darwinian evolutionists who helped to make the time ripe,
yet one cannot help feeling that the citation of them is apt to suggest two
fallacies. It may suggest that Darwin simply entered into the labours of
his predecessors, whereas, as a matter of fact, he knew very little about
them till after he had been for years at work. To write, as Samuel Butler
did, "Buffon planted, Erasmus Darwin and Lamarck watered, but it was Mr
Darwin who said 'That fruit is ripe,' and shook it into his lap"...seems to
us a quite misleading version of the facts of the case. The second fallacy
which the historical citation is a little apt to suggest is that the
filiation of ideas is a simple problem. On the contrary, the history of an
idea, like the pedigree of an organism, is often very intricate, and the
evolution of the evolution-idea is bound up with the whole progress of the
world. Thus in order to interpret Darwin's clear formulation of the idea
of organic evolution and his convincing presentation of it, we have to do
more than go back to his immediate predecessors, such as Buffon, Erasmus
Darwin, and Lamarck; we have to inquire into the acceptance of evolutionary
conceptions in regard to other orders of facts, such as the earth and the
solar system (See Chapter IX. "The Genetic View of Nature" in J.T. Merz's
"History of European Thought in the Nineteenth Century", Vol. 2, Edinburgh
and London, 1903.); we have to realise how the growing success of
scientific interpretation along other lines gave confidence to those who
refused to admit that there was any domain from which science could be
excluded as a trespasser; we have to take account of the development of
philosophical thought, and even of theological and religious movements; we
should also, if we are wise enough, consider social changes. In short, we
must abandon the idea that we can understand the history of any science as
such, without reference to contemporary evolution in other departments of
activity.
While there were many evolutionists before Darwin, few of them were expert
naturalists and few were known outside a small circle; what was of much
more importance was that the genetic view of nature was insinuating itself
in regard to other than biological orders of facts, here a little and there
a little, and that the scientific spirit had ripened since the days when
Cuvier laughed Lamarck out of court. How was it that Darwin succeeded
where others had failed? Because, in the first place, he had clear
visions--"pensees de la jeunesse, executees par l'age mur"--which a
University curriculum had not made impossible, which the "Beagle" voyage
made vivid, which an unrivalled British doggedness made real--visions of
the web of life, of the fountain of change within the organism, of the
struggle for existence and its winnowing, and of the spreading genealogical
tree. Because, in the second place, he put so much grit into the
verification of his visions, putting them to the proof in an argument which
is of its kind--direct demonstration being out of the question--quite
unequalled. Because, in the third place, he broke down the opposition
which the most scientific had felt to the seductive modal formula of
evolution by bringing forward a more plausible theory of the process than
had been previously suggested. Nor can one forget, since questions of this
magnitude are human and not merely academic, that he wrote so that all men
could understand.
AS REGARDS THE FACTORS OF EVOLUTION.
It is admitted by all who are acquainted with the history of biology that
the general idea of organic evolution as expressed in the Doctrine of
Descent was quite familiar to Darwin's grandfather, and to others before
and after him, as we have briefly indicated. It must also be admitted that
some of these pioneers of evolutionism did more than apply the evolution-
idea as a modal formula of becoming, they began to inquire into the factors
in the process. Thus there were pre-Darwinian theories of evolution, and
to these we must now briefly refer. (See Prof. W.A. Locy's "Biology and
its Makers". New York, 1908. Part II. "The Doctrine of Organic
Evolution".
In all biological thinking we have to work with the categories Organism--
Function--Environment, and theories of evolution may be classified in
relation to these. To some it has always seemed that the fundamental fact
is the living organism,--a creative agent, a striving will, a changeful
Proteus, selecting its environment, adjusting itself to it, self-
differentiating and self-adaptive. The necessity of recognising the
importance of the organism is admitted by all Darwinians who start with
inborn variations, but it is open to question whether the whole truth of
what we might call the Goethian position is exhausted in the postulate of
inherent variability.
To others it has always seemed that the emphasis should be laid on
Function,--on use and disuse, on doing and not doing. Practice makes
perfect; c'est a force de forger qu'on devient forgeron. This is one of
the fundamental ideas of Lamarckism; to some extent it met with Darwin's
approval; and it finds many supporters to-day. One of the ablest of these
--Mr Francis Darwin--has recently given strong reasons for combining a
modernised Lamarckism with what we usually regard as sound Darwinism.
(Presidential Address to the British Association meeting at Dublin in
1908.)
To others it has always seemed that the emphasis should be laid on the
Environment, which wakes the organism to action, prompts it to change,
makes dints upon it, moulds it, prunes it, and finally, perhaps, kills it.
It is again impossible to doubt that there is truth in this view, for even
if environmentally induced "modifications" be not transmissible,
environmentally induced "variations" are; and even if the direct influence
of the environment be less important than many enthusiastic supporters of
this view--may we call them Buffonians--think, there remains the indirect
influence which Darwinians in part rely on,--the eliminative process. Even
if the extreme view be held that the only form of discriminate elimination
that counts is inter-organismal competition, this might be included under
the rubric of the animate environment.
In many passages Buffon (See in particular Samuel Butler, "Evolution Old
and New", London, 1879; J.L. de Lanessan, "Buffon et Darwin", "Revue
Scientifique", XLIII. pages 385-391, 425-432, 1889.) definitely suggested
that environmental influences--especially of climate and food--were
directly productive of changes in organisms, but he did not discuss the
question of the transmissibility of the modifications so induced, and it is
difficult to gather from his inconsistent writings what extent of
transformation he really believed in. Prof. Osborn says of Buffon: "The
struggle for existence, the elimination of the least-perfected species, the
contest between the fecundity of certain species and their constant
destruction, are all clearly expressed in various passages." He quotes two
of these (op. cit. page 136.):
"Le cours ordinaire de la nature vivante, est en general toujours constant,
toujours le meme; son mouvement, toujours regulier, roule sur deux points
inebranlables: l'un, la fecondite sans bornes donnee a toutes les especes;
l'autre, les obstacles sans nombre qui reduisent cette fecondite a une
mesure determinee et ne laissent en tout temps qu'a peu pres la meme
quantite d'individus de chaque espece"..."Les especes les moins parfaites,
les plus delicates, les plus pesantes, les moins agissantes, les moins
armees, etc., ont deja disparu ou disparaitront."
Erasmus Darwin (See Ernst Krause and Charles Darwin, "Erasmus Darwin",
London, 1879.) had a firm grip of the "idea of the gradual formation and
improvement of the Animal world," and he had his theory of the process. No
sentence is more characteristic than this: "All animals undergo
transformations which are in part produced by their own exertions, in
response to pleasures and pains, and many of these acquired forms or
propensities are transmitted to their posterity." This is Lamarckism
before Lamarck, as his grandson pointed out. His central idea is that
wants stimulate efforts and that these result in improvements, which
subsequent generations make better still. He realised something of the
struggle for existence and even pointed out that this advantageously checks
the rapid multiplication. "As Dr Krause points out, Darwin just misses the
connection between this struggle and the Survival of the Fittest." (Osborn
op. cit. page 142.)
Lamarck (1744-1829) (See E. Perrier "La Philosophie Zoologique avant
Darwin", Paris, 1884; A. de Quatrefages, "Darwin et ses Precurseurs
Francais", Paris, 1870; Packard op. cit.; also Claus, "Lamarck als
Begrunder der Descendenzlehre", Wien, 1888; Haeckel, "Natural History of
Creation", English translation London, 1879; Lang "Zur Charakteristik der
Forschungswege von Lamarck und Darwin", Jena, 1889.) seems to have thought
out his theory of evolution without any knowledge of Erasmus Darwin's which
it closely resembled. The central idea of his theory was the cumulative
inheritance of functional modifications. "Changes in environment bring
about changes in the habits of animals. Changes in their wants necessarily
bring about parallel changes in their habits. If new wants become constant
or very lasting, they form new habits, the new habits involve the use of
new parts, or a different use of old parts, which results finally in the
production of new organs and the modification of old ones." He differed
from Buffon in not attaching importance, as far as animals are concerned,
to the direct influence of the environment, "for environment can effect no
direct change whatever upon the organisation of animals," but in regard to
plants he agreed with Buffon that external conditions directly moulded
them.
Treviranus (1776-1837) (See Huxley's article "Evolution in Biology",
"Encyclopaedia Britannica" (9th edit.), 1878, pages 744-751, and Sully's
article, "Evolution in Philosophy", ibid. pages 751-772.), whom Huxley
ranked beside Lamarck, was on the whole Buffonian, attaching chief
importance to the influence of a changeful environment both in modifying
and in eliminating, but he was also Goethian, for instance in his idea that
species like individuals pass through periods of growth, full bloom, and
decline. "Thus, it is not only the great catastrophes of Nature which have
caused extinction, but the completion of cycles of existence, out of which
new cycles have begun." A characteristic sentence is quoted by Prof.
Osborn: "In every living being there exists a capability of an endless
variety of form-assumption; each possesses the power to adapt its
organisation to the changes of the outer world, and it is this power, put
into action by the change of the universe, that has raised the simple
zoophytes of the primitive world to continually higher stages of
organisation, and has introduced a countless variety of species into
animate Nature."
Goethe (1749-1832) (See Haeckel, "Die Naturanschauung von Darwin, Goethe
und Lamarck", Jena, 1882.), who knew Buffon's work but not Lamarck's, is
peculiarly interesting as one of the first to use the evolution-idea as a
guiding hypothesis, e.g. in the interpretation of vestigial structures in
man, and to realise that organisms express an attempt to make a compromise
between specific inertia and individual change. He gave the finest
expression that science has yet known--if it has known it--of the kernel-
idea of what is called "bathmism," the idea of an "inherent growth-force"--
and at the same time he held that "the way of life powerfully reacts upon
all form" and that the orderly growth of form "yields to change from
externally acting causes."
Besides Buffon, Erasmus Darwin, Lamarck, Treviranus, and Goethe, there were
other "pioneers of evolution," whose views have been often discussed and
appraised. Etienne Geoffroy Saint-Hilaire (1772-1844), whose work Goethe
so much admired, was on the whole Buffonian, emphasising the direct action
of the changeful milieu. "Species vary with their environment, and
existing species have descended by modification from earlier and somewhat
simpler species." He had a glimpse of the selection idea, and believed in
mutations or sudden leaps--induced in the embryonic condition by external
influences. The complete history of evolution-theories will include many
instances of guesses at truth which were afterwards substantiated, thus the
geographer von Buch (1773-1853) detected the importance of the Isolation
factor on which Wagner, Romanes, Gulick and others have laid great stress,
but we must content ourselves with recalling one other pioneer, the author
of the "Vestiges of Creation" (1844), a work which passed through ten
editions in nine years and certainly helped to harrow the soil for Darwin's
sowing. As Darwin said, "it did excellent service in this country in
calling attention to the subject, in removing prejudice, and in thus
preparing the ground for the reception of analogous views." ("Origin of
Species" (6th edition), page xvii.) Its author, Robert Chambers (1802-
1871) was in part a Buffonian--maintaining that environment moulded
organisms adaptively, and in part a Goethian--believing in an inherent
progressive impulse which lifted organisms from one grade of organisation
to another.
AS REGARDS NATURAL SELECTION.
The only thinker to whom Darwin was directly indebted, so far as the theory
of Natural Selection is concerned, was Malthus, and we may once more quote
the well-known passage in the Autobiography: "In October, 1838, that is,
fifteen months after I had begun my systematic enquiry, I happened to read
for amusement 'Malthus on Population', and being well prepared to
appreciate the struggle for existence which everywhere goes on from long-
continued observation of the habits of animals and plants, it at once
struck me that under these circumstances favourable variations would tend
to be preserved, and unfavourable ones to be destroyed. The result of this
would be the formation of new species." ("The Life and Letters of Charles
Darwin", Vol. 1. page 83. London, 1887.)
Although Malthus gives no adumbration of the idea of Natural Selection in
his exposition of the eliminative processes which go on in mankind, the
suggestive value of his essay is undeniable, as is strikingly borne out by
the fact that it gave to Alfred Russel Wallace also "the long-sought clue
to the effective agent in the evolution of organic species." (A.R.
Wallace, "My Life, A Record of Events and Opinions", London, 1905, Vol. 1.
page 232.) One day in Ternate when he was resting between fits of fever,
something brought to his recollection the work of Malthus which he had read
twelve years before. "I thought of his clear exposition of 'the positive
checks to increase'--disease, accidents, war, and famine--which keep down
the population of savage races to so much lower an average than that of
more civilized peoples. It then occurred to me that these causes or their
equivalents are continually acting in the case of animals also; and as
animals usually breed much more rapidly than does mankind, the destruction
every year from these causes must be enormous in order to keep down the
numbers of each species, since they evidently do not increase regularly
from year to year, as otherwise the world would long ago have been densely
crowded with those that breed most quickly. Vaguely thinking over the
enormous and constant destruction which this implied, it occurred to me to
ask the question, Why do some die and some live? And the answer was
clearly, that on the whole the best fitted live. From the effects of
disease the most healthy escaped; from enemies the strongest, the swiftest,
or the most cunning; from famine the best hunters or those with the best
digestion; and so on. Then it suddenly flashed upon me that this self-
acting process would necessarily IMPROVE THE RACE, because in every
generation the inferior would inevitably be killed off and the superior
would remain--that is, THE FITTEST WOULD SURVIVE." (Ibid. Vol. 1. page
361.) We need not apologise for this long quotation, it is a tribute to
Darwin's magnanimous colleague, the Nestor of the evolutionist camp,--and
it probably indicates the line of thought which Darwin himself followed.
It is interesting also to recall the fact that in 1852, when Herbert
Spencer wrote his famous "Leader" article on "The Development Hypothesis"
in which he argued powerfully for the thesis that the whole animate world
is the result of an age-long process of natural transformation, he wrote
for "The Westminster Review" another important essay, "A Theory of
Population deduced from the General Law of Animal Fertility", towards the
close of which he came within an ace of recognising that the struggle for
existence was a factor in organic evolution. At a time when pressure of
population was practically interesting men's minds, Darwin, Wallace, and
Spencer were being independently led from a social problem to a biological
theory. There could be no better illustration, as Prof. Patrick Geddes has
pointed out, of the Comtian thesis that science is a "social phenomenon."
Therefore, as far more important than any further ferreting out of vague
hints of Natural Selection in books which Darwin never read, we would
indicate by a quotation the view that the central idea in Darwinism is
correlated with contemporary social evolution. "The substitution of Darwin
for Paley as the chief interpreter of the order of nature is currently
regarded as the displacement of an anthropomorphic view by a purely
scientific one: a little reflection, however, will show that what has
actually happened has been merely the replacement of the anthropomorphism
of the eighteenth century by that of the nineteenth. For the place vacated
by Paley's theological and metaphysical explanation has simply been
occupied by that suggested to Darwin and Wallace by Malthus in terms of the
prevalent severity of industrial competition, and those phenomena of the
struggle for existence which the light of contemporary economic theory has
enabled us to discern, have thus come to be temporarily exalted into a
complete explanation of organic progress." (P. Geddes, article "Biology",
"Chambers's Encyclopaedia".) It goes without saying that the idea
suggested by Malthus was developed by Darwin into a biological theory which
was then painstakingly verified by being used as an interpretative formula,
and that the validity of a theory so established is not affected by what
suggested it, but the practical question which this line of thought raises
in the mind is this: if Biology did thus borrow with such splendid results
from social theory, why should we not more deliberately repeat the
experiment?
Darwin was characteristically frank and generous in admitting that the
principle of Natural Selection had been independently recognised by Dr W.C.
Wells in 1813 and by Mr Patrick Matthew in 1831, but he had no knowledge of
these anticipations when he published the first edition of "The Origin of
Species". Wells, whose "Essay on Dew" is still remembered, read in 1813
before the Royal Society a short paper entitled "An account of a White
Female, part of whose skin resembles that of a Negro" (published in 1818).
In this communication, as Darwin said, "he observes, firstly, that all
animals tend to vary in some degree, and, secondly, that agriculturists
improve their domesticated animals by selection; and then, he adds, but
what is done in this latter case 'by art, seems to be done with equal
efficacy, though more slowly, by nature, in the formation of varieties of
mankind, fitted for the country which they inhabit.'" ("Origin of Species"
(6th edition) page xv.) Thus Wells had the clear idea of survival
dependent upon a favourable variation, but he makes no more use of the idea
and applies it only to man. There is not in the paper the least hint that
the author ever thought of generalising the remarkable sentence quoted
above.
Of Mr Patrick Matthew, who buried his treasure in an appendix to a work on
"Naval Timber and Arboriculture", Darwin said that "he clearly saw the full
force of the principle of natural selection." In 1860 Darwin wrote--very
characteristically--about this to Lyell: "Mr Patrick Matthew publishes a
long extract from his work on "Naval Timber and Arboriculture", published
in 1831, in which he briefly but completely anticipates the theory of
Natural Selection. I have ordered the book, as some passages are rather
obscure, but it is certainly, I think, a complete but not developed
anticipation. Erasmus always said that surely this would be shown to be
the case some day. Anyhow, one may be excused in not having discovered the
fact in a work on Naval Timber." ("Life and Letters" II. page 301.)
De Quatrefages and De Varigny have maintained that the botanist Naudin
stated the theory of evolution by natural selection in 1852. He explains
very clearly the process of artificial selection, and says that in the
garden we are following Nature's method. "We do not think that Nature has
made her species in a different fashion from that in which we proceed
ourselves in order to make our variations." But, as Darwin said, "he does
not show how selection acts under nature." Similarly it must be noted in
regard to several pre-Darwinian pictures of the struggle for existence
(such as Herder's, who wrote in 1790 "All is in struggle...each one for
himself" and so on), that a recognition of this is only the first step in
Darwinism.
Profs. E. Perrier and H.F. Osborn have called attention to a remarkable
anticipation of the selection-idea which is to be found in the speculations
of Etienne Geoffroy St Hilaire (1825-1828) on the evolution of modern
Crocodilians from the ancient Teleosaurs. Changing environment induced
changes in the respiratory system and far-reaching consequences followed.
The atmosphere, acting upon the pulmonary cells, brings about
"modifications which are favourable or destructive ('funestes'); these are
inherited, and they influence all the rest of the organisation of the
animal because if these modifications lead to injurious effects, the
animals which exhibit them perish and are replaced by others of a somewhat
different form, a form changed so as to be adapted to (a la convenance) the
new environment."
Prof. E.B. Poulton ("Science Progress", New Series, Vol. I. 1897. "A
Remarkable Anticipation of Modern Views on Evolution". See also Chap. VI.
in "Essays on Evolution", Oxford, 1908.) has shown that the anthropologist
James Cowles Prichard (1786-1848) must be included, even in spite of
himself, among the precursors of Darwin. In some passages of the second
edition of his "Researches into the Physical History of Mankind" (1826), he
certainly talks evolution and anticipates Prof. Weismann in denying the
transmission of acquired characters. He is, however, sadly self-
contradictory and his evolutionism weakens in subsequent editions--the only
ones that Darwin saw. Prof. Poulton finds in Prichard's work a recognition
of the operation of Natural Selection. "After enquiring how it is that
'these varieties are developed and preserved in connection with particular
climates and differences of local situation,' he gives the following very
significant answer: 'One cause which tends to maintain this relation is
obvious. Individuals and families, and even whole colonies, perish and
disappear in climates for which they are, by peculiarity of constitution,
not adapted. Of this fact proofs have been already mentioned.'" Mr
Francis Darwin and Prof. A.C. Seward discuss Prichard's "anticipations" in
"More Letters of Charles Darwin", Vol. I. page 43, and come to the
conclusion that the evolutionary passages are entirely neutralised by
others of an opposite trend. There is the same difficulty with Buffon.
Hints of the idea of Natural Selection have been detected elsewhere. James
Watt (See Prof. Patrick Geddes's article "Variation and Selection",
"Encyclopaedia Britannica (9th edition) 1888.), for instance, has been
reported as one of the anticipators (1851). But we need not prolong the
inquiry further, since Darwin did not know of any anticipations until after
he had published the immortal work of 1859, and since none of those who got
hold of the idea made any use of it. What Darwin did was to follow the
clue which Malthus gave him, to realise, first by genius and afterwards by
patience, how the complex and subtle struggle for existence works out a
natural selection of those organisms which vary in the direction of fitter
adaptation to the conditions of their life. So much success attended his
application of the Selection-formula that for a time he regarded Natural
Selection as almost the sole factor in evolution, variations being pre-
supposed; gradually, however, he came to recognise that there was some
validity in the factors which had been emphasized by Lamarck and by Buffon,
and in his well-known summing up in the sixth edition of the "Origin" he
says of the transformation of species: "This has been effected chiefly
through the natural selection of numerous successive, slight, favourable
variations; aided in an important manner by the inherited effects of the
use and disuse of parts; and in an unimportant manner, that is, in relation
to adaptive structures, whether past or present, by the direct action of
external conditions, and by variations which seem to us in our ignorance to
arise spontaneously."
To sum up: the idea of organic evolution, older than Aristotle, slowly
developed from the stage of suggestion to the stage of verification, and
the first convincing verification was Darwin's; from being an a priori
anticipation it has become an interpretation of nature, and Darwin is still
the chief interpreter; from being a modal interpretation it has advanced to
the rank of a causal theory, the most convincing part of which men will
never cease to call Darwinism.
III. THE SELECTION THEORY
By August Weismann.
Professor of Zoology in the University of Freiburg (Baden).
I. THE IDEA OF SELECTION.
Many and diverse were the discoveries made by Charles Darwin in the course
of a long and strenuous life, but none of them has had so far-reaching an
influence on the science and thought of his time as the theory of
selection. I do not believe that the theory of evolution would have made
its way so easily and so quickly after Darwin took up the cudgels in favour
of it, if he had not been able to support it by a principle which was
capable of solving, in a simple manner, the greatest riddle that living
nature presents to us,--I mean the purposiveness of every living form
relative to the conditions of its life and its marvellously exact
adaptation to these.
Everyone knows that Darwin was not alone in discovering the principle of
selection, and that the same idea occurred simultaneously and independently
to Alfred Russel Wallace. At the memorable meeting of the Linnean Society
on 1st July, 1858, two papers were read (communicated by Lyell and Hooker)
both setting forth the same idea of selection. One was written by Charles
Darwin in Kent, the other by Alfred Wallace in Ternate, in the Malay
Archipelago. It was a splendid proof of the magnanimity of these two
investigators, that they thus, in all friendliness and without envy, united
in laying their ideas before a scientific tribunal: their names will
always shine side by side as two of the brightest stars in the scientific
sky.
But it is with Charles Darwin that I am here chiefly concerned, since this
paper is intended to aid in the commemoration of the hundredth anniversary
of his birth.
The idea of selection set forth by the two naturalists was at the time
absolutely new, but it was also so simple that Huxley could say of it
later, "How extremely stupid not to have thought of that." As Darwin was
led to the general doctrine of descent, not through the labours of his
predecessors in the early years of the century, but by his own
observations, so it was in regard to the principle of selection. He was
struck by the innumerable cases of adaptation, as, for instance, that of
the woodpeckers and tree-frogs to climbing, or the hooks and feather-like
appendages of seeds, which aid in the distribution of plants, and he said
to himself that an explanation of adaptations was the first thing to be
sought for in attempting to formulate a theory of evolution.
But since adaptations point to CHANGES which have been undergone by the
ancestral forms of existing species, it is necessary, first of all, to
inquire how far species in general are VARIABLE. Thus Darwin's attention
was directed in the first place to the phenomenon of variability, and the
use man has made of this, from very early times, in the breeding of his
domesticated animals and cultivated plants. He inquired carefully how
breeders set to work, when they wished to modify the structure and
appearance of a species to their own ends, and it was soon clear to him
that SELECTION FOR BREEDING PURPOSES played the chief part.
But how was it possible that such processes should occur in free nature?
Who is here the breeder, making the selection, choosing out one individual
to bring forth offspring and rejecting others? That was the problem that
for a long time remained a riddle to him.
Darwin himself relates how illumination suddenly came to him. He had been
reading, for his own pleasure, Malthus' book on Population, and, as he had
long known from numerous observations, that every species gives rise to
many more descendants than ever attain to maturity, and that, therefore,
the greater number of the descendants of a species perish without
reproducing, the idea came to him that the decision as to which member of a
species was to perish, and which was to attain to maturity and reproduction
might not be a matter of chance, but might be determined by the
constitution of the individuals themselves, according as they were more or
less fitted for survival. With this idea the foundation of the theory of
selection was laid.
In ARTIFICIAL SELECTION the breeder chooses out for pairing only such
individuals as possess the character desired by him in a somewhat higher
degree than the rest of the race. Some of the descendants inherit this
character, often in a still higher degree, and if this method be pursued
throughout several generations, the race is transformed in respect of that
particular character.
NATURAL SELECTION depends on the same three factors as ARTIFICIAL
SELECTION: on VARIABILITY, INHERITANCE, and SELECTION FOR BREEDING, but
this last is here carried out not by a breeder but by what Darwin called
the "struggle for existence." This last factor is one of the special
features of the Darwinian conception of nature. That there are carnivorous
animals which take heavy toll in every generation of the progeny of the
animals on which they prey, and that there are herbivores which decimate
the plants in every generation had long been known, but it is only since
Darwin's time that sufficient attention has been paid to the facts that, in
addition to this regular destruction, there exists between the members of a
species a keen competition for space and food, which limits multiplication,
and that numerous individuals of each species perish because of
unfavourable climatic conditions. The "struggle for existence," which
Darwin regarded as taking the place of the human breeder in free nature, is
not a direct struggle between carnivores and their prey, but is the assumed
competition for survival between individuals OF THE SAME species, of which,
on an average, only those survive to reproduce which have the greatest
power of resistance, while the others, less favourably constituted, perish
early. This struggle is so keen, that, within a limited area, where the
conditions of life have long remained unchanged, of every species, whatever
be the degree of fertility, only two, ON AN AVERAGE, of the descendants of
each pair survive; the others succumb either to enemies, or to
disadvantages of climate, or to accident. A high degree of fertility is
thus not an indication of the special success of a species, but of the
numerous dangers that have attended its evolution. Of the six young
brought forth by a pair of elephants in the course of their lives only two
survive in a given area; similarly, of the millions of eggs which two
thread-worms leave behind them only two survive. It is thus possible to
estimate the dangers which threaten a species by its ratio of elimination,
or, since this cannot be done directly, by its fertility.
Although a great number of the descendants of each generation fall victims
to accident, among those that remain it is still the greater or lesser
fitness of the organism that determines the "selection for breeding
purposes," and it would be incomprehensible if, in this competition, it
were not ultimately, that is, on an average, the best equipped which
survive, in the sense of living long enough to reproduce.
Thus the principle of natural selection is THE SELECTION OF THE BEST FOR
REPRODUCTION, whether the "best" refers to the whole constitution, to one
or more parts of the organism, or to one or more stages of development.
Every organ, every part, every character of an animal, fertility and
intelligence included, must be improved in this manner, and be gradually
brought up in the course of generations to its highest attainable state of
perfection. And not only may improvement of parts be brought about in this
way, but new parts and organs may arise, since, through the slow and minute
steps of individual or "fluctuating" variations, a part may be added here
or dropped out there, and thus something new is produced.
The principle of selection solved the riddle as to how what was purposive
could conceivably be brought about without the intervention of a directing
power, the riddle which animate nature presents to our intelligence at
every turn, and in face of which the mind of a Kant could find no way out,
for he regarded a solution of it as not to be hoped for. For, even if we
were to assume an evolutionary force that is continually transforming the
most primitive and the simplest forms of life into ever higher forms, and
the homogeneity of primitive times into the infinite variety of the
present, we should still be unable to infer from this alone how each of the
numberless forms adapted to particular conditions of life should have
appeared PRECISELY AT THE RIGHT MOMENT IN THE HISTORY OF THE EARTH to which
their adaptations were appropriate, and precisely at the proper place in
which all the conditions of life to which they were adapted occurred: the
humming-birds at the same time as the flowers; the trichina at the same
time as the pig; the bark-coloured moth at the same time as the oak, and
the wasp-like moth at the same time as the wasp which protects it. Without
processes of selection we should be obliged to assume a "pre-established
harmony" after the famous Leibnitzian model, by means of which the clock of
the evolution of organisms is so regulated as to strike in exact
synchronism with that of the history of the earth! All forms of life are
strictly adapted to the conditions of their life, and can persist under
these conditions alone.
There must therefore be an intrinsic connection between the conditions and
the structural adaptations of the organism, and, SINCE THE CONDITIONS OF
LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE ADAPTATIONS MUST BE
CALLED FORTH BY THE CONDITIONS.
The selection theory teaches us how this is conceivable, since it enables
us to understand that there is a continual production of what is non-
purposive as well as of what is purposive, but the purposive alone
survives, while the non-purposive perishes in the very act of arising.
This is the old wisdom taught long ago by Empedocles.
II. THE LAMARCKIAN PRINCIPLE.
Lamarck, as is well known, formulated a definite theory of evolution at the
beginning of the nineteenth century, exactly fifty years before the Darwin-
Wallace principle of selection was given to the world. This brilliant
investigator also endeavoured to support his theory by demonstrating forces
which might have brought about the transformations of the organic world in
the course of the ages. In addition to other factors, he laid special
emphasis on the increased or diminished use of the parts of the body,
assuming that the strengthening or weakening which takes place from this
cause during the individual life, could be handed on to the offspring, and
thus intensified and raised to the rank of a specific character. Darwin
also regarded this LAMARCKIAN PRINCIPLE, as it is now generally called, as
a factor in evolution, but he was not fully convinced of the
transmissibility of acquired characters.
As I have here to deal only with the theory of selection, I need not
discuss the Lamarckian hypothesis, but I must express my opinion that there
is room for much doubt as to the cooperation of this principle in
evolution. Not only is it difficult to imagine how the transmission of
functional modifications could take place, but, up to the present time,
notwithstanding the endeavours of many excellent investigators, not a
single actual proof of such inheritance has been brought forward. Semon's
experiments on plants are, according to the botanist Pfeffer, not to be
relied on, and even the recent, beautiful experiments made by Dr Kammerer
on salamanders, cannot, as I hope to show elsewhere, be regarded as proof,
if only because they do not deal at all with functional modifications, that
is, with modifications brought about by use, and it is to these ALONE that
the Lamarckian principle refers.
III. OBJECTIONS TO THE THEORY OF SELECTION.
(a) Saltatory evolution.
The Darwinian doctrine of evolution depends essentially on THE CUMULATIVE
AUGMENTATION of minute variations in the direction of utility. But can
such minute variations, which are undoubtedly continually appearing among
the individuals of the same species, possess any selection-value; can they
determine which individuals are to survive, and which are to succumb; can
they be increased by natural selection till they attain to the highest
development of a purposive variation?
To many this seems so improbable that they have urged a theory of evolution
by leaps from species to species. Kolliker, in 1872, compared the
evolution of species with the processes which we can observe in the
individual life in cases of alternation of generations. But a polyp only
gives rise to a medusa because it has itself arisen from one, and there can
be no question of a medusa ever having arisen suddenly and de novo from a
polyp-bud, if only because both forms are adapted in their structure as a
whole, and in every detail to the conditions of their life. A sudden
origin, in a natural way, of numerous adaptations is inconceivable. Even
the degeneration of a medusoid from a free-swimming animal to a mere brood-
sac (gonophore) is not sudden and saltatory, but occurs by imperceptible
modifications throughout hundreds of years, as we can learn from the
numerous stages of the process of degeneration persisting at the same time
in different species.
If, then, the degeneration to a simple brood-sac takes place only by very
slow transitions, each stage of which may last for centuries, how could the
much more complex ASCENDING evolution possibly have taken place by sudden
leaps? I regard this argument as capable of further extension, for
wherever in nature we come upon degeneration, it is taking place by minute
steps and with a slowness that makes it not directly perceptible, and I
believe that this in itself justifies us in concluding that THE SAME MUST
BE TRUE OF ASCENDING evolution. But in the latter case the goal can seldom
be distinctly recognised while in cases of degeneration the starting-point
of the process can often be inferred, because several nearly related
species may represent different stages.
In recent years Bateson in particular has championed the idea of saltatory,
or so-called discontinuous evolution, and has collected a number of cases
in which more or less marked variations have suddenly appeared. These are
taken for the most part from among domesticated animals which have been
bred and crossed for a long time, and it is hardly to be wondered at that
their much mixed and much influenced germ-plasm should, under certain
conditions, give rise to remarkable phenomena, often indeed producing forms
which are strongly suggestive of monstrosities, and which would undoubtedly
not survive in free nature, unprotected by man. I should regard such cases
as due to an intensified germinal selection--though this is to anticipate a
little--and from this point of view it cannot be denied that they have a
special interest. But they seem to me to have no significance as far as
the transformation of species is concerned, if only because of the extreme
rarity of their occurrence.
There are, however, many variations which have appeared in a sudden and
saltatory manner, and some of these Darwin pointed out and discussed in
detail: the copper beech, the weeping trees, the oak with "fern-like
leaves," certain garden-flowers, etc. But none of them have persisted in
free nature, or evolved into permanent types.
On the other hand, wherever enduring types have arisen, we find traces of a
gradual origin by successive stages, even if, at first sight, their origin
may appear to have been sudden. This is the case with SEASONAL DIMORPHISM,
the first known cases of which exhibited marked differences between the two
generations, the winter and the summer brood. Take for instance the much
discussed and studied form Vanessa (Araschnia) levana-prorsa. Here the
differences between the two forms are so great and so apparently
disconnected, that one might almost believe it to be a sudden mutation,
were it not that old transition-stages can be called forth by particular
temperatures, and we know other butterflies, as for instance our Garden
Whites, in which the differences between the two generations are not nearly
so marked; indeed, they are so little apparent that they are scarcely
likely to be noticed except by experts. Thus here again there are small
initial steps, some of which, indeed, must be regarded as adaptations, such
as the green-sprinkled or lightly tinted under-surface which gives them a
deceptive resemblance to parsley or to Cardamine leaves.
Even if saltatory variations do occur, we cannot assume that these HAVE
EVER LED TO FORMS WHICH ARE CAPABLE OF SURVIVAL UNDER THE CONDITIONS OF
WILD LIFE. Experience has shown that in plants which have suddenly varied
the power of persistence is diminished. Korschinksky attributes to them
weaknesses of organisation in general; "they bloom late, ripen few of their
seeds, and show great sensitiveness to cold." These are not the characters
which make for success in the struggle for existence.
We must briefly refer here to the views--much discussed in the last decade
--of H. de Vries, who believes that the roots of transformation must be
sought for in SALTATORY VARIATIONS ARISING FROM INTERNAL CAUSES, and
distinguishes such MUTATIONS, as he has called them, from ordinary
individual variations, in that they breed true, that is, with strict
inbreeding they are handed on pure to the next generation. I have
elsewhere endeavoured to point out the weaknesses of this theory ("Vortrage
uber Descendenztheorie", Jena, 1904, II. 269. English Translation London,
1904, II. page 317.), and I am the less inclined to return to it here that
it now appears (See Poulton, "Essays on Evolution", Oxford, 1908, pages
xix-xxii.) that the far-reaching conclusions drawn by de Vries from his
observations on the Evening Primrose, Oenothera lamarckiana, rest upon a
very insecure foundation. The plant from which de Vries saw numerous
"species"--his "mutations"--arise was not, as he assumed, a WILD SPECIES
that had been introduced to Europe from America, but was probably a hybrid
form which was first discovered in the Jardin des Plantes in Paris, and
which does not appear to exist anywhere in America as a wild species.
This gives a severe shock to the "Mutation theory," for the other ACTUALLY
WILD species with which de Vries experimented showed no "mutations" but
yielded only negative results.
Thus we come to the conclusion that Darwin ("Origin of Species" (6th
edition), pages 176 et seq.) was right in regarding transformations as
taking place by minute steps, which, if useful, are augmented in the course
of innumerable generations, because their possessors more frequently
survive in the struggle for existence.
(b) SELECTION-VALUE OF THE INITIAL STEPS.
Is it possible that the significant deviations which we know as "individual
variations" can form the beginning of a process of selection? Can they
decide which is to perish and which to survive? To use a phrase of
Romanes, can they have SELECTION-VALUE?
Darwin himself answered this question, and brought together many excellent
examples to show that differences, apparently insignificant because very
small, might be of decisive importance for the life of the possessor. But
it is by no means enough to bring forward cases of this kind, for the
question is not merely whether finished adaptations have selection-value,
but whether the first beginnings of these, and whether the small, I might
almost say minimal increments, which have led up from these beginnings to
the perfect adaptation, have also had selection-value. To this question
even one who, like myself, has been for many years a convinced adherent of
the theory of selection, can only reply: WE MUST ASSUME SO, BUT WE CANNOT
PROVE IT IN ANY CASE. It is not upon demonstrative evidence that we rely
when we champion the doctrine of selection as a scientific truth; we base
our argument on quite other grounds. Undoubtedly there are many apparently
insignificant features, which can nevertheless be shown to be adaptations--
for instance, the thickness of the basin-shaped shell of the limpets that
live among the breakers on the shore. There can be no doubt that the
thickness of these shells, combined with their flat form, protects the
animals from the force of the waves breaking upon them,--but how have they
become so thick? What proportion of thickness was sufficient to decide
that of two variants of a limpet one should survive, the other be
eliminated? We can say nothing more than that we infer from the present
state of the shell, that it must have varied in regard to differences in
shell-thickness, and that these differences must have had selection-value,
--no proof therefore, but an assumption which we must show to be
convincing.
For a long time the marvellously complex RADIATE and LATTICE-WORK skeletons
of Radiolarians were regarded as a mere outflow of "Nature's infinite
wealth of form," as an instance of a purely morphological character with no
biological significance. But recent investigations have shown that these,
too, have an adaptive significance (Hacker). The same thing has been shown
by Schutt in regard to the lowly unicellular plants, the Peridineae, which
abound alike on the surface of the ocean and in its depths. It has been
shown that the long skeletal processes which grow out from these organisms
have significance not merely as a supporting skeleton, but also as an
extension of the superficial area, which increases the contact with the
water-particles, and prevents the floating organisms from sinking. It has
been established that the processes are considerably shorter in the colder
layers of the ocean, and that they may be twelve times as long (Chun,
"Reise der Valdivia", Leipzig, 1904.) in the warmer layers, thus
corresponding to the greater or smaller amount of friction which takes
place in the denser and less dense layers of the water.
The Peridineae of the warmer ocean layers have thus become long-rayed,
those of the colder layers short-rayed, not through the direct effect of
friction on the protoplasm, but through processes of selection, which
favoured the longer rays in warm water, since they kept the organism
afloat, while those with short rays sank and were eliminated. If we put
the question as to selection-value in this case, and ask how great the
variations in the length of processes must be in order to possess
selection-value; what can we answer except that these variations must have
been minimal, and yet sufficient to prevent too rapid sinking and
consequent elimination? Yet this very case would give the ideal
opportunity for a mathematical calculation of the minimal selection-value,
although of course it is not feasible from lack of data to carry out the
actual calculation.
But even in organisms of more than microscopic size there must frequently
be minute, even microscopic differences which set going the process of
selection, and regulate its progress to the highest possible perfection.
Many tropical trees possess thick, leathery leaves, as a protection against
the force of the tropical rain drops. The DIRECT influence of the rain
cannot be the cause of this power of resistance, for the leaves, while they
were still thin, would simply have been torn to pieces. Their toughness
must therefore be referred to selection, which would favour the trees with
slightly thicker leaves, though we cannot calculate with any exactness how
great the first stages of increase in thickness must have been. Our
hypothesis receives further support from the fact that, in many such trees,
the leaves are drawn out into a beak-like prolongation (Stahl and
Haberlandt) which facilitates the rapid falling off of the rain water, and
also from the fact that the leaves, while they are still young, hang limply
down in bunches which offer the least possible resistance to the rain.
Thus there are here three adaptations which can only be interpreted as due
to selection. The initial stages of these adaptations must undoubtedly
have had selection-value.
But even in regard to this case we are reasoning in a circle, not giving
"proofs," and no one who does not wish to believe in the selection-value of
the initial stages can be forced to do so. Among the many pieces of
presumptive evidence a particularly weighty one seems to me to be THE
SMALLNESS OF THE STEPS OF PROGRESS which we can observe in certain cases,
as for instance in leaf-imitation among butterflies, and in mimicry
generally. The resemblance to a leaf, for instance of a particular
Kallima, seems to us so close as to be deceptive, and yet we find in
another individual, or it may be in many others, a spot added which
increases the resemblance, and which could not have become fixed unless the
increased deceptiveness so produced had frequently led to the overlooking
of its much persecuted possessor. But if we take the selection-value of
the initial stages for granted, we are confronted with the further question
which I myself formulated many years ago: How does it happen THAT THE
NECESSARY BEGINNINGS OF A USEFUL VARIATION ARE ALWAYS PRESENT? How could
insects which live upon or among green leaves become all green, while those
that live on bark become brown? How have the desert animals become yellow
and the Arctic animals white? Why were the necessary variations always
present? How could the green locust lay brown eggs, or the privet
caterpillar develop white and lilac-coloured lines on its green skin?
It is of no use answering to this that the question is wrongly formulated
(Plate, "Selektionsprinzip u. Probleme der Artbildung" (3rd edition),
Leipzig, 1908.) and that it is the converse that is true; that the process
of selection takes place in accordance with the variations that present
themselves. This proposition is undeniably true, but so also is another,
which apparently negatives it: the variation required has in the majority
of cases actually presented itself. Selection cannot solve this
contradiction; it does not call forth the useful variation, but simply
works upon it. The ultimate reason why one and the same insect should
occur in green and in brown, as often happens in caterpillars and locusts,
lies in the fact that variations towards brown presented themselves, and so
also did variations towards green: THE KERNEL OF THE RIDDLE LIES IN THE
VARYING, and for the present we can only say, that small variations in
different directions present themselves in every species. Otherwise so
many different kinds of variations could not have arisen. I have
endeavoured to explain this remarkable fact by means of the intimate
processes that must take place within the germ-plasm, and I shall return to
the problem when dealing with "germinal selection."
We have, however, to make still greater demands on variation, for it is not
enough that the necessary variation should occur in isolated individuals,
because in that case there would be small prospect of its being preserved,
notwithstanding its utility. Darwin at first believed, that even single
variations might lead to transformation of the species, but later he became
convinced that this was impossible, at least without the cooperation of
other factors, such as isolation and sexual selection.
In the case of the GREEN CATERPILLARS WITH BRIGHT LONGITUDINAL STRIPES,
numerous individuals exhibiting this useful variation must have been
produced to start with. In all higher, that is, multicellular organisms,
the germ-substance is the source of all transmissible variations, and this
germ-plasm is not a simple substance but is made up of many primary
constituents. The question can therefore be more precisely stated thus:
How does it come about that in so many cases the useful variations present
themselves in numbers just where they are required, the white oblique lines
in the leaf-caterpillar on the under surface of the body, the accompanying
coloured stripes just above them? And, further, how has it come about that
in grass caterpillars, not oblique but longitudinal stripes, which are more
effective for concealment among grass and plants, have been evolved? And
finally, how is it that the same Hawk-moth caterpillars, which to-day show
oblique stripes, possessed longitudinal stripes in Tertiary times? We can
read this fact from the history of their development, and I have before
attempted to show the biological significance of this change of colour.
("Studien zur Descendenz-Theorie" II., "Die Enstehung der Zeichnung bei den
Schmetterlings-raupen," Leipzig, 1876.)
For the present I need only draw the conclusion that one and the same
caterpillar may exhibit the initial stages of both, and that it depends on
the manner in which these marking elements are INTENSIFIED and COMBINED by
natural selection whether whitish longitudinal or oblique stripes should
result. In this case then the "useful variations" were actually "always
there," and we see that in the same group of Lepidoptera, e.g. species of
Sphingidae, evolution has occurred in both directions according to whether
the form lived among grass or on broad leaves with oblique lateral veins,
and we can observe even now that the species with oblique stripes have
longitudinal stripes when young, that is to say, while the stripes have no
biological significance. The white places in the skin which gave rise,
probably first as small spots, to this protective marking could be combined
in one way or another according to the requirements of the species. They
must therefore either have possessed selection-value from the first, or, if
this was not the case at their earliest occurrence, there must have been
SOME OTHER FACTORS which raised them to the point of selection-value. I
shall return to this in discussing germinal selection. But the case may be
followed still farther, and leads us to the same alternative on a still
more secure basis.
Many years ago I observed in caterpillars of Smerinthus populi (the poplar
hawk-moth), which also possess white oblique stripes, that certain
individuals showed RED SPOTS above these stripes; these spots occurred only
on certain segments, and never flowed together to form continuous stripes.
In another species (Smerinthus tiliae) similar blood-red spots unite to
form a line-like coloured seam in the last stage of larval life, while in
S. ocellata rust-red spots appear in individual caterpillars, but more
rarely than in S. Populi, and they show no tendency to flow together.
Thus we have here the origin of a new character, arising from small
beginnings, at least in S. tiliae, in which species the coloured stripes
are a normal specific character. In the other species, S. populi and S.
ocellata, we find the beginnings of the same variation, in one more rarely
than in the other, and we can imagine that, in the course of time, in these
two species, coloured lines over the oblique stripes will arise. In any
case these spots are the elements of variation, out of which coloured lines
MAY be evolved, if they are combined in this direction through the agency
of natural selection. In S. populi the spots are often small, but
sometimes it seems as though several had united to form large spots.
Whether a process of selection in this direction will arise in S. populi
and S. ocellata, or whether it is now going on cannot be determined, since
we cannot tell in advance what biological value the marking might have for
these two species. It is conceivable that the spots may have no selection-
value as far as these species are concerned, and may therefore disappear
again in the course of phylogeny, or, on the other hand, that they may be
changed in another direction, for instance towards imitation of the rust-
red fungoid patches on poplar and willow leaves. In any case we may regard
the smallest spots as the initial stages of variation, the larger as a
cumulative summation of these. Therefore either these initial stages must
already possess selection-value, or, as I said before: THERE MUST BE SOME
OTHER REASON FOR THEIR CUMULATIVE SUMMATION. I should like to give one
more example, in which we can infer, though we cannot directly observe, the
initial stages.
All the Holothurians or sea-cucumbers have in the skin calcareous bodies of
different forms, usually thick and irregular, which make the skin tough and
resistant. In a small group of them--the species of Synapta--the
calcareous bodies occur in the form of delicate anchors of microscopic
size. Up till 1897 these anchors, like many other delicate microscopic
structures, were regarded as curiosities, as natural marvels. But a
Swedish observer, Oestergren, has recently shown that they have a
biological significance: they serve the footless Synapta as auxiliary
organs of locomotion, since, when the body swells up in the act of
creeping, they press firmly with their tips, which are embedded in the
skin, against the substratum on which the animal creeps, and thus prevent
slipping backwards. In other Holothurians this slipping is made impossible
by the fixing of the tube-feet. The anchors act automatically, sinking
their tips towards the ground when the corresponding part of the body
thickens, and returning to the original position at an angle of 45 degrees
to the upper surface when the part becomes thin again. The arms of the
anchor do not lie in the same plane as the shaft, and thus the curve of the
arms forms the outermost part of the anchor, and offers no further
resistance to the gliding of the animal. Every detail of the anchor, the
curved portion, the little teeth at the head, the arms, etc., can be
interpreted in the most beautiful way, above all the form of the anchor
itself, for the two arms prevent it from swaying round to the side. The
position of the anchors, too, is definite and significant; they lie
obliquely to the longitudinal axis of the animal, and therefore they act
alike whether the animal is creeping backwards or forwards. Moreover, the
tips would pierce through the skin if the anchors lay in the longitudinal
direction. Synapta burrows in the sand; it first pushes in the thin
anterior end, and thickens this again, thus enlarging the hole, then the
anterior tentacles displace more sand, the body is worked in a little
farther, and the process begins anew. In the first act the anchors are
passive, but they begin to take an active share in the forward movement
when the body is contracted again. Frequently the animal retains only the
posterior end buried in the sand, and then the anchors keep it in position,
and make rapid withdrawal possible.
Thus we have in these apparently random forms of the calcareous bodies,
complex adaptations in which every little detail as to direction, curve,
and pointing is exactly determined. That they have selection-value in
their present perfected form is beyond all doubt, since the animals are
enabled by means of them to bore rapidly into the ground and so to escape
from enemies. We do not know what the initial stages were, but we cannot
doubt that the little improvements, which occurred as variations of the
originally simple slimy bodies of the Holothurians, were preserved because
they already possessed selection-value for the Synaptidae. For such minute
microscopic structures whose form is so delicately adapted to the role they
have to play in the life of the animal, cannot have arisen suddenly and as
a whole, and every new variation of the anchor, that is, in the direction
of the development of the two arms, and every curving of the shaft which
prevented the tips from projecting at the wrong time, in short, every
little adaptation in the modelling of the anchor must have possessed
selection-value. And that such minute changes of form fall within the
sphere of fluctuating variations, that is to say, THAT THEY OCCUR is beyond
all doubt.
In many of the Synaptidae the anchors are replaced by calcareous rods bent
in the form of an S, which are said to act in the same way. Others, such
as those of the genus Ankyroderma, have anchors which project considerably
beyond the skin, and, according to Oestergren, serve "to catch plant-
particles and other substances" and so mask the animal. Thus we see that
in the Synaptidae the thick and irregular calcareous bodies of the
Holothurians have been modified and transformed in various ways in
adaptation to the footlessness of these animals, and to the peculiar
conditions of their life, and we must conclude that the earlier stages of
these changes presented themselves to the processes of selection in the
form of microscopic variations. For it is as impossible to think of any
origin other than through selection in this case as in the case of the
toughness, and the "drip-tips" of tropical leaves. And as these last could
not have been produced directly by the beating of the heavy rain-drops upon
them, so the calcareous anchors of Synapta cannot have been produced
directly by the friction of the sand and mud at the bottom of the sea, and,
since they are parts whose function is PASSIVE the Lamarckian factor of use
and disuse does not come into question. The conclusion is unavoidable,
that the microscopically small variations of the calcareous bodies in the
ancestral forms have been intensified and accumulated in a particular
direction, till they have led to the formation of the anchor. Whether this
has taken place by the action of natural selection alone, or whether the
laws of variation and the intimate processes within the germ-plasm have
cooperated will become clear in the discussion of germinal selection. This
whole process of adaptation has obviously taken place within the time that
has elapsed since this group of sea-cucumbers lost their tube-feet, those
characteristic organs of locomotion which occur in no group except the
Echinoderms, and yet have totally disappeared in the Synaptidae. And after
all what would animals that live in sand and mud do with tube-feet?
(c) COADAPTATION.
Darwin pointed out that one of the essential differences between artificial
and natural selection lies in the fact that the former can modify only a
few characters, usually only one at a time, while Nature preserves in the
struggle for existence all the variations of a species, at the same time
and in a purely mechanical way, if they possess selection-value.
Herbert Spencer, though himself an adherent of the theory of selection,
declared in the beginning of the nineties that in his opinion the range of
this principle was greatly over-estimated, if the great changes which have
taken place in so many organisms in the course of ages are to be
interpreted as due to this process of selection alone, since no
transformation of any importance can be evolved by itself; it is always
accompanied by a host of secondary changes. He gives the familiar example
of the Giant Stag of the Irish peat, the enormous antlers of which required
not only a much stronger skull cap, but also greater strength of the
sinews, muscles, nerves and bones of the whole anterior half of the animal,
if their mass was not to weigh down the animal altogether. It is
inconceivable, he says, that so many processes of selection should take
place SIMULTANEOUSLY, and we are therefore forced to fall back on the
Lamarckian factor of the use and disuse of functional parts. And how, he
asks, could natural selection follow two opposite directions of evolution
in different parts of the body at the same time, as for instance in the
case of the kangaroo, in which the forelegs must have become shorter, while
the hind legs and the tail were becoming longer and stronger?
Spencer's main object was to substantiate the validity of the Lamarckian
principle, the cooperation of which with selection had been doubted by
many. And it does seem as though this principle, if it operates in nature
at all, offers a ready and simple explanation of all such secondary
variations. Not only muscles, but nerves, bones, sinews, in short all
tissues which function actively, increase in strength in proportion as they
are used, and conversely they decrease when the claims on them diminish.
All the parts, therefore, which depend on the part that varied first, as
for instance the enlarged antlers of the Irish Elk, must have been
increased or decreased in strength, in exact proportion to the claims made
upon them,--just as is actually the case.
But beautiful as this explanation would be, I regard it as untenable,
because it assumes the TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS (so-
called "acquired" characters), and this is not only undemonstrable, but is
scarcely theoretically conceivable, for the secondary variations which
accompany or follow the first as correlative variations, occur also in
cases in which the animals concerned are sterile and THEREFORE CANNOT
TRANSMIT ANYTHING TO THEIR DESCENDANTS. This is true of WORKER BEES, and
particularly of ANTS, and I shall here give a brief survey of the present
state of the problem as it appears to me.
Much has been written on both sides of this question since the published
controversy on the subject in the nineties between Herbert Spencer and
myself. I should like to return to the matter in detail, if the space at
my disposal permitted, because it seems to me that the arguments I advanced
at that time are equally cogent to-day, notwithstanding all the objections
that have since been urged against them. Moreover, the matter is by no
means one of subordinate interest; it is the very kernel of the whole
question of the reality and value of the principle of selection. For if
selection alone does not suffice to explain "HARMONIOUS ADAPTATION" as I
have called Spencer's COADAPTATION, and if we require to call in the aid of
the Lamarckian factor it would be questionable whether selection could
explain any adaptations whatever. In this particular case--of worker bees
--the Lamarckian factor may be excluded altogether, for it can be
demonstrated that here at any rate the effects of use and disuse cannot be
transmitted.
But if it be asked why we are unwilling to admit the cooperation of the
Darwinian factor of selection and the Lamarckian factor, since this would
afford us an easy and satisfactory explanation of the phenomena, I answer:
BECAUSE THE LAMARCKIAN PRINCIPLE IS FALLACIOUS, AND BECAUSE BY ACCEPTING IT
WE CLOSE THE WAY TOWARDS DEEPER INSIGHT. It is not a spirit of
combativeness or a desire for self-vindication that induces me to take the
field once more against the Lamarckian principle, it is the conviction that
the progress of our knowledge is being obstructed by the acceptance of this
fallacious principle, since the facile explanation it apparently affords
prevents our seeking after a truer explanation and a deeper analysis.
The workers in the various species of ants are sterile, that is to say,
they take no regular part in the reproduction of the species, although
individuals among them may occasionally lay eggs. In addition to this they
have lost the wings, and the receptaculum seminis, and their compound eyes
have degenerated to a few facets. How could this last change have come
about through disuse, since the eyes of workers are exposed to light in the
same way as are those of the sexual insects and thus in this particular
case are not liable to "disuse" at all? The same is true of the
receptaculum seminis, which can only have been disused as far as its
glandular portion and its stalk are concerned, and also of the wings, the
nerves tracheae and epidermal cells of which could not cease to function
until the whole wing had degenerated, for the chitinous skeleton of the
wing does not function at all in the active sense.
But, on the other hand, the workers in all species have undergone
modifications in a positive direction, as, for instance, the greater
development of brain. In many species large workers have evolved,--the so-
called SOLDIERS, with enormous jaws and teeth, which defend the colony,--
and in others there are SMALL workers which have taken over other special
functions, such as the rearing of the young Aphides. This kind of division
of the workers into two castes occurs among several tropical species of
ants, but it is also present in the Italian species, Colobopsis truncata.
Beautifully as the size of the jaws could be explained as due to the
increased use made of them by the "soldiers," or the enlarged brain as due
to the mental activities of the workers, the fact of the infertility of
these forms is an insurmountable obstacle to accepting such an explanation.
Neither jaws nor brain can have been evolved on the Lamarckian principle.
The problem of coadaptation is no easier in the case of the ant than in the
case of the Giant Stag. Darwin himself gave a pretty illustration to show
how imposing the difference between the two kinds of workers in one species
would seem if we translated it into human terms. In regard to the Driver
ants (Anomma) we must picture to ourselves a piece of work, "for instance
the building of a house, being carried on by two kinds of workers, of which
one group was five feet four inches high, the other sixteen feet high."
("Origin of Species" (6th edition), page 232.)
Although the ant is a small animal as compared with man or with the Irish
Elk, the "soldier" with its relatively enormous jaws is hardly less heavily
burdened than the Elk with its antlers, and in the ant's case, too, a
strengthening of the skeleton, of the muscles, the nerves of the head, and
of the legs must have taken place parallel with the enlargement of the
jaws. HARMONIOUS ADAPTATION (coadaptation) has here been active in a high
degree, and yet these "soldiers" are sterile! There thus remains nothing
for it but to refer all their adaptations, positive and negative alike, to
processes of selection which have taken place in the rudiments of the
workers within the egg and sperm-cells of their parents. There is no way
out of the difficulty except the one Darwin pointed out. He himself did
not find the solution of the riddle at once. At first he believed that the
case of the workers among social insects presented "the most serious
special difficulty" in the way of his theory of natural selection; and it
was only after it had become clear to him, that it was not the sterile
insects themselves but their parents that were selected, according as they
produced more or less well adapted workers, that he was able to refer to
this very case of the conditions among ants "IN ORDER TO SHOW THE POWER OF
NATURAL SELECTION" ("Origin of Species", page 233; see also edition 1, page
242.). He explains his view by a simple but interesting illustration.
Gardeners have produced, by means of long continued artificial selection, a
variety of Stock, which bears entirely double, and therefore infertile
flowers (Ibid. page 230.). Nevertheless the variety continues to be
reproduced from seed, because in addition to the double and infertile
flowers, the seeds always produce a certain number of single, fertile
blossoms, and these are used to reproduce the double variety. These single
and fertile plants correspond "to the males and females of an ant-colony,
the infertile plants, which are regularly produced in large numbers, to the
neuter workers of the colony."
This illustration is entirely apt, the only difference between the two
cases consisting in the fact that the variation in the flower is not a
useful, but a disadvantageous one, which can only be preserved by
artificial selection on the part of the gardener, while the transformations
that have taken place parallel with the sterility of the ants are useful,
since they procure for the colony an advantage in the struggle for
existence, and they are therefore preserved by natural selection. Even the
sterility itself in this case is not disadvantageous, since the fertility
of the true females has at the same time considerably increased. We may
therefore regard the sterile forms of ants, which have gradually been
adapted in several directions to varying functions, AS A CERTAIN PROOF that
selection really takes place in the germ-cells of the fathers and mothers
of the workers, and that SPECIAL COMPLEXES OF PRIMORDIA (IDS) are present
in the workers and in the males and females, and these complexes contain
the primordia of the individual parts (DETERMINANTS). But since all living
entities vary, the determinants must also vary, now in a favourable, now in
an unfavourable direction. If a female produces eggs, which contain
favourably varying determinants in the worker-ids, then these eggs will
give rise to workers modified in the favourable direction, and if this
happens with many females, the colony concerned will contain a better kind
of worker than other colonies.
I digress here in order to give an account of the intimate processes,
which, according to my view, take place within the germ-plasm, and which I
have called "GERMINAL SELECTION." These processes are of importance since
they form the roots of variation, which in its turn is the root of natural
selection. I cannot here do more than give a brief outline of the theory
in order to show how the Darwin-Wallace theory of selection has gained
support from it.
With others, I regard the minimal amount of substance which is contained
within the nucleus of the germ-cells, in the form of rods, bands, or
granules, as the GERM-SUBSTANCE or GERM-PLASM, and I call the individual
granules IDS. There is always a multiplicity of such ids present in the
nucleus, either occurring individually, or united in the form of rods or
bands (chromosomes). Each id contains the primary constituents of a WHOLE
individual, so that several ids are concerned in the development of a new
individual.
In every being of complex structure thousands of primary constituents must
go to make up a single id; these I call DETERMINANTS, and I mean by this
name very small individual particles, far below the limits of microscopic
visibility, vital units which feed, grow, and multiply by division. These
determinants control the parts of the developing embryo,--in what manner
need not here concern us. The determinants differ among themselves, those
of a muscle are differently constituted from those of a nerve-cell or a
glandular cell, etc., and every determinant is in its turn made up of
minute vital units, which I call BIOPHORS, or the bearers of life.
According to my view, these determinants not only assimilate, like every
other living unit, but they VARY in the course of their growth, as every
living unit does; they may vary qualitatively if the elements of which they
are composed vary, they may grow and divide more or less rapidly, and their
variations give rise to CORRESPONDING variations of the organ, cell, or
cell-group which they determine. That they are undergoing ceaseless
fluctuations in regard to size and quality seems to me the inevitable
consequence of their unequal nutrition; for although the germ-cell as a
whole usually receives sufficient nutriment, minute fluctuations in the
amount carried to different parts within the germ-plasm cannot fail to
occur.
Now, if a determinant, for instance of a sensory cell, receives for a
considerable time more abundant nutriment than before, it will grow more
rapidly--become bigger, and divide more quickly, and, later, when the id
concerned develops into an embryo, this sensory cell will become stronger
than in the parents, possibly even twice as strong. This is an instance of
a HEREDITARY INDIVIDUAL VARIATION, arising from the germ.
The nutritive stream which, according to our hypothesis, favours the
determinant N by chance, that is, for reasons unknown to us, may remain
strong for a considerable time, or may decrease again; but even in the
latter case it is conceivable that the ascending movement of the
determinant may continue, because the strengthened determinant now ACTIVELY
nourishes itself more abundantly,--that is to say, it attracts the
nutriment to itself, and to a certain extent withdraws it from its fellow-
determinants. In this way, it may--as it seems to me--get into PERMANENT
UPWARD MOVEMENT, AND ATTAIN A DEGREE OF STRENGTH FROM WHICH THERE IS NO
FALLING BACK. Then positive or negative selection sets in, favouring the
variations which are advantageous, setting aside those which are
disadvantageous.
In a similar manner a DOWNWARD variation of the determinants may take
place, if its progress be started by a diminished flow of nutriment. The
determinants which are weakened by this diminished flow will have less
affinity for attracting nutriment because of their diminished strength, and
they will assimilate more feebly and grow more slowly, unless chance
streams of nutriment help them to recover themselves. But, as will
presently be shown, a change of direction cannot take place at EVERY stage
of the degenerative process. If a certain critical stage of downward
progress be passed, even favourable conditions of food-supply will no
longer suffice permanently to change the direction of the variation. Only
two cases are conceivable; if the determinant corresponds to a USEFUL
organ, only its removal can bring back the germ-plasm to its former level;
therefore personal selection removes the id in question, with its
determinants, from the germ-plasm, by causing the elimination of the
individual in the struggle for existence. But there is another conceivable
case; the determinants concerned may be those of an organ which has become
USELESS, and they will then continue unobstructed, but with exceeding
slowness, along the downward path, until the organ becomes vestigial, and
finally disappears altogether.
The fluctuations of the determinants hither and thither may thus be
transformed into a lasting ascending or descending movement; and THIS IS
THE CRUCIAL POINT OF THESE GERMINAL PROCESSES.
This is not a fantastic assumption; we can read it in the fact of the
degeneration of disused parts. USELESS ORGANS ARE THE ONLY ONES WHICH ARE
NOT HELPED TO ASCEND AGAIN BY PERSONAL SELECTION, AND THEREFORE IN THEIR
CASE ALONE CAN WE FORM ANY IDEA OF HOW THE PRIMARY CONSTITUENTS BEHAVE,
WHEN THEY ARE SUBJECT SOLELY TO INTRA-GERMINAL FORCES.
The whole determinant system of an id, as I conceive it, is in a state of
continual fluctuation upwards and downwards. In most cases the
fluctuations will counteract one another, because the passive streams of
nutriment soon change, but in many cases the limit from which a return is
possible will be passed, and then the determinants concerned will continue
to vary in the same direction, till they attain positive or negative
selection-value. At this stage personal selection intervenes and sets
aside the variation if it is disadvantageous, or favours--that is to say,
preserves--it if it is advantageous. Only THE DETERMINANT OF A USELESS
ORGAN IS UNINFLUENCED BY PERSONAL SELECTION, and, as experience shows, it
sinks downwards; that is, the organ that corresponds to it degenerates very
slowly but uninterruptedly till, after what must obviously be an immense
stretch of time, it disappears from the germ-plasm altogether.
Thus we find in the fact of the degeneration of disused parts the proof
that not all the fluctuations of a determinant return to equilibrium again,
but that, when the movement has attained to a certain strength, it
continues IN THE SAME DIRECTION. We have entire certainty in regard to
this as far as the downward progress is concerned, and we must assume it
also in regard to ascending variations, as the phenomena of artificial
selection certainly justify us in doing. If the Japanese breeders were
able to lengthen the tail feathers of the cock to six feet, it can only
have been because the determinants of the tail-feathers in the germ-plasm
had already struck out a path of ascending variation, and this movement was
taken advantage of by the breeder, who continually selected for
reproduction the individuals in which the ascending variation was most
marked. For all breeding depends upon the unconscious selection of
germinal variations.
Of course these germinal processes cannot be proved mathematically, since
we cannot actually see the play of forces of the passive fluctuations and
their causes. We cannot say how great these fluctuations are, and how
quickly or slowly, how regularly or irregularly they change. Nor do we
know how far a determinant must be strengthened by the passive flow of the
nutritive stream if it is to be beyond the danger of unfavourable
variations, or how far it must be weakened passively before it loses the
power of recovering itself by its own strength. It is no more possible to
bring forward actual proofs in this case than it was in regard to the
selection-value of the initial stages of an adaptation. But if we consider
that all heritable variations must have their roots in the germ-plasm, and
further, that when personal selection does not intervene, that is to say,
in the case of parts which have become useless, a degeneration of the part,
and therefore also of its determinant must inevitably take place; then we
must conclude that processes such as I have assumed are running their
course within the germ-plasm, and we can do this with as much certainty as
we were able to infer, from the phenomena of adaptation, the selection-
value of their initial stages. The fact of the degeneration of disused
parts seems to me to afford irrefutable proof that the fluctuations within
the germ-plasm ARE THE REAL ROOT OF ALL HEREDITARY VARIATION, and the
preliminary condition for the occurrence of the Darwin-Wallace factor of
selection. Germinal selection supplies the stones out of which personal
selection builds her temples and palaces: ADAPTATIONS. The importance for
the theory of the process of degeneration of disused parts cannot be over-
estimated, especially when it occurs in sterile animal forms, where we are
free from the doubt as to the alleged LAMARCKIAN FACTOR which is apt to
confuse our ideas in regard to other cases.
If we regard the variation of the many determinants concerned in the
transformation of the female into the sterile worker as having come about
through the gradual transformation of the ids into worker-ids, we shall see
that the germ-plasm of the sexual ants must contain three kinds of ids,
male, female, and worker ids, or if the workers have diverged into soldiers
and nest-builders, then four kinds. We understand that the worker-ids
arose because their determinants struck out a useful path of variation,
whether upward or downward, and that they continued in this path until the
highest attainable degree of utility of the parts determined was reached.
But in addition to the organs of positive or negative selection-value,
there were some which were indifferent as far as the success and especially
the functional capacity of the workers was concerned: wings, ovarian
tubes, receptaculum seminis, a number of the facets of the eye, perhaps
even the whole eye. As to the ovarian tubes it is possible that their
degeneration was an advantage for the workers, in saving energy, and if so
selection would favour the degeneration; but how could the presence of eyes
diminish the usefulness of the workers to the colony? or the minute
receptaculum seminis, or even the wings? These parts have therefore
degenerated BECAUSE THEY WERE OF NO FURTHER VALUE TO THE INSECT. But if
selection did not influence the setting aside of these parts because they
were neither of advantage nor of disadvantage to the species, then the
Darwinian factor of selection is here confronted with a puzzle which it
cannot solve alone, but which at once becomes clear when germinal selection
is added. For the determinants of organs that have no further value for
the organism, must, as we have already explained, embark on a gradual
course of retrograde development.
In ants the degeneration has gone so far that there are no wing-rudiments
present in ANY species, as is the case with so many butterflies, flies, and
locusts, but in the larvae the imaginal discs of the wings are still laid
down. With regard to the ovaries, degeneration has reached different
levels in different species of ants, as has been shown by the researches of
my former pupil, Elizabeth Bickford. In many species there are twelve
ovarian tubes, and they decrease from that number to one; indeed, in one
species no ovarian tube at all is present. So much at least is certain
from what has been said, that in this case EVERYTHING depends on the
fluctuations of the elements of the germ-plasm. Germinal selection, here
as elsewhere, presents the variations of the determinants, and personal
selection favours or rejects these, or,--if it be a question of organs
which have become useless,--it does not come into play at all, and allows
the descending variation free course.
It is obvious that even the problem of COADAPTATION IN STERILE ANIMALS can
thus be satisfactorily explained. If the determinants are oscillating
upwards and downwards in continual fluctuation, and varying more
pronouncedly now in one direction now in the other, useful variations of
every determinant will continually present themselves anew, and may, in the
course of generations, be combined with one another in various ways. But
there is one character of the determinants that greatly facilitates this
complex process of selection, that, after a certain limit has been reached,
they go on varying in the same direction. From this it follows that
development along a path once struck out may proceed without the continual
intervention of personal selection. This factor only operates, so to
speak, at the beginning, when it selects the determinants which are varying
in the right direction, and again at the end, when it is necessary to put a
check upon further variation. In addition to this, enormously long periods
have been available for all these adaptations, as the very gradual
transition stages between females and workers in many species plainly show,
and thus this process of transformation loses the marvellous and mysterious
character that seemed at the first glance to invest it, and takes rank,
without any straining, among the other processes of selection. It seems to
me that, from the facts that sterile animal forms can adapt themselves to
new vital functions, their superfluous parts degenerate, and the parts more
used adapt themselves in an ascending direction, those less used in a
descending direction, we must draw the conclusion that harmonious
adaptation here comes about WITHOUT THE COOPERATION OF THE LAMARCKIAN
PRINCIPLE. This conclusion once established, however, we have no reason to
refer the thousands of cases of harmonious adaptation, which occur in
exactly the same way among other animals or plants, to a principle, the
ACTIVE INTERVENTION OF WHICH IN THE TRANSFORMATION OF SPECIES IS NOWHERE
PROVED. WE DO NOT REQUIRE IT TO EXPLAIN THE FACTS, AND THEREFORE WE MUST
NOT ASSUME IT.
The fact of coadaptation, which was supposed to furnish the strongest
argument against the principle of selection, in reality yields the clearest
evidence in favour of it. We MUST assume it, BECAUSE NO OTHER POSSIBILITY
OF EXPLANATION IS OPEN TO US, AND BECAUSE THESE ADAPTATIONS ACTUALLY EXIST,
THAT IS TO SAY, HAVE REALLY TAKEN PLACE. With this conviction I attempted,
as far back as 1894, when the idea of germinal selection had not yet
occurred to me, to make "harmonious adaptation" (coadaptation) more easily
intelligible in some way or other, and so I was led to the idea, which was
subsequently expounded in detail by Baldwin, and Lloyd Morgan, and also by
Osborn, and Gulick as ORGANIC SELECTION. It seemed to me that it was not
necessary that all the germinal variations required for secondary
variations should have occurred SIMULTANEOUSLY, since, for instance, in the
case of the stag, the bones, muscles, sinews, and nerves would be incited
by the increasing heaviness of the antlers to greater activity in THE
INDIVIDUAL LIFE, and so would be strengthened. The antlers can only have
increased in size by very slow degrees, so that the muscles and bones may
have been able to keep pace with their growth in the individual life, until
the requisite germinal variations presented themselves. In this way a
disharmony between the increasing weight of the antlers and the parts which
support and move them would be avoided, since time would be given for the
appropriate germinal variations to occur, and so to set agoing the
HEREDITARY variation of the muscles, sinews, and bones. ("The Effect of
External Influences upon Development", Romanes Lecture, Oxford, 1894.)
I still regard this idea as correct, but I attribute less importance to
"organic selection" than I did at that time, in so far that I do not
believe that it ALONE could effect complex harmonious adaptations.
Germinal selection now seems to me to play the chief part in bringing about
such adaptations. Something the same is true of the principle I have
called "Panmixia". As I became more and more convinced, in the course of
years, that the LAMARCKIAN PRINCIPLE ought not to be called in to explain
the dwindling of disused parts, I believed that this process might be
simply explained as due to the cessation of the conservative effect of
natural selection. I said to myself that, from the moment in which a part
ceases to be of use, natural selection withdraws its hand from it, and then
it must inevitably fall from the height of its adaptiveness, because
inferior variants would have as good a chance of persisting as better ones,
since all grades of fitness of the part in question would be mingled with
one another indiscriminately. This is undoubtedly true, as Romanes pointed
out ten years before I did, and this mingling of the bad with the good
probably does bring about a deterioration of the part concerned. But it
cannot account for the steady diminution, which always occurs when a part
is in process of becoming rudimentary, and which goes on until it
ultimately disappears altogether. The process of dwindling cannot
therefore be explained as due to panmixia alone; we can only find a
sufficient explanation in germinal selection.
IV. DERIVATIVES OF THE THEORY OF SELECTION.
The impetus in all directions given by Darwin through his theory of
selection has been an immeasurable one, and its influence is still felt. It
falls within the province of the historian of science to enumerate all the
ideas which, in the last quarter of the nineteenth century, grew out of
Darwin's theories, in the endeavour to penetrate more deeply into the
problem of the evolution of the organic world. Within the narrow limits to
which this paper is restricted, I cannot attempt to discuss any of these.
V. ARGUMENTS FOR THE REALITY OF THE PROCESSES OF SELECTION.
(a) SEXUAL SELECTION.
Sexual selection goes hand in hand with natural selection. From the very
first I have regarded sexual selection as affording an extremely important
and interesting corroboration of natural selection, but, singularly enough,
it is precisely against this theory that an adverse judgment has been
pronounced in so many quarters, and it is only quite recently, and probably
in proportion as the wealth of facts in proof of it penetrates into a wider
circle, that we seem to be approaching a more general recognition of this
side of the problem of adaptation. Thus Darwin's words in his preface to
the second edition (1874) of his book, "The Descent of Man and Sexual
Selection", are being justified: "My conviction as to the operation of
natural selection remains unshaken," and further, "If naturalists were to
become more familiar with the idea of sexual selection, it would, I think,
be accepted to a much greater extent, and already it is fully and
favourably accepted by many competent judges." Darwin was able to speak
thus because he was already acquainted with an immense mass of facts,
which, taken together, yield overwhelming evidence of the validity of the
principle of sexual selection.
NATURAL SELECTION chooses out for reproduction the individuals that are
best equipped for the struggle for existence, and it does so at every stage
of development; it thus improves the species in all its stages and forms.
SEXUAL SELECTION operates only on individuals that are already capable of
reproduction, and does so only in relation to the attainment of
reproduction. It arises from the rivalry of one sex, usually the male, for
the possession of the other, usually the female. Its influence can
therefore only DIRECTLY affect one sex, in that it equips it better for
attaining possession of the other. But the effect may extend indirectly to
the female sex, and thus the whole species may be modified, without,
however, becoming any more capable of resistance in the struggle for
existence, for sexual selection only gives rise to adaptations which are
likely to give their possessor the victory over rivals in the struggle for
possession of the female, and which are therefore peculiar to the wooing
sex: the manifold "secondary sexual characters." The diversity of these
characters is so great that I cannot here attempt to give anything
approaching a complete treatment of them, but I should like to give a
sufficient number of examples to make the principle itself, in its various
modes of expression, quite clear.
One of the chief preliminary postulates of sexual selection is the unequal
number of individuals in the two sexes, for if every male immediately finds
his mate there can be no competition for the possession of the female.
Darwin has shown that, for the most part, the inequality between the sexes
is due simply to the fact that there are more males than females, and
therefore the males must take some pains to secure a mate. But the
inequality does not always depend on the numerical preponderance of the
males, it is often due to polygamy; for, if one male claims several
females, the number of females in proportion to the rest of the males will
be reduced. Since it is almost always the males that are the wooers, we
must expect to find the occurrence of secondary sexual characters chiefly
among them, and to find it especially frequent in polygamous species. And
this is actually the case.
If we were to try to guess--without knowing the facts--what means the male
animals make use of to overcome their rivals in the struggle for the
possession of the female, we might name many kinds of means, but it would
be difficult to suggest any which is not actually employed in some animal
group or other. I begin with the mere difference in strength, through
which the male of many animals is so sharply distinguished from the female,
as, for instance, the lion, walrus, "sea-elephant," and others. Among
these the males fight violently for the possession of the female, who falls
to the victor in the combat. In this simple case no one can doubt the
operation of selection, and there is just as little room for doubt as to
the selection-value of the initial stages of the variation. Differences in
bodily strength are apparent even among human beings, although in their
case the struggle for the possession of the female is no longer decided by
bodily strength alone.
Combats between male animals are often violent and obstinate, and the
employment of the natural weapons of the species in this way has led to
perfecting of these, e.g. the tusks of the boar, the antlers of the stag,
and the enormous, antler-like jaws of the stag-beetle. Here again it is
impossible to doubt that variations in these organs presented themselves,
and that these were considerable enough to be decisive in combat, and so to
lead to the improvement of the weapon.
Among many animals, however, the females at first withdraw from the males;
they are coy, and have to be sought out, and sometimes held by force. This
tracking and grasping of the females by the males has given rise to many
different characters in the latter, as, for instance, the larger eyes of
the male bee, and especially of the males of the Ephemerids (May-flies),
some species of which show, in addition to the usual compound eyes, large,
so-called turban-eyes, so that the whole head is covered with seeing
surfaces. In these species the females are very greatly in the minority (1-
100), and it is easy to understand that a keen competition for them must
take place, and that, when the insects of both sexes are floating freely in
the air, an unusually wide range of vision will carry with it a decided
advantage. Here again the actual adaptations are in accordance with the
preliminary postulates of the theory. We do not know the stages through
which the eye has passed to its present perfected state, but, since the
number of simple eyes (facets) has become very much greater in the male
than in the female, we may assume that their increase is due to a gradual
duplication of the determinants of the ommatidium in the germ-plasm, as I
have already indicated in regard to sense-organs in general. In this case,
again, the selection-value of the initial stages hardly admits of doubt;
better vision DIRECTLY secures reproduction.
In many cases THE ORGAN OF SMELL shows a similar improvement. Many lower
Crustaceans (Daphnidae) have better developed organs of smell in the male
sex. The difference is often slight and amounts only to one or two
olfactory filaments, but certain species show a difference of nearly a
hundred of these filaments (Leptodora). The same thing occurs among
insects.
We must briefly consider the clasping or grasping organs which have
developed in the males among many lower Crustaceans, but here natural
selection plays its part along with sexual selection, for the union of the
sexes is an indispensable condition for the maintenance of the species, and
as Darwin himself pointed out, in many cases the two forms of selection
merge into each other. This fact has always seemed to me to be a proof of
natural selection, for, in regard to sexual selection, it is quite obvious
that the victory of the best-equipped could have brought about the
improvement only of the organs concerned, the factors in the struggle, such
as the eye and the olfactory organ.
We come now to the EXCITANTS; that is, to the group of sexual characters
whose origin through processes of selection has been most frequently called
in question. We may cite the LOVE-CALLS produced by many male insects,
such as crickets and cicadas. These could only have arisen in animal
groups in which the female did not rapidly flee from the male, but was
inclined to accept his wooing from the first. Thus, notes like the
chirping of the male cricket serve to entice the females. At first they
were merely the signal which showed the presence of a male in the
neighbourhood, and the female was gradually enticed nearer and nearer by
the continued chirping. The male that could make himself heard to the
greatest distance would obtain the largest following, and would transmit
the beginnings, and, later, the improvement of his voice to the greatest
number of descendants. But sexual excitement in the female became
associated with the hearing of the love-call, and then the sound-producing
organ of the male began to improve, until it attained to the emission of
the long-drawn-out soft notes of the mole-cricket or the maenad-like cry of
the cicadas. I cannot here follow the process of development in detail,
but will call attention to the fact that the original purpose of the voice,
the announcing of the male's presence, became subsidiary, and the exciting
of the female became the chief goal to be aimed at. The loudest singers
awakened the strongest excitement, and the improvement resulted as a matter
of course. I conceive of the origin of bird-song in a somewhat similar
manner, first as a means of enticing, then of exciting the female.
One more kind of secondary sexual character must here be mentioned: the
odour which emanates from so many animals at the breeding season. It is
possible that this odour also served at first merely to give notice of the
presence of individuals of the other sex, but it soon became an excitant,
and as the individuals which caused the greatest degree of excitement were
preferred, it reached as high a pitch of perfection as was possible to it.
I shall confine myself here to the comparatively recently discovered
fragrance of butterflies. Since Fritz Muller found out that certain
Brazilian butterflies gave off fragrance "like a flower," we have become
acquainted with many such cases, and we now know that in all lands, not
only many diurnal Lepidoptera but nocturnal ones also give off a delicate
odour, which is agreeable even to man. The ethereal oil to which this
fragrance is due is secreted by the skin-cells, usually of the wing, as I
showed soon after the discovery of the SCENT-SCALES. This is the case in
the males; the females have no SPECIAL scent-scales recognisable as such by
their form, but they must, nevertheless, give off an extremely delicate
fragrance, although our imperfect organ of smell cannot perceive it, for
the males become aware of the presence of a female, even at night, from a
long distance off, and gather round her. We may therefore conclude, that
both sexes have long given forth a very delicate perfume, which announced
their presence to others of the same species, and that in many species (NOT
IN ALL) these small beginnings became, in the males, particularly strong
scent-scales of characteristic form (lute, brush, or lyre-shaped). At
first these scales were scattered over the surface of the wing, but
gradually they concentrated themselves, and formed broad, velvety bands, or
strong, prominent brushes, and they attained their highest pitch of
evolution when they became enclosed within pits or folds of the skin, which
could be opened to let the delicious fragrance stream forth suddenly
towards the female. Thus in this case also we see that characters, the
original use of which was to bring the sexes together, and so to maintain
the species, have been evolved in the males into means for exciting the
female. And we can hardly doubt, that the females are most readily enticed
to yield to the butterfly that sends out the strongest fragrance,--that is
to say, that excites them to the highest degree. It is a pity that our
organs of smell are not fine enough to examine the fragrance of male
Lepidoptera in general, and to compare it with other perfumes which attract
these insects. (See Poulton, "Essays on Evolution", 1908, pages 316, 317.)
As far as we can perceive them they resemble the fragrance of flowers, but
there are Lepidoptera whose scent suggests musk. A smell of musk is also
given off by several plants: it is a sexual excitant in the musk-deer, the
musk-sheep, and the crocodile.
As far as we know, then, it is perfumes similar to those of flowers that
the male Lepidoptera give off in order to entice their mates, and this is a
further indication that animals, like plants, can to a large extent meet
the claims made upon them by life, and produce the adaptations which are
most purposive,--a further proof, too, of my proposition that the useful
variations, so to speak, are ALWAYS THERE. The flowers developed the
perfumes which entice their visitors, and the male Lepidoptera developed
the perfumes which entice and excite their mates.
There are many pretty little problems to be solved in this connection, for
there are insects, such as some flies, that are attracted by smells which
are unpleasant to us, like those from decaying flesh and carrion. But
there are also certain flowers, some orchids for instance, which give forth
no very agreeable odour, but one which is to us repulsive and disgusting;
and we should therefore expect that the males of such insects would give
off a smell unpleasant to us, but there is no case known to me in which
this has been demonstrated.
In cases such as we have discussed, it is obvious that there is no possible
explanation except through selection. This brings us to the last kind of
secondary sexual characters, and the one in regard to which doubt has been
most frequently expressed,--decorative colours and decorative forms, the
brilliant plumage of the male pheasant, the humming-birds, and the bird of
Paradise, as well as the bright colours of many species of butterfly, from
the beautiful blue of our little Lycaenidae to the magnificent azure of the
large Morphinae of Brazil. In a great many cases, though not by any means
in all, the male butterflies are "more beautiful" than the females, and in
the Tropics in particular they shine and glow in the most superb colours.
I really see no reason why we should doubt the power of sexual selection,
and I myself stand wholly on Darwin's side. Even though we certainly
cannot assume that the females exercise a conscious choice of the
"handsomest" mate, and deliberate like the judges in a court of justice
over the perfections of their wooers, we have no reason to doubt that
distinctive forms (decorative feathers) and colours have a particularly
exciting effect upon the female, just as certain odours have among animals
of so many different groups, including the butterflies. The doubts which
existed for a considerable time, as a result of fallacious experiments, as
to whether the colours of flowers really had any influence in attracting
butterflies have now been set at rest through a series of more careful
investigations; we now know that the colours of flowers are there on
account of the butterflies, as Sprengel first showed, and that the blossoms
of Phanerogams are selected in relation to them, as Darwin pointed out.
Certainly it is not possible to bring forward any convincing proof of the
origin of decorative colours through sexual selection, but there are many
weighty arguments in favour of it, and these form a body of presumptive
evidence so strong that it almost amounts to certainty.
In the first place, there is the analogy with other secondary sexual
characters. If the song of birds and the chirping of the cricket have been
evolved through sexual selection, if the penetrating odours of male
animals,--the crocodile, the musk-deer, the beaver, the carnivores, and,
finally, the flower-like fragrances of the butterflies have been evolved to
their present pitch in this way, why should decorative colours have arisen
in some other way? Why should the eye be less sensitive to SPECIFICALLY
MALE colours and other VISIBLE signs ENTICING TO THE FEMALE, than the
olfactory sense to specifically male odours, or the sense of hearing to
specifically male sounds? Moreover, the decorative feathers of birds are
almost always spread out and displayed before the female during courtship.
I have elsewhere ("The Evolution Theory", London, 1904, I. page 219.)
pointed out that decorative colouring and sweet-scentedness may replace one
another in Lepidoptera as well as in flowers, for just as some modestly
coloured flowers (mignonette and violet) have often a strong perfume, while
strikingly coloured ones are sometimes quite devoid of fragrance, so we
find that the most beautiful and gaily-coloured of our native Lepidoptera,
the species of Vanessa, have no scent-scales, while these are often
markedly developed in grey nocturnal Lepidoptera. Both attractions may,
however, be combined in butterflies, just as in flowers. Of course, we
cannot explain why both means of attraction should exist in one genus, and
only one of them in another, since we do not know the minutest details of
the conditions of life of the genera concerned. But from the sporadic
distribution of scent-scales in Lepidoptera, and from their occurrence or
absence in nearly related species, we may conclude that fragrance is a
relatively MODERN acquirement, more recent than brilliant colouring.
One thing in particular that stamps decorative colouring as a product of
selection is ITS GRADUAL INTENSIFICATION by the addition of new spots,
which we can quite well observe, because in many cases the colours have
been first acquired by the males, and later transmitted to the females by
inheritance. The scent-scales are never thus transmitted, probably for the
same reason that the decorative colours of many birds are often not
transmitted to the females: because with these they would be exposed to
too great elimination by enemies. Wallace was the first to point out that
in species with concealed nests the beautiful feathers of the male occurred
in the female also, as in the parrots, for instance, but this is not the
case in species which brood on an exposed nest. In the parrots one can
often observe that the general brilliant colouring of the male is found in
the female, but that certain spots of colour are absent, and these have
probably been acquired comparatively recently by the male and have not yet
been transmitted to the female.
Isolation of the group of individuals which is in process of varying is
undoubtedly of great value in sexual selection, for even a solitary
conspicuous variation will become dominant much sooner in a small isolated
colony, than among a large number of members of a species.
Anyone who agrees with me in deriving variations from germinal selection
will regard that process as an essential aid towards explaining the
selection of distinctive courtship-characters, such as coloured spots,
decorative feathers, horny outgrowths in birds and reptiles, combs,
feather-tufts, and the like, since the beginnings of these would be
presented with relative frequency in the struggle between the determinants
within the germ-plasm. The process of transmission of decorative feathers
to the female results, as Darwin pointed out and illustrated by interesting
examples, in the COLOUR-TRANSFORMATION OF A WHOLE SPECIES, and this
process, as the phyletically older colouring of young birds shows, must, in
the course of thousands of years, have repeated itself several times in a
line of descent.
If we survey the wealth of phenomena presented to us by secondary sexual
characters, we can hardly fail to be convinced of the truth of the
principle of sexual selection. And certainly no one who has accepted
natural selection should reject sexual selection, for, not only do the two
processes rest upon the same basis, but they merge into one another, so
that it is often impossible to say how much of a particular character
depends on one and how much on the other form of selection.
(b) NATURAL SELECTION.
An actual proof of the theory of sexual selection is out of the question,
if only because we cannot tell when a variation attains to selection-value.
It is certain that a delicate sense of smell is of value to the male moth
in his search for the female, but whether the possession of one additional
olfactory hair, or of ten, or of twenty additional hairs leads to the
success of its possessor we are unable to tell. And we are groping even
more in the dark when we discuss the excitement caused in the female by
agreeable perfumes, or by striking and beautiful colours. That these do
make an impression is beyond doubt; but we can only assume that slight
intensifications of them give any advantage, and we MUST assume this SINCE
OTHERWISE SECONDARY SEXUAL CHARACTERS REMAIN INEXPLICABLE.
The same thing is true in regard to natural selection. It is not possible
to bring forward any actual proof of the selection-value of the initial
stages, and the stages in the increase of variations, as has been already
shown. But the selection-value of a finished adaptation can in many cases
be statistically determined. Cesnola and Poulton have made valuable
experiments in this direction. The former attached forty-five individuals
of the green, and sixty-five of the brown variety of the praying mantis
(Mantis religiosa), by a silk thread to plants, and watched them for
seventeen days. The insects which were on a surface of a colour similar to
their own remained uneaten, while twenty-five green insects on brown parts
of plants had all disappeared in eleven days.
The experiments of Poulton and Sanders ("Report of the British Association"
(Bristol, 1898), London, 1899, pages 906-909.) were made with 600 pupae of
Vanessa urticae, the "tortoise-shell butterfly." The pupae were
artificially attached to nettles, tree-trunks, fences, walls, and to the
ground, some at Oxford, some at St Helens in the Isle of Wight. In the
course of a month 93 per cent of the pupae at Oxford were killed, chiefly
by small birds, while at St Helens 68 per cent perished. The experiments
showed very clearly that the colour and character of the surface on which
the pupa rests--and thus its own conspicuousness--are of the greatest
importance. At Oxford only the four pupae which were fastened to nettles
emerged; all the rest--on bark, stones and the like--perished. At St
Helens the elimination was as follows: on fences where the pupae were
conspicuous, 92 per cent; on bark, 66 per cent; on walls, 54 per cent; and
among nettles, 57 per cent. These interesting experiments confirm our
views as to protective coloration, and show further, THAT THE RATIO OF
ELIMINATION IN THE SPECIES IS A VERY HIGH ONE, AND THAT THEREFORE SELECTION
MUST BE VERY KEEN.
We may say that the process of selection follows as a logical necessity
from the fulfilment of the three preliminary postulates of the theory:
variability, heredity, and the struggle for existence, with its enormous
ratio of elimination in all species. To this we must add a fourth factor,
the INTENSIFICATION of variations which Darwin established as a fact, and
which we are now able to account for theoretically on the basis of germinal
selection. It may be objected that there is considerable uncertainty about
this LOGICAL proof, because of our inability to demonstrate the selection-
value of the initial stages and the individual stages of increase. We have
therefore to fall back on PRESUMPTIVE EVIDENCE. This is to be found in THE
INTERPRETATIVE VALUE OF THE THEORY. Let us consider this point in greater
detail.
In the first place, it is necessary to emphasise what is often overlooked,
namely, that the theory not only explains the TRANSFORMATIONS of species,
it also explains THEIR REMAINING THE SAME; in addition to the principle of
varying, it contains within itself that of PERSISTING. It is part of the
essence of selection, that it not only causes a part to VARY till it has
reached its highest pitch of adaptation, but that it MAINTAINS IT AT THIS
PITCH. THIS CONSERVING INFLUENCE OF NATURAL SELECTION is of great
importance, and was early recognised by Darwin; it follows naturally from
the principle of the survival of the fittest.
We understand from this how it is that a species which has become fully
adapted to certain conditions of life ceases to vary, but remains
"constant," as long as the conditions of life FOR IT remain unchanged,
whether this be for thousands of years, or for whole geological epochs.
But the most convincing proof of the power of the principle of selection
lies in the innumerable multitude of phenomena which cannot be explained in
any other way. To this category belong all structures which are only
PASSIVELY of advantage to the organism, because none of these can have
arisen by the alleged LAMARCKIAN PRINCIPLE. These have been so often
discussed that we need do no more than indicate them here. Until quite
recently the sympathetic coloration of animals--for instance, the whiteness
of Arctic animals--was referred, at least in part, to the DIRECT influence
of external factors, but the facts can best be explained by referring them
to the processes of selection, for then it is unnecessary to make the
gratuitous assumption that many species are sensitive to the stimulus of
cold and that others are not. The great majority of Arctic land-animals,
mammals and birds, are white, and this proves that they were all able to
present the variation which was most useful for them. The sable is brown,
but it lives in trees, where the brown colouring protects and conceals it
more effectively. The musk-sheep (Ovibos moschatus) is also brown, and
contrasts sharply with the ice and snow, but it is protected from beasts of
prey by its gregarious habit, and therefore it is of advantage to be
visible from as great a distance as possible. That so many species have
been able to give rise to white varieties does not depend on a special
sensitiveness of the skin to the influence of cold, but to the fact that
Mammals and Birds have a general tendency to vary towards white. Even with
us, many birds--starlings, blackbirds, swallows, etc.--occasionally produce
white individuals, but the white variety does not persist, because it
readily falls a victim to the carnivores. This is true of white fawns,
foxes, deer, etc. The whiteness, therefore, arises from internal causes,
and only persists when it is useful. A great many animals living in a
GREEN ENVIRONMENT have become clothed in green, especially insects,
caterpillars, and Mantidae, both persecuted and persecutors.
That it is not the direct effect of the environment which calls forth the
green colour is shown by the many kinds of caterpillar which rest on leaves
and feed on them, but are nevertheless brown. These feed by night and
betake themselves through the day to the trunk of the tree, and hide in the
furrows of the bark. We cannot, however, conclude from this that they were
UNABLE to vary towards green, for there are Arctic animals which are white
only in winter and brown in summer (Alpine hare, and the ptarmigan of the
Alps), and there are also green leaf-insects which remain green only while
they are young and difficult to see on the leaf, but which become brown
again in the last stage of larval life, when they have outgrown the leaf.
They then conceal themselves by day, sometimes only among withered leaves
on the ground, sometimes in the earth itself. It is interesting that in
one genus, Chaerocampa, one species is brown in the last stage of larval
life, another becomes brown earlier, and in many species the last stage is
not wholly brown, a part remaining green. Whether this is a case of a
double adaptation, or whether the green is being gradually crowded out by
the brown, the fact remains that the same species, even the same
individual, can exhibit both variations. The case is the same with many of
the leaf-like Orthoptera, as, for instance, the praying mantis (Mantis
religiosa) which we have already mentioned.
But the best proofs are furnished by those often-cited cases in which the
insect bears a deceptive resemblance to another object. We now know many
such cases, such as the numerous imitations of green or withered leaves,
which are brought about in the most diverse ways, sometimes by mere
variations in the form of the insect and in its colour, sometimes by an
elaborate marking, like that which occurs in the Indian leaf-butterflies,
Kallima inachis. In the single butterfly-genus Anaea, in the woods of
South America, there are about a hundred species which are all gaily
coloured on the upper surface, and on the reverse side exhibit the most
delicate imitation of the colouring and pattern of a leaf, generally
without any indication of the leaf-ribs, but extremely deceptive
nevertheless. Anyone who has seen only one such butterfly may doubt
whether many of the insignificant details of the marking can really be of
advantage to the insect. Such details are for instance the apparent holes
and splits in the apparently dry or half-rotten leaf, which are usually due
to the fact that the scales are absent on a circular or oval patch so that
the colourless wing-membrane lies bare, and one can look through the spot
as through a window. Whether the bird which is seeking or pursuing the
butterflies takes these holes for dewdrops, or for the work of a devouring
insect, does not affect the question; the mirror-like spot undoubtedly
increases the general deceptiveness, for the same thing occurs in many
leaf-butterflies, though not in all, and in some cases it is replaced in
quite a peculiar manner. In one species of Anaea (A. divina), the resting
butterfly looks exactly like a leaf out of the outer edge of which a large
semicircular piece has been eaten, possibly by a caterpillar; but if we
look more closely it is obvious that there is no part of the wing absent,
and that the semicircular piece is of a clear, pale yellow colour, while
the rest of the wing is of a strongly contrasted dark brown.
But the deceptive resemblance may be caused in quite a different manner. I
have often speculated as to what advantage the brilliant white C could give
to the otherwise dusky-coloured "Comma butterfly" (Grapta C. album).
Poulton's recent observations ("Proc. Ent. Soc"., London, May 6, 1903.)
have shown that this represents the imitation of a crack such as is often
seen in dry leaves, and is very conspicuous because the light shines
through it.
The utility obviously lies in presenting to the bird the very familiar
picture of a broken leaf with a clear shining slit, and we may conclude,
from the imitation of such small details, that the birds are very sharp
observers and that the smallest deviation from the usual arrests their
attention and incites them to closer investigation. It is obvious that
such detailed--we might almost say such subtle--deceptive resemblances
could only have come about in the course of long ages through the
acquirement from time to time of something new which heightened the already
existing resemblance.
In face of facts like these there can be no question of chance, and no one
has succeeded so far in finding any other explanation to replace that by
selection. For the rest, the apparent leaves are by no means perfect
copies of a leaf; many of them only represent the torn or broken piece, or
the half or two-thirds of a leaf, but then the leaves themselves frequently
do not present themselves to the eye as a whole, but partially concealed
among other leaves. Even those butterflies which, like the species of
Kallima and Anaea, represent the whole of a leaf with stalk, ribs, apex,
and the whole breadth, are not actual copies which would satisfy a
botanist; there is often much wanting. In Kallima the lateral ribs of the
leaf are never all included in the markings; there are only two or three on
the left side and at most four or five on the right, and in many
individuals these are rather obscure, while in others they are
comparatively distinct. This furnishes us with fresh evidence in favour of
their origin through processes of selection, for a botanically perfect
picture could not arise in this way; there could only be a fixing of such
details as heightened the deceptive resemblance.
Our postulate of origin through selection also enables us to understand why
the leaf-imitation is on the lower surface of the wing in the diurnal
Lepidoptera, and on the upper surface in the nocturnal forms, corresponding
to the attitude of the wings in the resting position of the two groups.
The strongest of all proofs of the theory, however, is afforded by cases of
true "mimicry," those adaptations discovered by Bates in 1861, consisting
in the imitation of one species by another, which becomes more and more
like its model. The model is always a species that enjoys some special
protection from enemies, whether because it is unpleasant to taste, or
because it is in some way dangerous.
It is chiefly among insects and especially among butterflies that we find
the greatest number of such cases. Several of these have been minutely
studied, and every detail has been investigated, so that it is difficult to
understand how there can still be disbelief in regard to them. If the many
and exact observations which have been carefully collected and critically
discussed, for instance by Poulton ("Essays on Evolution", 1889-1907,
Oxford, 1908, passim, e.g. page 269.) were thoroughly studied, the
arguments which are still frequently urged against mimicry would be found
untenable; we can hardly hope to find more convincing proof of the
actuality of the processes of selection than these cases put into our
hands. The preliminary postulates of the theory of mimicry have been
disputed, for instance, that diurnal butterflies are persecuted and eaten
by birds, but observations specially directed towards this point in India,
Africa, America and Europe have placed it beyond all doubt. If it were
necessary I could myself furnish an account of my own observations on this
point.
In the same way it has been established by experiment and observation in
the field that in all the great regions of distribution there are
butterflies which are rejected by birds and lizards, their chief enemies,
on account of their unpleasant smell or taste. These butterflies are
usually gaily and conspicuously coloured and thus--as Wallace first
interpreted it--are furnished with an easily recognisable sign: a sign of
unpalatableness or WARNING COLOURS. If they were not thus recognisable
easily and from a distance, they would frequently be pecked at by birds,
and then rejected because of their unpleasant taste; but as it is, the
insect-eaters recognise them at once as unpalatable booty and ignore them.
Such IMMUNE (The expression does not refer to all the enemies of this
butterfly; against ichneumon-flies, for instance, their unpleasant smell
usually gives no protection.) species, wherever they occur, are imitated by
other palatable species, which thus acquire a certain degree of protection.
It is true that this explanation of the bright, conspicuous colours is only
a hypothesis, but its foundations,--unpalatableness, and the liability of
other butterflies to be eaten,--are certain, and its consequences--the
existence of mimetic palatable forms--confirm it in the most convincing
manner. Of the many cases now known I select one, which is especially
remarkable, and which has been thoroughly investigated, Papilio dardanus
(merope), a large, beautiful, diurnal butterfly which ranges from Abyssinia
throughout the whole of Africa to the south coast of Cape Colony.
The males of this form are everywhere ALMOST the same in colour and in form
of wings, save for a few variations in the sparse black markings on the
pale yellow ground. But the females occur in several quite different forms
and colourings, and one of these only, the Abyssinian form, is like the
male, while the other three or four are MIMETIC, that is to say, they copy
a butterfly of quite a different family the Danaids, which are among the
IMMUNE forms. In each region the females have thus copied two or three
different immune species. There is much that is interesting to be said in
regard to these species, but it would be out of keeping with the general
tenor of this paper to give details of this very complicated case of
polymorphism in P. dardanus. Anyone who is interested in the matter will
find a full and exact statement of the case in as far as we know it, in
Poulton's "Essays on Evolution" (pages 373-375). (Professor Poulton has
corrected some wrong descriptions which I had unfortunately overlooked in
the Plates of my book "Vortrage uber Descendenztheorie", and which refer to
Papilio dardanus (merope). These mistakes are of no importance as far as
and understanding of the mimicry-theory is concerned, but I hope shortly to
be able to correct them in a later edition.) I need only add that three
different mimetic female forms have been reared from the eggs of a single
female in South Africa. The resemblance of these forms to their immune
models goes so far that even the details of the LOCAL forms of the models
are copied by the mimetic species.
It remains to be said that in Madagascar a butterfly, Papilio meriones,
occurs, of which both sexes are very similar in form and markings to the
non-mimetic male of P. dardanus, so that it probably represents the
ancestor of this latter species.
In face of such facts as these every attempt at another explanation must
fail. Similarly all the other details of the case fulfil the preliminary
postulates of selection, and leave no room for any other interpretation.
That the males do not take on the protective colouring is easily explained,
because they are in general more numerous, and the females are more
important for the preservation of the species, and must also live longer in
order to deposit their eggs. We find the same state of things in many
other species, and in one case (Elymnias undularis) in which the male is
also mimetically coloured, it copies quite a differently coloured immune
species from the model followed by the female. This is quite intelligible
when we consider that if there were TOO MANY false immune types, the birds
would soon discover that there were palatable individuals among those with
unpalatable warning colours. Hence the imitation of different immune
species by Papilio dardanus!
I regret that lack of space prevents my bringing forward more examples of
mimicry and discussing them fully. But from the case of Papilio dardanus
alone there is much to be learnt which is of the highest importance for our
understanding of transformations. It shows us chiefly what I once called,
somewhat strongly perhaps, THE OMNIPOTENCE OF NATURAL SELECTION in answer
to an opponent who had spoken of its "inadequacy." We here see that one
and the same species is capable of producing four or five different
patterns of colouring and marking; thus the colouring and marking are not,
as has often been supposed, a necessary outcome of the specific nature of
the species, but a true adaptation, which cannot arise as a direct effect
of climatic conditions, but solely through what I may call the sorting out
of the variations produced by the species, according to their utility.
That caterpillars may be either green or brown is already something more
than could have been expected according to the old conception of species,
but that one and the same butterfly should be now pale yellow, with black;
now red with black and pure white; now deep black with large, pure white
spots; and again black with a large ochreous-yellow spot, and many small
white and yellow spots; that in one sub-species it may be tailed like the
ancestral form, and in another tailless like its Danaid model,--all this
shows a far-reaching capacity for variation and adaptation that wide never
have expected if we did not see the facts before us. How it is possible
that the primary colour-variations should thus be intensified and combined
remains a puzzle even now; we are reminded of the modern three-colour
printing,--perhaps similar combinations of the primary colours take place
in this case; in any case the direction of these primary variations is
determined by the artist whom we know as natural selection, for there is no
other conceivable way in which the model could affect the butterfly that is
becoming more and more like it. The same climate surrounds all four forms
of female; they are subject to the same conditions of nutrition. Moreover,
Papilio dardanus is by no means the only species of butterfly which
exhibits different kinds of colour-pattern on its wings. Many species of
the Asiatic genus Elymnias have on the upper surface a very good imitation
of an immune Euploeine (Danainae), often with a steel-blue ground-colour,
while the under surface is well concealed when the butterfly is at rest,--
thus there are two kinds of protective coloration each with a different
meaning! The same thing may be observed in many non-mimetic butterflies,
for instance in all our species of Vanessa, in which the under side shows a
grey-brown or brownish-black protective coloration, but we do not yet know
with certainty what may be the biological significance of the gaily
coloured upper surface.
In general it may be said that mimetic butterflies are comparatively rare
species, but there are exceptions, for instance Limenitis archippus in
North America, of which the immune model (Danaida plexippus) also occurs in
enormous numbers.
In another mimicry-category the imitators are often more numerous than the
models, namely in the case of the imitation of DANGEROUS INSECTS by
harmless species. Bees and wasps are dreaded for their sting, and they are
copied by harmless flies of the genera Eristalis and Syrphus, and these
mimics often occur in swarms about flowering plants without damage to
themselves or to their models; they are feared and are therefore left
unmolested.
In regard also to the FAITHFULNESS OF THE COPY the facts are quite in
harmony with the theory, according to which the resemblance must have
arisen and increased BY DEGREES. We can recognise this in many cases, for
even now the mimetic species show very VARYING DEGREES OF RESEMBLANCE to
their immune model. If we compare, for instance, the many different
imitators of Danaida chrysippus we find that, with their brownish-yellow
ground-colour, and the position and size, and more or less sharp limitation
of their clear marginal spots, they have reached very different degrees of
nearness to their model. Or compare the female of Elymnias undularis with
its model Danaida genutia; there is a general resemblance, but the marking
of the Danaida is very roughly imitated in Elymnias.
Another fact that bears out the theory of mimicry is, that even when the
resemblance in colour-pattern is very great, the WING-VENATION, which is
so constant, and so important in determining the systematic position of
butterflies, is never affected by the variation. The pursuers of the
butterfly have no time to trouble about entomological intricacies.
I must not pass over a discovery of Poulton's which is of great theoretical
importance--that mimetic butterflies may reach the same effect by very
different means. ("Journ. Linn. Soc. London (Zool.)", Vol. XXVI. 1898,
pages 598-602.) Thus the glass-like transparency of the wing of a certain
Ithomiine (Methona) and its Pierine mimic (Dismorphia orise) depends on a
diminution in the size of the scales; in the Danaine genus Ituna it is due
to the fewness of the scales, and in a third imitator, a moth (Castnia
linus var. heliconoides) the glass-like appearance of the wing is due
neither to diminution nor to absence of scales, but to their absolute
colourlessness and transparency, and to the fact that they stand upright.
In another moth mimic (Anthomyza) the arrangement of the transparent scales
is normal. Thus it is not some unknown external influence that has brought
about the transparency of the wing in these five forms, as has sometimes
been supposed. Nor is it a hypothetical INTERNAL evolutionary tendency,
for all three vary in a different manner. The cause of this agreement can
only lie in selection, which preserves and intensifies in each species the
favourable variations that present themselves. The great faithfulness of
the copy is astonishing in these cases, for it is not THE WHOLE wing which
is transparent; certain markings are black in colour, and these contrast
sharply with the glass-like ground. It is obvious that the pursuers of
these butterflies must be very sharp-sighted, for otherwise the agreement
between the species could never have been pushed so far. The less the
enemies see and observe, the more defective must the imitation be, and if
they had been blind, no visible resemblance between the species which
required protection could ever have arisen.
A seemingly irreconcilable contradiction to the mimicry theory is presented
in the following cases, which were known to Bates, who, however, never
succeeded in bringing them into line with the principle of mimicry.
In South America there are, as we have already said, many mimics of the
immune Ithomiinae (or as Bates called them Heliconidae). Among these there
occur not merely species which are edible, and thus require the protection
of a disguise, but others which are rejected on account of their
unpalatableness. How could the Ithomiine dress have developed in their
case, and of what use is it, since the species would in any case be immune?
In Eastern Brazil, for instance, there are four butterflies, which bear a
most confusing resemblance to one another in colour, marking, and form of
wing, and all four are unpalatable to birds. They belong to four different
genera and three sub-families, and we have to inquire: Whence came this
resemblance and what end does it serve? For a long time no satisfactory
answer could be found, but Fritz Muller (In "Kosmos", 1879, page 100.),
seventeen years after Bates, offered a solution to the riddle, when he
pointed out that young birds could not have an instinctive knowledge of the
unpalatableness of the Ithomiines, but must learn by experience which
species were edible and which inedible. Thus each young bird must have
tasted at least one individual of each inedible species and discovered its
unpalatability, before it learnt to avoid, and thus to spare the species.
But if the four species resemble each other very closely the bird will
regard them all as of the same kind, and avoid them all. Thus there
developed a process of selection which resulted in the survival of the
Ithomiine-like individuals, and in so great an increase of resemblance
between the four species, that they are difficult to distinguish one from
another even in a collection. The advantage for the four species, living
side by side as they do e.g. in Bahia, lies in the fact that only one
individual from the MIMICRY-RING ("inedible association") need be tasted by
a young bird, instead of at least four individuals, as would otherwise be
the case. As the number of young birds is great, this makes a considerable
difference in the ratio of elimination.
These interesting mimicry-rings (trusts), which have much significance for
the theory, have been the subject of numerous and careful investigations,
and at least their essential features are now fully established. Muller
took for granted, without making any investigations, that young birds only
learn by experience to distinguish between different kinds of victims. But
Lloyd Morgan's ("Habit and Instinct", London, 1896.) experiments with young
birds proved that this is really the case, and at the same time furnished
an additional argument against the LAMARCKIAN PRINCIPLE.
In addition to the mimicry-rings first observed in South America, others
have been described from Tropical India by Moore, and by Poulton and Dixey
from Africa, and we may expect to learn many more interesting facts in this
connection. Here again the preliminary postulates of the theory are
satisfied. And how much more that would lead to the same conclusion might
be added!
As in the case of mimicry many species have come to resemble one another
through processes of selection, so we know whole classes of phenomena in
which plants and animals have become adapted to one another, and have thus
been modified to a considerable degree. I refer particularly to the
relation between flowers and insects; but as there is an article on "The
Biology of Flowers" in this volume, I need not discuss the subject, but
will confine myself to pointing out the significance of these remarkable
cases for the theory of selection. Darwin has shown that the originally
inconspicuous blossoms of the phanerogams were transformed into flowers
through the visits of insects, and that, conversely, several large orders
of insects have been gradually modified by their association with flowers,
especially as regards the parts of their body actively concerned. Bees and
butterflies in particular have become what they are through their relation
to flowers. In this case again all that is apparently contradictory to the
theory can, on closer investigation, be beautifully interpreted in
corroboration of it. Selection can give rise only to what is of use to the
organism actually concerned, never to what is of use to some other
organism, and we must therefore expect to find that in flowers only
characters of use to THEMSELVES have arisen, never characters which are of
use to insects only, and conversely that in the insects characters useful
to them and not merely to the plants would have originated. For a long
time it seemed as if an exception to this rule existed in the case of the
fertilisation of the yucca blossoms by a little moth, Pronuba yuccasella.
This little moth has a sickle-shaped appendage to its mouth-parts which
occurs in no other Lepidopteron, and which is used for pushing the yellow
pollen into the opening of the pistil, thus fertilising the flower. Thus
it appears as if a new structure, which is useful only to the plant, has
arisen in the insect. But the difficulty is solved as soon as we learn
that the moth lays its eggs in the fruit-buds of the Yucca, and that the
larvae, when they emerge, feed on the developing seeds. In effecting the
fertilisation of the flower the moth is at the same time making provision
for its own offspring, since it is only after fertilisation that the seeds
begin to develop. There is thus nothing to prevent our referring this
structural adaptation in Pronuba yuccasella to processes of selection,
which have gradually transformed the maxillary palps of the female into the
sickle-shaped instrument for collecting the pollen, and which have at the
same time developed in the insect the instinct to press the pollen into the
pistil.
In this domain, then, the theory of selection finds nothing but
corroboration, and it would be impossible to substitute for it any other
explanation, which, now that the facts are so well known, could be regarded
as a serious rival to it. That selection is a factor, and a very powerful
factor in the evolution of organisms, can no longer be doubted. Even
although we cannot bring forward formal proofs of it IN DETAIL, cannot
calculate definitely the size of the variations which present themselves,
and their selection-value, cannot, in short, reduce the whole process to a
mathematical formula, yet we must assume selection, because it is the only
possible explanation applicable to whole classes of phenomena, and because,
on the other hand, it is made up of factors which we know can be proved
actually to exist, and which, IF they exist, must of logical necessity
cooperate in the manner required by the theory. WE MUST ACCEPT IT BECAUSE
THE PHENOMENA OF EVOLUTION AND ADAPTATION MUST HAVE A NATURAL BASIS, AND
BECAUSE IT IS THE ONLY POSSIBLE EXPLANATION OF THEM. (This has been
discussed in many of my earlier works. See for instance "The All-
Sufficiency of Natural Selection, a reply to Herbert Spencer", London,
1893.)
Many people are willing to admit that selection explains adaptations, but
they maintain that only a part of the phenomena are thus explained, because
everything does not depend upon adaptation. They regard adaptation as, so
to speak, a special effort on the part of Nature, which she keeps in
readiness to meet particularly difficult claims of the external world on
organisms. But if we look at the matter more carefully we shall find that
adaptations are by no means exceptional, but that they are present
everywhere in such enormous numbers, that it would be difficult in regard
to any structure whatever, to prove that adaptation had NOT played a part
in its evolution.
How often has the senseless objection been urged against selection that it
can create nothing, it can only reject. It is true that it cannot create
either the living substance or the variations of it; both must be given.
But in rejecting one thing it preserves another, intensifies it, combines
it, and in this way CREATES what is new. EVERYTHING in organisms depends
on adaptation; that is to say, everything must be admitted through the
narrow door of selection, otherwise it can take no part in the building up
of the whole. But, it is asked, what of the direct effect of external
conditions, temperature, nutrition, climate and the like? Undoubtedly
these can give rise to variations, but they too must pass through the door
of selection, and if they cannot do this they are rejected, eliminated from
the constitution of the species.
It may, perhaps, be objected that such external influences are often of a
compelling power, and that every animal MUST submit to them, and that thus
selection has no choice and can neither select nor reject. There may be
such cases; let us assume for instance that the effect of the cold of the
Arctic regions was to make all the mammals become black; the result would
be that they would all be eliminated by selection, and that no mammals
would be able to live there at all. But in most cases a certain percentage
of animals resists these strong influences, and thus selection secures a
foothold on which to work, eliminating the unfavourable variation, and
establishing a useful colouring, consistent with what is required for the
maintenance of the species.
Everything depends upon adaptation! We have spoken much of adaptation in
colouring, in connection with the examples brought into prominence by
Darwin, because these are conspicuous, easily verified, and at the same
time convincing for the theory of selection. But is it only desert and
polar animals whose colouring is determined through adaptation? Or the
leaf-butterflies, and the mimetic species, or the terrifying markings, and
"warning-colours" and a thousand other kinds of sympathetic colouring? It
is, indeed, never the colouring alone which makes up the adaptation; the
structure of the animal plays a part, often a very essential part, in the
protective disguise, and thus MANY variations may cooperate towards ONE
common end. And it is to be noted that it is by no means only external
parts that are changed; internal parts are ALWAYS modified at the same
time--for instance, the delicate elements of the nervous system on which
depend the INSTINCT of the insect to hold its wings, when at rest, in a
perfectly definite position, which, in the leaf-butterfly, has the effect
of bringing the two pieces on which the marking occurs on the anterior and
posterior wing into the same direction, and thus displaying as a whole the
fine curve of the midrib on the seeming leaf. But the wing-holding instinct
is not regulated in the same way in all leaf-butterflies; even our
indigenous species of Vanessa, with their protective ground-colouring, have
quite a distinctive way of holding their wings so that the greater part of
the anterior wing is covered by the posterior when the butterfly is at
rest. But the protective colouring appears on the posterior wing and on
the tip of the anterior, TO PRECISELY THE DISTANCE TO WHICH IT IS LEFT
UNCOVERED. This occurs, as Standfuss has shown, in different degree in our
two most nearly allied species, the uncovered portion being smaller in V.
urticae than in V. polychloros. In this case, as in most leaf-butterflies,
the holding of the wing was probably the primary character; only after that
was thoroughly established did the protective marking develop. In any
case, the instinctive manner of holding the wings is associated with the
protective colouring, and must remain as it is if the latter is to be
effective. How greatly instincts may change, that is to say, may be
adapted, is shown by the case of the Noctuid "shark" moth, Xylina vetusta.
This form bears a most deceptive resemblance to a piece of rotten wood, and
the appearance is greatly increased by the modification of the innate
impulse to flight common to so many animals, which has here been
transformed into an almost contrary instinct. This moth does not fly away
from danger, but "feigns death," that is, it draws antennae, legs and wings
close to the body, and remains perfectly motionless. It may be touched,
picked up, and thrown down again, and still it does not move. This
remarkable instinct must surely have developed simultaneously with the
wood-colouring; at all events, both cooperating variations are now present,
and prove that both the external and the most minute internal structure
have undergone a process of adaptation.
The case is the same with all structural variations of animal parts, which
are not absolutely insignificant. When the insects acquired wings they
must also have acquired the mechanism with which to move them--the
musculature, and the nervous apparatus necessary for its automatic
regulation. All instincts depend upon compound reflex mechanisms and are
just as indispensable as the parts they have to set in motion, and all may
have arisen through processes of selection if the reasons which I have
elsewhere given for this view are correct. ("The Evolution Theory",
London, 1904, page 144.)
Thus there is no lack of adaptations within the organism, and particularly
in its most important and complicated parts, so that we may say that there
is no actively functional organ that has not undergone a process of
adaptation relative to its function and the requirements of the organism.
Not only is every gland structurally adapted, down to the very minutest
histological details, to its function, but the function is equally minutely
adapted to the needs of the body. Every cell in the mucous lining of the
intestine is exactly regulated in its relation to the different nutritive
substances, and behaves in quite a different way towards the fats, and
towards nitrogenous substances, or peptones.
I have elsewhere called attention to the many adaptations of the whale to
the surrounding medium, and have pointed out--what has long been known, but
is not universally admitted, even now--that in it a great number of
important organs have been transformed in adaptation to the peculiar
conditions of aquatic life, although the ancestors of the whale must have
lived, like other hair-covered mammals, on land. I cited a number of these
transformations--the fish-like form of the body, the hairlessness of the
skin, the transformation of the fore-limbs to fins, the disappearance of
the hind-limbs and the development of a tail fin, the layer of blubber
under the skin, which affords the protection from cold necessary to a warm-
blooded animal, the disappearance of the ear-muscles and the auditory
passages, the displacement of the external nares to the forehead for the
greater security of the breathing-hole during the brief appearance at the
surface, and certain remarkable changes in the respiratory and circulatory
organs which enable the animal to remain for a long time under water. I
might have added many more, for the list of adaptations in the whale to
aquatic life is by no means exhausted; they are found in the histological
structure and in the minutest combinations in the nervous system. For it
is obvious that a tail-fin must be used in quite a different way from a
tail, which serves as a fly-brush in hoofed animals, or as an aid to
springing in the kangaroo or as a climbing organ; it will require quite
different reflex-mechanisms and nerve-combinations in the motor centres.
I used this example in order to show how unnecessary it is to assume a
special internal evolutionary power for the phylogenesis of species, for
this whole order of whales is, so to speak, MADE UP OF ADAPTATIONS; it
deviates in many essential respects from the usual mammalian type, and all
the deviations are adaptations to aquatic life. But if precisely the most
essential features of the organisation thus depend upon adaptation, what is
left for a phyletic force to do, since it is these essential features of
the structure it would have to determine? There are few people now who
believe in a phyletic evolutionary power, which is not made up of the
forces known to us--adaptation and heredity--but the conviction that EVERY
part of an organism depends upon adaptation has not yet gained a firm
footing. Nevertheless, I must continue to regard this conception as the
correct one, as I have long done.
I may be permitted one more example. The feather of a bird is a marvellous
structure, and no one will deny that as a whole it depends upon adaptation.
But what part of it DOES NOT depend upon adaptation? The hollow quill, the
shaft with its hard, thin, light cortex, and the spongy substance within
it, its square section compared with the round section of the quill, the
flat barbs, their short, hooked barbules which, in the flight-feathers,
hook into one another with just sufficient firmness to resist the pressure
of the air at each wing-beat, the lightness and firmness of the whole
apparatus, the elasticity of the vane, and so on. And yet all this belongs
to an organ which is only passively functional, and therefore can have
nothing to do with the LAMARCKIAN PRINCIPLE. Nor can the feather have
arisen through some magical effect of temperature, moisture, electricity,
or specific nutrition, and thus selection is again our only anchor of
safety.
But--it will be objected--the substance of which the feather consists, this
peculiar kind of horny substance, did not first arise through selection in
the course of the evolution of the birds, for it formed the covering of the
scales of their reptilian ancestors. It is quite true that a similar
substance covered the scales of the Reptiles, but why should it not have
arisen among them through selection? Or in what other way could it have
arisen, since scales are also passively useful parts? It is true that if
we are only to call adaptation what has been acquired by the species we
happen to be considering, there would remain a great deal that could not be
referred to selection; but we are postulating an evolution which has
stretched back through aeons, and in the course of which innumerable
adaptations took place, which had not merely ephemeral persistence in a
genus, a family or a class, but which was continued into whole Phyla of
animals, with continual fresh adaptations to the special conditions of each
species, family, or class, yet with persistence of the fundamental
elements. Thus the feather, once acquired, persisted in all birds, and the
vertebral column, once gained by adaptation in the lowest forms, has
persisted in all the Vertebrates, from Amphioxus upwards, although with
constant readaptation to the conditions of each particular group. Thus
everything we can see in animals is adaptation, whether of to-day, or of
yesterday, or of ages long gone by; every kind of cell, whether glandular,
muscular, nervous, epidermic, or skeletal, is adapted to absolutely
definite and specific functions, and every organ which is composed of these
different kinds of cells contains them in the proper proportions, and in
the particular arrangement which best serves the function of the organ; it
is thus adapted to its function.
All parts of the organism are tuned to one another, that is, THEY ARE
ADAPTED TO ONE ANOTHER, and in the same way THE ORGANISM AS A WHOLE IS
ADAPTED TO THE CONDITIONS OF ITS LIFE, AND IT IS SO AT EVERY STAGE OF ITS
EVOLUTION.
But all adaptations CAN be referred to selection; the only point that
remains doubtful is whether they all MUST be referred to it.
However that may be, whether the LAMARCKIAN PRINCIPLE is a factor that has
cooperated with selection in evolution, or whether it is altogether
fallacious, the fact remains, that selection is the cause of a great part
of the phyletic evolution of organisms on our earth. Those who agree with
me in rejecting the LAMARCKIAN PRINCIPLE will regard selection as the only
GUIDING factor in evolution, which creates what is new out of the
transmissible variations, by ordering and arranging these, selecting them
in relation to their number and size, as the architect does his building-
stones so that a particular style must result. ("Variation under
Domestication", 1875 II. pages 426, 427.) But the building-stones
themselves, the variations, have their basis in the influences which cause
variation in those vital units which are handed on from one generation to
another, whether, taken together they form the WHOLE organism, as in
Bacteria and other low forms of life, or only a germ-substance, as in
unicellular and multicellular organisms. (The Author and Editor are
indebted to Professor Poulton for kindly assisting in the revision of the
proof of this Essay.)
IV. VARIATION.
By HUGO DE VRIES,
Professor of Botany in the University of Amsterdam.
I. DIFFERENT KINDS OF VARIABILITY.
Before Darwin, little was known concerning the phenomena of variability.
The fact, that hardly two leaves on a tree were exactly the same, could not
escape observation: small deviations of the same kind were met with
everywhere, among individuals as well as among the organs of the same
plant. Larger aberrations, spoken of as monstrosities, were for a long
time regarded as lying outside the range of ordinary phenomena. A special
branch of inquiry, that of Teratology, was devoted to them, but it
constituted a science by itself, sometimes connected with morphology, but
having scarcely any bearing on the processes of evolution and heredity.
Darwin was the first to take a broad survey of the whole range of
variations in the animal and vegetable kingdoms. His theory of Natural
Selection is based on the fact of variability. In order that this
foundation should be as strong as possible he collected all the facts,
scattered in the literature of his time, and tried to arrange them in a
scientific way. He succeeded in showing that variations may be grouped
along a line of almost continuous gradations, beginning with simple
differences in size and ending with monstrosities. He was struck by the
fact that, as a rule, the smaller the deviations, the more frequently they
appear, very abrupt breaks in characters being of rare occurrence.
Among these numerous degrees of variability Darwin was always on the look
out for those which might, with the greatest probability, be considered as
affording material for natural selection to act upon in the development of
new species. Neither of the extremes complied with his conceptions. He
often pointed out, that there are a good many small fluctuations, which in
this respect must be absolutely useless. On the other hand, he strongly
combated the belief, that great changes would be necessary to explain the
origin of species. Some authors had propounded the idea that highly
adapted organs, e.g. the wings of a bird, could not have been developed in
any other way than by a comparatively sudden modification of a well defined
and important kind. Such a conception would allow of great breaks or
discontinuity in the evolution of highly differentiated animals and plants,
shortening the time for the evolution of the whole organic kingdom and
getting over numerous difficulties inherent in the theory of slow and
gradual progress. It would, moreover, account for the genetic relation of
the larger groups of both animals and plants. It would, in a word,
undoubtedly afford an easy means of simplifying the problem of descent with
modification.
Darwin, however, considered such hypotheses as hardly belonging to the
domain of science; they belong, he said, to the realm of miracles. That
species have a capacity for change is admitted by all evolutionists; but
there is no need to invoke modifications other than those represented by
ordinary variability. It is well known that in artificial selection this
tendency to vary has given rise to numerous distinct races, and there is no
reason for denying that it can do the same in nature, by the aid of natural
selection. On both lines an advance may be expected with equal
probability.
His main argument, however, is that the most striking and most highly
adapted modifications may be acquired by successive variations. Each of
these may be slight, and they may affect different organs, gradually
adapting them to the same purpose. The direction of the adaptations will
be determined by the needs in the struggle for life, and natural selection
will simply exclude all such changes as occur on opposite or deviating
lines. In this way, it is not variability itself which is called upon to
explain beautiful adaptations, but it is quite sufficient to suppose that
natural selection has operated during long periods in the same way.
Eventually, all the acquired characters, being transmitted together, would
appear to us, as if they had all been simultaneously developed.
Correlations must play a large part in such special evolutions: when one
part is modified, so will be other parts. The distribution of nourishment
will come in as one of the causes, the reactions of different organs to the
same external influences as another. But no doubt the more effective cause
is that of the internal correlations, which, however, are still but dimly
understood. Darwin repeatedly laid great stress on this view, although a
definite proof of its correctness could not be given in his time. Such
proof requires the direct observation of a mutation, and it should be
stated here that even the first observations made in this direction have
clearly confirmed Darwin's ideas. The new evening primroses which have
sprung in my garden from the old form of Oenothera Lamarckiana, and which
have evidently been derived from it, in each case, by a single mutation, do
not differ from their parent species in one character only, but in almost
all their organs and qualities. Oenothera gigas, for example, has stouter
stems and denser foliage; the leaves are larger and broader; its thick
flower-buds produce gigantic flowers, but only small fruits with large
seeds. Correlative changes of this kind are seen in all my new forms, and
they lend support to the view that in the gradual development of highly
adapted structures, analogous correlations may have played a large part.
They easily explain large deviations from an original type, without
requiring the assumption of too many steps.
Monstrosities, as their name implies, are widely different in character
from natural species; they cannot, therefore, be adduced as evidence in the
investigation of the origin of species. There is no doubt that they may
have much in common as regards their manner of origin, and that the origin
of species, once understood, may lead to a better understanding of the
monstrosities. But the reverse is not true, at least not as regards the
main lines of development. Here, it is clear, monstrosities cannot have
played a part of any significance.
Reversions, or atavistic changes, would seem to give a better support to
the theory of descent through modifications. These have been of paramount
importance on many lines of evolution of the animal as well as of the
vegetable kingdom. It is often assumed that monocotyledons are descended
from some lower group of dicotyledons, probably allied to that which
includes the buttercup family. On this view the monocotyledons must be
assumed to have lost the cambium and all its influence on secondary growth,
the differentiation of the flower into calyx and corolla, the second
cotyledon or seed-leaf and several other characters. Losses of characters
such as these may have been the result of abrupt changes, but this does not
prove that the characters themselves have been produced with equal
suddenness. On the contrary, Darwin shows very convincingly that a
modification may well be developed by a series of steps, and afterwards
suddenly disappear. Many monstrosities, such as those represented by
twisted stems, furnish direct proofs in support of this view, since they
are produced by the loss of one character and this loss implies secondary
changes in a large number of other organs and qualities.
Darwin criticises in detail the hypothesis of great and abrupt changes and
comes to the conclusion that it does not give even a shadow of an
explanation of the origin of species. It is as improbable as it is
unnecessary.
Sports and spontaneous variations must now be considered. It is well known
that they have produced a large number of fine horticultural varieties.
The cut-leaved maple and many other trees and shrubs with split leaves are
known to have been produced at a single step; this is true in the case of
the single-leaf strawberry plant and of the laciniate variety of the
greater celandine: many white flowers, white or yellow berries and
numerous other forms had a similar origin. But changes such as these do
not come under the head of adaptations, as they consist for the most part
in the loss of some quality or organ belonging to the species from which
they were derived. Darwin thinks it impossible to attribute to this cause
the innumerable structures, which are so well adapted to the habits of life
of each species. At the present time we should say that such adaptations
require progressive modifications, which are additions to the stock of
qualities already possessed by the ancestors, and cannot, therefore, be
explained on the ground of a supposed analogy with sports, which are for
the most part of a retrogressive nature.
Excluding all these more or less sudden changes, there remains a long
series of gradations of variability, but all of these are not assumed by
Darwin to be equally fit for the production of new species. In the first
place, he disregards all mere temporary variations, such as size, albinism,
etc.; further, he points out that very many species have almost certainly
been produced by steps, not greater, and probably not very much smaller,
than those separating closely related varieties. For varieties are only
small species. Next comes the question of polymorphic species: their
occurrence seems to have been a source of much doubt and difficulty in
Darwin's mind, although at present it forms one of the main supports of the
prevailing explanation of the origin of new species. Darwin simply states
that this kind of variability seems to be of a peculiar nature; since
polymorphic species are now in a stable condition their occurrence gives no
clue as to the mode of origin of new species. Polymorphic species are the
expression of the result of previous variability acting on a large scale;
but they now simply consist of more or less numerous elementary species,
which, as far as we know, do not at present exhibit a larger degree of
variability than any other more uniform species. The vernal whitlow-grass
(Draba verna) and the wild pansy are the best known examples; both have
spread over almost the whole of Europe and are split up into hundreds of
elementary forms. These sub-species show no signs of any extraordinary
degree of variability, when cultivated under conditions necessary for the
exclusion of inter-crossing. Hooker has shown, in the case of some ferns
distributed over still wider areas, that the extinction of some of the
intermediate forms in such groups would suffice to justify the elevation of
the remaining types to the rank of distinct species. Polymorphic species
may now be regarded as the link which unites ordinary variability with the
historical production of species. But it does not appear that they had
this significance for Darwin; and, in fact, they exhibit no phenomena which
could explain the processes by which one species has been derived from
another. By thus narrowing the limits of the species-producing variability
Darwin was led to regard small deviations as the source from which natural
selection derives material upon which to act. But even these are not all
of the same type, and Darwin was well aware of the fact.
It should here be pointed out that in order to be selected, a change must
first have been produced. This proposition, which now seems self-evident,
has, however, been a source of much difference of opinion among Darwin's
followers. The opinion that natural selection produces changes in useful
directions has prevailed for a long time. In other words, it was assumed
that natural selection, by the simple means of singling out, could induce
small and useful changes to increase and to reach any desired degree of
deviation from the original type. In my opinion this view was never
actually held by Darwin. It is in contradiction with the acknowledged aim
of all his work,--the explanation of the origin of species by means of
natural forces and phenomena only. Natural selection acts as a sieve; it
does not single out the best variations, but it simply destroys the larger
number of those which are, from some cause or another, unfit for their
present environment. In this way it keeps the strains up to the required
standard, and, in special circumstances, may even improve them.
Returning to the variations which afford the material for the sieving-
action of natural selection, we may distinguish two main kinds. It is true
that the distinction between these was not clear at the time of Darwin, and
that he was unable to draw a sharp line between them. Nevertheless, in
many cases, he was able to separate them, and he often discussed the
question which of the two would be the real source of the differentiation
of species. Certain variations constantly occur, especially such as are
connected with size, weight, colour, etc. They are usually too small for
natural selection to act upon, having hardly any influence in the struggle
for life: others are more rare, occurring only from time to time, perhaps
once or twice in a century, perhaps even only once in a thousand years.
Moreover, these are of another type, not simply affecting size, number or
weight, but bringing about something new, which may be useful or not.
Whenever the variation is useful natural selection will take hold of it and
preserve it; in other cases the variation may either persist or disappear.
In his criticism of miscellaneous objections brought forward against the
theory of natural selection after the publication of the first edition of
"The Origin of Species", Darwin stated his view on this point very
clearly:--"The doctrine of natural selection or the survival of the
fittest, which implies that when variations or individual differences of a
beneficial nature happen to arise, these will be preserved." ("Origin of
Species" (6th edition), page 169, 1882.) In this sentence the words
"HAPPEN TO ARISE" appear to me of prominent significance. They are
evidently due to the same general conception which prevailed in Darwin's
Pangenesis hypothesis. (Cf. de Vries, "Intracellulare Pangenesis", page
73, Jena, 1889, and "Die Mutationstheorie", I. page 63. Leipzig, 1901.)
A distinction is indicated between ordinary fluctuations which are always
present, and such variations as "happen to arise" from time to time. ((I
think it right to point out that the interpretation of this passage from
the "Origin" by Professor de Vries is not accepted as correct either by Mr
Francis Darwin or by myself. We do not believe that Darwin intended to
draw any distinction between TWO TYPES of variation; the words "when
variations or individual differences of a beneficial nature happen to
arise" are not in our opinion meant to imply a distinction between ordinary
fluctuations and variations which "happen to arise," but we believe that
"or" is here used in the sense of ALIAS. With the permission of Professor
de Vries, the following extract is quoted from a letter in which he replied
to the objection raised to his reading of the passage in question:
"As to your remarks on the passage on page 6, I agree that it is now
impossible to see clearly how far Darwin went in his distinction of the
different kinds of variability. Distinctions were only dimly guessed at by
him. But in our endeavour to arrive at a true conception of his view I
think that the chapter on Pangenesis should be our leading guide, and that
we should try to interpret the more difficult passages by that chapter. A
careful and often repeated study of the Pangenesis hypothesis has convinced
me that Darwin, when he wrote that chapter, was well aware that ordinary
variability has nothing to do with evolution, but that other kinds of
variation were necessary. In some chapters he comes nearer to a clear
distinction than in others. To my mind the expression 'happen to arise' is
the sharpest indication of his inclining in this direction. I am quite
convinced that numerous expressions in his book become much clearer when
looked at in this way."
The statement in this passage that "Darwin was well aware that ordinary
variability has nothing to do with evolution, but that other kinds of
variation were necessary" is contradicted by many passages in the "Origin".
A.C.S.)) The latter afford the material for natural selection to act upon
on the broad lines of organic development, but the first do not.
Fortuitous variations are the species-producing kind, which the theory
requires; continuous fluctuations constitute, in this respect, a useless
type.
Of late, the study of variability has returned to the recognition of this
distinction. Darwin's variations, which from time to time happen to arise,
are MUTATIONS, the opposite type being commonly designed fluctuations. A
large mass of facts, collected during the last few decades, has confirmed
this view, which in Darwin's time could only be expressed with much
reserve, and everyone knows that Darwin was always very careful in
statements of this kind.
From the same chapter I may here cite the following paragraph: "Thus as I
am inclined to believe, morphological differences,...such as the
arrangement of the leaves, the divisions of the flower or of the ovarium,
the position of the ovules, etc.--first appeared in many cases as
fluctuating variations, which sooner or later became constant through the
nature of the organism and of the surrounding conditions...but NOT THROUGH
NATURAL SELECTION (The italics are mine (H. de V.).); for as these
morphological characters do not affect the welfare of the species, any
slight deviation in them could not have been governed or accumulated
through this latter agency." ("Origin of Species" (6th edition), page
176.) We thus see that in Darwin's opinion, all small variations had not
the same importance. In favourable circumstances some could become
constant, but others could not.
Since the appearance of the first edition of "The Origin of Species"
fluctuating variability has been thoroughly studied by Quetelet. He
discovered the law, which governs all phenomena of organic life falling
under this head. It is a very simple law, and states that individual
variations follow the laws of probability. He proved it, in the first
place, for the size of the human body, using the measurements published for
Belgian recruits; he then extended it to various other measurements of
parts of the body, and finally concluded that it must be of universal
validity for all organic beings. It must hold true for all characters in
man, physical as well as intellectual and moral qualities; it must hold
true for the plant kingdom as well as for the animal kingdom; in short, it
must include the whole living world.
Quetelet's law may be most easily studied in those cases where the
variability relates to measure, number and weight, and a vast number of
facts have since confirmed its exactness and its validity for all kinds of
organisms, organs and qualities. But if we examine it more closely, we
find that it includes just those minute variations, which, as Darwin
repeatedly pointed out, have often no significance for the origin of
species. In the phenomena, described by Quetelet's law nothing "happens to
arise"; all is governed by the common law, which states that small
deviations from the mean type are frequent, but that larger aberrations are
rare, the rarer as they are larger. Any degree of variation will be found
to occur, if only the number of individuals studied is large enough: it is
even possible to calculate before hand, how many specimens must be compared
in order to find a previously fixed degree of deviation.
The variations, which from time to time happen to appear, are evidently not
governed by this law. They cannot, as yet, be produced at will: no
sowings of thousands or even of millions of plants will induce them,
although by such means the chance of their occurring will obviously be
increased. But they are known to occur, and to occur suddenly and
abruptly. They have been observed especially in horticulture, where they
are ranged in the large and ill-defined group called sports. Korschinsky
has collected all the evidence which horticultural literature affords on
this point. (S. Korschinsky, "Heterogenesis und Evolution", "Flora", Vol.
LXXXIX. pages 240-363, 1901.) Several cases of the first appearance of a
horticultural novelty have been recorded: this has always happened in the
same way; it appeared suddenly and unexpectedly without any definite
relation to previously existing variability. Dwarf types are one of the
commonest and most favourite varieties of flowering plants; they are not
originated by a repeated selection of the smallest specimens, but appear at
once, without intermediates and without any previous indication. In many
instances they are only about half the height of the original type, thus
constituting obvious novelties. So it is in other cases described by
Korschinsky: these sports or mutations are now recognised to be the main
source of varieties of horticultural plants.
As already stated, I do not pretend that the production of horticultural
novelties is the prototype of the origin of new species in nature. I
assume that they are, as a rule, derived from the parent species by the
loss of some organ or quality, whereas the main lines of the evolution of
the animal and vegetable kingdom are of course determined by progressive
changes. Darwin himself has often pointed out this difference. But the
saltatory origin of horticultural novelties is as yet the simplest parallel
for natural mutations, since it relates to forms and phenomena, best known
to the general student of evolution.
The point which I wish to insist upon is this. The difference between
small and ever present fluctuations and rare and more sudden variations was
clear to Darwin, although the facts known at his time were too meagre to
enable a sharp line to be drawn between these two great classes of
variability. Since Darwin's time evidence, which proves the correctness of
his view, has accumulated with increasing rapidity. Fluctuations
constitute one type; they are never absent and follow the law of chance,
but they do not afford the material from which to build new species.
Mutations, on the other hand, only happen to occur from time to time. They
do not necessarily produce greater changes than fluctuations, but such as
may become, or rather are from their very nature, constant. It is this
constancy which is the mark of specific characters, and on this basis every
new specific character may be assumed to have arisen by mutation.
Some authors have tried to show that the theory of mutation is opposed to
Darwin's views. But this is erroneous. On the contrary, it is in fullest
harmony with the great principle laid down by Darwin. In order to be acted
upon by that complex of environmental forces, which Darwin has called
natural selection, the changes must obviously first be there. The manner
in which they are produced is of secondary importance and has hardly any
bearing on the theory of descent with modification. ("Life and Letters"
II. 125.)
A critical survey of all the facts of variability of plants in nature as
well as under cultivation has led me to the conviction, that Darwin was
right in stating that those rare beneficial variations, which from time to
time happen to arise,--the now so-called mutations--are the real source of
progress in the whole realm of the organic world.
II. EXTERNAL AND INTERNAL CAUSES OF VARIABILITY.
All phenomena of animal and plant life are governed by two sets of causes;
one of these is external, the other internal. As a rule the internal
causes determine the nature of a phenomenon--what an organism can do and
what it cannot do. The external causes, on the other hand, decide when a
certain variation will occur, and to what extent its features may be
developed.
As a very clear and wholly typical instance I cite the cocks-combs
(Celosia). This race is distinguished from allied forms by its faculty of
producing the well-known broad and much twisted combs. Every single
individual possesses this power, but all individuals do not exhibit it in
its most complete form. In some cases this faculty may not be exhibited at
the top of the main stem, although developed in lateral branches: in
others it begins too late for full development. Much depends upon
nourishment and cultivation, but almost always the horticulturist has to
single out the best individuals and to reject those which do not come up to
the standard.
The internal causes are of a historical nature. The external ones may be
defined as nourishment and environment. In some cases nutrition is the
main factor, as, for instance, in fluctuating variability, but in natural
selection environment usually plays the larger part.
The internal or historical causes are constant during the life-time of a
species, using the term species in its most limited sense, as designating
the so-called elementary species or the units out of which the ordinary
species are built up. These historical causes are simply the specific
characters, since in the origin of a species one or more of these must have
been changed, thus producing the characters of the new type. These changes
must, of course, also be due partly to internal and partly to external
causes.
In contrast to these changes of the internal causes, the ordinary
variability which is exhibited during the life-time of a species is called
fluctuating variability. The name mutations or mutating variability is
then given to the changes in the specific characters. It is desirable to
consider these two main divisions of variability separately.
In the case of fluctuations the internal causes, as well as the external
ones, are often apparent. The specific characters may be designated as the
mean about which the observed forms vary. Almost every character may be
developed to a greater or a less degree, but the variations of the single
characters producing a small deviation from the mean are usually the
commonest. The limits of these fluctuations may be called wide or narrow,
according to the way we look at them, but in numerous cases the extreme on
the favoured side hardly surpasses double the value of that on the other
side. The degree of this development, for every individual and for every
organ, is dependent mainly on nutrition. Better nourishment or an
increased supply of food produces a higher development; only it is not
always easy to determine which direction is the fuller and which is the
poorer one. The differences among individuals grown from different seeds
are described as examples of individual variability, but those which may be
observed on the same plant, or on cuttings, bulbs or roots derived from one
individual are referred to as cases of partial variability. Partial
variability, therefore, determines the differences among the flowers,
fruits, leaves or branches of one individual: in the main, it follows the
same laws as individual variability, but the position of a branch on a
plant also determines its strength, and the part it may take in the
nourishment of the whole. Composite flowers and umbels therefore have, as
a rule, fewer rays on weak branches than on the strong main ones. The
number of carpels in the fruits of poppies becomes very small on the weak
lateral branches, which are produced towards the autumn, as well as on
crowded, and therefore on weakened individuals. Double flowers follow the
same rule, and numerous other instances could easily be adduced.
Mutating variability occurs along three main lines. Either a character may
disappear, or, as we now say, become latent; or a latent character may
reappear, reproducing thereby a character which was once prominent in more
or less remote ancestors. The third and most interesting case is that of
the production of quite new characters which never existed in the
ancestors. Upon this progressive mutability the main development of the
animal and vegetable kingdom evidently depends. In contrast to this, the
two other cases are called retrogressive and degressive mutability. In
nature retrogressive mutability plays a large part; in agriculture and in
horticulture it gives rise to numerous varieties, which have in the past
been preserved, either on account of their usefulness or beauty, or simply
as fancy-types. In fact the possession of numbers of varieties may be
considered as the main character of domesticated animals and cultivated
plants.
In the case of retrogressive and degressive mutability the internal cause
is at once apparent, for it is this which causes the disappearance or
reappearance of some character. With progressive mutations the case is not
so simple, since the new character must first be produced and then
displayed. These two processes are theoretically different, but they may
occur together or after long intervals. The production of the new
character I call premutation, and the displaying mutation. Both of course
must have their external as well as their internal causes, as I have
repeatedly pointed out in my work on the Mutation Theory. ("Die
Mutationstheorie", 2 vols., Leipzig, 1901.)
It is probable that nutrition plays as important a part among the external
causes of mutability as it does among those of fluctuating variability.
Observations in support of this view, however, are too scanty to allow of a
definite judgment. Darwin assumed an accumulative influence of external
causes in the case of the production of new varieties or species. The
accumulation might be limited to the life-time of a single individual, or
embrace that of two or more generations. In the end a degree of
instability in the equilibrium of one or more characters might be attained,
great enough for a character to give way under a small shock produced by
changed conditions of life. The character would then be thrown over from
the old state of equilibrium into a new one.
Characters which happen to be in this state of unstable equilibrium are
called mutable. They may be either latent or active, being in the former
case derived from old active ones or produced as new ones (by the process,
designated premutation). They may be inherited in this mutable condition
during a long series of generations. I have shown that in the case of the
evening primrose of Lamarck this state of mutability must have existed for
at least half a century, for this species was introduced from Texas into
England about the year 1860, and since then all the strains derived from
its first distribution over the several countries of Europe show the same
phenomena in producing new forms. The production of the dwarf evening
primrose, or Oenothera nanella, is assumed to be due to one of the factors,
which determines the tall stature of the parent form, becoming latent; this
would, therefore, afford an example of retrogressive mutation. Most of the
other types of my new mutants, on the other hand, seem to be due to
progressive mutability.
The external causes of this curious period of mutability are as yet wholly
unknown and can hardly be guessed at, since the origin of the Oenothera
Lamarckiana is veiled in mystery. The seeds, introduced into England about
1860, were said to have come from Texas, but whether from wild or from
cultivated plants we do not know. Nor has the species been recorded as
having been observed in the wild condition. This, however, is nothing
peculiar. The European types of Oenothera biennis and O. muricata are in
the same condition. The first is said to have been introduced from
Virginia, and the second from Canada, but both probably from plants
cultivated in the gardens of these countries. Whether the same elementary
species are still growing on those spots is unknown, mainly because the
different sub-species of the species mentioned have not been systematically
studied and distinguished.
The origin of new species, which is in part the effect of mutability, is,
however, due mainly to natural selection. Mutability provides the new
characters and new elementary species. Natural selection, on the other
hand, decides what is to live and what to die. Mutability seems to be
free, and not restricted to previously determined lines. Selection,
however, may take place along the same main lines in the course of long
geological epochs, thus directing the development of large branches of the
animal and vegetable kingdom. In natural selection it is evident that
nutrition and environment are the main factors. But it is probable that,
while nutrition may be one of the main causes of mutability, environment
may play the chief part in the decisions ascribed to natural selection.
Relations to neighbouring plants and to injurious or useful animals, have
been considered the most important determining factors ever since the time
when Darwin pointed out their prevailing influence.
From this discussion of the main causes of variability we may derive the
proposition that the study of every phenomenon in the field of heredity, of
variability, and of the origin of new species will have to be considered
from two standpoints; on one hand we have the internal causes, on the other
the external ones. Sometimes the first are more easily detected, in other
cases the latter are more accessible to investigation. But the complete
elucidation of any phenomenon of life must always combine the study of the
influence of internal with that of external causes.
III. POLYMORPHIC VARIABILITY IN CEREALS.
One of the propositions of Darwin's theory of the struggle for life
maintains that the largest amount of life can be supported on any area, by
great diversification or divergence in the structure and constitution of
its inhabitants. Every meadow and every forest affords a proof of this
thesis. The numerical proportion of the different species of the flora is
always changing according to external influences. Thus, in a given meadow,
some species will flower abundantly in one year and then almost disappear,
until, after a series of years, circumstances allow them again to multiply
rapidly. Other species, which have taken their places, will then become
rare. It follows from this principle, that notwithstanding the constantly
changing conditions, a suitable selection from the constituents of a meadow
will ensure a continued high production. But, although the principle is
quite clear, artificial selection has, as yet, done very little towards
reaching a really high standard.
The same holds good for cereals. In ordinary circumstances a field will
give a greater yield, if the crop grown consists of a number of
sufficiently differing types. Hence it happens that almost all older
varieties of wheat are mixtures of more or less diverging forms. In the
same variety the numerical composition will vary from year to year, and in
oats this may, in bad years, go so far as to destroy more than half of the
harvest, the wind-oats (Avena fatua), which scatter their grain to the
winds as soon as it ripens, increasing so rapidly that they assume the
dominant place. A severe winter, a cold spring and other extreme
conditions of life will destroy one form more completely than another, and
it is evident that great changes in the numerical composition of the
mixture may thus be brought about.
This mixed condition of the common varieties of cereals was well known to
Darwin. For him it constituted one of the many types of variability. It
is of that peculiar nature to which, in describing other groups, he applies
the term polymorphy. It does not imply that the single constituents of the
varieties are at present really changing their characters. On the other
hand, it does not exclude the possibility of such changes. It simply
states that observation shows the existence of different forms; how these
have originated is a question which it does not deal with. In his well-
known discussion of the variability of cereals, Darwin is mainly concerned
with the question, whether under cultivation they have undergone great
changes or only small ones. The decision ultimately depends on the
question, how many forms have originally been taken into cultivation.
Assuming five or six initial species, the variability must be assumed to
have been very large, but on the assumption that there were between ten and
fifteen types, the necessary range of variability is obviously much
smaller. But in regard to this point, we are of course entirely without
historical data.
Few of the varieties of wheat show conspicuous differences, although their
number is great. If we compare the differentiating characters of the
smaller types of cereals with those of ordinary wild species, even within
the same genus or family, they are obviously much less marked. All these
small characters, however, are strictly inherited, and this fact makes it
very probable that the less obvious constituents of the mixtures in
ordinary fields must be constant and pure as long as they do not
intercross. Natural crossing is in most cereals a phenomenon of rare
occurrence, common enough to admit of the production of all possible hybrid
combinations, but requiring the lapse of a long series of years to reach
its full effect.
Darwin laid great stress on this high amount of variability in the plants
of the same variety, and illustrated it by the experience of Colonel Le
Couteur ("On the Varieties, Properties, and Classification of Wheat",
Jersey, 1837.) on his farm on the isle of Jersey, who cultivated upwards of
150 varieties of wheat, which he claimed were as pure as those of any other
agriculturalist. But Professor La Gasca of Madrid, who visited him, drew
attention to aberrant ears, and pointed out, that some of them might be
better yielders than the majority of plants in the crop, whilst others
might be poor types. Thence he concluded that the isolation of the better
ones might be a means of increasing his crops. Le Couteur seems to have
considered the constancy of such smaller types after isolation as
absolutely probable, since he did not even discuss the possibility of their
being variable or of their yielding a changeable or mixed progeny. This
curious fact proves that he considered the types, discovered in his fields
by La Gasca to be of the same kind as his other varieties, which until that
time he had relied upon as being pure and uniform. Thus we see, that for
him, the variability of cereals was what we now call polymorphy. He looked
through his fields for useful aberrations, and collected twenty-three new
types of wheat. He was, moreover, clear about one point, which, on being
rediscovered after half a century, has become the starting-point for the
new Swedish principle of selecting agricultural plants. It was the
principle of single-ear sowing, instead of mixing the grains of all the
selected ears together. By sowing each ear on a separate plot he intended
not only to multiply them, but also to compare their value. This
comparison ultimately led him to the choice of some few valuable sorts, one
of which, the "Bellevue de Talavera," still holds its place among the
prominent sorts of wheat cultivated in France. This variety seems to be
really a uniform type, a quality very useful under favourable conditions of
cultivation, but which seems to have destroyed its capacity for further
improvement by selection.
The principle of single-ear sowing, with a view to obtain pure and uniform
strains without further selection, has, until a few years ago, been almost
entirely lost sight of. Only a very few agriculturists have applied it:
among these are Patrick Shirreff ("Die Verbesserung der Getreide-Arten",
translated by R. Hesse, Halle, 1880.) in Scotland and Willet M. Hays
("Wheat, varieties, breeding, cultivation", Univ. Minnesota, Agricultural
Experimental Station, Bull. no. 62, 1899.) in Minnesota. Patrick Shirreff
observed the fact, that in large fields of cereals, single plants may from
time to time be found with larger ears, which justify the expectation of a
far greater yield. In the course of about twenty-five years he isolated in
this way two varieties of wheat and two of oats. He simply multiplied them
as fast as possible, without any selection, and put them on the market.
Hays was struck by the fact that the yield of wheat in Minnesota was far
beneath that in the neighbouring States. The local varieties were Fife and
Blue Stem. They gave him, on inspection, some better specimens,
"phenomenal yielders" as he called them. These were simply isolated and
propagated, and, after comparison with the parent-variety and with some
other selected strains of less value, were judged to be of sufficient
importance to be tested by cultivation all over the State of Minnesota.
They have since almost supplanted the original types, at least in most
parts of the State, with the result that the total yield of wheat in
Minnesota is said to have been increased by about a million dollars yearly.
Definite progress in the method of single-ear sowing has, however, been
made only recently. It had been foreshadowed by Patrick Shirreff, who
after the production of the four varieties already mentioned, tried to
carry out his work on a larger scale, by including numerous minor
deviations from the main type. He found by doing so that the chances of
obtaining a better form were sufficiently increased to justify the trial.
But it was Nilsson who discovered the almost inexhaustible polymorphy of
cereals and other agricultural crops and made it the starting-point for a
new and entirely trustworthy method of the highest utility. By this means
he has produced during the last fifteen years a number of new and valuable
races, which have already supplanted the old types on numerous farms in
Sweden and which are now being introduced on a large scale into Germany and
other European countries.
It is now twenty years since the station at Svalof was founded. During the
first period of its work, embracing about five years, selection was
practised on the principle which was then generally used in Germany. In
order to improve a race a sample of the best ears was carefully selected
from the best fields of the variety. These ears were considered as
representatives of the type under cultivation, and it was assumed that by
sowing their grains on a small plot a family could be obtained, which could
afterwards be improved by a continuous selection. Differences between the
collected ears were either not observed or disregarded. At Svalof this
method of selection was practised on a far larger scale than on any German
farm, and the result was, broadly speaking, the same. This may be stated
in the following words: improvement in a few cases, failure in all the
others. Some few varieties could be improved and yielded excellent new
types, some of which have since been introduced into Swedish agriculture
and are now prominent races in the southern and middle parts of the
country. But the station had definite aims, and among them was the
improvement of the Chevalier barley. This, in Middle Sweden, is a fine
brewer's barley, but liable to failure during unfavourable summers on
account of its slender stems. It was selected with a view of giving it
stiffer stems, but in spite of all the care and work bestowed upon it no
satisfactory result was obtained.
This experience, combined with a number of analogous failures, could not
fail to throw doubt upon the whole method. It was evident that good
results were only exceptions, and that in most cases the principle was not
one that could be relied upon. The exceptions might be due to unknown
causes, and not to the validity of the method; it became therefore of much
more interest to search for the causes than to continue the work along
these lines.
In the year 1892 a number of different varieties of cereals were cultivated
on a large scale and a selection was again made from them. About two
hundred samples of ears were chosen, each apparently constituting a
different type. Their seeds were sown on separate plots and manured and
treated as much as possible in the same manner. The plots were small and
arranged in rows so as to facilitate the comparison of allied types.
During the whole period of growth and during the ripening of the ears the
plots were carefully studied and compared: they were harvested separately;
ears and kernels were counted and weighed, and notes were made concerning
layering, rust and other cereal pests.
The result of this experiment was, in the main, no distinct improvement.
Nilsson was especially struck by the fact that the plots, which should
represent distinct types, were far from uniform. Many of them were as
multiform as the fields from which the parent-ears were taken. Others
showed variability in a less degree, but in almost all of them it was clear
that a pure race had not been obtained. The experiment was a fair one,
inasmuch as it demonstrated the polymorphic variability of cereals beyond
all doubt and in a degree hitherto unsuspected; but from the standpoint of
the selectionist it was a failure. Fortunately there were, however, one or
two exceptions. A few lots showed a perfect uniformity in regard to all
the stalks and ears: these were small families. This fact suggested the
idea that each might have been derived from a single ear. During the
selection in the previous summer, Nilsson had tried to find as many ears as
possible of each new type which he recognised in his fields. But the
variability of his crops was so great, that he was rarely able to include
more than two or three ears in the same group, and, in a few cases, he
found only one representative of the supposed type. It might, therefore,
be possible that those small uniform plots were the direct progeny of ears,
the grains of which had not been mixed with those from other ears before
sowing. Exact records had, of course, been kept of the chosen samples, and
the number of ears had been noted in each case. It was, therefore,
possible to answer the question and it was found that those plots alone
were uniform on which the kernels of one single ear only had been sown.
Nilsson concluded that the mixture of two or more ears in a single sowing
might be the cause of the lack of uniformity in the progeny. Apparently
similar ears might be different in their progeny.
Once discovered, this fact was elevated to the rank of a leading principle
and tested on as large a scale as possible. The fields were again
carefully investigated and every single ear, which showed a distinct
divergence from the main type in one character or another, was selected. A
thousand samples were chosen, but this time each sample consisted of one
ear only. Next year, the result corresponded to the expectation.
Uniformity prevailed almost everywhere; only a few lots showed a
discrepancy, which might be ascribed to the accidental selection of hybrid
ears. It was now clear that the progeny of single ears was, as a rule,
pure, whereas that of mixed ears was impure. The single-ear selection or
single-ear sowing, which had fallen into discredit in Germany and elsewhere
in Europe, was rediscovered. It proved to be the only trustworthy
principle of selection. Once isolated, such single-parent races are
constant from seed and remain true to their type. No further selection is
needed; they have simply to be multiplied and their real value tested.
Patrick Shirreff, in his early experiments, Le Couteur, Hays and others had
observed the rare occurrence of exceptionally good yielders and the value
of their isolation to the agriculturist. The possibility of error in the
choice of such striking specimens and the necessity of judging their value
by their progeny were also known to these investigators, but they had not
the slightest idea of all the possibilities suggested by their principle.
Nilsson, who is a botanist as well as an agriculturist, discovered that,
besides these exceptionably good yielders, every variety of a cereal
consists of hundreds of different types, which find the best conditions for
success when grown together, but which, after isolation, prove to be
constant. Their preference for mixed growth is so definite, that once
isolated, their claims on manure and treatment are found to be much higher
than those of the original mixed variety. Moreover, the greatest care is
necessary to enable them to retain their purity, and as soon as they are
left to themselves they begin to deteriorate through accidental crosses and
admixtures and rapidly return to the mixed condition.
Reverting now to Darwin's discussion of the variability of cereals, we may
conclude that subsequent investigation has proved it to be exactly of the
kind which he describes. The only difference is that in reality it reaches
a degree, quite unexpected by Darwin and his contemporaries. But it is
polymorphic variability in the strictest sense of the word. How the single
constituents of a variety originate we do not see. We may assume, and
there can hardly be a doubt about the truth of the assumption, that a new
character, once produced, will slowly but surely be combined through
accidental crosses with a large number of previously existing types, and so
will tend to double the number of the constituents of the variety. But
whether it first appears suddenly or whether it is only slowly evolved we
cannot determine. It would, of course, be impossible to observe either
process in such a mixture. Only cultures of pure races, of single-parent
races as we have called them, can afford an opportunity for this kind of
observation. In the fields of Svalof new and unexpected qualities have
recently been seen, from time to time, to appear suddenly. These
characters are as distinct as the older ones and appear to be constant from
the moment of their origin.
Darwin has repeatedly insisted that man does not cause variability. He
simply selects the variations given to him by the hand of nature. He may
repeat this process in order to accumulate different new characters in the
same family, thus producing varieties of a higher order. This process of
accumulation would, if continued for a longer time, lead to the
augmentation of the slight differences characteristic of varieties into the
greater differences characteristic of species and genera. It is in this
way that horticultural and agricultural experience contribute to the
problem of the conversion of varieties into species, and to the explanation
of the admirable adaptations of each organism to its complex conditions of
life. In the long run new forms, distinguished from their allies by quite
a number of new characters, would, by the extermination of the older
intermediates, become distinct species.
Thus we see that the theory of the origin of species by means of natural
selection is quite independent of the question, how the variations to be
selected arise. They may arise slowly, from simple fluctuations, or
suddenly, by mutations; in both cases natural selection will take hold of
them, will multiply them if they are beneficial, and in the course of time
accumulate them, so as to produce that great diversity of organic life,
which we so highly admire.
Darwin has left the decision of this difficult and obviously subordinate
point to his followers. But in his Pangenesis hypothesis he has given us
the clue for a close study and ultimate elucidation of the subject under
discussion.
V. HEREDITY AND VARIATION IN MODERN LIGHTS.
By W. BATESON, M.A., F.R.S.
Professor of Biology in the University of Cambridge.
Darwin's work has the property of greatness in that it may be admired from
more aspects than one. For some the perception of the principle of Natural
Selection stands out as his most wonderful achievement to which all the
rest is subordinate. Others, among whom I would range myself, look up to
him rather as the first who plainly distinguished, collected, and
comprehensively studied that new class of evidence from which hereafter a
true understanding of the process of Evolution may be developed. We each
prefer our own standpoint of admiration; but I think that it will be in
their wider aspect that his labours will most command the veneration of
posterity.
A treatise written to advance knowledge may be read in two moods. The
reader may keep his mind passive, willing merely to receive the impress of
the writer's thought; or he may read with his attention strained and alert,
asking at every instant how the new knowledge can be used in a further
advance, watching continually for fresh footholds by which to climb higher
still. Of Shelley it has been said that he was a poet for poets: so
Darwin was a naturalist for naturalists. It is when his writings are used
in the critical and more exacting spirit with which we test the outfit for
our own enterprise that we learn their full value and strength. Whether we
glance back and compare his performance with the efforts of his
predecessors, or look forward along the course which modern research is
disclosing, we shall honour most in him not the rounded merit of finite
accomplishment, but the creative power by which he inaugurated a line of
discovery endless in variety and extension. Let us attempt thus to see his
work in true perspective between the past from which it grew, and the
present which is its consequence. Darwin attacked the problem of Evolution
by reference to facts of three classes: Variation; Heredity; Natural
Selection. His work was not as the laity suppose, a sudden and unheralded
revelation, but the first fruit of a long and hitherto barren controversy.
The occurrence of variation from type, and the hereditary transmission of
such variation had of course been long familiar to practical men, and
inferences as to the possible bearing of those phenomena on the nature of
specific difference had been from time to time drawn by naturalists.
Maupertuis, for example, wrote "Ce qui nous reste a examiner, c'est comment
d'un seul individu, il a pu naitre tant d'especes si differentes." And
again "La Nature contient le fonds de toutes ces varietes: mais le hasard
ou l'art les mettent en oeuvre. C'est ainsi que ceux dont l'industrie
s'applique a satisfaire le gout des curieux, sont, pour ainsi dire,
creatures d'especes nouvelles." ("Venus Physique, contenant deux
Dissertations, l'une sur l'origine des Hommes et des Animaux: Et l'autre
sur l'origine des Noirs" La Haye, 1746, pages 124 and 129. For an
introduction to the writings of Maupertuis I am indebted to an article by
Professor Lovejoy in "Popular Sci. Monthly", 1902.)
Such passages, of which many (though few so emphatic) can be found in
eighteenth century writers, indicate a true perception of the mode of
Evolution. The speculations hinted at by Buffon (For the fullest account
of the views of these pioneers of Evolution, see the works of Samuel
Butler, especially "Evolution, Old and New" (2nd edition) 1882. Butler's
claims on behalf of Buffon have met with some acceptance; but after reading
what Butler has said, and a considerable part of Buffon's own works, the
word "hinted" seems to me a sufficiently correct description of the part he
played. It is interesting to note that in the chapter on the Ass, which
contains some of his evolutionary passages, there is a reference to
"plusieurs idees tres-elevees sur la generation" contained in the Letters
of Maupertuis.), developed by Erasmus Darwin, and independently proclaimed
above all by Lamarck, gave to the doctrine of descent a wide renown. The
uniformitarian teaching which Lyell deduced from geological observation had
gained acceptance. The facts of geographical distribution (See especially
W. Lawrence, "Lectures on Physiology", London, 1823, pages 213 f.) had been
shown to be obviously inconsistent with the Mosaic legend. Prichard, and
Lawrence, following the example of Blumenbach, had successfully
demonstrated that the races of Man could be regarded as different forms of
one species, contrary to the opinion up till then received. These
treatises all begin, it is true, with a profound obeisance to the sons of
Noah, but that performed, they continue on strictly modern lines. The
question of the mutability of species was thus prominently raised.
Those who rate Lamarck no higher than did Huxley in his contemptuous phrase
"buccinator tantum," will scarcely deny that the sound of the trumpet had
carried far, or that its note was clear. If then there were few who had
already turned to evolution with positive conviction, all scientific men
must at least have known that such views had been promulgated; and many
must, as Huxley says, have taken up his own position of "critical
expectancy." (See the chapter contributed to the "Life and Letters of
Charles Darwin" II. page 195. I do not clearly understand the sense in
which Darwin wrote (Autobiography, ibid. I. page 87): "It has sometimes
been said that the success of the "Origin" proved 'that the subject was in
the air,' or 'that men's minds were prepared for it.' I do not think that
this is strictly true, for I occasionally sounded not a few naturalists,
and never happened to come across a single one who seemed to doubt about
the permanence of species." This experience may perhaps have been an
accident due to Darwin's isolation. The literature of the period abounds
with indications of "critical expectancy." A most interesting expression
of that feeling is given in the charming account of the "Early Days of
Darwinism" by Alfred Newton, "Macmillan's Magazine", LVII. 1888, page 241.
He tells how in 1858 when spending a dreary summer in Iceland, he and his
friend, the ornithologist John Wolley, in default of active occupation,
spent their days in discussion. "Both of us taking a keen interest in
Natural History, it was but reasonable that a question, which in those days
was always coming up wherever two or more naturalists were gathered
together, should be continually recurring. That question was, 'What is a
species?' and connected therewith was the other question, 'How did a
species begin?'...Now we were of course fairly well acquainted with what
had been published on these subjects." He then enumerates some of these
publications, mentioning among others T. Vernon Wollaston's "Variation of
Species"--a work which has in my opinion never been adequately appreciated.
He proceeds: "Of course we never arrived at anything like a solution of
these problems, general or special, but we felt very strongly that a
solution ought to be found, and that quickly, if the study of Botany and
Zoology was to make any great advance." He then describes how on his
return home he received the famous number of the "Linnean Journal" on a
certain evening. "I sat up late that night to read it; and never shall I
forget the impression it made upon me. Herein was contained a perfectly
simple solution of all the difficulties which had been troubling me for
months past...I went to bed satisfied that a solution had been found.")
Why, then, was it, that Darwin succeeded where the rest had failed? The
cause of that success was two-fold. First, and obviously, in the principle
of Natural Selection he had a suggestion which would work. It might not go
the whole way, but it was true as far as it went. Evolution could thus in
great measure be fairly represented as a consequence of demonstrable
processes. Darwin seldom endangers the mechanism he devised by putting on
it strains much greater than it can bear. He at least was under no
illusion as to the omnipotence of Selection; and he introduces none of the
forced pleading which in recent years has threatened to discredit that
principle.
For example, in the latest text of the "Origin" ("Origin", (6th edition
(1882), page 421.) we find him saying:
"But as my conclusions have lately been much misrepresented, and it has
been stated that I attribute the modification of species exclusively to
natural selection, I may be permitted to remark that in the first edition
of this work, and subsequently, I placed in a most conspicuous position--
namely, at the close of the Introduction--the following words: 'I am
convinced that natural selection has been the main but not the exclusive
means of modification.'"
But apart from the invention of this reasonable hypothesis, which may well,
as Huxley estimated, "be the guide of biological and psychological
speculation for the next three or four generations," Darwin made a more
significant and imperishable contribution. Not for a few generations, but
through all ages he should be remembered as the first who showed clearly
that the problems of Heredity and Variation are soluble by observation, and
laid down the course by which we must proceed to their solution. (Whatever
be our estimate of the importance of Natural Selection, in this we all
agree. Samuel Butler, the most brilliant, and by far the most interesting
of Darwin's opponents--whose works are at length emerging from oblivion--in
his Preface (1882) to the 2nd edition of "Evolution, Old and New", repeats
his earlier expression of homage to one whom he had come to regard as an
enemy: "To the end of time, if the question be asked, 'Who taught people
to believe in Evolution?' the answer must be that it was Mr. Darwin. This
is true, and it is hard to see what palm of higher praise can be awarded to
any philosopher.") The moment of inspiration did not come with the reading
of Malthus, but with the opening of the "first note-book on Transmutation
of Species." ("Life and Letters", I. pages 276 and 83.) Evolution is a
process of Variation and Heredity. The older writers, though they had some
vague idea that it must be so, did not study Variation and Heredity.
Darwin did, and so begat not a theory, but a science.
The extent to which this is true, the scientific world is only beginning to
realise. So little was the fact appreciated in Darwin's own time that the
success of his writings was followed by an almost total cessation of work
in that special field. Of the causes which led to this remarkable
consequence I have spoken elsewhere. They proceeded from circumstances
peculiar to the time; but whatever the causes there is no doubt that this
statement of the result is historically exact, and those who make it their
business to collect facts elucidating the physiology of Heredity and
Variation are well aware that they will find little to reward their quest
in the leading scientific Journals of the Darwinian epoch.
In those thirty years the original stock of evidence current and in
circulation even underwent a process of attrition. As in the story of the
Eastern sage who first wrote the collected learning of the universe for his
sons in a thousand volumes, and by successive compression and burning
reduced them to one, and from this by further burning distilled the single
ejaculation of the Faith, "There is no god but God and Mohamed is the
Prophet of God," which was all his maturer wisdom deemed essential:--so in
the books of that period do we find the corpus of genetic knowledge dwindle
to a few prerogative instances, and these at last to the brief formula of
an unquestioned creed.
And yet in all else that concerns biological science this period was, in
very truth, our Golden Age, when the natural history of the earth was
explored as never before; morphology and embryology were exhaustively
ransacked; the physiology of plants and animals began to rival chemistry
and physics in precision of method and in the rapidity of its advances; and
the foundations of pathology were laid.
In contrast with this immense activity elsewhere the neglect which befel
the special physiology of Descent, or Genetics as we now call it, is
astonishing. This may of course be interpreted as meaning that the
favoured studies seemed to promise a quicker return for effort, but it
would be more true to say that those who chose these other pursuits did so
without making any such comparison; for the idea that the physiology of
Heredity and Variation was a coherent science, offering possibilities of
extraordinary discovery, was not present to their minds at all. In a word,
the existence of such a science was well nigh forgotten. It is true that
in ancillary periodicals, as for example those that treat of entomology or
horticulture, or in the writings of the already isolated systematists (This
isolation of the systematists is the one most melancholy sequela of
Darwinism. It seems an irony that we should read in the peroration to the
"Origin" that when the Darwinian view is accepted "Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that form be a
true species. This, I feel sure, and I speak after experience, will be no
slight relief. The endless disputes whether or not some fifty species of
British brambles are good species will cease." "Origin", 6th edition
(1882), page 425. True they have ceased to attract the attention of those
who lead opinion, but anyone who will turn to the literature of systematics
will find that they have not ceased in any other sense. Should there not
be something disquieting in the fact that among the workers who come most
into contact with specific differences, are to be found the only men who
have failed to be persuaded of the unreality of those differences?),
observations with this special bearing were from time to time related, but
the class of fact on which Darwin built his conceptions of Heredity and
Variation was not seen in the highways of biology. It formed no part of
the official curriculum of biological students, and found no place among
the subjects which their teachers were investigating.
During this period nevertheless one distinct advance was made, that with
which Weismann's name is prominently connected. In Darwin's genetic scheme
the hereditary transmission of parental experience and its consequences
played a considerable role. Exactly how great that role was supposed to
be, he with his habitual caution refrained from specifying, for the
sufficient reason that he did not know. Nevertheless much of the process
of Evolution, especially that by which organs have become degenerate and
rudimentary, was certainly attributed by Darwin to such inheritance, though
since belief in the inheritance of acquired characters fell into disrepute,
the fact has been a good deal overlooked. The "Origin" without "use and
disuse" would be a materially different book. A certain vacillation is
discernible in Darwin's utterances on this question, and the fact gave to
the astute Butler an opportunity for his most telling attack. The
discussion which best illustrates the genetic views of the period arose in
regard to the production of the rudimentary condition of the wings of many
beetles in the Madeira group of islands, and by comparing passages from the
"Origin" (6th edition pages 109 and 401. See Butler, "Essays on Life, Art,
and Science", page 265, reprinted 1908, and "Evolution, Old and New",
chapter XXII. (2nd edition), 1882.) Butler convicts Darwin of saying first
that this condition was in the main the result of Selection, with disuse
aiding, and in another place that the main cause of degeneration was
disuse, but that Selection had aided. To Darwin however I think the point
would have seemed one of dialectics merely. To him the one paramount
purpose was to show that somehow an Evolution by means of Variation and
Heredity might have brought about the facts observed, and whether they had
come to pass in the one way or the other was a matter of subordinate
concern.
To us moderns the question at issue has a diminished significance. For
over all such debates a change has been brought by Weismann's challenge for
evidence that use and disuse have any transmitted effects at all. Hitherto
the transmission of many acquired characteristics had seemed to most
naturalists so obvious as not to call for demonstration. (W. Lawrence was
one of the few who consistently maintained the contrary opinion. Prichard,
who previously had expressed himself in the same sense, does not, I believe
repeat these views in his later writings, and there are signs that he came
to believe in the transmission of acquired habits. See Lawrence, "Lect.
Physiol." 1823, pages 436-437, 447 Prichard, Edin. Inaug. Disp. 1808 (not
seen by me), quoted ibid. and "Nat. Hist. Man", 1843, pages 34 f.)
Weismann's demand for facts in support of the main proposition revealed at
once that none having real cogency could be produced. The time-honoured
examples were easily shown to be capable of different explanations. A few
certainly remain which cannot be so summarily dismissed, but--though it is
manifestly impossible here to do justice to such a subject--I think no one
will dispute that these residual and doubtful phenomena, whatever be their
true nature, are not of a kind to help us much in the interpretation of any
of those complex cases of adaptation which on the hypothesis of unguided
Natural Selection are especially difficult to understand. Use and disuse
were invoked expressly to help us over these hard places; but whatever
changes can be induced in offspring by direct treatment of the parents,
they are not of a kind to encourage hope of real assistance from that
quarter. It is not to be denied that through the collapse of this second
line of argument the Selection hypothesis has had to take an increased and
perilous burden. Various ways of meeting the difficulty have been
proposed, but these mostly resolve themselves into improbable attempts to
expand or magnify the powers of Natural Selection.
Weismann's interpellation, though negative in purpose, has had a lasting
and beneficial effect, for through his thorough demolition of the old loose
and distracting notions of inherited experience, the ground has been
cleared for the construction of a true knowledge of heredity based on
experimental fact.
In another way he made a contribution of a more positive character, for his
elaborate speculations as to the genetic meaning of cytological appearances
have led to a minute investigation of the visible phenomena occurring in
those divisions by which germ-cells arise. Though the particular views he
advocated have very largely proved incompatible with the observed facts of
heredity, yet we must acknowledge that it was chiefly through the stimulus
of Weismann's ideas that those advances in cytology were made; and though
the doctrine of the continuity of germ-plasm cannot be maintained in the
form originally propounded, it is in the main true and illuminating. (It
is interesting to see how nearly Butler was led by natural penetration, and
from absolutely opposite conclusions, back to this underlying truth: "So
that each ovum when impregnate should be considered not as descended from
its ancestors, but as being a continuation of the personality of every ovum
in the chain of its ancestry, which every ovum IT ACTUALLY IS quite as
truly as the octogenarian IS the same identity with the ovum from which he
has been developed. This process cannot stop short of the primordial cell,
which again will probably turn out to be but a brief resting-place. We
therefore prove each one of us to BE ACTUALLY the primordial cell which
never died nor dies, but has differentiated itself into the life of the
world, all living beings whatever, being one with it and members one of
another," "Life and Habit", 1878, page 86.) Nevertheless in the present
state of knowledge we are still as a rule quite unable to connect
cytological appearances with any genetic consequence and save in one
respect (obviously of extreme importance--to be spoken of later) the two
sets of phenomena might, for all we can see, be entirely distinct.
I cannot avoid attaching importance to this want of connection between the
nuclear phenomena and the features of bodily organisation. All attempts to
investigate Heredity by cytological means lie under the disadvantage that
it is the nuclear changes which can alone be effectively observed.
Important as they must surely be, I have never been persuaded that the rest
of the cell counts for nothing. What we know of the behaviour and
variability of chromosomes seems in my opinion quite incompatible with the
belief that they alone govern form, and are the sole agents responsible in
heredity. (This view is no doubt contrary to the received opinion. I am
however interested to see it lately maintained by Driesch ("Science and
Philosophy of the Organism", London, 1907, page 233), and from the recent
observations of Godlewski it has received distinct experimental support.)
If, then, progress was to be made in Genetics, work of a different kind was
required. To learn the laws of Heredity and Variation there is no other
way than that which Darwin himself followed, the direct examination of the
phenomena. A beginning could be made by collecting fortuitous observations
of this class, which have often thrown a suggestive light, but such
evidence can be at best but superficial and some more penetrating
instrument of research is required. This can only be provided by actual
experiments in breeding.
The truth of these general considerations was becoming gradually clear to
many of us when in 1900 Mendel's work was rediscovered. Segregation, a
phenomenon of the utmost novelty, was thus revealed. From that moment not
only in the problem of the origin of species, but in all the great problems
of biology a new era began. So unexpected was the discovery that many
naturalists were convinced it was untrue, and at once proclaimed Mendel's
conclusions as either altogether mistaken, or if true, of very limited
application. Many fantastic notions about the workings of Heredity had
been asserted as general principles before: this was probably only another
fancy of the same class.
Nevertheless those who had a preliminary acquaintance with the facts of
Variation were not wholly unprepared for some such revelation. The
essential deduction from the discovery of segregation was that the
characters of living things are dependent on the presence of definite
elements or factors, which are treated as units in the processes of
Heredity. These factors can thus be recombined in various ways. They act
sometimes separately, and sometimes they interact in conjunction with each
other, producing their various effects. All this indicates a definiteness
and specific order in heredity, and therefore in variation. This order
cannot by the nature of the case be dependent on Natural Selection for its
existence, but must be a consequence of the fundamental chemical and
physical nature of living things. The study of Variation had from the
first shown that an orderliness of this kind was present. The bodies and
the properties of living things are cosmic, not chaotic. No matter how low
in the scale we go, never do we find the slightest hint of a diminution in
that all-pervading orderliness, nor can we conceive an organism existing
for a moment in any other state. Moreover not only does this order prevail
in normal forms, but again and again it is to be seen in newly-sprung
varieties, which by general consent cannot have been subjected to a
prolonged Selection. The discovery of Mendelian elements admirably
coincided with and at once gave a rationale of these facts. Genetic
Variation is then primarily the consequence of additions to, or omissions
from, the stock of elements which the species contains. The further
investigation of the species-problem must thus proceed by the analytical
method which breeding experiments provide.
In the nine years which have elapsed since Mendel's clue became generally
known, progress has been rapid. We now understand the process by which a
polymorphic race maintains its polymorphism. When a family consists of
dissimilar members, given the numerical proportions in which these members
are occurring, we can represent their composition symbolically and state
what types can be transmitted by the various members. The difficulty of
the "swamping effects of intercrossing" is practically at an end. Even the
famous puzzle of sex-limited inheritance is solved, at all events in its
more regular manifestations, and we know now how it is brought about that
the normal sisters of a colour-blind man can transmit the colour-blindness
while his normal brothers cannot transmit it.
We are still only on the fringe of the inquiry. It can be seen extending
and ramifying in many directions. To enumerate these here would be
impossible. A whole new range of possibilities is being brought into view
by study of the interrelations between the simple factors. By following up
the evidence as to segregation, indications have been obtained which can
only be interpreted as meaning that when many factors are being
simultaneously redistributed among the germ-cells, certain of them exert
what must be described as a repulsion upon other factors. We cannot
surmise whither this discovery may lead.
In the new light all the old problems wear a fresh aspect. Upon the
question of the nature of Sex, for example, the bearing of Mendelian
evidence is close. Elsewhere I have shown that from several sets of
parallel experiments the conclusion is almost forced upon us that, in the
types investigated, of the two sexes the female is to be regarded as
heterozygous in sex, containing one unpaired dominant element, while the
male is similarly homozygous in the absence of that element. (In other
words, the ova are each EITHER female, OR male (i.e. non-female), but the
sperms are all non-female.) It is not a little remarkable that on this
point--which is the only one where observations of the nuclear processes of
gameto-genesis have yet been brought into relation with the visible
characteristics of the organisms themselves--there should be diametrical
opposition between the results of breeding experiments and those derived
from cytology.
Those who have followed the researches of the American school will be aware
that, after it had been found in certain insects that the spermatozoa were
of two kinds according as they contained or did not contain the accessory
chromosome, E.B. Wilson succeeded in proving that the sperms possessing
this accessory body were destined to form FEMALES on fertilisation, while
sperms without it form males, the eggs being apparently indifferent.
Perhaps the most striking of all this series of observations is that lately
made by T.H. Morgan (Morgan, "Proc. Soc. Exp. Biol. Med." V. 1908, and von
Baehr, "Zool. Anz." XXXII. page 507, 1908.), since confirmed by von Baehr,
that in a Phylloxeran two kinds of spermatids are formed, respectively with
and without an accessory (in this case, DOUBLE) chromosome. Of these, only
those possessing the accessory body become functional spermatozoa, the
others degenerating. We have thus an elucidation of the puzzling fact that
in these forms fertilisation results in the formation of FEMALES only. How
the males are formed--for of course males are eventually produced by the
parthenogenetic females--we do not know.
If the accessory body is really to be regarded as bearing the factor for
femaleness, then in Mendelian terms female is DD and male is DR. The eggs
are indifferent and the spermatozoa are each male, OR female. But
according to the evidence derived from a study of the sex-limited descent
of certain features in other animals the conclusion seems equally clear
that in them female must be regarded as DR and male as RR. The eggs are
thus each either male or female and the spermatozoa are indifferent. How
this contradictory evidence is to be reconciled we do not yet know. The
breeding work concerns fowls, canaries, and the Currant moth (Abraxas
grossulariata). The accessory chromosome has been now observed in most of
the great divisions of insects (As Wilson has proved, the unpaired body is
not a universal feature even in those orders in which it has been observed.
Nearly allied types may differ. In some it is altogether unpaired. In
others it is paired with a body of much smaller size, and by selection of
various types all gradations can be demonstrated ranging to the condition
in which the members of the pair are indistinguishable from each other.),
except, as it happens, Lepidoptera. At first sight it seems difficult to
suppose that a feature apparently so fundamental as sex should be
differently constituted in different animals, but that seems at present the
least improbable inference. I mention these two groups of facts as
illustrating the nature and methods of modern genetic work. We must
proceed by minute and specific analytical investigation. Wherever we look
we find traces of the operation of precise and specific rules.
In the light of present knowledge it is evident that before we can attack
the Species-problem with any hope of success there are vast arrears to be
made up. He would be a bold man who would now assert that there was no
sense in which the term Species might not have a strict and concrete
meaning in contradistinction to the term Variety. We have been taught to
regard the difference between species and variety as one of degree. I
think it unlikely that this conclusion will bear the test of further
research. To Darwin the question, What is a variation? presented no
difficulties. Any difference between parent and offspring was a variation.
Now we have to be more precise. First we must, as de Vries has shown,
distinguish real, genetic, variation from FLUCTUATIONAL variations, due to
environmental and other accidents, which cannot be transmitted. Having
excluded these sources of error the variations observed must be expressed
in terms of the factors to which they are due before their significance can
be understood. For example, numbers of the variations seen under
domestication, and not a few witnessed in nature, are simply the
consequence of some ingredient being in an unknown way omitted from the
composition of the varying individual. The variation may on the contrary
be due to the addition of some new element, but to prove that it is so is
by no means an easy matter. Casual observation is useless, for though
these latter variations will always be dominants, yet many dominant
characteristics may arise from another cause, namely the meeting of
complementary factors, and special study of each case in two generations at
least is needed before these two phenomena can be distinguished.
When such considerations are fully appreciated it will be realised that
medleys of most dissimilar occurrences are all confused together under the
term Variation. One of the first objects of genetic analysis is to
disentangle this mass of confusion.
To those who have made no study of heredity it sometimes appears that the
question of the effect of conditions in causing variation is one which we
should immediately investigate, but a little thought will show that before
any critical inquiry into such possibilities can be attempted, a knowledge
of the working of heredity under conditions as far as possible uniform must
be obtained. At the time when Darwin was writing, if a plant brought into
cultivation gave off an albino variety, such an event was without
hesitation ascribed to the change of life. Now we see that albino GAMETES,
germs, that is to say, which are destitute of the pigment-forming factor,
may have been originally produced by individuals standing an indefinite
number of generations back in the ancestry of the actual albino, and it is
indeed almost certain that the variation to which the appearance of the
albino is due cannot have taken place in a generation later than that of
the grandparents. It is true that when a new DOMINANT appears we should
feel greater confidence that we were witnessing the original variation, but
such events are of extreme rarity, and no such case has come under the
notice of an experimenter in modern times, as far as I am aware. That they
must have appeared is clear enough. Nothing corresponding to the Brown-
breasted Game fowl is known wild, yet that colour is a most definite
dominant, and at some moment since Gallus bankiva was domesticated, the
element on which that special colour depends must have at least once been
formed in the germ-cell of a fowl; but we need harder evidence than any
which has yet been produced before we can declare that this novelty came
through over-feeding, or change of climate, or any other disturbance
consequent on domestication. When we reflect on the intricacies of genetic
problems as we must now conceive them there come moments when we feel
almost thankful that the Mendelian principles were unknown to Darwin. The
time called for a bold pronouncement, and he made it, to our lasting profit
and delight. With fuller knowledge we pass once more into a period of
cautious expectation and reserve.
In every arduous enterprise it is pleasanter to look back at difficulties
overcome than forward to those which still seem insurmountable, but in the
next stage there is nothing to be gained by disguising the fact that the
attributes of living things are not what we used to suppose. If they are
more complex in the sense that the properties they display are throughout
so regular (I have in view, for example, the marvellous and specific
phenomena of regeneration, and those discovered by the students of
"Entwicklungsmechanik". The circumstances of its occurrence here preclude
any suggestion that this regularity has been brought about by the workings
of Selection. The attempts thus to represent the phenomena have resulted
in mere parodies of scientific reasoning.) that the Selection of minute
random variations is an unacceptable account of the origin of their
diversity, yet by virtue of that very regularity the problem is limited in
scope and thus simplified.
To begin with, we must relegate Selection to its proper place. Selection
permits the viable to continue and decides that the non-viable shall
perish; just as the temperature of our atmosphere decides that no liquid
carbon shall be found on the face of the earth: but we do not suppose that
the form of the diamond has been gradually achieved by a process of
Selection. So again, as the course of descent branches in the successive
generations, Selection determines along which branch Evolution shall
proceed, but it does not decide what novelties that branch shall bring
forth. "La Nature contient le fonds de toutes ces varietes, mais le hazard
ou l'art les mettent en oeuvre," as Maupertuis most truly said.
Not till knowledge of the genetic properties of organisms has attained to
far greater completeness can evolutionary speculations have more than a
suggestive value. By genetic experiment, cytology and physiological
chemistry aiding, we may hope to acquire such knowledge. In 1872 Nathusius
wrote ("Vortrage uber Viehzucht und Rassenerkenntniss", page 120, Berlin,
1872.): "Das Gesetz der Vererbung ist noch nicht erkannt; der Apfel ist
noch nicht vom Baum der Erkenntniss gefallen, welcher, der Sage nach,
Newton auf den rechten Weg zur Ergrundung der Gravitationsgesetze fuhrte."
We cannot pretend that the words are not still true, but in Mendelian
analysis the seeds of that apple-tree at last are sown.
If we were asked what discovery would do most to forward our inquiry, what
one bit of knowledge would more than any other illuminate the problem, I
think we may give the answer without hesitation. The greatest advance that
we can foresee will be made when it is found possible to connect the
geometrical phenomena of development with the chemical. The geometrical
symmetry of living things is the key to a knowledge of their regularity,
and the forces which cause it. In the symmetry of the dividing cell the
basis of that resemblance we call Heredity is contained. To imitate the
morphological phenomena of life we have to devise a system which can
divide. It must be able to divide, and to segment as--grossly--a vibrating
plate or rod does, or as an icicle can do as it becomes ribbed in a
continuous stream of water; but with this distinction, that the
distribution of chemical differences and properties must simultaneously be
decided and disposed in orderly relation to the pattern of the
segmentation. Even if a model which would do this could be constructed it
might prove to be a useful beginning.
This may be looking too far ahead. If we had to choose some one piece of
more proximate knowledge which we would more especially like to acquire, I
suppose we should ask for the secret of interracial sterility. Nothing has
yet been discovered to remove the grave difficulty, by which Huxley in
particular was so much oppressed, that among the many varieties produced
under domestication--which we all regard as analogous to the species seen
in nature--no clear case of interracial sterility has been demonstrated.
The phenomenon is probably the only one to which the domesticated products
seem to afford no parallel. No solution of the difficulty can be offered
which has positive value, but it is perhaps worth considering the facts in
the light of modern ideas. It should be observed that we are not
discussing incompatibility of two species to produce offspring (a totally
distinct phenomenon), but the sterility of the offspring which many of them
do produce.
When two species, both perfectly fertile severally, produce on crossing a
sterile progeny, there is a presumption that the sterility is due to the
development in the hybrid of some substance which can only be formed by the
meeting of two complementary factors. That some such account is correct in
essence may be inferred from the well-known observation that if the hybrid
is not totally sterile but only partially so, and thus is able to form some
good germ-cells which develop into new individuals, the sterility of these
daughter-individuals is sensibly reduced or may be entirely absent. The
fertility once re-established, the sterility does not return in the later
progeny, a fact strongly suggestive of segregation. Now if the sterility
of the cross-bred be really the consequence of the meeting of two
complementary factors, we see that the phenomenon could only be produced
among the divergent offspring of one species by the acquisition of at least
TWO new factors; for if the acquisition of a single factor caused sterility
the line would then end. Moreover each factor must be separately acquired
by distinct individuals, for if both were present together, the possessors
would by hypothesis be sterile. And in order to imitate the case of
species each of these factors must be acquired by distinct breeds. The
factors need not, and probably would not, produce any other perceptible
effects; they might, like the colour-factors present in white flowers, make
no difference in the form or other characters. Not till the cross was
actually made between the two complementary individuals would either factor
come into play, and the effects even then might be unobserved until an
attempt was made to breed from the cross-bred.
Next, if the factors responsible for sterility were acquired, they would in
all probability be peculiar to certain individuals and would not readily be
distributed to the whole breed. Any member of the breed also into which
BOTH the factors were introduced would drop out of the pedigree by virtue
of its sterility. Hence the evidence that the various domesticated breeds
say of dogs or fowls can when mated together produce fertile offspring, is
beside the mark. The real question is, Do they ever produce sterile
offspring? I think the evidence is clearly that sometimes they do, oftener
perhaps than is commonly supposed. These suggestions are quite amenable to
experimental tests. The most obvious way to begin is to get a pair of
parents which are known to have had any sterile offspring, and to find the
proportions in which these steriles were produced. If, as I anticipate,
these proportions are found to be definite, the rest is simple.
In passing, certain other considerations may be referred to. First, that
there are observations favouring the view that the production of totally
sterile cross-breds is seldom a universal property of two species, and that
it may be a matter of individuals, which is just what on the view here
proposed would be expected. Moreover, as we all know now, though
incompatibility may be dependent to some extent on the degree to which the
species are dissimilar, no such principle can be demonstrated to determine
sterility or fertility in general. For example, though all our Finches can
breed together, the hybrids are all sterile. Of Ducks some species can
breed together without producing the slightest sterility; others have
totally sterile offspring, and so on. The hybrids between several genera
of Orchids are perfectly fertile on the female side, and some on the male
side also, but the hybrids produced between the Turnip (Brassica napus) and
the Swede (Brassica campestris), which, according to our estimates of
affinity should be nearly allied forms, are totally sterile. (See Sutton,
A.W., "Journ. Linn. Soc." XXXVIII. page 341, 1908.) Lastly, it may be
recalled that in sterility we are almost certainly considering a meristic
phenomenon. FAILURE TO DIVIDE is, we may feel fairly sure, the immediate
"cause" of the sterility. Now, though we know very little about the
heredity of meristic differences, all that we do know points to the
conclusion that the less-divided is dominant to the more-divided, and we
are thus justified in supposing that there are factors which can arrest or
prevent cell-division. My conjecture therefore is that in the case of
sterility of cross-breds we see the effect produced by a complementary pair
of such factors. This and many similar problems are now open to our
analysis.
The question is sometimes asked, Do the new lights on Variation and
Heredity make the process of Evolution easier to understand? On the whole
the answer may be given that they do. There is some appearance of loss of
simplicity, but the gain is real. As was said above, the time is not ripe
for the discussion of the origin of species. With faith in Evolution
unshaken--if indeed the word faith can be used in application to that which
is certain--we look on the manner and causation of adapted differentiation
as still wholly mysterious. As Samuel Butler so truly said: "To me it
seems that the 'Origin of Variation,' whatever it is, is the only true
'Origin of Species'" ("Life and Habit", London, page 263, 1878.), and of
that Origin not one of us knows anything. But given Variation--and it is
given: assuming further that the variations are not guided into paths of
adaptation--and both to the Darwinian and to the modern school this
hypothesis appears to be sound if unproven--an evolution of species
proceeding by definite steps is more, rather than less, easy to imagine
than an evolution proceeding by the accumulation of indefinite and
insensible steps. Those who have lost themselves in contemplating the
miracles of Adaptation (whether real or spurious) have not unnaturally
fixed their hopes rather on the indefinite than on the definite changes.
The reasons are obvious. By suggesting that the steps through which an
adaptative mechanism arose were indefinite and insensible, all further
trouble is spared. While it could be said that species arise by an
insensible and imperceptible process of variation, there was clearly no use
in tiring ourselves by trying to perceive that process. This labour-saving
counsel found great favour. All that had to be done to develop evolution-
theory was to discover the good in everything, a task which, in the
complete absence of any control or test whereby to check the truth of the
discovery, is not very onerous. The doctrine "que tout est au mieux" was
therefore preached with fresh vigour, and examples of that illuminating
principle were discovered with a facility that Pangloss himself might have
envied, till at last even the spectators wearied of such dazzling
performances.
But in all seriousness, why should indefinite and unlimited variation have
been regarded as a more probable account of the origin of Adaptation?
Only, I think, because the obstacle was shifted one plane back, and so
looked rather less prominent. The abundance of Adaptation, we all grant,
is an immense, almost an unsurpassable difficulty in all non-Lamarckian
views of Evolution; but if the steps by which that adaptation arose were
fortuitous, to imagine them insensible is assuredly no help. In one most
important respect indeed, as has often been observed, it is a
multiplication of troubles. For the smaller the steps, the less could
Natural Selection act upon them. Definite variations--and of the
occurrence of definite variations in abundance we have now the most
convincing proof--have at least the obvious merit that they can make and
often do make a real difference in the chances of life.
There is another aspect of the Adaptation problem to which I can only
allude very briefly. May not our present ideas of the universality and
precision of Adaptation be greatly exaggerated? The fit of organism to its
environment is not after all so very close--a proposition unwelcome
perhaps, but one which could be illustrated by very copious evidence.
Natural Selection is stern, but she has her tolerant moods.
We have now most certain and irrefragable proof that much definiteness
exists in living things apart from Selection, and also much that may very
well have been preserved and so in a sense constituted by Selection. Here
the matter is likely to rest. There is a passage in the sixth edition of
the "Origin" which has I think been overlooked. On page 70 Darwin says
"The tuft of hair on the breast of the wild turkey-cock cannot be of any
use, and it is doubtful whether it can be ornamental in the eyes of the
female bird." This tuft of hair is a most definite and unusual structure,
and I am afraid that the remark that it "cannot be of any use" may have
been made inadvertently; but it may have been intended, for in the first
edition the usual qualification was given and must therefore have been
deliberately excised. Anyhow I should like to think that Darwin did throw
over that tuft of hair, and that he felt relief when he had done so.
Whether however we have his great authority for such a course or not, I
feel quite sure that we shall be rightly interpreting the facts of nature
if we cease to expect to find purposefulness wherever we meet with definite
structures or patterns. Such things are, as often as not, I suspect rather
of the nature of tool-marks, mere incidents of manufacture, benefiting
their possessor not more than the wire-marks in a sheet of paper, or the
ribbing on the bottom of an oriental plate renders those objects more
attractive in our eyes.
If Variation may be in any way definite, the question once more arises, may
it not be definite in direction? The belief that it is has had many
supporters, from Lamarck onwards, who held that it was guided by need, and
others who, like Nageli, while laying no emphasis on need, yet were
convinced that there was guidance of some kind. The latter view under the
name of "Orthogenesis," devised I believe by Eimer, at the present day
commends itself to some naturalists. The objection to such a suggestion is
of course that no fragment of real evidence can be produced in its support.
On the other hand, with the experimental proof that variation consists
largely in the unpacking and repacking of an original complexity, it is not
so certain as we might like to think that the order of these events is not
pre-determined. For instance the original "pack" may have been made in
such a way that at the nth division of the germ-cells of a Sweet Pea a
colour-factor might be dropped, and that at the n plus n prime division the
hooded variety be given off, and so on. I see no ground whatever for
holding such a view, but in fairness the possibility should not be
forgotten, and in the light of modern research it scarcely looks so
absurdly improbable as before.
No one can survey the work of recent years without perceiving that
evolutionary orthodoxy developed too fast, and that a great deal has got to
come down; but this satisfaction at least remains, that in the experimental
methods which Mendel inaugurated, we have means of reaching certainty in
regard to the physiology of Heredity and Variation upon which a more
lasting structure may be built.
VI. THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY.
By EDUARD STRASBURGER,
Professor of Botany in the University of Bonn.
Since 1875 an unexpected insight has been gained into the internal
structure of cells. Those who are familiar with the results of
investigations in this branch of Science are convinced that any modern
theory of heredity must rest on a basis of cytology and cannot be at
variance with cytological facts. Many histological discoveries, both such
as have been proved correct and others which may be accepted as probably
well founded, have acquired a fundamental importance from the point of view
of the problems of heredity.
My aim is to describe the present position of our knowledge of Cytology.
The account must be confined to essentials and cannot deal with far-
reaching and controversial questions. In cases where difference of opinion
exists, I adopt my own view for which I hold myself responsible. I hope to
succeed in making myself intelligible even without the aid of
illustrations: in order to convey to the uninitiated an adequate idea of
the phenomena connected with the life of a cell, a greater number of
figures would be required than could be included within the scope of this
article.
So long as the most eminent investigators (As for example the illustrious
Wilhelm Hofmeister in his "Lehre von der Pflanzenzelle" (1867).) believed
that the nucleus of a cell was destroyed in the course of each division and
that the nuclei of the daughter-cells were produced de novo, theories of
heredity were able to dispense with the nucleus. If they sought, as did
Charles Darwin, who showed a correct grasp of the problem in the
enunciation of his Pangenesis hypothesis, for histological connecting
links, their hypotheses, or at least the best of them, had reference to the
cell as a whole. It was known to Darwin that the cell multiplied by
division and was derived from a similar pre-existing cell. Towards 1870 it
was first demonstrated that cell-nuclei do not arise de novo, but are
invariably the result of division of pre-existing nuclei. Better methods
of investigation rendered possible a deeper insight into the phenomena
accompanying cell and nuclear divisions and at the same time disclosed the
existence of remarkable structures. The work of O. Butschli, O. Hertwig,
W. Flemming H. Fol and of the author of this article (For further reference
to literature, see my article on "Die Ontogenie der Zelle seit 1875", in
the "Progressus Rei Botanicae", Vol. I. page 1, Jena, 1907.), have
furnished conclusive evidence in favour of these facts. It was found that
when the reticular framework of a nucleus prepares to divide, it separates
into single segments. These then become thicker and denser, taking up with
avidity certain stains, which are used as aids to investigation, and
finally form longer or shorter, variously bent, rodlets of uniform
thickness. In these organs which, on account of their special property of
absorbing certain stains, were styled Chromosomes (By W. Waldeyer in
1888.), there may usually be recognised a separation into thicker and
thinner discs; the former are often termed Chromomeres. (Discovered by W.
Pfitzner in 1880.) In the course of division of the nucleus, the single
rows of chromomeres in the chromosomes are doubled and this produces a
band-like flattening and leads to the longitudinal splitting by which each
chromosome is divided into two exactly equal halves. The nuclear membrane
then disappears and fibrillar cell-plasma or cytoplasm invades the nuclear
area. In animal cells these fibrillae in the cytoplasm centre on definite
bodies (Their existence and their multiplication by fission were
demonstrated by E. van Beneden and Th. Boveri in 1887.), which it is
customary to speak of as Centrosomes. Radiating lines in the adjacent
cell-plasma suggest that these bodies constitute centres of force. The
cells of the higher plants do not possess such individualised centres; they
have probably disappeared in the course of phylogenetic development: in
spite of this, however, in the nuclear division-figures the fibrillae of
the cell-plasma are seen to radiate from two opposite poles. In both
animal and plant cells a fibrillar bipolar spindle is formed, the fibrillae
of which grasp the longitudinally divided chromosomes from two opposite
sides and arrange them on the equatorial plane of the spindle as the so-
called nuclear or equatorial plate. Each half-chromosome is connected with
one of the spindle poles only and is then drawn towards that pole. (These
important facts, suspected by W. Flemming in 1882, were demonstrated by E.
Heuser, L. Guignard, E. van Beneden, M. Nussbaum, and C. Rabl.)
The formation of the daughter-nuclei is then effected. The changes which
the daughter-chromosomes undergo in the process of producing the daughter-
nuclei repeat in the reverse order the changes which they went through in
the course of their progressive differentiation from the mother-nucleus.
The division of the cell-body is completed midway between the two daughter-
nuclei. In animal cells, which possess no chemically differentiated
membrane, separation is effected by simple constriction, while in the case
of plant cells provided with a definite wall, the process begins with the
formation of a cytoplasmic separating layer.
The phenomena observed in the course of the division of the nucleus show
beyond doubt that an exact halving of its substance is of the greatest
importance. (First shown by W. Roux in 1883.) Compared with the method of
division of the nucleus, that of the cytoplasm appears to be very simple.
This led to the conception that the cell-nucleus must be the chief if not
the sole carrier of hereditary characters in the organism. It is for this
reason that the detailed investigation of fertilisation phenomena
immediately followed researches into the nucleus. The fundamental
discovery of the union of two nuclei in the sexual act was then made (By O.
Hertwig in 1875.) and this afforded a new support for the correct
conception of the nuclear functions. The minute study of the behaviour of
the other constituents of sexual cells during fertilisation led to the
result, that the nucleus alone is concerned with handing on hereditary
characters (This was done by O. Hertwig and the author of this essay
simultaneously in 1884.) from one generation to another. Especially
important, from the point of view of this conclusion, is the study of
fertilisation in Angiosperms (Flowering plants); in these plants the male
sexual cells lose their cell-body in the pollen-tube and the nucleus only--
the sperm-nucleus--reaches the egg. The cytoplasm of the male sexual cell
is therefore not necessary to ensure a transference of hereditary
characters from parents to offspring. I lay stress on the case of the
Angiosperms because researches recently repeated with the help of the
latest methods failed to obtain different results. As regards the
descendants of angiospermous plants, the same laws of heredity hold good as
for other sexually differentiated organisms; we may, therefore, extend to
the latter what the Angiosperms so clearly teach us.
The next advance in the hitherto rapid progress in our knowledge of nuclear
division was delayed, because it was not at once recognised that there are
two absolutely different methods of nuclear division. All such nuclear
divisions were united under the head of indirect or mitotic divisions;
these were also spoken of as karyo-kineses, and were distinguished from the
direct or amitotic divisions which are characterised by a simple
constriction of the nuclear body. So long as the two kinds of indirect
nuclear division were not clearly distinguished, their correct
interpretation was impossible. This was accomplished after long and
laborious research, which has recently been carried out and with results
which should, perhaps, be regarded as provisional.
Soon after the new study of the nucleus began, investigators were struck by
the fact that the course of nuclear division in the mother-cells, or more
correctly in the grandmother-cells, of spores, pollen-grains, and embryo-
sacs of the more highly organised plants and in the spermatozoids and eggs
of the higher animals, exhibits similar phenomena, distinct from those
which occur in the somatic cells.
In the nuclei of all those cells which we may group together as gonotokonts
(At the suggestion of J.P. Lotsy in 1904.) (i.e. cells concerned in
reproduction) there are fewer chromosomes than in the adjacent body-cells
(somatic cells). It was noticed also that there is a peculiarity
characteristic of the gonotokonts, namely the occurrence of two nuclear
divisions rapidly succeeding one another. It was afterwards recognised
that in the first stage of nuclear division in the gonotokonts the
chromosomes unite in pairs: it is these chromosome-pairs, and not the two
longitudinal halves of single chromosomes, which form the nuclear plate in
the equatorial plane of the nuclear spindle. It has been proposed to call
these pairs gemini. (J.E.S. Moore and A.L. Embleton, "Proc. Roy. Soc."
London, Vol. LXXVII. page 555, 1906; V. Gregoire, 1907.) In the course of
this division the spindle-fibrillae attach themselves to the gemini, i.e.
to entire chromosomes and direct them to the points where the new daughter-
nuclei are formed, that is to those positions towards which the
longitudinal halves of the chromosomes travel in ordinary nuclear
divisions. It is clear that in this way the number of chromosomes which
the daughter-nuclei contain, as the result of the first stage in division
in the gonotokonts, will be reduced by one half, while in ordinary
divisions the number of chromosomes always remains the same. The first
stage in the division of the nucleus in the gonotokonts has therefore been
termed the reduction division. (In 1887 W. Flemming termed this the
heterotypic form of nuclear division.) This stage in division determines
the conditions for the second division which rapidly ensues. Each of the
paired chromosomes of the mother-nucleus has already, as in an ordinary
nuclear division, completed the longitudinal fission, but in this case it
is not succeeded by the immediate separation of the longitudinal halves and
their allotment to different nuclei. Each chromosome, therefore, takes its
two longitudinal halves into the same daughter-nucleus. Thus, in each
daughter-nucleus the longitudinal halves of the chromosomes are present
ready for the next stage in the division; they only require to be arranged
in the nuclear plate and then distributed among the granddaughter-nuclei.
This method of division, which takes place with chromosomes already split,
and which have only to provide for the distribution of their longitudinal
halves to the next nuclear generation, has been called homotypic nuclear
division. (The name was proposed by W. Flemming in 1887; the nature of
this type of division was, however, not explained until later.)
Reduction division and homotypic nuclear division are included together
under the term allotypic nuclear division and are distinguished from the
ordinary or typical nuclear division. The name Meiosis (By J. Bretland
Farmer and J.E.S. Moore in 1905.) has also been proposed for these two
allotypic nuclear divisions. The typical divisions are often spoken of as
somatic.
Observers who were actively engaged in this branch of recent histological
research soon noticed that the chromosomes of a given organism are
differentiated in definite numbers from the nuclear network in the course
of division. This is especially striking in the gonotokonts, but it
applies also to the somatic tissues. In the latter, one usually finds
twice as many chromosomes as in the gonotokonts. Thus the conclusion was
gradually reached that the doubling of chromosomes, which necessarily
accompanies fertilisation, is maintained in the product of fertilisation,
to be again reduced to one half in the gonotokonts at the stage of
reduction-division. This enabled us to form a conception as to the essence
of true alternation of generations, in which generations containing single
and double chromosomes alternate with one another.
The single-chromosome generation, which I will call the HAPLOID, must have
been the primitive generation in all organisms; it might also persist as
the only generation. Every sexual differentiation in organisms, which
occurred in the course of phylogenetic development, was followed by
fertilisation and therefore by the creation of a diploid or double-
chromosome product. So long as the germination of the product of
fertilisation, the zygote, began with a reducing process, a special DIPLOID
generation was not represented. This, however, appeared later as a product
of the further evolution of the zygote, and the reduction division was
correspondingly postponed. In animals, as in plants, the diploid
generation attained the higher development and gradually assumed the
dominant position. The haploid generation suffered a proportional
reduction, until it finally ceased to have an independent existence and
became restricted to the role of producing the sexual products within the
body of the diploid generation. Those who do not possess the necessary
special knowledge are unable to realise what remains of the first haploid
generation in a phanerogamic plant or in a vertebrate animal. In
Angiosperms this is actually represented only by the short developmental
stages which extend from the pollen mother-cells to the sperm-nucleus of
the pollen-tube, and from the embryo-sac mother-cell to the egg and the
endosperm tissue. The embryo-sac remains enclosed in the diploid ovule,
and within this from the fertilised egg is formed the embryo which
introduces the new diploid generation. On the full development of the
diploid embryo of the next generation, the diploid ovule of the preceding
diploid generation is separated from the latter as a ripe seed. The
uninitiated sees in the more highly organised plants only a succession of
diploid generations. Similarly all the higher animals appear to us as
independent organisms with diploid nuclei only. The haploid generation is
confined in them to the cells produced as the result of the reduction
division of the gonotokonts; the development of these is completed with the
homotypic stage of division which succeeds the reduction division and
produces the sexual products.
The constancy of the numbers in which the chromosomes separate themselves
from the nuclear network during division gave rise to the conception that,
in a certain degree, chromosomes possess individuality. Indeed the most
careful investigations (Particularly those of V. Gregoire and his pupils.)
have shown that the segments of the nuclear network, which separate from
one another and condense so as to produce chromosomes for a new division,
correspond to the segments produced from the chromosomes of the preceding
division. The behaviour of such nuclei as possess chromosomes of unequal
size affords confirmatory evidence of the permanence of individual
chromosomes in corresponding sections of an apparently uniform nuclear
network. Moreover at each stage in division chromosomes with the same
differences in size reappear. Other cases are known in which thicker
portions occur in the substance of the resting nucleus, and these agree in
number with the chromosomes. In this network, therefore, the individual
chromosomes must have retained their original position. But the
chromosomes cannot be regarded as the ultimate hereditary units in the
nuclei, as their number is too small. Moreover, related species not
infrequently show a difference in the number of their chromosomes, whereas
the number of hereditary units must approximately agree. We thus picture
to ourselves the carriers of hereditary characters as enclosed in the
chromosomes; the transmitted fixed number of chromosomes is for us only the
visible expression of the conception that the number of hereditary units
which the chromosomes carry must be also constant. The ultimate hereditary
units may, like the chromosomes themselves, retain a definite position in
the resting nucleus. Further, it may be assumed that during the separation
of the chromosomes from one another and during their assumption of the rod-
like form, the hereditary units become aggregated in the chromomeres and
that these are characterised by a constant order of succession. The
hereditary units then grow, divide into two and are uniformly distributed
by the fission of the chromosomes between their longitudinal halves.
As the contraction and rod-like separation of the chromosomes serve to
isnure the transmission of all hereditary units in the products of division
of a nucleus, so, on the other hand, the reticular distension of each
chromosome in the so-called resting nucleus may effect a separation of the
carriers of hereditary units from each other and facilitate the specific
activity of each of them.
In the stages preliminary to their division, the chromosomes become denser
and take up a substance which increases their staining capacity; this is
called chromatin. This substance collects in the chromomeres and may form
the nutritive material for the carriers of hereditary units which we now
believe to be enclosed in them. The chromatin cannot itself be the
hereditary substance, as it afterwards leaves the chromosomes, and the
amount of it is subject to considerable variation in the nucleus, according
to its stage of development. Conjointly with the materials which take part
in the formation of the nuclear spindle and other processes in the cell,
the chromatin accumulates in the resting nucleus to form the nucleoli.
Naturally connected with the conclusion that the nuclei are the carriers of
hereditary characters in the organism, is the question whether enucleate
organisms can also exist. Phylogenetic considerations give an affirmative
answer to this question. The differentiation into nucleus and cytoplasm
represents a division of labour in the protoplast. A study of organisms
which belong to the lowest class of the organic world teaches us how this
was accomplished. Instead of well-defined nuclei, scattered granules have
been described in the protoplasm of several of these organisms (Bacteria,
Cyanophyceae, Protozoa.), characterised by the same reactions as nuclear
material, provided also with a nuclear network, but without a limiting
membrane. (This is the result of the work of R. Hertwig and of the most
recently published investigations.) Thus the carriers of hereditary
characters may originally have been distributed in the common protoplasm,
afterwards coming together and eventually assuming a definite form as
special organs of the cell. It may be also assumed that in the protoplasm
and in the primitive types of nucleus, the carriers of the same hereditary
unit were represented in considerable quantity; they became gradually
differentiated to an extent commensurate with newly acquired characters.
It was also necessary that, in proportion as this happened, the mechanism
of nuclear division must be refined. At first processes resembling a
simple constriction would suffice to provide for the distribution of all
hereditary units to each of the products of division, but eventually in
both organic kingdoms nuclear division, which alone insured the qualitative
identity of the products of division, became a more marked feature in the
course of cell-multiplication.
Where direct nuclear division occurs by constriction in the higher
organisms, it does not result in the halving of hereditary units. So far
as my observations go, direct nuclear division occurs in the more highly
organised plants only in cells which have lost their specific functions.
Such cells are no longer capable of specific reproduction. An interesting
case in this connection is afforded by the internodal cells of the
Characeae, which possess only vegetative functions. These cells grow
vigorously and their cytoplasm increases, their growth being accompanied by
a correspondingly direct multiplication of the nuclei. They serve chiefly
to nourish the plant, but, unlike the other cells, they are incapable of
producing any offspring. This is a very instructive case, because it
clearly shows that the nuclei are not only carriers of hereditary
characters, but that they also play a definite part in the metabolism of
the protoplasts.
Attention was drawn to the fact that during the reducing division of nuclei
which contain chromosomes of unequal size, gemini are constantly produced
by the pairing of chromosomes of the same size. This led to the conclusion
that the pairing chromosomes are homologous, and that one comes from the
father, the other from the mother. (First stated by T.H. Montgomery in
1901 and by W.S. Sutton in 1902.) This evidently applies also to the
pairing of chromosomes in those reduction-divisions in which differences in
size do not enable us to distinguish the individual chromosomes. In this
case also each pair would be formed by two homologous chromosomes, the one
of paternal, the other of maternal origin. When the separation of these
chromosomes and their distribution to both daughter-nuclei occur a
chromosome of each kind is provided for each of these nuclei. It would
seem that the components of each pair might pass to either pole of the
nuclear spindle, so that the paternal and maternal chromosomes would be
distributed in varying proportion between the daughter-nuclei; and it is
not impossible that one daughter-nucleus might occasionally contain
paternal chromosomes only and its sister-nucleus exclusively maternal
chromosomes.
The fact that in nuclei containing chromosomes of various sizes, the
chromosomes which pair together in reduction-division are always of equal
size, constitutes a further and more important proof of their qualitative
difference. This is supported also by ingenious experiments which led to
an unequal distribution of chromosomes in the products of division of a
sea-urchin's egg, with the result that a difference was induced in their
further development. (Demonstrated by Th. Boveri in 1902.)
The recently discovered fact that in diploid nuclei the chromosomes are
arranged in pairs affords additional evidence in favour of the unequal
value of the chromosomes. This is still more striking in the case of
chromosomes of different sizes. It has been shown that in the first
division-figure in the nucleus of the fertilised egg the chromosomes of
corresponding size form pairs. They appear with this arrangement in all
subsequent nuclear divisions in the diploid generation. The longitudinal
fissions of the chromosomes provide for the unaltered preservation of this
condition. In the reduction nucleus of the gonotokonts the homologous
chromosomes being near together need not seek out one another; they are
ready to form gemini. The next stage is their separation to the haploid
daughter-nuclei, which have resulted from the reduction process.
Peculiar phenomena in the reduction nucleus accompany the formation of
gemini in both organic kingdoms. (This has been shown more particularly by
the work of L. Guignard, M. Mottier, J.B. Farmer, C.B. Wilson, V. Hacker
and more recently by V. Gregoire and his pupil C.A. Allen, by the
researches conducted in the Bonn Botanical Institute, and by A. and K.E.
Schreiner.) Probably for the purpose of entering into most intimate
relation, the pairs are stretched to long threads in which the chromomeres
come to lie opposite one another. (C.A. Allen, A. and K.E. Schreiner, and
Strasburger.) It seems probable that these are homologous chromomeres, and
that the pairs afterwards unite for a short time, so that an exchange of
hereditary units is rendered possible. (H. de Vries and Strasburger.)
This cannot be actually seen, but certain facts of heredity point to the
conclusion that this occurs. It follows from these phenomena that any
exchange which may be effected must be one of homologous carriers of
hereditary units only. These units continue to form exchangeable segments
after they have undergone unequal changes; they then constitute
allelotropic pairs. We may thus calculate what sum of possible
combinations the exchange of homologous hereditary units between the
pairing chromosomes provides for before the reduction division and the
subsequent distribution of paternal and maternal chromosomes in the haploid
daughter-nuclei. These nuclei then transmit their characters to the sexual
cells, the conjugation of which in fertilization again produces the most
varied combinations. (A. Weismann gave the impulse to these ideas in his
theory on "Amphimixis".) In this way all the cooperations which the
carriers of hereditary characters are capable of in a species are produced;
this must give it an appreciable advantage in the struggle for life.
The admirers of Charles Darwin must deeply regret that he did not live to
see the results achieved by the new Cytology. What service would they have
been to him in the presentation of his hypothesis of Pangenesis; what an
outlook into the future would they have given to his active mind!
The Darwinian hypothesis of Pangenesis rests on the conception that all
inheritable properties are represented in the cells by small invisible
particles or gemmules and that these gemmules increase by division.
Cytology began to develop on new lines some years after the publication in
1868 of Charles Darwin's "Provisional hypothesis of Pangenesis" ("Animals
and Plants under Domestication", London, 1868, Chapter XXVII.), and when he
died in 1882 it was still in its infancy. Darwin would have soon suggested
the substitution of the nuclei for his gemmules. At least the great
majority of present-day investigators in the domain of cytology have been
led to the conclusion that the nucleus is the carrier of hereditary
characters, and they also believe that hereditary characters are
represented in the nucleus as distinct units. Such would be Darwin's
gemmules, which in conformity with the name of his hypothesis may be called
pangens (So called by H. de Vries in 1889.): these pangens multiply by
division. All recently adopted views may be thus linked on to this part of
Darwin's hypothesis. It is otherwise with Darwin's conception to which
Pangenesis owes its name, namely the view that all cells continually give
off gemmules, which migrate to other places in the organism, where they
unite to form reproductive cells. When Darwin foresaw this possibility,
the continuity of the germinal substance was still unknown (Demonstrated by
Nussbaum in 1880, by Sachs in 1882, and by Weismann in 1885.), a fact which
excludes a transference of gemmules.
But even Charles Darwin's genius was confined within finite boundaries by
the state of science in his day.
It is not my province to deal with other theories of development which
followed from Darwin's Pangenesis, or to discuss their histological
probabilities. We can, however, affirm that Charles Darwin's idea that
invisible gemmules are the carriers of hereditary characters and that they
multiply by division has been removed from the position of a provisional
hypothesis to that of a well-founded theory. It is supported by histology,
and the results of experimental work in heredity, which are now assuming
extraordinary prominence, are in close agreement with it.
VII. "THE DESCENT OF MAN"
By G. SCHWALBE.
Professor of Anatomy in the University of Strassburg.
The problem of the origin of the human race, of the descent of man, is
ranked by Huxley in his epoch-making book "Man's Place in Nature", as the
deepest with which biology has to concern itself, "the question of
questions,"--the problem which underlies all others. In the same brilliant
and lucid exposition, which appeared in 1863, soon after the publication of
Darwin's "Origin of Species", Huxley stated his own views in regard to this
great problem. He tells us how the idea of a natural descent of man
gradually grew up in his mind, it was especially the assertions of Owen in
regard to the total difference between the human and the simian brain that
called forth strong dissent from the great anatomist Huxley, and he easily
succeeded in showing that Owen's supposed differences had no real
existence; he even established, on the basis of his own anatomical
investigations, the proposition that the anatomical differences between the
Marmoset and the Chimpanzee are much greater than those between the
Chimpanzee and Man.
But why do we thus introduce the study of Darwin's "Descent of Man", which
is to occupy us here, by insisting on the fact that Huxley had taken the
field in defence of the descent of man in 1863, while Darwin's book on the
subject did not appear till 1871? It is in order that we may clearly
understand how it happened that from this time onwards Darwin and Huxley
followed the same great aim in the most intimate association.
Huxley and Darwin working at the same Problema maximum! Huxley fiery,
impetuous, eager for battle, contemptuous of the resistance of a dull
world, or energetically triumphing over it. Darwin calm, weighing every
problem slowly, letting it mature thoroughly,--not a fighter, yet having
the greater and more lasting influence by virtue of his immense mass of
critically sifted proofs. Darwin's friend, Huxley, was the first to do him
justice, to understand his nature, and to find in it the reason why the
detailed and carefully considered book on the descent of man made its
appearance so late. Huxley, always generous, never thought of claiming
priority for himself. In enthusiastic language he tells how Darwin's
immortal work, "The Origin of Species", first shed light for him on the
problem of the descent of man; the recognition of a vera causa in the
transformation of species illuminated his thoughts as with a flash. He was
now content to leave what perplexed him, what he could not yet solve, as he
says himself, "in the mighty hands of Darwin." Happy in the bustle of
strife against old and deep-rooted prejudices, against intolerance and
superstition, he wielded his sharp weapons on Darwin's behalf; wearing
Darwin's armour he joyously overthrew adversary after adversary. Darwin
spoke of Huxley as his "general agent." ("Life and Letters of Thomas Henry
Huxley", Vol. I. page 171, London, 1900.) Huxley says of himself "I am
Darwin's bulldog." (Ibid. page 363.)
Thus Huxley openly acknowledged that it was Darwin's "Origin of Species"
that first set the problem of the descent of man in its true light, that
made the question of the origin of the human race a pressing one. That
this was the logical consequence of his book Darwin himself had long felt.
He had been reproached with intentionally shirking the application of his
theory to Man. Let us hear what he says on this point in his
autobiography: "As soon as I had become, in the year 1837 or 1838,
convinced that species were mutable productions, I could not avoid the
belief that man must come under the same law. Accordingly I collected
notes on the subject for my own satisfaction, and not for a long time with
any intention of publishing. Although in the 'Origin of Species' the
derivation of any particular species is never discussed, yet I thought it
best, in order THAT NO HONOURABLE MAN SHOULD ACCUSE ME OF CONCEALING MY
VIEWS (No italics in original.), to add that by the work 'light would be
thrown on the origin of man and his history.' It would have been useless
and injurious to the success of the book to have paraded, without giving
any evidence, my conviction with respect to his origin." ("Life and
Letters of Charles Darwin", Vol. 1. page 93.)
In a letter written in January, 1860, to the Rev. L. Blomefield, Darwin
expresses himself in similar terms. "With respect to man, I am very far
from wishing to obtrude my belief; but I thought it dishonest to quite
conceal my opinion." (Ibid. Vol. II. page 263.)
The brief allusion in the "Origin of Species" is so far from prominent and
so incidental that it was excusable to assume that Darwin had not touched
upon the descent of man in this work. It was solely the desire to have his
mass of evidence sufficiently complete, solely Darwin's great
characteristic of never publishing till he had carefully weighed all
aspects of his subject for years, solely, in short, his most fastidious
scientific conscience that restrained him from challenging the world in
1859 with a book in which the theory of the descent of man was fully set
forth. Three years, frequently interrupted by ill-health, were needed for
the actual writing of the book ("Life and Letters", Vol. I. page 94.): the
first edition, which appeared in 1871, was followed in 1874 by a much
improved second edition, the preparation of which he very reluctantly
undertook. (Ibid. Vol. III. page 175.)
This, briefly, is the history of the work, which, with the "Origin of
Species", marks an epoch in the history of biological sciences--the work
with which the cautious, peace-loving investigator ventured forth from his
contemplative life into the arena of strife and unrest, and laid himself
open to all the annoyances that deep-rooted belief and prejudice, and the
prevailing tendency of scientific thought at the time could devise.
Darwin did not take this step lightly. Of great interest in this
connection is a letter written to Wallace on Dec. 22, 1857 (Ibid. Vol. II.
page 109.), in which he says "You ask whether I shall discuss 'man.' I
think I shall avoid the whole subject, as so surrounded with prejudices;
though I fully admit that it is the highest and most interesting problem
for the naturalist." But his conscientiousness compelled him to state
briefly his opinion on the subject in the "Origin of Species" in 1859.
Nevertheless he did not escape reproaches for having been so reticent.
This is unmistakably apparent from a letter to Fritz Muller dated February
22 (1869?), in which he says: "I am thinking of writing a little essay on
the Origin of Mankind, as I have been taunted with concealing my opinions."
(Ibid. Vol. III. page 112.)
It might be thought that Darwin behaved thus hesitatingly, and was so slow
in deciding on the full publication of his collected material in regard to
the descent of man, because he had religious difficulties to overcome.
But this was not the case, as we can see from his admirable confession of
faith, the publication of which we owe to his son Francis. (Ibid. Vol. I.
pages 304-317.) Whoever wishes really to understand the lofty character of
this great man should read these immortal lines in which he unfolds to us
in simple and straightforward words the development of his conception of
the universe. He describes how, though he was still quite orthodox during
his voyage round the world on board the "Beagle", he came gradually to see,
shortly afterwards (1836-1839) that the Old Testament was no more to be
trusted than the Sacred Books of the Hindoos; the miracles by which
Christianity is supported, the discrepancies between the accounts in the
different Gospels, gradually led him to disbelieve in Christianity as a
divine revelation. "Thus," he writes ("Life and Letters", Vol. 1. page
309.), "disbelief crept over me at a very slow rate, but was at last
complete. The rate was so slow that I felt no distress." But Darwin was
too modest to presume to go beyond the limits laid down by science. He
wanted nothing more than to be able to go, freely and unhampered by belief
in authority or in the Bible, as far as human knowledge could lead him. We
learn this from the concluding words of his chapter on religion: "The
mystery of the beginning of all things is insoluble by us; and I for one
must be content to remain an Agnostic." (Loc. cit. page 313.)
Darwin was always very unwilling to give publicity to his views in regard
to religion. In a letter to Asa Gray on May 22, 1860 (Ibid. Vol. II. page
310.), he declares that it is always painful to him to have to enter into
discussion of religious problems. He had, he said, no intention of writing
atheistically.
Finally, let us cite one characteristic sentence from a letter from Darwin
to C. Ridley (Ibid. Vol. III. page. 236. ("C. Ridley," Mr Francis Darwin
points out to me, should be H.N. Ridley. A.C.S.)) (Nov. 28, 1878.) A
clergyman, Dr Pusey, had asserted that Darwin had written the "Origin of
Species" with some relation to theology. Darwin writes emphatically, "Many
years ago, when I was collecting facts for the 'Origin', my belief in what
is called a personal God was as firm as that of Dr Pusey himself, and as to
the eternity of matter I never troubled myself about such insoluble
questions." The expression "many years ago" refers to the time of his
voyage round the world, as has already been pointed out. Darwin means by
this utterance that the views which had gradually developed in his mind in
regard to the origin of species were quite compatible with the faith of the
Church.
If we consider all these utterances of Darwin in regard to religion and to
his outlook on life (Weltanschauung), we shall see at least so much, that
religious reflection could in no way have influenced him in regard to the
writing and publishing of his book on "The Descent of Man". Darwin had
early won for himself freedom of thought, and to this freedom he remained
true to the end of his life, uninfluenced by the customs and opinions of
the world around him.
Darwin was thus inwardly fortified and armed against the host of calumnies,
accusations, and attacks called forth by the publication of the "Origin of
Species", and to an even greater extent by the appearance of the "Descent
of Man". But in his defence he could rely on the aid of a band of
distinguished auxiliaries of the rarest ability. His faithful confederate,
Huxley, was joined by the botanist Hooker, and, after longer resistance, by
the famous geologist Lyell, whose "conversion" afforded Darwin peculiar
satisfaction. All three took the field with enthusiasm in defence of the
natural descent of man. From Wallace, on the other hand, though he shared
with him the idea of natural selection, Darwin got no support in this
matter. Wallace expressed himself in a strange manner. He admitted
everything in regard to the morphological descent of man, but maintained,
in a mystic way, that something else, something of a spiritual nature must
have been added to what man inherited from his animal ancestors. Darwin,
whose esteem for Wallace was extraordinarily high, could not understand how
he could give utterance to such a mystical view in regard to man; the idea
seemed to him so "incredibly strange" that he thought some one else must
have added these sentences to Wallace's paper.
Even now there are thinkers who, like Wallace, shrink from applying to man
the ultimate consequences of the theory of descent. The idea that man is
derived from ape-like forms is to them unpleasant and humiliating.
So far I have been depicting the development of Darwin's work on the
descent of man. In what follows I shall endeavour to give a condensed
survey of the contents of the book.
It must at once be said that the contents of Darwin's work fall into two
parts, dealing with entirely different subjects. "The Descent of Man"
includes a very detailed investigation in regard to secondary sexual
characters in the animal series, and on this investigation Darwin founded a
new theory, that of sexual selection. With astonishing patience he
gathered together an immense mass of material, and showed, in regard to
Arthropods and Vertebrates, the wide distribution of secondary characters,
which develop almost exclusively in the male, and which enable him, on the
one hand, to get the better of his rivals in the struggle for the female by
the greater perfection of his weapons, and on the other hand, to offer
greater allurements to the female through the higher development of
decorative characters, of song, or of scent-producing glands. The best
equipped males will thus crowd out the less well-equipped in the matter of
reproduction, and thus the relevant characters will be increased and
perfected through sexual selection. It is, of course, a necessary
assumption that these secondary sexual characters may be transmitted to the
female, although perhaps in rudimentary form.
As we have said, this theory of sexual selection takes up a great deal of
space in Darwin's book, and it need only be considered here in so far as
Darwin applied it to the descent of man. To this latter problem the whole
of Part I is devoted, while Part III contains a discussion of sexual
selection in relation to man, and a general summary. Part II treats of
sexual selection in general, and may be disregarded in our present study.
Moreover, many interesting details must necessarily be passed over in what
follows, for want of space.
The first part of the "Descent of Man" begins with an enumeration of the
proofs of the animal descent of man taken from the structure of the human
body. Darwin chiefly emphasises the fact that the human body consists of
the same organs and of the same tissues as those of the other mammals; he
shows also that man is subject to the same diseases and tormented by the
same parasites as the apes. He further dwells on the general agreement
exhibited by young, embryonic forms, and he illustrates this by two figures
placed one above the other, one representing a human embryo, after Eaker,
the other a dog embryo, after Bischoff. ("Descent of Man" (Popular
Edition, 1901), fig. 1, page 14.)
Darwin finds further proofs of the animal origin of man in the reduced
structures, in themselves extremely variable, which are either absolutely
useless to their possessors, or of so little use that they could never have
developed under existing conditions. Of such vestiges he enumerates: the
defective development of the panniculus carnosus (muscle of the skin) so
widely distributed among mammals, the ear-muscles, the occasional
persistence of the animal ear-point in man, the rudimentary nictitating
membrane (plica semilunaris) in the human eye, the slight development of
the organ of smell, the general hairiness of the human body, the frequently
defective development or entire absence of the third molar (the wisdom
tooth), the vermiform appendix, the occasional reappearance of a bony canal
(foramen supracondyloideum) at the lower end of the humerus, the
rudimentary tail of man (the so-called taillessness), and so on. Of these
rudimentary structures the occasional occurrence of the animal ear-point in
man is most fully discussed. Darwin's attention was called to this
interesting structure by the sculptor Woolner. He figures such a case
observed in man, and also the head of an alleged orang-foetus, the
photograph of which he received from Nitsche.
Darwin's interpretation of Woolner's case as having arisen through a
folding over of the free edge of a pointed ear has been fully borne out by
my investigations on the external ear. (G. Schwalbe, "Das Darwin'sche
Spitzohr beim menschlichen Embryo", "Anatom. Anzeiger", 1889, pages 176-
189, and other papers.) In particular, it was established by these
investigations that the human foetus, about the middle of its embryonic
life, possesses a pointed ear somewhat similar to that of the monkey genus
Macacus. One of Darwin's statements in regard to the head of the orang-
foetus must be corrected. A LARGE ear with a point is shown in the
photograph ("Descent of Man", fig.3, page 24.), but it can easily be
demonstrated--and Deniker has already pointed this out--that the figure is
not that of an orang-foetus at all, for that form has much smaller ears
with no point; nor can it be a gibbon-foetus, as Deniker supposes, for the
gibbon ear is also without a point. I myself regard it as that of a
Macacus-embryo. But this mistake, which is due to Nitsche, in no way
affects the fact recognised by Darwin, that ear-forms showing the point
characteristic of the animal ear occur in man with extraordinary frequency.
Finally, there is a discussion of those rudimentary structures which occur
only in ONE sex, such as the rudimentary mammary glands in the male, the
vesicula prostatica, which corresponds to the uterus of the female, and
others. All these facts tell in favour of the common descent of man and
all other vertebrates. The conclusion of this section is characteristic:
"IT IS ONLY OUR NATURAL PREJUDICE, AND THAT ARROGANCE WHICH MADE OUR
FOREFATHERS DECLARE THAT THEY WERE DESCENDED FROM DEMI-GODS, WHICH LEADS US
TO DEMUR TO THIS CONCLUSION. BUT THE TIME WILL BEFORE LONG COME, WHEN IT
WILL BE THOUGHT WONDERFUL THAT NATURALISTS, WHO WERE WELL ACQUAINTED WITH
THE COMPARATIVE STRUCTURE AND DEVELOPMENT OF MAN, AND OTHER MAMMALS, SHOULD
HAVE BELIEVED THAT EACH WAS THE WORK OF A SEPARATE ACT OF CREATION."
(Ibid. page 36.)
In the second chapter there is a more detailed discussion, again based upon
an extraordinary wealth of facts, of the problem as to the manner in which,
and the causes through which, man evolved from a lower form. Precisely the
same causes are here suggested for the origin of man, as for the origin of
species in general. Variability, which is a necessary assumption in regard
to all transformations, occurs in man to a high degree. Moreover, the
rapid multiplication of the human race creates conditions which necessitate
an energetic struggle for existence, and thus afford scope for the
intervention of natural selection. Of the exercise of ARTIFICIAL selection
in the human race, there is nothing to be said, unless we cite such cases
as the grenadiers of Frederick William I, or the population of ancient
Sparta. In the passages already referred to and in those which follow, the
transmission of acquired characters, upon which Darwin does not dwell, is
taken for granted. In man, direct effects of changed conditions can be
demonstrated (for instance in regard to bodily size), and there are also
proofs of the influence exerted on his physical constitution by increased
use or disuse. Reference is here made to the fact, established by Forbes,
that the Quechua-Indians of the high plateaus of Peru show a striking
development of lungs and thorax, as a result of living constantly at high
altitudes.
Such special forms of variation as arrests of development (microcephalism)
and reversion to lower forms are next discussed. Darwin himself felt
("Descent of Man", page 54.) that these subjects are so nearly related to
the cases mentioned in the first chapter, that many of them might as well
have been dealt with there. It seems to me that it would have been better
so, for the citation of additional instances of reversion at this place
rather disturbs the logical sequence of his ideas as to the conditions
which have brought about the evolution of man from lower forms. The
instances of reversion here discussed are microcephalism, which Darwin
wrongly interpreted as atavistic, supernumerary mammae, supernumerary
digits, bicornuate uterus, the development of abnormal muscles, and so on.
Brief mention is also made of correlative variations observed in man.
Darwin next discusses the question as to the manner in which man attained
to the erect position from the state of a climbing quadruped. Here again
he puts the influence of Natural Selection in the first rank. The
immediate progenitors of man had to maintain a struggle for existence in
which success was to the more intelligent, and to those with social
instincts. The hand of these climbing ancestors, which had little skill
and served mainly for locomotion, could only undergo further development
when some early member of the Primate series came to live more on the
ground and less among trees.
A bipedal existence thus became possible, and with it the liberation of the
hand from locomotion, and the one-sided development of the human foot. The
upright position brought about correlated variations in the bodily
structure; with the free use of the hand it became possible to manufacture
weapons and to use them; and this again resulted in a degeneration of the
powerful canine teeth and the jaws, which were then no longer necessary for
defence. Above all, however, the intelligence immediately increased, and
with it skull and brain. The nakedness of man, and the absence of a tail
(rudimentariness of the tail vertebrae) are next discussed. Darwin is
inclined to attribute the nakedness of man, not to the action of natural
selection on ancestors who originally inhabited a tropical land, but to
sexual selection, which, for aesthetic reasons, brought about the loss of
the hairy covering in man, or primarily in woman. An interesting
discussion of the loss of the tail, which, however, man shares with the
anthropoid apes, some other monkeys and lemurs, forms the conclusion of the
almost superabundant material which Darwin worked up in the second chapter.
His object was to show that some of the most distinctive human characters
are in all probability directly or indirectly due to natural selection.
With characteristic modesty he adds ("Descent of Man", page 92.): "Hence,
if I have erred in giving to natural selection great power, which I am very
far from admitting, or in having exaggerated its power, which is in itself
probable, I have at least, as I hope, done good service in aiding to
overthrow the dogma of separate creations." At the end of the chapter he
touches upon the objection as to man's helpless and defenceless condition.
Against this he urges his intelligence and social instincts.
The two following chapters contain a detailed discussion of the objections
drawn from the supposed great differences between the mental powers of men
and animals. Darwin at once admits that the differences are enormous, but
not that any fundamental difference between the two can be found. Very
characteristic of him is the following passage: "In what manner the mental
powers were first developed in the lowest organisms, is as hopeless an
enquiry as how life itself first originated. These are problems for the
distant future, if they are ever to be solved by man." (Ibid. page 100.)
After some brief observations on instinct and intelligence, Darwin brings
forward evidence to show that the greater number of the emotional states,
such as pleasure and pain, happiness and misery, love and hate are common
to man and the higher animals. He goes on to give various examples showing
that wonder and curiosity, imitation, attention, memory and imagination
(dreams of animals), can also be observed in the higher mammals, especially
in apes. In regard even to reason there are no sharply defined limits. A
certain faculty of deliberation is characteristic of some animals, and the
more thoroughly we know an animal the more intelligence we are inclined to
credit it with. Examples are brought forward of the intelligent and
deliberate actions of apes, dogs and elephants. But although no sharply
defined differences exist between man and animals, there is, nevertheless,
a series of other mental powers which are characteristics usually regarded
as absolutely peculiar to man. Some of these characteristics are examined
in detail, and it is shown that the arguments drawn from them are not
conclusive. Man alone is said to be capable of progressive improvement;
but against this must be placed as something analogous in animals, the fact
that they learn cunning and caution through long continued persecution.
Even the use of tools is not in itself peculiar to man (monkeys use sticks,
stones and twigs), but man alone fashions and uses implements DESIGNED FOR
A SPECIAL PURPOSE. In this connection the remarks taken from Lubbock in
regard to the origin and gradual development of the earliest flint
implements will be read with interest; these are similar to the
observations on modern eoliths, and their bearing on the development of the
stone-industry. It is interesting to learn from a letter to Hooker ("Life
and Letters", Vol. II. page 161, June 22, 1859.), that Darwin himself at
first doubted whether the stone implements discovered by Boucher de Perthes
were really of the nature of tools. With the relentless candour as to
himself which characterised him, he writes four years later in a letter to
Lyell in regard to this view of Boucher de Perthes' discoveries: "I know
something about his errors, and looked at his book many years ago, and am
ashamed to think that I concluded the whole was rubbish! Yet he has done
for man something like what Agassiz did for glaciers." (Ibid. Vol. III.
page 15, March 17, 1863.)
To return to Darwin's further comparisons between the higher mental powers
of man and animals. He takes much of the force from the argument that man
alone is capable of abstraction and self-consciousness by his own
observations on dogs. One of the main differences between man and animals,
speech, receives detailed treatment. He points out that various animals
(birds, monkeys, dogs) have a large number of different sounds for
different emotions, that, further, man produces in common with animals a
whole series of inarticulate cries combined with gestures, and that dogs
learn to understand whole sentences of human speech. In regard to human
language, Darwin expresses a view contrary to that held by Max Muller
("Descent of Man", page 132.): "I cannot doubt that language owes its
origin to the imitation and modification of various natural sounds, the
voices of other animals, and man's own instinctive cries, aided by signs
and gestures." The development of actual language presupposes a higher
degree of intelligence than is found in any kind of ape. Darwin remarks on
this point (Ibid. pages 136, 137.): "The fact of the higher apes not using
their vocal organs for speech no doubt depends on their intelligence not
having been sufficiently advanced."
The sense of beauty, too, has been alleged to be peculiar to man. In
refutation of this assertion Darwin points to the decorative colours of
birds, which are used for display. And to the last objection, that man
alone has religion, that he alone has a belief in God, it is answered "that
numerous races have existed, and still exist, who have no idea of one or
more gods, and who have no words in their languages to express such an
idea." (Ibid. page 143.)
The result of the investigations recorded in this chapter is to show that,
great as the difference in mental powers between man and the higher animals
may be, it is undoubtedly only a difference "of degree and not of kind."
("Descent of Man", page 193.)
In the fourth chapter Darwin deals with the MORAL SENSE or CONSCIENCE,
which is the most important of all differences between man and animals. It
is a result of social instincts, which lead to sympathy for other members
of the same society, to non-egoistic actions for the good of others.
Darwin shows that social tendencies are found among many animals, and that
among these love and kin-sympathy exist, and he gives examples of animals
(especially dogs) which may exhibit characters that we should call moral in
man (e.g. disinterested self-sacrifice for the sake of others). The early
ape-like progenitors of the human race were undoubtedly social. With the
increase of intelligence the moral sense develops farther; with the
acquisition of speech public opinion arises, and finally, moral sense
becomes habit. The rest of Darwin's detailed discussions on moral
philosophy may be passed over.
The fifth chapter may be very briefly summarised. In it Darwin shows that
the intellectual and moral faculties are perfected through natural
selection. He inquires how it can come about that a tribe at a low level
of evolution attains to a higher, although the best and bravest among them
often pay for their fidelity and courage with their lives without leaving
any descendants. In this case it is the sentiment of glory, praise and
blame, the admiration of others, which bring about the increase of the
better members of the tribe. Property, fixed dwellings, and the
association of families into a community are also indispensable
requirements for civilisation. In the longer second section of the fifth
chapter Darwin acts mainly as recorder. On the basis of numerous
investigations, especially those of Greg, Wallace, and Galton, he inquires
how far the influence of natural selection can be demonstrated in regard to
civilised nations. In the final section, which deals with the proofs that
all civilised nations were once barbarians, Darwin again uses the results
gained by other investigators, such as Lubbock and Tylor. There are two
sets of facts which prove the proposition in question. In the first place,
we find traces of a former lower state in the customs and beliefs of all
civilised nations, and in the second place, there are proofs to show that
savage races are independently able to raise themselves a few steps in the
scale of civilisation, and that they have thus raised themselves.
In the sixth chapter of the work, Morphology comes into the foreground once
more. Darwin first goes back, however, to the argument based on the great
difference between the mental powers of the highest animals and those of
man. That this is only quantitative, not qualitative, he has already
shown. Very instructive in this connection is the reference to the
enormous difference in mental powers in another class. No one would draw
from the fact that the cochineal insect (Coccus) and the ant exhibit
enormous differences in their mental powers, the conclusion that the ant
should therefore be regarded as something quite distinct, and withdrawn
from the class of insects altogether.
Darwin next attempts to establish the SPECIFIC genealogical tree of man,
and carefully weighs the differences and resemblances between the different
families of the Primates. The erect position of man is an adaptive
character, just as are the various characters referable to aquatic life in
the seals, which, notwithstanding these, are ranked as a mere family of the
Carnivores. The following utterance is very characteristic of Darwin
("Descent of Man", page 231.): "If man had not been his own classifier, he
would never have thought of founding a separate order for his own
reception." In numerous characters not mentioned in systematic works, in
the features of the face, in the form of the nose, in the structure of the
external ear, man resembles the apes. The arrangement of the hair in man
has also much in common with the apes; as also the occurrence of hair on
the forehead of the human embryo, the beard, the convergence of the hair of
the upper and under arm towards the elbow, which occurs not only in the
anthropoid apes, but also in some American monkeys. Darwin here adopts
Wallace's explanation of the origin of the ascending direction of the hair
in the forearm of the orang,--that it has arisen through the habit of
holding the hands over the head in rain. But this explanation cannot be
maintained when we consider that this disposition of the hair is widely
distributed among the most different mammals, being found in the dog, in
the sloth, and in many of the lower monkeys.
After further careful analysis of the anatomical characters Darwin reaches
the conclusion that the New World monkeys (Platyrrhine) may be excluded
from the genealogical tree altogether, but that man is an offshoot from the
Old World monkeys (Catarrhine) whose progenitors existed as far back as the
Miocene period. Among these Old World monkeys the forms to which man shows
the greatest resemblance are the anthropoid apes, which, like him, possess
neither tail nor ischial callosities. The platyrrhine and catarrhine
monkeys have their primitive ancestor among extinct forms of the Lemuridae.
Darwin also touches on the question of the original home of the human race
and supposes that it may have been in Africa, because it is there that
man's nearest relatives, the gorilla and the chimpanzee, are found. But he
regards speculation on this point as useless. It is remarkable that, in
this connection, Darwin regards the loss of the hair-covering in man as
having some relation to a warm climate, while elsewhere he is inclined to
make sexual selection responsible for it. Darwin recognises the great gap
between man and his nearest relatives, but similar gaps exist at other
parts of the mammalian genealogical tree: the allied forms have become
extinct. After the extermination of the lower races of mankind, on the one
hand, and of the anthropoid apes on the other, which will undoubtedly take
place, the gulf will be greater than ever, since the baboons will then
bound it on the one side, and the white races on the other. Little weight
need be attached to the lack of fossil remains to fill up this gap, since
the discovery of these depends upon chance. The last part of the chapter
is devoted to a discussion of the earlier stages in the genealogy of man.
Here Darwin accepts in the main the genealogical tree, which had meantime
been published by Haeckel, who traces the pedigree back through Monotremes,
Reptiles, Amphibians, and Fishes, to Amphioxus.
Then follows an attempt to reconstruct, from the atavistic characters, a
picture of our primitive ancestor who was undoubtedly an arboreal animal.
The occurrence of rudiments of parts in one sex which only come to full
development in the other is next discussed. This state of things Darwin
regards as derived from an original hermaphroditism. In regard to the
mammary glands of the male he does not accept the theory that they are
vestigial, but considers them rather as not fully developed.
The last chapter of Part I deals with the question whether the different
races of man are to be regarded as different species, or as sub-species of
a race of monophyletic origin. The striking differences between the races
are first emphasised, and the question of the fertility or infertility of
hybrids is discussed. That fertility is the more usual is shown by the
excessive fertility of the hybrid population of Brazil. This, and the
great variability of the distinguishing characters of the different races,
as well as the fact that all grades of transition stages are found between
these, while considerable general agreement exists, tell in favour of the
unity of the races and lead to the conclusion that they all had a common
primitive ancestor.
Darwin therefore classifies all the different races as sub-species of ONE
AND THE SAME SPECIES. Then follows an interesting inquiry into the reasons
for the extinction of human races. He recognises as the ultimate reason
the injurious effects of a change of the conditions of life, which may
bring about an increase in infantile mortality, and a diminished fertility.
It is precisely the reproductive system, among animals also, which is most
susceptible to changes in the environment.
The final section of this chapter deals with the formation of the races of
mankind. Darwin discusses the question how far the direct effect of
different conditions of life, or the inherited effects of increased use or
disuse may have brought about the characteristic differences between the
different races. Even in regard to the origin of the colour of the skin he
rejects the transmitted effects of an original difference of climate as an
explanation. In so doing he is following his tendency to exclude
Lamarckian explanations as far as possible. But here he makes gratuitous
difficulties from which, since natural selection fails, there is no escape
except by bringing in the principle of sexual selection, to which, he
regarded it as possible, skin-colouring, arrangement of hair, and form of
features might be traced. But with his characteristic conscientiousness he
guards himself thus: "I do not intend to assert that sexual selection will
account for all the differences between the races." ("Descent of Man",
page 308.)
I may be permitted a remark as to Darwin's attitude towards Lamarck.
While, at an earlier stage, when he was engaged in the preliminary labours
for his immortal work, "The Origin of Species", Darwin expresses himself
very forcibly against the views of Lamarck, speaking of Lamarckian
"nonsense," ("Life and Letters", Vol. II. page 23.), and of Lamarck's
"absurd, though clever work" (Loc. cit. page 39.) and expressly declaring,
"I attribute very little to the direct action of climate, etc." (Loc. cit.
(1856), page 82.) yet in later life he became more and more convinced of
the influence of external conditions. In 1876, that is, two years after
the appearance of the second edition of "The Descent of Man", he writes
with his usual candid honesty: "In my opinion the greatest error which I
have committed, has been not allowing sufficient weight to the direct
action of the environment, i.e. food, climate, etc. independently of
natural selection." (Ibid. Vol. III. page 159.) It is certain from this
change of opinion that, if he had been able to make up his mind to issue a
third edition of "The Descent of Man", he would have ascribed a much
greater influence to the effect of external conditions in explaining the
different characters of the races of man than he did in the second edition.
He would also undoubtedly have attributed less influence to sexual
selection as a factor in the origin of the different bodily
characteristics, if indeed he would not have excluded it altogether.
In Part III of the "Descent" two additional chapters are devoted to the
discussion of sexual selection in relation to man. These may be very
briefly referred to. Darwin here seeks to show that sexual selection has
been operative on man and his primitive progenitor. Space fails me to
follow out his interesting arguments. I can only mention that he is
inclined to trace back hairlessness, the development of the beard in man,
and the characteristic colour of the different human races to sexual
selection. Since bareness of the skin could be no advantage, but rather a
disadvantage, this character cannot have been brought about by natural
selection. Darwin also rejected a direct influence of climate as a cause
of the origin of the skin-colour. I have already expressed the opinion,
based on the development of his views as shown in his letters, that in a
third edition Darwin would probably have laid more stress on the influence
of external environment. He himself feels that there are gaps in his
proofs here, and says in self-criticism: "The views here advanced, on the
part which sexual selection has played in the history of man, want
scientific precision." ("Descent of Man", page 924.) I need here only
point out that it is impossible to explain the graduated stages of skin-
colour by sexual selection, since it would have produced races sharply
defined by their colour and not united to other races by transition stages,
and this, it is well known, is not the case. Moreover, the fact
established by me ("Die Hautfarbe des Menschen", "Mitteilungen der
Anthropologischen Gesellschaft in Wien", Vol. XXXIV. pages 331-352.), that
in all races the ventral side of the trunk is paler than the dorsal side,
and the inner surface of the extremities paler than the outer side, cannot
be explained by sexual selection in the Darwinian sense.
With this I conclude my brief survey of the rich contents of Darwin's book.
I may be permitted to conclude by quoting the magnificent final words of
"The Descent of Man": "We must, however, acknowledge, as it seems to me,
that man, with all his noble qualities, with sympathy which feels for the
most debased, with benevolence which extends not only to other men but to
the humblest living creature, with his god-like intellect which has
penetrated into the movements and constitution of the solar system--with
all these exalted powers--Man still bears in his bodily frame the indelible
stamp of his lowly origin." (Ibid. page 947.)
What has been the fate of Darwin's doctrines since his great achievement?
How have they been received and followed up by the scientific and lay
world? And what do the successors of the mighty hero and genius think now
in regard to the origin of the human race?
At the present time we are incomparably more favourably placed than Darwin
was for answering this question of all questions. We have at our command
an incomparably greater wealth of material than he had at his disposal.
And we are more fortunate than he in this respect, that we now know
transition-forms which help to fill up the gap, still great, between the
lowest human races and the highest apes. Let us consider for a little the
more essential additions to our knowledge since the publication of "The
Descent of Man".
Since that time our knowledge of animal embryos has increased enormously.
While Darwin was obliged to content himself with comparing a human embryo
with that of a dog, there are now available the youngest embryos of monkeys
of all possible groups (Orang, Gibbon, Semnopithecus, Macacus), thanks to
Selenka's most successful tour in the East Indies in search of such
material. We can now compare corresponding stages of the lower monkeys and
of the Anthropoid apes with human embryos, and convince ourselves of their
great resemblance to one another, thus strengthening enormously the armour
prepared by Darwin in defence of his view on man's nearest relatives. It
may be said that Selenka's material fils up the blanks in Darwin's array of
proofs in the most satisfactory manner.
The deepening of our knowledge of comparative anatomy also gives us much
surer foundations than those on which Darwin was obliged to build. Just of
late there have been many workers in the domain of the anatomy of apes and
lemurs, and their investigations extend to the most different organs. Our
knowledge of fossil apes and lemurs has also become much wider and more
exact since Darwin's time: the fossil lemurs have been especially worked
up by Cope, Forsyth Major, Ameghino, and others. Darwin knew very little
about fossil monkeys. He mentions two or three anthropoid apes as
occurring in the Miocene of Europe ("Descent of Man", page 240.), but only
names Dryopithecus, the largest form from the Miocene of France. It was
erroneously supposed that this form was related to Hylobates. We now know
not only a form that actually stands near to the gibbon (Pliopithecus), and
remains of other anthropoids (Pliohylobates and the fossil chimpanzee,
Palaeopithecus), but also several lower catarrhine monkeys, of which
Mesopithecus, a form nearly related to the modern Sacred Monkeys (a species
of Semnopithecus) and found in strata of the Miocene period in Greece, is
the most important. Quite recently, too, Ameghino's investigations have
made us acquainted with fossil monkeys from South America (Anthropops,
Homunculus), which, according to their discoverer, are to be regarded as in
the line of human descent.
What Darwin missed most of all--intermediate forms between apes and man--
has been recently furnished. (E. Dubois, as is well known, discovered in
1893, near Trinil in Java, in the alluvial deposits of the river Bengawan,
an important form represented by a skull-cap, some molars, and a femur.
His opinion--much disputed as it has been--that in this form, which he
named Pithecanthropus, he has found a long-desired transition-form is
shared by the present writer. And although the geological age of these
fossils, which, according to Dubois, belong to the uppermost Tertiary
series, the Pliocene, has recently been fixed at a later date (the older
Diluvium), the MORPHOLOGICAL VALUE of these interesting remains, that is,
the intermediate position of Pithecanthropus, still holds good. Volz says
with justice ("Das geologische Alter der Pithecanthropus-Schichten bei
Trinil, Ost-Java". "Neues Jahrb. f.Mineralogie". Festband, 1907.), that
even if Pithecanthropus is not THE missing link, it is undoubtedly _A_
missing link.
As on the one hand there has been found in Pithecanthropus a form which,
though intermediate between apes and man, is nevertheless more closely
allied to the apes, so on the other hand, much progress has been made since
Darwin's day in the discovery and description of the older human remains.
Since the famous roof of a skull and the bones of the extremities belonging
to it were found in 1856 in the Neandertal near Dusseldorf, the most varied
judgments have been expressed in regard to the significance of the remains
and of the skull in particular. In Darwin's "Descent of Man" there is only
a passing allusion to them ("Descent of Man", page 82.) in connection with
the discussion of the skull-capacity, although the investigations of
Schaaffhausen, King, and Huxley were then known. I believe I have shown,
in a series of papers, that the skull in question belongs to a form
different from any of the races of man now living, and, with King and Cope,
I regard it as at least a different species from living man, and have
therefore designated it Homo primigenius. The form unquestionably belongs
to the older Diluvium, and in the later Diluvium human forms already
appear, which agree in all essential points with existing human races.
As far back as 1886 the value of the Neandertal skull was greatly enhanced
by Fraipont's discovery of two skulls and skeletons from Spy in Belgium.
These are excellently described by their discoverer ("La race humaine de
Neanderthal ou de Canstatt en Belgique". "Arch. de Biologie", VII. 1887.),
and are regarded as belonging to the same group of forms as the Neandertal
remains. In 1899 and the following years came the discovery by Gorjanovic-
Kramberger of different skeletal parts of at least ten individuals in a
cave near Krapina in Croatia. (Gorjanovic-Kramberger "Der diluviale Mensch
von Krapina in Kroatien", 1906.) It is in particular the form of the lower
jaw which is different from that of all recent races of man, and which
clearly indicates the lowly position of Homo primigenius, while, on the
other hand, the long-known skull from Gibraltar, which I ("Studien zur
Vorgeschichte des Menschen", 1906, pages 154 ff.) have referred to Homo
primigenius, and which has lately been examined in detail by Sollas ("On
the cranial and facial characters of the Neandertal Race". "Trans. R.
Soc." London, vol. 199, 1908, page 281.), has made us acquainted with the
surprising shape of the eye-orbit, of the nose, and of the whole upper part
of the face. Isolated lower jaws found at La Naulette in Belgium, and at
Malarnaud in France, increase our material which is now as abundant as
could be desired. The most recent discovery of all is that of a skull dug
up in August of this year (1908) by Klaatsch and Hauser in the lower grotto
of the Le Moustier in Southern France, but this skull has not yet been
fully described. Thus Homo primigenius must also be regarded as occupying
a position in the gap existing between the highest apes and the lowest
human races, Pithecanthropus, standing in the lower part of it, and Homo
primigenius in the higher, near man. In order to prevent misunderstanding,
I should like here to emphasise that in arranging this structural series--
anthropoid apes, Pithecanthropus, Homo primigenius, Homo sapiens--I have no
intention of establishing it as a direct genealogical series. I shall have
something to say in regard to the genetic relations of these forms, one to
another, when discussing the different theories of descent current at the
present day. ((Since this essay was written Schoetensack has discovered
near Heidelberg and briefly described an exceedingly interesting lower jaw
from rocks between the Pliocene and Diluvial beds. This exhibits
interesting differences from the forms of lower jaw of Homo primigenius.
(Schoetensack "Der Unterkiefer des Homo heidelbergensis". Leipzig, 1908.)
G.S.))
In quite a different domain from that of morphological relationship, namely
in the physiological study of the blood, results have recently been gained
which are of the highest importance to the doctrine of descent. Uhlenhuth,
Nuttall, and others have established the fact that the blood-serum of a
rabbit which has previously had human blood injected into it, forms a
precipitate with human blood. This biological reaction was tried with a
great variety of mammalian species, and it was found that those far removed
from man gave no precipitate under these conditions. But as in other cases
among mammals all nearly related forms yield an almost equally marked
precipitate, so the serum of a rabbit treated with human blood and then
added to the blood of an anthropoid ape gives ALMOST as marked a
precipitate as in human blood; the reaction to the blood of the lower
Eastern monkeys is weaker, that to the Western monkeys weaker still; indeed
in this last case there is only a slight clouding after a considerable time
and no actual precipitate. The blood of the Lemuridae (Nuttall) gives no
reaction or an extremely weak one, that of the other mammals none whatever.
We have in this not only a proof of the literal blood-relationship between
man and apes, but the degree of relationship with the different main groups
of apes can be determined beyond possibility of mistake.
Finally, it must be briefly mentioned that in regard to remains of human
handicraft also, the material at our disposal has greatly increased of late
years, that, as a result of this, the opinions of archaeologists have
undergone many changes, and that, in particular, their views in regard to
the age of the human race have been greatly influenced. There is a
tendency at the present time to refer the origin of man back to Tertiary
times. It is true that no remains of Tertiary man have been found, but
flints have been discovered which, according to the opinion of most
investigators, bear traces either of use, or of very primitive workmanship.
Since Rutot's time, following Mortillet's example, investigators have
called these "eoliths," and they have been traced back by Verworn to the
Miocene of the Auvergne, and by Rutot even to the upper Oligocene.
Although these eoliths are even nowadays the subject of many different
views, the preoccupation with them has kept the problem of the age of the
human race continually before us.
Geology, too, has made great progress since the days of Darwin and Lyell,
and has endeavoured with satisfactory results to arrange the human remains
of the Diluvial period in chronological order (Penck). I do not intend to
enter upon the question of the primitive home of the human race; since the
space at my disposal will not allow of my touching even very briefly upon
all the departments of science which are concerned in the problem of the
descent of man. How Darwin would have rejoiced over each of the
discoveries here briefly outlined! What use he would have made of the new
and precious material, which would have prevented the discouragement from
which he suffered when preparing the second edition of "The Descent of
Man"! But it was not granted to him to see this progress towards filling
up the gaps in his edifice of which he was so painfully conscious.
He did, however, have the satisfaction of seeing his ideas steadily gaining
ground, notwithstanding much hostility and deep-rooted prejudice. Even in
the years between the appearance of "The Origin of Species" and of the
first edition of the "Descent", the idea of a natural descent of man, which
was only briefly indicated in the work of 1859, had been eagerly welcomed
in some quarters. It has been already pointed out how brilliantly Huxley
contributed to the defence and diffusion of Darwin's doctrines, and how in
"Man's Place in Nature" he has given us a classic work as a foundation for
the doctrine of the descent of man. As Huxley was Darwin's champion in
England, so in Germany Carl Vogt, in particular, made himself master of the
Darwinian ideas. But above all it was Haeckel who, in energy, eagerness
for battle, and knowledge may be placed side by side with Huxley, who took
over the leadership in the controversy over the new conception of the
universe. As far back as 1866, in his "Generelle Morphologie", he had
inquired minutely into the question of the descent of man, and not content
with urging merely the general theory of descent from lower animal forms,
he drew up for the first time genealogical trees showing the close
relationships of the different animal groups; the last of these illustrated
the relationships of Mammals, and among them of all groups of the Primates,
including man. It was Haeckel's genealogical trees that formed the basis
of the special discussion of the relationships of man, in the sixth chapter
of Darwin's "Descent of Man".
In the last section of this essay I shall return to Haeckel's conception of
the special descent of man, the main features of which he still upholds,
and rightly so. Haeckel has contributed more than any one else to the
spread of the Darwinian doctrine.
I can only allow myself a few words as to the spread of the theory of the
natural descent of man in other countries. The Parisian anthropological
school, founded and guided by the genius of Broca, took up the idea of the
descent of man, and made many notable contributions to it (Broca,
Manouvrier, Mahoudeau, Deniker and others). In England itself Darwin's
work did not die. Huxley took care of that, for he, with his lofty and
unprejudiced mind, dominated and inspired English biology until his death
on June 29, 1895. He had the satisfaction shortly before his death of
learning of Dubois' discovery, which he illustrated by a humorous sketch.
("Life and Letters of Thomas Henry Huxley", Vol. II. page 394.) But there
are still many followers in Darwin's footsteps in England. Keane has
worked at the special genealogical tree of the Primates; Keith has inquired
which of the anthropoid apes has the greatest number of characters in
common with man; Morris concerns himself with the evolution of man in
general, especially with his acquisition of the erect position. The recent
discoveries of Pithecanthropus and Homo primigenius are being vigorously
discussed; but the present writer is not in a position to form an opinion
of the extent to which the idea of descent has penetrated throughout
England generally.
In Italy independent work in the domain of the descent of man is being
produced, especially by Morselli; with him are associated, in the
investigation of related problems, Sergi and Giuffrida-Ruggeri. From the
ranks of American investigators we may single out in particular the eminent
geologist Cope, who championed with much decision the idea of the specific
difference of Homo neandertalensis (primigenius) and maintained a more
direct descent of man from the fossil Lemuridae. In South America too, in
Argentina, new life is stirring in this department of science. Ameghino in
Buenos Ayres has awakened the fossil primates of the Pampas formation to
new life; he even believes that in Tetraprothomo, represented by a femur,
he has discovered a direct ancestor of man. Lehmann-Nitsche is working at
the other side of the gulf between apes and men, and he describes a
remarkable first cervical vertebra (atlas) from Monte Hermoso as belonging
to a form which may bear the same relation to Homo sapiens in South America
as Homo primigenius does in the Old World. After a minute investigation he
establishes a human species Homo neogaeus, while Ameghino ascribes this
atlas vertebra to his Tetraprothomo.
Thus throughout the whole scientific world there is arising a new life, an
eager endeavour to get nearer to Huxley's problema maximum, to penetrate
more deeply into the origin of the human race. There are to-day very few
experts in anatomy and zoology who deny the animal descent of man in
general. Religious considerations, old prejudices, the reluctance to
accept man, who so far surpasses mentally all other creatures, as descended
from "soulless" animals, prevent a few investigators from giving full
adherence to the doctrine. But there are very few of these who still
postulate a special act of creation for man. Although the majority of
experts in anatomy and zoology accept unconditionally the descent of man
from lower forms, there is much diversity of opinion among them in regard
to the special line of descent.
In trying to establish any special hypothesis of descent, whether by the
graphic method of drawing up genealogical trees or otherwise, let us always
bear in mind Darwin's words ("Descent of Man", page 229.) and use them as a
critical guiding line: "As we have no record of the lines of descent, the
pedigree can be discovered only by observing the degrees of resemblance
between the beings which are to be classed." Darwin carries this further
by stating "that resemblances in several unimportant structures, in useless
and rudimentary organs, or not now functionally active, or in an
embryological condition, are by far the most serviceable for
classification." (Loc. cit.) It has also to be remembered that NUMEROUS
separate points of agreement are of much greater importance than the amount
of similarity or dissimilarity in a few points.
The hypotheses as to descent current at the present day may be divided into
two main groups. The first group seeks for the roots of the human race not
among any of the families of the apes--the anatomically nearest forms--nor
among their very similar but less specialised ancestral forms, the fossil
representatives of which we can know only in part, but, setting the monkeys
on one side, it seeks for them lower down among the fossil Eocene Pseudo-
lemuridae or Lemuridae (Cope), or even among the primitive pentadactylous
Eocene forms, which may either have led directly to the evolution of man
(Adloff), or have given rise to an ancestral form common to apes and men
(Klaatsch (Klaatsch in his last publications speaks in the main only of an
ancestral form common to men and anthropoid apes.), Giuffrida-Ruggeri).
The common ancestral form, from which man and apes are thus supposed to
have arisen independently, may explain the numerous resemblances which
actually exist between them. That is to say, all the characters upon which
the great structural resemblance between apes and man depends must have
been present in their common ancestor. Let us take an example of such a
common character. The bony external ear-passage is in general as highly
developed in the lower Eastern monkeys and the anthropoid apes as in man.
This character must, therefore, have already been present in the common
primitive form. In that case it is not easy to understand why the Western
monkeys have not also inherited the character, instead of possessing only a
tympanic ring. But it becomes more intelligible if we assume that forms
with a primitive tympanic ring were the original type, and that from these
were evolved, on the one hand, the existing New World monkeys with
persistent tympanic ring, and on the other an ancestral form common to the
lower Old World monkeys, the anthropoid apes and man. For man shares with
these the character in question, and it is also one of the "unimportant"
characters required by Darwin. Thus we have two divergent lines arising
from the ancestral form, the Western monkeys (Platyrrhine) on the one hand,
and an ancestral form common to the lower Eastern monkeys, the anthropoid
apes, and man, on the other. But considerations similar to those which
showed it to be impossible that man should have developed from an ancestor
common to him and the monkeys, yet outside of and parallel with these, may
be urged also against the likelihood of a parallel evolution of the lower
Eastern monkeys, the anthropoid apes, and man. The anthropoid apes have in
common with man many characters which are not present in the lower Old
World monkeys. These characters must therefore have been present in the
ancestral form common to the three groups. But here, again, it is
difficult to understand why the lower Eastern monkeys should not also have
inherited these characters. As this is not the case, there remains no
alternative but to assume divergent evolution from an indifferent form.
The lower Eastern monkeys are carrying on the evolution in one direction--I
might almost say towards a blind alley--while anthropoids and men have
struck out a progressive path, at first in common, which explains the many
points of resemblance between them, without regarding man as derived
directly from the anthropoids. Their many striking points of agreement
indicate a common descent, and cannot be explained as phenomena of
convergence.
I believe I have shown in the above sketch that a theory which derives man
directly from lower forms without regarding apes as transition-types leads
ad absurdum. The close structural relationship between man and monkeys can
only be understood if both are brought into the same line of evolution. To
trace man's line of descent directly back to the old Eocene mammals,
alongside of, but with no relation to these very similar forms, is to
abandon the method of exact comparison, which, as Darwin rightly
recognised, alone justifies us in drawing up genealogical trees on the
basis of resemblances and differences. The farther down we go the more
does the ground slip from beneath our feet. Even the Lemuridae show very
numerous divergent conditions, much more so the Eocene mammals (Creodonta,
Condylarthra), the chief resemblance of which to man consists in the
possession of pentadactylous hands and feet! Thus the farther course of
the line of descent disappears in the darkness of the ancestry of the
mammals. With just as much reason we might pass by the Vertebrates
altogether, and go back to the lower Invertebrates, but in that case it
would be much easier to say that man has arisen independently, and has
evolved, without relation to any animals, from the lowest primitive form to
his present isolated and dominant position. But this would be to deny all
value to classification, which must after all be the ultimate basis of a
genealogical tree. We can, as Darwin rightly observed, only infer the line
of descent from the degree of resemblance between single forms. If we
regard man as directly derived from primitive forms very far back, we have
no way of explaining the many points of agreement between him and the
monkeys in general, and the anthropoid apes in particular. These must
remain an inexplicable marvel.
I have thus, I trust, shown that the first class of special theories of
descent, which assumes that man has developed, parallel with the monkeys,
but without relation to them, from very low primitive forms cannot be
upheld, because it fails to take into account the close structural affinity
of man and monkeys. I cannot but regard this hypothesis as lamentably
retrograde, for it makes impossible any application of the facts that have
been discovered in the course of the anatomical and embryological study of
man and monkeys, and indeed prejudges investigations of that class as
pointless. The whole method is perverted; an unjustifiable theory of
descent is first formulated with the aid of the imagination, and then we
are asked to declare that all structural relations between man and monkeys,
and between the different groups of the latter, are valueless,--the fact
being that they are the only true basis on which a genealogical tree can be
constructed.
So much for this most modern method of classification, which has probably
found adherents because it would deliver us from the relationship to apes
which many people so much dislike. In contrast to it we have the second
class of special hypotheses of descent, which keeps strictly to the nearest
structural relationships. This is the only basis that justifies the
drawing up of a special hypothesis of descent. If this fundamental
proposition be recognised, it will be admitted that the doctrine of special
descent upheld by Haeckel, and set forth in Darwin's "Descent of Man", is
still valid to-day. In the genealogical tree, man's place is quite close
to the anthropoid apes; these again have as their nearest relatives the
lower Old World monkeys, and their progenitors must be sought among the
less differentiated Platyrrhine monkeys, whose most important characters
have been handed on to the present day New World monkeys. How the
different genera are to be arranged within the general scheme indicated
depends in the main on the classificatory value attributed to individual
characters. This is particularly true in regard to Pithecanthropus, which
I consider as the root of a branch which has sprung from the anthropoid ape
root and has led up to man; the latter I have designated the family of the
Hominidae.
For the rest, there are, as we have said, various possible ways of
constructing the narrower genealogy within the limits of this branch
including men and apes, and these methods will probably continue to change
with the accumulation of new facts. Haeckel himself has modified his
genealogical tree of the Primates in certain details since the publication
of his "Generelle Morphologie" in 1866, but its general basis remains the
same. (Haeckel's latest genealogical tree is to be found in his most
recent work, "Unsere Ahnenreihe". Jena, 1908.) All the special
genealogical trees drawn up on the lines laid down by Haeckel and Darwin--
and that of Dubois may be specially mentioned--are based, in general, on
the close relationship of monkeys and men, although they may vary in
detail. Various hypotheses have been formulated on these lines, with
special reference to the evolution of man. "Pithecanthropus" is regarded
by some authorities as the direct ancestor of man, by others as a side-
track failure in the attempt at the evolution of man. The problem of the
monophyletic or polyphyletic origin of the human race has also been much
discussed. Sergi (Sergi G. "Europa", 1908.) inclines towards the
assumption of a polyphyletic origin of the three main races of man, the
African primitive form of which has given rise also to the gorilla and
chimpanzee, the Asiatic to the Orang, the Gibbon, and Pithecanthropus.
Kollmann regards existing human races as derived from small primitive races
(pigmies), and considers that Homo primigenius must have arisen in a
secondary and degenerative manner.
But this is not the place, nor have I the space to criticise the various
special theories of descent. One, however, must receive particular notice.
According to Ameghino, the South American monkeys (Pitheculites) from the
oldest Tertiary of the Pampas are the forms from which have arisen the
existing American monkeys on the one hand, and on the other, the extinct
South American Homunculidae, which are also small forms. From these last,
anthropoid apes and man have, he believes, been evolved. Among the
progenitors of man, Ameghino reckons the form discovered by him
(Tetraprothomo), from which a South American primitive man, Homo pampaeus,
might be directly evolved, while on the other hand all the lower Old World
monkeys may have arisen from older fossil South American forms
(Clenialitidae), the distribution of which may be explained by the bridge
formerly existing between South America and Africa, as may be the
derivation of all existing human races from Homo pampaeus. (See Ameghino's
latest paper, "Notas preliminares sobre el Tetraprothomo argentinus", etc.
"Anales del Museo nacional de Buenos Aires", XVI. pages 107-242, 1907.)
The fossil forms discovered by Ameghino deserve the most minute
investigation, as does also the fossil man from South America of which
Lehmann-Nitsche ("Nouvelles recherches sur la formation pampeenne et
l'homme fossile de la Republique Argentine". "Rivista del Museo de la
Plata", T. XIV. pages 193-488.) has made a thorough study.
It is obvious that, notwithstanding the necessity for fitting man's line of
descent into the genealogical tree of the Primates, especially the apes,
opinions in regard to it differ greatly in detail. This could not be
otherwise, since the different Primate forms, especially the fossil forms,
are still far from being exhaustively known. But one thing remains
certain,--the idea of the close relationship between man and monkeys set
forth in Darwin's "Descent of Man". Only those who deny the many points of
agreement, the sole basis of classification, and thus of a natural
genealogical tree, can look upon the position of Darwin and Haeckel as
antiquated, or as standing on an insufficient foundation. For such a
genealogical tree is nothing more than a summarised representation of what
is known in regard to the degree of resemblance between the different
forms.
Darwin's work in regard to the descent of man has not been surpassed; the
more we immerse ourselves in the study of the structural relationships
between apes and man, the more is our path illumined by the clear light
radiating from him, and through his calm and deliberate investigation,
based on a mass of material in the accumulation of which he has never had
an equal. Darwin's fame will be bound up for all time with the
unprejudiced investigation of the question of all questions, the descent of
the human race.
VIII. CHARLES DARWIN AS AN ANTHROPOLOGIST.
By ERNST HAECKEL.
Professor of Zoology in the University of Jena.
The great advance that anthropology has made in the second half of the
nineteenth century is due in the first place, to Darwin's discovery of the
origin of man. No other problem in the whole field of research is so
momentous as that of "Man's place in nature," which was justly described by
Huxley (1863) as the most fundamental of all questions. Yet the scientific
solution of this problem was impossible until the theory of descent had
been established.
It is now a hundred years since the great French biologist Jean Lamarck
published his "Philosophie Zoologique". By a remarkable coincidence the
year in which that work was issued, 1809, was the year of the birth of his
most distinguished successor, Charles Darwin. Lamarck had already
recognised that the descent of man from a series of other Vertebrates--that
is, from a series of Ape-like Primates--was essentially involved in the
general theory of transformation which he had erected on a broad inductive
basis; and he had sufficient penetration to detect the agencies that had
been at work in the evolution of the erect bimanous man from the arboreal
and quadrumanous ape. He had, however, few empirical arguments to advance
in support of his hypothesis, and it could not be established until the
further development of the biological sciences--the founding of comparative
embryology by Baer (1828) and of the cell-theory by Schleiden and Schwann
(1838), the advance of physiology under Johannes Muller (1833), and the
enormous progress of palaeontology and comparative anatomy between 1820 and
1860--provided this necessary foundation. Darwin was the first to
coordinate the ample results of these lines of research. With no less
comprehensiveness than discrimination he consolidated them as a basis of a
modified theory of descent, and associated with them his own theory of
natural selection, which we take to be distinctive of "Darwinism" in the
stricter sense. The illuminating truth of these cumulative arguments was
so great in every branch of biology that, in spite of the most vehement
opposition, the battle was won within a single decade, and Darwin secured
the general admiration and recognition that had been denied to his
forerunner, Lamarck, up to the hour of his death (1829).
Before, however, we consider the momentous influence that Darwinism has had
in anthropology, we shall find it useful to glance at its history in the
course of the last half century, and notice the various theories that have
contributed to its advance. The first attempt to give extensive expression
to the reform of biology by Darwin's work will be found in my "Generelle
Morphologie" (1866) ("Generelle Morphologie der Organismen", 2 vols.,
Berlin, 1866.) which was followed by a more popular treatment of the
subject in my "Naturliche Schopfungsgeschichte (1868) (English translation;
"The History of Creation", London, 1876.), a compilation from the earlier
work. In the first volume of the "Generelle Morphologie" I endeavoured to
show the great importance of evolution in settling the fundamental
questions of biological philosophy, especially in regard to comparative
anatomy. In the second volume I dealt broadly with the principle of
evolution, distinguishing ontogeny and phylogeny as its two coordinate main
branches, and associating the two in the Biogenetic Law. The Law may be
formulated thus: "Ontogeny (embryology or the development of the
individual) is a concise and compressed recapitulation of phylogeny (the
palaeontological or genealogical series) conditioned by laws of heredity
and adaptation." The "Systematic introduction to general evolution," with
which the second volume of the "Generelle Morphologie" opens, was the first
attempt to draw up a natural system of organisms (in harmony with the
principles of Lamarck and Darwin) in the form of a hypothetical pedigree,
and was provisionally set forth in eight genealogical tables.
In the nineteenth chapter of the "Generelle Morphologie"--a part of which
has been republished, without any alteration, after a lapse of forty years
--I made a critical study of Lamarck's theory of descent and of Darwin's
theory of selection, and endeavoured to bring the complex phenomena of
heredity and adaptation under definite laws for the first time. Heredity I
divided into conservative and progressive: adaptation into indirect (or
potential) and direct (or actual). I then found it possible to give some
explanation of the correlation of the two physiological functions in the
struggle for life (selection), and to indicate the important laws of
divergence (or differentiation) and complexity (or division of labour),
which are the direct and inevitable outcome of selection. Finally, I
marked off dysteleology as the science of the aimless (vestigial, abortive,
atrophied, and useless) organs and parts of the body. In all this I worked
from a strictly monistic standpoint, and sought to explain all biological
phenomena on the mechanical and naturalistic lines that had long been
recognised in the study of inorganic nature. Then (1866), as now, being
convinced of the unity of nature, the fundamental identity of the agencies
at work in the inorganic and the organic worlds, I discarded vitalism,
teleology, and all hypotheses of a mystic character.
It was clear from the first that it was essential, in the monistic
conception of evolution, to distinguish between the laws of conservative
and progressive heredity. Conservative heredity maintains from generation
to generation the enduring characters of the species. Each organism
transmits to its descendants a part of the morphological and physiological
qualities that it has received from its parents and ancestors. On the
other hand, progressive heredity brings new characters to the species--
characters that were not found in preceding generations. Each organism may
transmit to its offspring a part of the morphological and physiological
features that it has itself acquired, by adaptation, in the course of its
individual career, through the use or disuse of particular organs, the
influence of environment, climate, nutrition, etc. At that time I gave the
name of "progressive heredity" to this inheritance of acquired characters,
as a short and convenient expression, but have since changed the term to
"transformative heredity" (as distinguished from conservative). This term
is preferable, as inherited regressive modifications (degeneration,
retrograde metamorphisis, etc.) come under the same head.
Transformative heredity--or the transmission of acquired characters--is one
of the most important principles in evolutionary science. Unless we admit
it most of the facts of comparative anatomy and physiology are
inexplicable. That was the conviction of Darwin no less than of Lamarck,
of Spencer as well as Virchow, of Huxley as well as Gegenbaur, indeed of
the great majority of speculative biologists. This fundamental principle
was for the first time called in question and assailed in 1885 by August
Weismann of Freiburg, the eminent zoologist to whom the theory of evolution
owes a great deal of valuable support, and who has attained distinction by
his extension of the theory of selection. In explanation of the phenomena
of heredity he introduced a new theory, the "theory of the continuity of
the germ-plasm." According to him the living substance in all organisms
consists of two quite distinct kinds of plasm, somatic and germinal. The
permanent germ-plasm, or the active substance of the two germ-cells (egg-
cell and sperm-cell), passes unchanged through a series of generations, and
is not affected by environmental influences. The environment modifies only
the soma-plasm, the organs and tissues of the body. The modifications that
these parts undergo through the influence of the environment or their own
activity (use and habit), do not affect the germ-plasm, and cannot
therefore be transmitted.
This theory of the continuity of the germ-plasm has been expounded by
Weismann during the last twenty-four years in a number of able volumes, and
is regarded by many biologists, such as Mr Francis Galton, Sir E. Ray
Lankester, and Professor J. Arthur Thomson (who has recently made a
thoroughgoing defence of it in his important work "Heredity" (London,
1908.)), as the most striking advance in evolutionary science. On the
other hand, the theory has been rejected by Herbert Spencer, Sir W. Turner,
Gegenbaur, Kolliker, Hertwig, and many others. For my part I have, with
all respect for the distinguished Darwinian, contested the theory from the
first, because its whole foundation seems to me erroneous, and its
deductions do not seem to be in accord with the main facts of comparative
morphology and physiology. Weismann's theory in its entirety is a finely
conceived molecular hypothesis, but it is devoid of empirical basis. The
notion of the absolute and permanent independence of the germ-plasm, as
distinguished from the soma-plasm, is purely speculative; as is also the
theory of germinal selection. The determinants, ids, and idants, are
purely hypothetical elements. The experiments that have been devised to
demonstrate their existence really prove nothing.
It seems to me quite improper to describe this hypothetical structure as
"Neodarwinism." Darwin was just as convinced as Lamarck of the
transmission of acquired characters and its great importance in the scheme
of evolution. I had the good fortune to visit Darwin at Down three times
and discuss with him the main principles of his system, and on each
occasion we were fully agreed as to the incalculable importance of what I
call transformative inheritance. It is only proper to point out that
Weismann's theory of the germ-plasm is in express contradiction to the
fundamental principles of Darwin and Lamarck. Nor is it more acceptable in
what one may call its "ultradarwinism"--the idea that the theory of
selection explains everything in the evolution of the organic world. This
belief in the "omnipotence of natural selection" was not shared by Darwin
himself. Assuredly, I regard it as of the utmost value, as the process of
natural selection through the struggle for life affords an explanation of
the mechanical origin of the adapted organisation. It solves the great
problem: how could the finely adapted structure of the animal or plant
body be formed unless it was built on a preconceived plan? It thus enables
us to dispense with the teleology of the metaphysician and the dualist, and
to set aside the old mythological and poetic legends of creation. The idea
had occurred in vague form to the great Empedocles 2000 years before the
time of Darwin, but it was reserved for modern research to give it ample
expression. Nevertheless, natural selection does not of itself give the
solution of all our evolutionary problems. It has to be taken in
conjunction with the transformism of Lamarck, with which it is in complete
harmony.
The monumental greatness of Charles Darwin, who surpasses every other
student of science in the nineteenth century by the loftiness of his
monistic conception of nature and the progressive influence of his ideas,
is perhaps best seen in the fact that not one of his many successors has
succeeded in modifying his theory of descent in any essential point or in
discovering an entirely new standpoint in the interpretation of the organic
world. Neither Nageli nor Weismann, neither De Vries nor Roux, has done
this. Nageli, in his "Mechanisch-Physiologische Theorie der
Abstammungslehre" (Munich, 1884.), which is to a great extent in agreement
with Weismann, constructed a theory of the idioplasm, that represents it
(like the germ-plasm) as developing continuously in a definite direction
from internal causes. But his internal "principle of progress" is at the
bottom just as teleological as the vital force of the Vitalists, and the
micellar structure of the idioplasm is just as hypothetical as the
"dominant" structure of the germ-plasm. In 1889 Moritz Wagner sought to
explain the origin of species by migration and isolation, and on that basis
constructed a special "migration-theory." This, however, is not out of
harmony with the theory of selection. It merely elevates one single factor
in the theory to a predominant position. Isolation is only a special case
of selection, as I had pointed out in the fifteenth chapter of my "Natural
history of creation". The "mutation-theory" of De Vries ("Die
Mutationstheorie", Leipzig, 1903.), that would explain the origin of
species by sudden and saltatory variations rather than by gradual
modification, is regarded by many botanists as a great step in advance, but
it is generally rejected by zoologists. It affords no explanation of the
facts of adaptation, and has no causal value.
Much more important than these theories is that of Wilhelm Roux ("Der Kampf
der Theile im Organismus", Leipzig, 1881.) of "the struggle of parts within
the organism, a supplementation of the theory of mechanical adaptation."
He explains the functional autoformation of the purposive structure by a
combination of Darwin's principle of selection with Lamarck's idea of
transformative heredity, and applies the two in conjunction to the facts of
histology. He lays stress on the significance of functional adaptation,
which I had described in 1866, under the head of cumulative adaptation, as
the most important factor in evolution. Pointing out its influence in the
cell-life of the tissues, he puts "cellular selection" above "personal
selection," and shows how the finest conceivable adaptations in the
structure of the tissue may be brought about quite mechanically, without
preconceived plan. This "mechanical teleology" is a valuable extension of
Darwin's monistic principle of selection to the whole field of cellular
physiology and histology, and is wholly destructive of dualistic vitalism.
The most important advance that evolution has made since Darwin and the
most valuable amplification of his theory of selection is, in my opinion,
the work of Richard Semon: "Die Mneme als erhaltendes Prinzip im Wechsel
des organischen Geschehens" (Leipzig, 1904.). He offers a psychological
explanation of the facts of heredity by reducing them to a process of
(unconscious) memory. The physiologist Ewald Hering had shown in 1870 that
memory must be regarded as a general function of organic matter, and that
we are quite unable to explain the chief vital phenomena, especially those
of reproduction and inheritance, unless we admit this unconscious memory.
In my essay "Die Perigenesis der Plastidule" (Berlin, 1876.) I elaborated
this far-reaching idea, and applied the physical principle of transmitted
motion to the plastidules, or active molecules of plasm. I concluded that
"heredity is the memory of the plastidules, and variability their power of
comprehension." This "provisional attempt to give a mechanical explanation
of the elementary processes of evolution" I afterwards extended by showing
that sensitiveness is (as Carl Nageli, Ernst Mach, and Albrecht Rau express
it) a general quality of matter. This form of panpsychism finds its
simplest expression in the "trinity of substance."
To the two fundamental attributes that Spinoza ascribed to substance--
Extension (matter as occupying space) and Cogitation (energy, force)--we
now add the third fundamental quality of Psychoma (sensitiveness, soul). I
further elaborated this trinitarian conception of substance in the
nineteenth chapter of my "Die Lebenswunder" (1904) ("Wonders of Life",
London, 1904.), and it seems to me well calculated to afford a monistic
solution of many of the antitheses of philosophy.
This important Mneme-theory of Semon and the luminous physiological
experiments and observations associated with it not only throw considerable
light on transformative inheritance, but provide a sound physiological
foundation for the biogenetic law. I had endeavoured to show in 1874, in
the first chapter of my "Anthropogenie" (English translation; "The
Evolution of Man", 2 volumes, London, 1879 and 1905.), that this
fundamental law of organic evolution holds good generally, and that there
is everywhere a direct causal connection between ontogeny and phylogeny.
"Phylogenesis is the mechanical cause of ontogenesis"; in other words, "The
evolution of the stem or race is--in accordance with the laws of heredity
and adaptation--the real cause of all the changes that appear, in a
condensed form, in the development of the individual organism from the
ovum, in either the embryo or the larva."
It is now fifty years since Charles Darwin pointed out, in the thirteenth
chapter of his epoch-making "Origin of Species", the fundamental importance
of embryology in connection with his theory of descent:
"The leading facts in embryology, which are second to none in importance,
are explained on the principle of variations in the many descendants from
some one ancient progenitor, having appeared at a not very early period of
life, and having been inherited at a corresponding period." ("Origin of
Species" (6th edition), page 396.)
He then shows that the striking resemblance of the embryos and larvae of
closely related animals, which in the mature stage belong to widely
different species and genera, can only be explained by their descent from a
common progenitor. Fritz Muller made a closer study of these important
phenomena in the instructive instance of the Crustacean larva, as given in
his able work "Fur Darwin" (1864). (English translation; "Facts and
Arguments for Darwin", London, 1869.) I then, in 1872, extended the range
so as to include all animals (with the exception of the unicellular
Protozoa) and showed, by means of the theory of the Gastraea, that all
multicellular, tissue-forming animals--all the Metazoa--develop in
essentially the same way from the primary germ-layers. I conceived the
embryonic form, in which the whole structure consists of only two layers of
cells, and is known as the gastrula, to be the ontogenetic recapitulation,
maintained by tenacious heredity, of a primitive common progenitor of all
the Metazoa, the Gastraea. At a later date (1895) Monticelli discovered
that this conjectural ancestral form is still preserved in certain
primitive Coelenterata--Pemmatodiscus, Kunstleria, and the nearly-related
Orthonectida.
The general application of the biogenetic law to all classes of animals and
plants has been proved in my "Systematische Phylogenie". (3 volumes,
Berlin, 1894-96.) It has, however, been frequently challenged, both by
botanists and zoologists, chiefly owing to the fact that many have failed
to distinguish its two essential elements, palingenesis and cenogenesis.
As early as 1874 I had emphasised, in the first chapter of my "Evolution of
Man", the importance of discriminating carefully between these two sets of
phenomena:
"In the evolutionary appreciation of the facts of embryology we must take
particular care to distinguish sharply and clearly between the primary,
palingenetic evolutionary processes and the secondary, cenogenetic
processes. The palingenetic phenomena, or embryonic RECAPITULATIONS, are
due to heredity, to the transmission of characters from one generation to
another. They enable us to draw direct inferences in regard to
corresponding structures in the development of the species (e.g. the chorda
or the branchial arches in all vertebrate embryos). The cenogenetic
phenomena, on the other hand, or the embryonic VARIATIONS, cannot be traced
to inheritance from a mature ancestor, but are due to the adaptation of the
embryo or the larva to certain conditions of its individual development
(e.g. the amnion, the allantois, and the vitelline arteries in the embryos
of the higher vertebrates). These cenogenetic phenomena are later
additions; we must not infer from them that there were corresponding
processes in the ancestral history, and hence they are apt to mislead."
The fundamental importance of these facts of comparative anatomy, atavism,
and the rudimentary organs, was pointed out by Darwin in the first part of
his classic work, "The Descent of Man and Selection in Relation to Sex"
(1871). ("Descent of Man" (Popular Edition), page 927.) In the "General
summary and conclusion" (chapter XXI.) he was able to say, with perfect
justice: "He who is not content to look, like a savage, at the phenomena
of nature as disconnected, cannot any longer believe that man is the work
of a separate act of creation. He will be forced to admit that the close
resemblance of the embryo of man to that, for instance, of a dog--the
construction of his skull, limbs, and whole frame on the same plan with
that of other mammals, independently of the uses to which the parts may be
put--the occasional reappearance of various structures, for instance of
several muscles, which man does not normally possess, but which are common
to the Quadrumana--and a crowd of analogous facts--all point in the
plainest manner to the conclusion that man is the co-descendant with other
mammals of a common progenitor."
These few lines of Darwin's have a greater scientific value than hundreds
of those so-called "anthropological treatises," which give detailed
descriptions of single organs, or mathematical tables with series of
numbers and what are claimed to be "exact analyses," but are devoid of
synoptic conclusions and a philosophical spirit.
Charles Darwin is not generally recognised as a great anthropologist, nor
does the school of modern anthropologists regard him as a leading
authority. In Germany, especially, the great majority of the members of
the anthropological societies took up an attitude of hostility to him from
the very beginning of the controversy in 1860. "The Descent of Man" was
not merely rejected, but even the discussion of it was forbidden on the
ground that it was "unscientific."
The centre of this inveterate hostility for thirty years--especially after
1877--was Rudolph Virchow of Berlin, the leading investigator in
pathological anatomy, who did so much for the reform of medicine by his
establishment of cellular pathology in 1858. As a prominent representative
of "exact" or "descriptive" anthropology, and lacking a broad equipment in
comparative anatomy and ontogeny, he was unable to accept the theory of
descent. In earlier years, and especially during his splendid period of
activity at Wurzburg (1848-1856), he had been a consistent free-thinker,
and had in a number of able articles (collected in his "Gesammelte
Abhandlungen") ("Gesammelte Abhandlungen zur wissenschaftlichen Medizin",
Berlin, 1856.) upheld the unity of human nature, the inseparability of body
and spirit. In later years at Berlin, where he was more occupied with
political work and sociology (especially after 1866), he abandoned the
positive monistic position for one of agnosticism and scepticism, and made
concessions to the dualistic dogma of a spiritual world apart from the
material frame.
In the course of a Scientific Congress at Munich in 1877 the conflict of
these antithetic views of nature came into sharp relief. At this memorable
Congress I had undertaken to deliver the first address (September 18th) on
the subject of "Modern evolution in relation to the whole of science." I
maintained that Darwin's theory not only solved the great problem of the
origin of species, but that its implications, especially in regard to the
nature of man, threw considerable light on the whole of science, and on
anthropology in particular. The discovery of the real origin of man by
evolution from a long series of mammal ancestors threw light on his place
in nature in every aspect, as Huxley had already shown in his excellent
lectures of 1863. Just as all the organs and tissues of the human body had
originated from those of the nearest related mammals, certain ape-like
forms, so we were bound to conclude that his mental qualities also had been
derived from those of his extinct primate ancestor.
This monistic view of the origin and nature of man, which is now admitted
by nearly all who have the requisite acquaintance with biology, and
approach the subject without prejudice, encountered a sharp opposition at
that time. The opposition found its strongest expression in an address
that Virchow delivered at Munich four days afterwards (September 22nd), on
"The freedom of science in the modern State." He spoke of the theory of
evolution as an unproved hypothesis, and declared that it ought not to be
taught in the schools, because it was dangerous to the State. "We must
not," he said, "teach that man has descended from the ape or any other
animal." When Darwin, usually so lenient in his judgment, read the English
translation of Virchow's speech, he expressed his disapproval in strong
terms. But the great authority that Virchow had--an authority well founded
in pathology and sociology--and his prestige as President of the German
Anthropological Society, had the effect of preventing any member of the
Society from raising serious opposition to him for thirty years. Numbers
of journals and treatises repeated his dogmatic statement: "It is quite
certain that man has descended neither from the ape nor from any other
animal." In this he persisted till his death in 1902. Since that time the
whole position of German anthropology has changed. The question is no
longer whether man was created by a distinct supernatural act or evolved
from other mammals, but to which line of the animal hierarchy we must look
for the actual series of ancestors. The interested reader will find an
account of this "battle of Munich" (1877) in my three Berlin lectures
(April, 1905) ("Der Kampf um die Entwickelungs-Gedanken". (English
translation; "Last Words on Evolution", London, 1906.)
The main points in our genealogical tree were clearly recognised by Darwin
in the sixth chapter of the "Descent of Man". Lowly organised fishes, like
the lancelet (Amphioxus), are descended from lower invertebrates resembling
the larvae of an existing Tunicate (Appendicularia). From these primitive
fishes were evolved higher fishes of the ganoid type and others of the type
of Lepidosiren (Dipneusta). It is a very small step from these to the
Amphibia:
"In the class of mammals the steps are not difficult to conceive which led
from the ancient Monotremata to the ancient Marsupials; and from these to
the early progenitors of the placental mammals. We may thus ascend to the
Lemuridae; and the interval is not very wide from these to the Simiadae.
The Simiadae then branched off into two great stems, the New World and Old
World monkeys; and from the latter, at a remote period, Man, the wonder and
glory of the Universe, proceeded." ("Descent of Man" (Popular Edition),
page 255.)
In these few lines Darwin clearly indicated the way in which we were to
conceive our ancestral series within the vertebrates. It is fully
confirmed by all the arguments of comparative anatomy and embryology, of
palaeontology and physiology; and all the research of the subsequent forty
years has gone to establish it. The deep interest in geology which Darwin
maintained throughout his life and his complete knowledge of palaeontology
enabled him to grasp the fundamental importance of the palaeontological
record more clearly than anthropologists and zoologists usually do.
There has been much debate in subsequent decades whether Darwin himself
maintained that man was descended from the ape, and many writers have
sought to deny it. But the lines I have quoted verbatim from the
conclusion of the sixth chapter of the "Descent of Man" (1871) leave no
doubt that he was as firmly convinced of it as was his great precursor Jean
Lamarck in 1809. Moreover, Darwin adds, with particular explicitness, in
the "general summary and conclusion" (chapter XXI.) of that standard work
("Descent of Man", page 930.):
"By considering the embryological structure of man--the homologies which he
presents with the lower animals,--the rudiments which he retains,--and the
reversions to which he is liable, we can partly recall in imagination the
former condition of our early progenitors; and can approximately place them
in their proper place in the zoological series. We thus learn that man is
descended from a hairy, tailed quadruped, probably arboreal in its habits,
and an inhabitant of the Old World. This creature, if its whole structure
had been examined by a naturalist, would have been classed amongst the
Quadrumana, as surely as the still more ancient progenitor of the Old and
New World monkeys."
These clear and definite lines leave no doubt that Darwin--so critical and
cautious in regard to important conclusions--was quite as firmly convinced
of the descent of man from the apes (the Catarrhinae, in particular) as
Lamarck was in 1809 and Huxley in 1863.
It is to be noted particularly that, in these and other observations on the
subject, Darwin decidedly assumes the monophyletic origin of the mammals,
including man. It is my own conviction that this is of the greatest
importance. A number of difficult questions in regard to the development
of man, in respect of anatomy, physiology, psychology, and embryology, are
easily settled if we do not merely extend our progonotaxis to our nearest
relatives, the anthropoid apes and the tailed monkeys from which these have
descended, but go further back and find an ancestor in the group of the
Lemuridae, and still further back to the Marsupials and Monotremata. The
essential identity of all the Mammals in point of anatomical structure and
embryonic development--in spite of their astonishing differences in
external appearance and habits of life--is so palpably significant that
modern zoologists are agreed in the hypothesis that they have all sprung
from a common root, and that this root may be sought in the earlier
Palaeozoic Amphibia.
The fundamental importance of this comparative morphology of the Mammals,
as a sound basis of scientific anthropology, was recognised just before the
beginning of the nineteenth century, when Lamarck first emphasised (1794)
the division of the animal kingdom into Vertebrates and Invertebrates.
Even thirteen years earlier (1781), when Goethe made a close study of the
mammal skeleton in the Anatomical Institute at Jena, he was intensely
interested to find that the composition of the skull was the same in man as
in the other mammals. His discovery of the os intermaxillare in man
(1784), which was contradicted by most of the anatomists of the time, and
his ingenious "vertebral theory of the skull," were the splendid fruit of
his morphological studies. They remind us how Germany's greatest
philosopher and poet was for many years ardently absorbed in the
comparative anatomy of man and the mammals, and how he divined that their
wonderful identity in structure was no mere superficial resemblance, but
pointed to a deep internal connection. In my "Generelle Morphologie"
(1866), in which I published the first attempts to construct phylogenetic
trees, I have given a number of remarkable theses of Goethe, which may be
called "phyletic prophecies." They justify us in regarding him as a
precursor of Darwin.
In the ensuing forty years I have made many conscientious efforts to
penetrate further along that line of anthropological research that was
opened up by Goethe, Lamarck, and Darwin. I have brought together the many
valuable results that have constantly been reached in comparative anatomy,
physiology, ontogeny, and palaeontology, and maintained the effort to
reform the classification of animals and plants in an evolutionary sense.
The first rough drafts of pedigrees that were published in the "Generelle
Morphologie" have been improved time after time in the ten editions of my
"Naturaliche Schopfungsgeschichte" (1868-1902). (English translation; "The
History of Creation", London, 1876.) A sounder basis for my phyletic
hypotheses, derived from a discriminating combination of the three great
records--morphology, ontogeny, and palaeontology--was provided in the three
volumes of my "Systematische Phylogenie (Berlin, 1894-96.) (1894 Protists
and Plants, 1895 Vertebrates, 1896 Invertebrates). In my "Anthropogenie"
(Leipzig, 1874, 5th edition 1905. English translation; "The Evolution of
Man", London, 1905.) I endeavoured to employ all the known facts of
comparative ontogeny (embryology) for the purpose of completing my scheme
of human phylogeny (evolution). I attempted to sketch the historical
development of each organ of the body, beginning with the most elementary
structures in the germ-layers of the Gastraea. At the same time I drew up
a corrected statement of the most important steps in the line of our
ancestral series.
At the fourth International Congress of Zoology at Cambridge (August 26th,
1898) I delivered an address on "Our present knowledge of the Descent of
Man." It was translated into English, enriched with many valuable notes
and additions, by my friend and pupil in earlier days Dr Hans Gadow
(Cambridge), and published under the title: "The Last Link; our present
knowledge of the Descent of Man". (London, 1898.) The determination of
the chief animal forms that occur in the line of our ancestry is there
restricted to thirty types, and these are distributed in six main groups.
The first half of this "Progonotaxis hominis," which has no support from
fossil evidence, comprises three groups: (i) Protista (unicellular
organisms, 1-5: (ii) Invertebrate Metazoa (Coelenteria 6-8, Vermalia 9-
11): (iii) Monorrhine Vertebrates (Acrania 12-13, Cyclostoma 14-15). The
second half, which is based on fossil records, also comprises three groups:
(iv) Palaeozoic cold-blooded Craniota (Fishes 16-18, Amphibia 19, Reptiles
20: (v) Mesozoic Mammals (Monotrema 21, Marsupialia 22, Mallotheria 23):
(vi) Cenozoic Primates (Lemuridae 24-25, Tailed Apes 26-27, Anthropomorpha
28-30). An improved and enlarged edition of this hypothetic "Progonotaxis
hominis" was published in 1908, in my essay "Unsere Ahnenreihe".
("Festschrift zur 350-jahrigen Jubelfeier der Thuringer Universitat Jena".
Jena, 1908.)
If I have succeeded in furthering, in some degree, by these anthropological
works, the solution of the great problem of Man's place in nature, and
particularly in helping to trace the definite stages in our ancestral
series, I owe the success, not merely to the vast progress that biology has
made in the last half century, but largely to the luminous example of the
great investigators who have applied themselves to the problem, with so
much assiduity and genius, for a century and a quarter--I mean Goethe and
Lamarck, Gegenbaur and Huxley, but, above all, Charles Darwin. It was the
great genius of Darwin that first brought together the scattered material
of biology and shaped it into that symmetrical temple of scientific
knowledge, the theory of descent. It was Darwin who put the crown on the
edifice by his theory of natural selection. Not until this broad inductive
law was firmly established was it possible to vindicate the special
conclusion, the descent of man from a series of other Vertebrates. By his
illuminating discovery Darwin did more for anthropology than thousands of
those writers, who are more specifically titled anthropologists, have done
by their technical treatises. We may, indeed, say that it is not merely as
an exact observer and ingenious experimenter, but as a distinguished
anthropologist and far-seeing thinker, that Darwin takes his place among
the greatest men of science of the nineteenth century.
To appreciate fully the immortal merit of Darwin in connection with
anthropology, we must remember that not only did his chief work, "The
Origin of Species", which opened up a new era in natural history in 1859,
sustain the most virulent and widespread opposition for a lengthy period,
but even thirty years later, when its principles were generally recognised
and adopted, the application of them to man was energetically contested by
many high scientific authorities. Even Alfred Russel Wallace, who
discovered the principle of natural selection independently in 1858, did
not concede that it was applicable to the higher mental and moral qualities
of man. Dr Wallace still holds a spiritualist and dualist view of the
nature of man, contending that he is composed of a material frame
(descended from the apes) and an immortal immaterial soul (infused by a
higher power). This dual conception, moreover, is still predominant in the
wide circles of modern theology and metaphysics, and has the general and
influential adherence of the more conservative classes of society.
In strict contradiction to this mystical dualism, which is generally
connected with teleology and vitalism, Darwin always maintained the
complete unity of human nature, and showed convincingly that the
psychological side of man was developed, in the same way as the body, from
the less advanced soul of the anthropoid ape, and, at a still more remote
period, from the cerebral functions of the older vertebrates. The eighth
chapter of the "Origin of Species", which is devoted to instinct, contains
weighty evidence that the instincts of animals are subject, like all other
vital processes, to the general laws of historic development. The special
instincts of particular species were formed by adaptation, and the
modifications thus acquired were handed on to posterity by heredity; in
their formation and preservation natural selection plays the same part as
in the transformation of every other physiological function. The higher
moral qualities of civilised man have been derived from the lower mental
functions of the uncultivated barbarians and savages, and these in turn
from the social instincts of the mammals. This natural and monistic
psychology of Darwin's was afterwards more fully developed by his friend
George Romanes in his excellent works "Mental Evolution in Animals" and
"Mental Evolution in Man". (London, 1885; 1888.)
Many valuable and most interesting contributions to this monistic
psychology of man were made by Darwin in his fine work on "The Descent of
Man and Selection in Relation to Sex", and again in his supplementary work,
"The Expression of the Emotions in Man and Animals". To understand the
historical development of Darwin's anthropology one must read his life and
the introduction to "The Descent of Man". From the moment that he was
convinced of the truth of the principle of descent--that is to say, from
his thirtieth year, in 1838--he recognised clearly that man could not be
excluded from its range. He recognised as a logical necessity the
important conclusion that "man is the co-descendant with other species of
some ancient, lower, and extinct form." For many years he gathered notes
and arguments in support of this thesis, and for the purpose of showing the
probable line of man's ancestry. But in the first edition of "The Origin
of Species" (1859) he restricted himself to the single line, that by this
work "light would be thrown on the origin of man and his history." In the
fifty years that have elapsed since that time the science of the origin and
nature of man has made astonishing progress, and we are now fairly agreed
in a monistic conception of nature that regards the whole universe,
including man, as a wonderful unity, governed by unalterable and eternal
laws. In my philosophical book "Die Weltratsel" (1899) ("The Riddle of the
Universe", London, 1900.) and in the supplementary volume "Die
Lebenswunder" (1904) "The Wonders of Life", London, 1904.), I have
endeavoured to show that this pure monism is securely established, and that
the admission of the all-powerful rule of the same principle of evolution
throughout the universe compels us to formulate a single supreme law--the
all-embracing "Law of Substance," or the united laws of the constancy of
matter and the conservation of energy. We should never have reached this
supreme general conception if Charles Darwin--a "monistic philosopher" in
the true sense of the word--had not prepared the way by his theory of
descent by natural selection, and crowned the great work of his life by the
association of this theory with a naturalistic anthropology.
IX. SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN.
By J.G. FRAZER.
Fellow of Trinity College, Cambridge.
On a bright day in late autumn a good many years ago I had ascended the
hill of Panopeus in Phocis to examine the ancient Greek fortifications
which crest its brow. It was the first of November, but the weather was
very hot; and when my work among the ruins was done, I was glad to rest
under the shade of a clump of fine holly-oaks, to inhale the sweet
refreshing perfume of the wild thyme which scented all the air, and to
enjoy the distant prospects, rich in natural beauty, rich too in memories
of the legendary and historic past. To the south the finely-cut peak of
Helicon peered over the low intervening hills. In the west loomed the
mighty mass of Parnassus, its middle slopes darkened by pine-woods like
shadows of clouds brooding on the mountain-side; while at its skirts
nestled the ivy-mantled walls of Daulis overhanging the deep glen, whose
romantic beauty accords so well with the loves and sorrows of Procne and
Philomela, which Greek tradition associated with the spot. Northwards,
across the broad plain to which the hill of Panopeus descends, steep and
bare, the eye rested on the gap in the hills through which the Cephissus
winds his tortuous way to flow under grey willows, at the foot of barren
stony hills, till his turbid waters lose themselves, no longer in the vast
reedy swamps of the now vanished Copaic Lake, but in the darkness of a
cavern in the limestone rock. Eastward, clinging to the slopes of the
bleak range of which the hill of Panopeus forms part, were the ruins of
Chaeronea, the birthplace of Plutarch; and out there in the plain was
fought the disastrous battle which laid Greece at the feet of Macedonia.
There, too, in a later age East and West met in deadly conflict, when the
Roman armies under Sulla defeated the Asiatic hosts of Mithridates. Such
was the landscape spread out before me on one of those farewell autumn days
of almost pathetic splendour, when the departing summer seems to linger
fondly, as if loth to resign to winter the enchanted mountains of Greece.
Next day the scene had changed: summer was gone. A grey November mist
hung low on the hills which only yesterday had shone resplendent in the
sun, and under its melancholy curtain the dead flat of the Chaeronean
plain, a wide treeless expanse shut in by desolate slopes, wore an aspect
of chilly sadness befitting the battlefield where a nation's freedom was
lost.
But crowded as the prospect from Panopeus is with memories of the past, the
place itself, now so still and deserted, was once the scene of an event
even more ancient and memorable, if Greek story-tellers can be trusted.
For here, they say, the sage Prometheus created our first parents by
fashioning them, like a potter, out of clay. (Pausanias X. 4.4. Compare
Apollodorus, "Bibliotheca", I. 7. 1; Ovid, "Metamorph." I. 82 sq.; Juvenal,
"Sat". XIV. 35. According to another version of the tale, this creation of
mankind took place not at Panopeus, but at Iconium in Lycaonia. After the
original race of mankind had been destroyed in the great flood of
Deucalion, the Greek Noah, Zeus commanded Prometheus and Athena to create
men afresh by moulding images out of clay, breathing the winds into them,
and making them live. See "Etymologicum Magnum", s.v. "'Ikonion", pages
470 sq. It is said that Prometheus fashioned the animals as well as men,
giving to each kind of beast its proper nature. See Philemon, quoted by
Stobaeus, "Florilegium" II. 27. The creation of man by Prometheus is
figured on ancient works of art. See J. Toutain, "Etudes de Mythologie et
d'Histoire des Religions Antiques" (Paris, 1909), page 190. According to
Hesiod ("Works and Days", 60 sqq.) it was Hephaestus who at the bidding of
Zeus moulded the first woman out of moist earth.) The very spot where he
did so can still be seen. It is a forlorn little glen or rather hollow
behind the hill of Panopeus, below the ruined but still stately walls and
towers which crown the grey rocks of the summit. The glen, when I visited
it that hot day after the long drought of summer, was quite dry; no water
trickled down its bushy sides, but in the bottom I found a reddish
crumbling earth, a relic perhaps of the clay out of which the potter
Prometheus moulded the Greek Adam and Eve. In a volume dedicated to the
honour of one who has done more than any other in modern times to shape the
ideas of mankind as to their origin it may not be out of place to recall
this crude Greek notion of the creation of the human race, and to compare
or contrast it with other rudimentary speculations of primitive peoples on
the same subject, if only for the sake of marking the interval which
divides the childhood from the maturity of science.
The simple notion that the first man and woman were modelled out of clay by
a god or other superhuman being is found in the traditions of many peoples.
This is the Hebrew belief recorded in Genesis: "The Lord God formed man of
the dust of the ground, and breathed into his nostrils the breath of life;
and man became a living soul." (Genesis ii.7.) To the Hebrews this
derivation of our species suggested itself all the more naturally because
in their language the word for "ground" (adamah) is in form the feminine of
the word for man (adam). (S.R. Driver and W.H.Bennett, in their
commentaries on Genesis ii. 7.) From various allusions in Babylonian
literature it would seem that the Babylonians also conceived man to have
been moulded out of clay. (H. Zimmern, in E. Schrader's "Die
Keilinschriften und das Alte Testament"3 (Berlin, 1902), page 506.)
According to Berosus, the Babylonian priest whose account of creation has
been preserved in a Greek version, the god Bel cut off his own head, and
the other gods caught the flowing blood, mixed it with earth, and fashioned
men out of the bloody paste; and that, they said, is why men are so wise,
because their mortal clay is tempered with divine blood. (Eusebius,
"Chronicon", ed. A. Schoene, Vol. I. (Berlin, 1875), col. 16.) In Egyptian
mythology Khnoumou, the Father of the gods, is said to have moulded men out
of clay. (G. Maspero, "Histoire Ancienne des Peuples de l'Orient
Classique", I. (Paris, 1895), page 128.) We cannot doubt that such crude
conceptions of the origin of our race were handed down to the civilised
peoples of antiquity by their savage or barbarous forefathers. Certainly
stories of the same sort are known to be current among savages and
barbarians.
Thus the Australian blacks in the neighbourhood of Melbourne said that
Pund-jel, the creator, cut three large sheets of bark with his big knife.
On one of these he placed some clay and worked it up with his knife into a
proper consistence. He then laid a portion of the clay on one of the other
pieces of bark and shaped it into a human form; first he made the feet,
then the legs, then the trunk, the arms, and the head. Thus he made a clay
man on each of the two pieces of bark; and being well pleased with them he
danced round them for joy. Next he took stringy bark from the Eucalyptus
tree, made hair of it, and stuck it on the heads of his clay men. Then he
looked at them again, was pleased with his work, and again danced round
them for joy. He then lay down on them, blew his breath hard into their
mouths, their noses, and their navels; and presently they stirred, spoke,
and rose up as full-grown men. (R. Brough Smyth, "The Aborigines of
Victoria" (Melbourne, 1878), I. 424. This and many of the following
legends of creation have been already cited by me in a note on Pausanias X.
4. 4 ("Pausanias's Description of Greece, translated with a Commentary"
(London, 1898), Vol V. pages 220 sq.).) The Maoris of New Zealand say that
Tiki made man after his own image. He took red clay, kneaded it, like the
Babylonian Bel, with his own blood, fashioned it in human form, and gave
the image breath. As he had made man in his own likeness he called him
Tiki-ahua or Tiki's likeness. (R. Taylor "Te Ika A Maui, or New Zealand
and its Inhabitants", Second Edition (London, 1870), page 117. Compare E.
Shortland, "Maori Religion and Mythology" (London, 1882), pages 21 sq.) A
very generally received tradition in Tahiti was that the first human pair
was made by Taaroa, the chief god. They say that after he had formed the
world he created man out of red earth, which was also the food of mankind
until bread-fruit was produced. Further, some say that one day Taaroa
called for the man by name, and when he came he made him fall asleep. As
he slept, the creator took out one of his bones (ivi) and made a woman of
it, whom he gave to the man to be his wife, and the pair became the
progenitors of mankind. This narrative was taken down from the lips of the
natives in the early years of the mission to Tahiti. The missionary who
records it observes: "This always appeared to me a mere recital of the
Mosaic account of creation, which they had heard from some European, and I
never placed any reliance on it, although they have repeatedly told me it
was a tradition among them before any foreigner arrived. Some have also
stated that the woman's name was Ivi, which would be by them pronounced as
if written "Eve". "Ivi" is an aboriginal word, and not only signifies a
bone, but also a widow, and a victim slain in war. Notwithstanding the
assertion of the natives, I am disposed to think that "Ivi", or Eve, is the
only aboriginal part of the story, as far as it respects the mother of the
human race. (W. Ellis, "Polynesian Researches", Second Edition (London,
1832), I. 110 sq. "Ivi" or "iwi" is the regular word for "bone" in the
various Polynesian languages. See E. Tregear, "The Maori-Polynesian
Comparative Dictionary" (Wellington, New Zealand, 1891), page 109.)
However, the same tradition has been recorded in other parts of Polynesia
besides Tahiti. Thus the natives of Fakaofo or Bowditch Island say that
the first man was produced out of a stone. After a time he bethought him
of making a woman. So he gathered earth and moulded the figure of a woman
out of it, and having done so he took a rib out of his left side and thrust
it into the earthen figure, which thereupon started up a live woman. He
called her Ivi (Eevee) or "rib" and took her to wife, and the whole human
race sprang from this pair. (G. Turner, "Samoa" (London, 1884), pages 267
sq.) The Maoris also are reported to believe that the first woman was made
out of the first man's ribs. (J.L. Nicholas, "Narrative of a Voyage to New
Zealand" (London, 1817), I. 59, who writes "and to add still more to this
strange coincidence, the general term for bone is 'Hevee'.") This wide
diffusion of the story in Polynesia raises a doubt whether it is merely, as
Ellis thought, a repetition of the Biblical narrative learned from
Europeans. In Nui, or Netherland Island, it was the god Aulialia who made
earthen models of a man and woman, raised them up, and made them live. He
called the man Tepapa and the woman Tetata. (G. Turner, "Samoa", pages 300
sq.)
In the Pelew Islands they say that a brother and sister made men out of
clay kneaded with the blood of various animals, and that the characters of
these first men and of their descendants were determined by the characters
of the animals whose blood had been kneaded with the primordial clay; for
instance, men who have rat's blood in them are thieves, men who have
serpent's blood in them are sneaks, and men who have cock's blood in them
are brave. (J. Kubary, "Die Religion der Pelauer", in A. Bastian's
"Allerlei aus Volks- und Menschenkunde" (Berlin, 1888), I. 3, 56.)
According to a Melanesian legend, told in Mota, one of the Banks Islands,
the hero Qat moulded men of clay, the red clay from the marshy river-side
at Vanua Lava. At first he made men and pigs just alike, but his brothers
remonstrated with him, so he beat down the pigs to go on all fours and made
men walk upright. Qat fashioned the first woman out of supple twigs, and
when she smiled he knew she was a living woman. (R.H. Codrington, "The
Melanesians" (Oxford, 1891), page 158.) A somewhat different version of
the Melanesian story is told at Lakona, in Santa Maria. There they say
that Qat and another spirit ("vui") called Marawa both made men. Qat made
them out of the wood of dracaena-trees. Six days he worked at them,
carving their limbs and fitting them together. Then he allowed them six
days to come to life. Three days he hid them away, and three days more he
worked to make them live. He set them up and danced to them and beat his
drum, and little by little they stirred, till at last they could stand all
by themselves. Then Qat divided them into pairs and called each pair
husband and wife. Marawa also made men out of a tree, but it was a
different tree, the tavisoviso. He likewise worked at them six days, beat
his drum, and made them live, just as Qat did. But when he saw them move,
he dug a pit and buried them in it for six days, and then, when he scraped
away the earth to see what they were doing, he found them all rotten and
stinking. That was the origin of death. (R.H. Codrington op. cit., pages
157 sq.)
The inhabitants of Noo-Hoo-roa, in the Kei Islands say that their ancestors
were fashioned out of clay by the supreme god, Dooadlera, who breathed life
into the clay figures. (C.M. Pleyte, "Ethnographische Beschrijving der
Kei-Eilanden", "Tijdschrift van het Nederlandsch Aardrijkskundig
Genootschap", Tweede Serie X. (1893), page 564.) The aborigines of
Minahassa, in the north of Celebes, say that two beings called Wailan
Wangko and Wangi were alone on an island, on which grew a cocoa-nut tree.
Said Wailan Wangko to Wangi, "Remain on earth while I climb up the tree."
Said Wangi to Wailan Wangko, "Good." But then a thought occurred to Wangi
and he climbed up the tree to ask Wailan Wangko why he, Wangi, should
remain down there all alone. Said Wailan Wangko to Wangi, "Return and take
earth and make two images, a man and a woman." Wangi did so, and both
images were men who could move but could not speak. So Wangi climbed up
the tree to ask Wailan Wangko, "How now? The two images are made, but they
cannot speak." Said Wailan Wangko to Wangi, "Take this ginger and go and
blow it on the skulls and the ears of these two images, that they may be
able to speak; call the man Adam and the woman Ewa." (N. Graafland "De
Minahassa" (Rotterdam, 1869), I. pages 96 sq.) In this narrative the names
of the man and woman betray European influence, but the rest of the story
may be aboriginal. The Dyaks of Sakarran in British Borneo say that the
first man was made by two large birds. At first they tried to make men out
of trees, but in vain. Then they hewed them out of rocks, but the figures
could not speak. Then they moulded a man out of damp earth and infused
into his veins the red gum of the kumpang-tree. After that they called to
him and he answered; they cut him and blood flowed from his wounds.
(Horsburgh, quoted by H. Ling Roth, "The Natives of Sarawak and of British
North Borneo" (London, 1896), I. pages 299 sq. Compare The Lord Bishop of
Labuan, "On the Wild Tribes of the North-West Coast of Borneo,"
"Transactions of the Ethnological Society of London", New Series, II.
(1863), page 27.)
The Kumis of South-Eastern India related to Captain Lewin, the Deputy
Commissioner of Hill Tracts, the following tradition of the creation of
man. "God made the world and the trees and the creeping things first, and
after that he set to work to make one man and one woman, forming their
bodies of clay; but each night, on the completion of his work, there came a
great snake, which, while God was sleeping, devoured the two images. This
happened twice or thrice, and God was at his wit's end, for he had to work
all day, and could not finish the pair in less than twelve hours; besides,
if he did not sleep, he would be no good," said Captain Lewin's informant.
"If he were not obliged to sleep, there would be no death, nor would
mankind be afflicted with illness. It is when he rests that the snake
carries us off to this day. Well, he was at his wit's end, so at last he
got up early one morning and first made a dog and put life into it, and
that night, when he had finished the images, he set the dog to watch them,
and when the snake came, the dog barked and frightened it away. This is
the reason at this day that when a man is dying the dogs begin to howl; but
I suppose God sleeps heavily now-a-days, or the snake is bolder, for men
die all the same." (Capt. T.H. Lewin, "Wild Races of South-Eastern India"
(London, 1870), pages 224-26.) The Khasis of Assam tell a similar tale.
(A. Bastian, "Volkerstamme am Brahmaputra und verwandtschaftliche Nachbarn"
(Berlin, 1883), page 8; Major P.R.T. Gurdon, "The Khasis" (London, 1907),
page 106.)
The Ewe-speaking tribes of Togo-land, in West Africa, think that God still
makes men out of clay. When a little of the water with which he moistens
the clay remains over, he pours it on the ground and out of that he makes
the bad and disobedient people. When he wishes to make a good man he makes
him out of good clay; but when he wishes to make a bad man, he employs only
bad clay for the purpose. In the beginning God fashioned a man and set him
on the earth; after that he fashioned a woman. The two looked at each
other and began to laugh, whereupon God sent them into the world. (J.
Spieth, "Die Ewe-Stamme, Material zur Kunde des Ewe-Volkes in Deutsch-Togo"
(Berlin, 1906), pages 828, 840.) The Innuit or Esquimaux of Point Barrow,
in Alaska, tell of a time when there was no man in the land, till a spirit
named "a se lu", who resided at Point Barrow, made a clay man, set him up
on the shore to dry, breathed into him and gave him life. ("Report of the
International Expedition to Point Barrow" (Washington, 1885), page 47.)
Other Esquimaux of Alaska relate how the Raven made the first woman out of
clay to be a companion to the first man; he fastened water-grass to the
back of the head to be hair, flapped his wings over the clay figure, and it
arose, a beautiful young woman. (E.W. Nelson, "The Eskimo about Bering
Strait", "Eighteenth Annual Report of the Bureau of American Ethnology",
Part I. (Washington, 1899), page 454.) The Acagchemem Indians of
California said that a powerful being called Chinigchinich created man out
of clay which he found on the banks of a lake; male and female created he
them, and the Indians of the present day are their descendants. (Friar
Geronimo Boscana, "Chinigchinich", appended to (A. Robinson's) "Life in
California" (New York, 1846), page 247.) A priest of the Natchez Indians
in Louisiana told Du Pratz "that God had kneaded some clay, such as that
which potters use and had made it into a little man; and that after
examining it, and finding it well formed, he blew up his work, and
forthwith that little man had life, grew, acted, walked, and found himself
a man perfectly well shaped." As to the mode in which the first woman was
created, the priest had no information, but thought she was probably made
in the same way as the first man; so Du Pratz corrected his imperfect
notions by reference to Scripture. (M. Le Page Du Pratz, "The History of
Louisiana" (London, 1774), page 330.) The Michoacans of Mexico said that
the great god Tucapacha first made man and woman out of clay, but that when
the couple went to bathe in a river they absorbed so much water that the
clay of which they were composed all fell to pieces. Then the creator went
to work again and moulded them afresh out of ashes, and after that he
essayed a third time and made them of metal. This last attempt succeeded.
The metal man and woman bathed in the river without falling to pieces, and
by their union they became the progenitors of mankind. (A. de Herrera,
"General History of the vast Continent and Islands of America", translated
into English by Capt. J. Stevens (London, 1725, 1726), III. 254; Brasseur
de Bourbourg, "Histoire des Nations Civilisees du Mexique et de l'Amerique-
Centrale" (Paris, 1857--1859), III. 80 sq; compare id. I. 54 sq.)
According to a legend of the Peruvian Indians, which was told to a Spanish
priest in Cuzco about half a century after the conquest, it was in
Tiahuanaco that man was first created, or at least was created afresh after
the deluge. "There (in Tiahuanaco)," so runs the legend, "the Creator
began to raise up the people and nations that are in that region, making
one of each nation of clay, and painting the dresses that each one was to
wear; those that were to wear their hair, with hair, and those that were to
be shorn, with hair cut. And to each nation was given the language, that
was to be spoken, and the songs to be sung, and the seeds and food that
they were to sow. When the Creator had finished painting and making the
said nations and figures of clay, he gave life and soul to each one, as
well men as women, and ordered that they should pass under the earth.
Thence each nation came up in the places to which he ordered them to go."
(E.J. Payne, "History of the New World called America", I. (Oxford, 1892),
page 462.)
These examples suffice to prove that the theory of the creation of man out
of dust or clay has been current among savages in many parts of the world.
But it is by no means the only explanation which the savage philosopher has
given of the beginnings of human life on earth. Struck by the resemblances
which may be traced between himself and the beasts, he has often supposed,
like Darwin himself, that mankind has been developed out of lower forms of
animal life. For the simple savage has none of that high notion of the
transcendant dignity of man which makes so many superior persons shrink
with horror from the suggestion that they are distant cousins of the
brutes. He on the contrary is not too proud to own his humble relations;
indeed his difficulty often is to perceive the distinction between him and
them. Questioned by a missionary, a Bushman of more than average
intelligence "could not state any difference between a man and a brute--he
did not know but a buffalo might shoot with bows and arrows as well as man,
if it had them." (Reverend John Campbell, "Travels in South Africa"
(London, 1822, II. page 34.) When the Russians first landed on one of the
Alaskan islands, the natives took them for cuttle-fish "on account of the
buttons on their clothes." (I. Petroff, "Report on the Population,
Industries, and Resources of Alaska", page 145.) The Giliaks of the Amoor
think that the outward form and size of an animal are only apparent; in
substance every beast is a real man, just like a Giliak himself, only
endowed with an intelligence and strength, which often surpass those of
mere ordinary human beings. (L. Sternberg, "Die Religion der Giljaken",
"Archiv fur Religionswissenschaft", VIII. (1905), page 248.) The
Borororos, an Indian tribe of Brazil, will have it that they are parrots of
a gorgeous red plumage which live in their native forests. Accordingly
they treat the birds as their fellow-tribesmen, keeping them in captivity,
refusing to eat their flesh, and mourning for them when they die. (K. von
den Steinen, "Unter den Naturvolkern Zentral-Brasiliens" (Berlin, 1894),
pages 352 sq., 512.)
This sense of the close relationship of man to the lower creation is the
essence of totemism, that curious system of superstition which unites by a
mystic bond a group of human kinsfolk to a species of animals or plants.
Where that system exists in full force, the members of a totem clan
identify themselves with their totem animals in a way and to an extent
which we find it hard even to imagine. For example, men of the Cassowary
clan in Mabuiag think that cassowaries are men or nearly so. "Cassowary,
he all same as relation, he belong same family," is the account they give
of their relationship with the long-legged bird. Conversely they hold that
they themselves are cassowaries for all practical purposes. They pride
themselves on having long thin legs like a cassowary. This reflection
affords them peculiar satisfaction when they go out to fight, or to run
away, as the case may be; for at such times a Cassowary man will say to
himself, "My leg is long and thin, I can run and not feel tired; my legs
will go quickly and the grass will not entangle them." Members of the
Cassowary clan are reputed to be pugnacious, because the cassowary is a
bird of very uncertain temper and can kick with extreme violence. (A.C.
Haddon, "The Ethnography of the Western Tribe of Torres Straits", "Journal
of the Anthropological Institute", XIX. (1890), page 393; "Reports of the
Cambridge Anthropological Expedition to Torres Straits", V. (Cambridge,
1904), pages 166, 184.) So among the Ojibways men of the Bear clan are
reputed to be surly and pugnacious like bears, and men of the Crane clan to
have clear ringing voices like cranes. (W.W. Warren, "History of the
Ojibways", "Collections of the Minnesota Historical Society", V. (Saint
Paul, Minn. 1885), pages 47, 49.) Hence the savage will often speak of his
totem animal as his father or his brother, and will neither kill it himself
nor allow others to do so, if he can help it. For example, if somebody
were to kill a bird in the presence of a native Australian who had the bird
for his totem, the black might say, "What for you kill that fellow? that my
father!" or "That brother belonging to me you have killed; why did you do
it?" (E. Palmer, "Notes on some Australian Tribes", "Journal of the
Anthropological Institute", XIII. (1884), page 300.) Bechuanas of the
Porcupine clan are greatly afflicted if anybody hurts or kills a porcupine
in their presence. They say, "They have killed our brother, our master,
one of ourselves, him whom we sing of"; and so saying they piously gather
the quills of their murdered brother, spit on them, and rub their eyebrows
with them. They think they would die if they touched its flesh. In like
manner Bechuanas of the Crocodile clan call the crocodile one of
themselves, their master, their brother; and they mark the ears of their
cattle with a long slit like a crocodile's mouth by way of a family crest.
Similarly Bechuanas of the Lion clan would not, like the members of other
clans, partake of lion's flesh; for how, say they, could they eat their
grandfather? If they are forced in self-defence to kill a lion, they do so
with great regret and rub their eyes carefully with its skin, fearing to
lose their sight if they neglected this precaution. (T. Arbousset et F.
Daumas, "Relation d'un Voyage d'Exploration au Nord-Est de la Colonie du
Cap de Bonne-Esperance" (Paris, 1842), pages 349 sq., 422-24.) A Mandingo
porter has been known to offer the whole of his month's pay to save the
life of a python, because the python was his totem and he therefore
regarded the reptile as his relation; he thought that if he allowed the
creature to be killed, the whole of his own family would perish, probably
through the vengeance to be taken by the reptile kinsfolk of the murdered
serpent. (M. le Docteur Tautain, "Notes sur les Croyances et Pratiques
Religieuses des Banmanas", "Revue d'Ethnographie", III. (1885), pages 396
sq.; A. Rancon, "Dans la Haute-Gambie, Voyage d'Exploration Scientifique"
(Paris, 1894), page 445.)
Sometimes, indeed, the savage goes further and identifies the revered
animal not merely with a kinsman but with himself; he imagines that one of
his own more or less numerous souls, or at all events that a vital part of
himself, is in the beast, so that if it is killed he must die. Thus, the
Balong tribe of the Cameroons, in West Africa, think that every man has
several souls, of which one is lodged in an elephant, a wild boar, a
leopard, or what not. When any one comes home, feels ill, and says, "I
shall soon die," and is as good as his word, his friends are of opinion
that one of his souls has been shot by a hunter in a wild boar or a
leopard, for example, and that that is the real cause of his death. (J.
Keller, "Ueber das Land und Volk der Balong", "Deutsches Kolonialblatt", 1
October, 1895, page 484.) A Catholic missionary, sleeping in the hut of a
chief of the Fan negroes, awoke in the middle of the night to see a huge
black serpent of the most dangerous sort in the act of darting at him. He
was about to shoot it when the chief stopped him, saying, "In killing that
serpent, it is me that you would have killed. Fear nothing, the serpent is
my elangela." (Father Trilles, "Chez les Fang, leurs Moeurs, leur Langue,
leur Religion", "Les Missions Catholiques", XXX. (1898), page 322.) At
Calabar there used to be some years ago a huge old crocodile which was well
known to contain the spirit of a chief who resided in the flesh at Duke
Town. Sporting Vice-Consuls, with a reckless disregard of human life, from
time to time made determined attempts to injure the animal, and once a
peculiarly active officer succeeded in hitting it. The chief was
immediately laid up with a wound in his leg. He SAID that a dog had bitten
him, but few people perhaps were deceived by so flimsy a pretext. (Miss
Mary H. Kingsley, "Travels in West Africa" (London, 1897), pages 538 sq.
As to the external or bush souls of human beings, which in this part of
Africa are supposed to be lodged in the bodies of animals, see Miss Mary H.
Kingsley op. cit. pages 459-461; R. Henshaw, "Notes on the Efik belief in
'bush soul'", "Man", VI.(1906), pages 121 sq.; J. Parkinson, "Notes on the
Asaba people (Ibos) of the Niger", "Journal of the Anthropological
Institute", XXXVI. (1906), pages 314 sq.) Once when Mr Partridge's canoe-
men were about to catch fish near an Assiga town in Southern Nigeria, the
natives of the town objected, saying, "Our souls live in those fish, and if
you kill them we shall die." (Charles Partridge, "Cross River Natives"
(London, 1905), pages 225 sq.) On another occasion, in the same region, an
Englishman shot a hippopotamus near a native village. The same night a
woman died in the village, and her friends demanded and obtained from the
marksman five pounds as compensation for the murder of the woman, whose
soul or second self had been in that hippopotamus. (C.H. Robinson,
"Hausaland" (London, 1896), pages 36 sq.) Similarly at Ndolo, in the Congo
region, we hear of a chief whose life was bound up with a hippopotamus, but
he prudently suffered no one to fire at the animal. ("Notes Analytiques
sur les Collections Ethnographiques du Musee du Congo", I. (Brussels, 1902-
06), page 150.
Amongst people who thus fail to perceive any sharp line of distinction
between beasts and men it is not surprising to meet with the be