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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