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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”
“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.
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.
Botany School, Cambridge,
March 20, 1909.
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).
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: A. 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:
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.
DATES OF THE PUBLICATION Of CHARLES DARWIN’S BOOKS AND OF THE PRINCIPAL EVENTS IN HIS LIFE
Charles Darwin born at Shrewsbury, February 12.
“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.)
“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.”
“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.”
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.”
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.”
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.”
“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.”
“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.”
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.
Contributed Geological Introduction to Part I. (“Fossil Mammalia”) of the “Zoology of the Voyage of H.M.S. ‘Beagle'” by Richard Owen.
“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”.
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.)
Publication of the “Journal of Researches” as a separate book.
Publication of “Geological Observations on South America”; being Part III. of the “Geology of the Voyage of the ‘Beagle'”.
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.”
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.”
“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’.”
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.”
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.”
Publication of the second edition of the “Origin” (3000 copies).
Publication of a “Naturalist’s Voyage”.
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.”
Publication of the book “On the various contrivances by which Orchids are fertilised by Insects”.
Read paper before the Linnean Society “On the Movements and Habits of Climbing plants”. (Published as a book in 1875.)
Publication of the fourth edition of the “Origin” (1250 copies).
“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.”
Publication of the fifth edition of the “Origin”.
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’.”
Publication of the sixth edition of the “Origin”.
Publication of “The Expression of the Emotions in Man and Animals”.
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”.
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.
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”.
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.
Publication of the second edition of “The Effects of Cross and Self fertilisation”.
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.)
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”.
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.”
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.
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,
II. DARWIN’S PREDECESSORS.
By J. ARTHUR THOMSON.
Professor of Natural History in the University of Aberdeen.
In seeking to discover Darwin’s relation to his predecessors it is useful to distinguish the various services which he rendered to the theory of organic evolution.
(I) As everyone knows, the general idea of the Doctrine of Descent is that the plants and animals of the present-day are the lineal descendants of ancestors on the whole somewhat simpler, that these again are descended from yet simpler forms, and so on backwards towards the literal “Protozoa” and “Protophyta” about which we unfortunately know nothing. Now no one supposes that Darwin originated this idea, which in rudiment at least is as old as Aristotle. What Darwin did was to make it current intellectual coin. He gave it a form that commended itself to the scientific and public intelligence of the day, and he won wide-spread conviction by showing with consummate skill that it was an effective formula to work with, a key which no lock refused. In a scholarly, critical, and pre-eminently fair-minded way, admitting difficulties and removing them, foreseeing objections and forestalling them, he showed that the doctrine of descent supplied a modal interpretation of how our present-day fauna and flora have come to be.
(II) In the second place, Darwin applied the evolution-idea to particular problems, such as the descent of man, and showed what a powerful organon it is, introducing order into masses of uncorrelated facts, interpreting enigmas both of structure and function, both bodily and mental, and, best of all, stimulating and guiding further investigation. But here again it cannot be claimed that Darwin was original. The problem of the descent or ascent of man, and other particular cases of evolution, had attracted not a few naturalists before Darwin’s day, though no one (except Herbert Spencer in the psychological domain (1855)) had come near him in precision and thoroughness of inquiry.
(III) In the third place, Darwin contributed largely to a knowledge of the factors in the evolution-process, especially by his analysis of what occurs in the case of domestic animals and cultivated plants, and by his elaboration of the theory of Natural Selection, which Alfred Russel Wallace independently stated at the same time, and of which there had been a few previous suggestions of a more or less vague description. It was here that Darwin’s originality was greatest, for he revealed to naturalists the many different forms–often very subtle–which natural selection takes, and with the insight of a disciplined scientific imagination he realised what a mighty engine of progress it has been and is.
(IV) As an epoch-marking contribution, not only to Aetiology but to Natural History in the widest sense, we rank the picture which Darwin gave to the world of the web of life, that is to say, of the inter-relations and linkages in Nature. For the Biology of the individual–if that be not a contradiction in terms–no idea is more fundamental than that of the correlation of organs, but Darwin’s most characteristic contribution was not less fundamental,–it was the idea of the correlation of organisms. This, again, was not novel; we find it in the works of naturalist like Christian Conrad Sprengel, Gilbert White, and Alexander von Humboldt, but the realisation of its full import was distinctively Darwinian.
AS REGARDS THE GENERAL IDEA OF ORGANIC EVOLUTION.
While it is true, as Prof. H.F. Osborn puts it, that “‘Before and after Darwin’ will always be the ante et post urbem conditam of biological history,” it is also true that the general idea of organic evolution is very ancient. In his admirable sketch “From the Greeks to Darwin” (“Columbia University Biological Series”, Vol. I. New York and London, 1894. We must acknowledge our great indebtness to this fine piece of work.), Prof. Osborn has shown that several of the ancient philosophers looked upon Nature as a gradual development and as still in process of change. In the suggestions of Empedocles, to take the best instance, there were “four sparks of truth,–first, that the development of life was a gradual process; second, that plants were evolved before animals; third, that imperfect forms were gradually replaced (not succeeded) by perfect forms; fourth, that the natural cause of the production of perfect forms was the extinction of the imperfect.” (Op. cit. page 41.) But the fundamental idea of one stage giving origin to another was absent. As the blue Aegean teemed with treasures of beauty and threw many upon its shores, so did Nature produce like a fertile artist what had to be rejected as well as what was able to survive, but the idea of one species emerging out of another was not yet conceived.
Aristotle’s views of Nature (See G.J. Romanes, “Aristotle as a Naturalist”, “Contemporary Review”, Vol. LIX. page 275, 1891; G. Pouchet “La Biologie Aristotelique”, Paris, 1885; E. Zeller, “A History of Greek Philosophy”, London, 1881, and “Ueber die griechischen Vorganger Darwin’s”, “Abhandl. Berlin Akad.” 1878, pages 111-124.) seem to have been more definitely evolutionist than those of his predecessors, in this sense, at least, that he recognised not only an ascending scale, but a genetic series from polyp to man and an age-long movement towards perfection. “It is due to the resistance of matter to form that Nature can only rise by degrees from lower to higher types.” “Nature produces those things which, being continually moved by a certain principle contained in themselves, arrive at a certain end.”
To discern the outcrop of evolution-doctrine in the long interval between Aristotle and Bacon seems to be very difficult, and some of the instances that have been cited strike one as forced. Epicurus and Lucretius, often called poets of evolution, both pictured animals as arising directly out of the earth, very much as Milton’s lion long afterwards pawed its way out. Even when we come to Bruno who wrote that “to the sound of the harp of the Universal Apollo (the World Spirit), the lower organisms are called by stages to higher, and the lower stages are connected by intermediate forms with the higher,” there is great room, as Prof. Osborn points out (op. cit. page 81.), for difference of opinion as to how far he was an evolutionist in our sense of the term.
The awakening of natural science in the sixteenth century brought the possibility of a concrete evolution theory nearer, and in the early seventeenth century we find evidences of a new spirit–in the embryology of Harvey and the classifications of Ray. Besides sober naturalists there were speculative dreamers in the sixteenth and seventeenth centuries who had at least got beyond static formulae, but, as Professor Osborn points out (op. cit. page 87.), “it is a very striking fact, that the basis of our modern methods of studying the Evolution problem was established not by the early naturalists nor by the speculative writers, but by the Philosophers.” He refers to Bacon, Descartes, Leibnitz, Hume, Kant, Lessing, Herder, and Schelling. “They alone were upon the main track of modern thought. It is evident that they were groping in the dark for a working theory of the Evolution of life, and it is remarkable that they clearly perceived from the outset that the point to which observation should be directed was not the past but the present mutability of species, and further, that this mutability was simply the variation of individuals on an extended scale.”
Bacon seems to have been one of the first to think definitely about the mutability of species, and he was far ahead of his age in his suggestion of what we now call a Station of Experimental Evolution. Leibnitz discusses in so many words how the species of animals may be changed and how intermediate species may once have linked those that now seem discontinuous. “All natural orders of beings present but a single chain”…”All advances by degrees in Nature, and nothing by leaps.” Similar evolutionist statements are to be found in the works of the other “philosophers,” to whom Prof. Osborn refers, who were, indeed, more scientific than the naturalists of their day. It must be borne in mind that the general idea of organic evolution–that the present is the child of the past–is in great part just the idea of human history projected upon the natural world, differentiated by the qualification that the continuous “Becoming” has been wrought out by forces inherent in the organisms themselves and in their environment.
A reference to Kant (See Brock, “Die Stellung Kant’s zur Deszendenztheorie,” “Biol. Centralbl.” VIII. 1889, pages 641-648. Fritz Schultze, “Kant und Darwin”, Jena, 1875.) should come in historical order after Buffon, with whose writings he was acquainted, but he seems, along with Herder and Schelling, to be best regarded as the culmination of the evolutionist philosophers–of those at least who interested themselves in scientific problems. In a famous passage he speaks of “the agreement of so many kinds of animals in a certain common plan of structure”…an “analogy of forms” which “strengthens the supposition that they have an actual blood-relationship, due to derivation from a common parent.” He speaks of “the great Family of creatures, for as a Family we must conceive it, if the above-mentioned continuous and connected relationship has a real foundation.” Prof. Osborn alludes to the scientific caution which led Kant, biology being what it was, to refuse to entertain the hope “that a Newton may one day arise even to make the production of a blade of grass comprehensible, according to natural laws ordained by no intention.” As Prof. Haeckel finely observes, Darwin rose up as Kant’s Newton. (Mr Alfred Russel Wallace writes: “We claim for Darwin that he is the Newton of natural history, and that, just so surely as that the discovery and demonstration by Newton of the law of gravitation established order in place of chaos and laid a sure foundation for all future study of the starry heavens, so surely has Darwin, by his discovery of the law of natural selection and his demonstration of the great principle of the preservation of useful variations in the struggle for life, not only thrown a flood of light on the process of development of the whole organic world, but also established a firm foundation for all future study of nature” (“Darwinism”, London, 1889, page 9). See also Prof. Karl Pearson’s “Grammar of Science” (2nd edition), London, 1900, page 32. See Osborn, op. cit. Page 100.))
The scientific renaissance brought a wealth of fresh impressions and some freedom from the tyranny of tradition, and the twofold stimulus stirred the speculative activity of a great variety of men from old Claude Duret of Moulins, of whose weird transformism (1609) Dr Henry de Varigny (“Experimental Evolution”. London, 1892. Chap. 1. page 14.) gives us a glimpse, to Lorenz Oken (1799-1851) whose writings are such mixtures of sense and nonsense that some regard him as a far-seeing prophet and others as a fatuous follower of intellectual will-o’-the-wisps. Similarly, for De Maillet, Maupertuis, Diderot, Bonnet, and others, we must agree with Professor Osborn that they were not actually in the main Evolution movement. Some have been included in the roll of honour on very slender evidence, Robinet for instance, whose evolutionism seems to us extremely dubious. (See J. Arthur Thomson, “The Science of Life”. London, 1899. Chap. XVI. “Evolution of Evolution Theory”.)
The first naturalist to give a broad and concrete expression to the evolutionist doctrine of descent was Buffon (1707-1788), but it is interesting to recall the fact that his contemporary Linnaeus (1707-1778), protagonist of the counter-doctrine of the fixity of species (See Carus Sterne (Ernest Krause), “Die allgemeine Weltanschauung in ihrer historischen Entwickelung”. Stuttgart, 1889. Chapter entitled “Bestandigkeit oder Veranderlichkeit der Naturwesen”.), went the length of admitting (in 1762) that new species might arise by intercrossing. Buffon’s position among the pioneers of the evolution-doctrine is weakened by his habit of vacillating between his own conclusions and the orthodoxy of the Sorbonne, but there is no doubt that he had a firm grasp of the general idea of “l’enchainement des etres.”
Erasmus Darwin (1731-1802), probably influenced by Buffon, was another firm evolutionist, and the outline of his argument in the “Zoonomia” (“Zoonomia, or the Laws of Organic Life”, 2 vols. London, 1794; Osborn op. cit. page 145.) might serve in part at least to-day. “When we revolve in our minds the metamorphoses of animals, as from the tadpole to the frog; secondly, the changes produced by artificial cultivation, as in the breeds of horses, dogs, and sheep; thirdly, the changes produced by conditions of climate and of season, as in the sheep of warm climates being covered with hair instead of wool, and the hares and partridges of northern climates becoming white in winter: when, further, we observe the changes of structure produced by habit, as seen especially in men of different occupations; or the changes produced by artificial mutilation and prenatal influences, as in the crossing of species and production of monsters; fourth, when we observe the essential unity of plan in all warm-blooded animals,–we are led to conclude that they have been alike produced from a similar living filament”…”From thus meditating upon the minute portion of time in which many of the above changes have been produced, would it be too bold to imagine, in the great length of time since the earth began to exist, perhaps millions of years before the commencement of the history of mankind, that all warm-blooded animals have arisen from one living filament?”…”This idea of the gradual generation of all things seems to have been as familiar to the ancient philosophers as to the modern ones, and to have given rise to the beautiful hieroglyphic figure of the proton oon, or first great egg, produced by night, that is, whose origin is involved in obscurity, and animated by Eros, that is, by Divine Love; from whence proceeded all things which exist.”
Lamarck (1744-1829) seems to have become an evolutionist independently of Erasmus Darwin’s influence, though the parallelism between them is striking. He probably owed something to Buffon, but he developed his theory along a different line. Whatever view be held in regard to that theory there is no doubt that Lamarck was a thorough-going evolutionist. Professor Haeckel speaks of the “Philosophie Zoologique” as “the first connected and thoroughly logical exposition of the theory of descent.” (See Alpheus S. Packard, “Lamarck, the Founder of Evolution, His Life and Work, with Translations of his writings on Organic Evolution”. London, 1901.)
Besides the three old masters, as we may call them, Buffon, Erasmus Darwin, and Lamarck, there were other quite convinced pre-Darwinian evolutionists. The historian of the theory of descent must take account of Treviranus whose “Biology or Philosophy of Animate Nature” is full of evolutionary suggestions; of Etienne Geoffroy St Hilaire, who in 1830, before the French Academy of Sciences, fought with Cuvier, the fellow-worker of his youth, an intellectual duel on the question of descent; of Goethe, one of the founders of morphology and the greatest poet of Evolution–who, in his eighty-first year, heard the tidings of Geoffroy St Hilaire’s defeat with an interest which transcended the political anxieties of the time; and of many others who had gained with more or less confidence and clearness a new outlook on Nature. It will be remembered that Darwin refers to thirty-four more or less evolutionist authors in his Historical Sketch, and the list might be added to. Especially when we come near to 1858 do the numbers increase, and one of the most remarkable, as also most independent champions of the evolution-idea before that date was Herbert Spencer, who not only marshalled the arguments in a very forcible way in 1852, but applied the formula in detail in his “Principles of Psychology” in 1855. (See Edward Clodd, “Pioneers of Evolution”, London, page 161, 1897.)
It is right and proper that we should shake ourselves free from all creationist appreciations of Darwin, and that we should recognise the services of pre-Darwinian evolutionists who helped to make the time ripe, yet one cannot help feeling that the citation of them is apt to suggest two fallacies. It may suggest that Darwin simply entered into the labours of his predecessors, whereas, as a matter of fact, he knew very little about them till after he had been for years at work. To write, as Samuel Butler did, “Buffon planted, Erasmus Darwin and Lamarck watered, but it was Mr Darwin who said ‘That fruit is ripe,’ and shook it into his lap”…seems to us a quite misleading version of the facts of the case. The second fallacy which the historical citation is a little apt to suggest is that the filiation of ideas is a simple problem. On the contrary, the history of an idea, like the pedigree of an organism, is often very intricate, and the evolution of the evolution-idea is bound up with the whole progress of the world. Thus in order to interpret Darwin’s clear formulation of the idea of organic evolution and his convincing presentation of it, we have to do more than go back to his immediate predecessors, such as Buffon, Erasmus Darwin, and Lamarck; we have to inquire into the acceptance of evolutionary conceptions in regard to other orders of facts, such as the earth and the solar system (See Chapter IX. “The Genetic View of Nature” in J.T. Merz’s “History of European Thought in the Nineteenth Century”, Vol. 2, Edinburgh and London, 1903.); we have to realise how the growing success of scientific interpretation along other lines gave confidence to those who refused to admit that there was any domain from which science could be excluded as a trespasser; we have to take account of the development of philosophical thought, and even of theological and religious movements; we should also, if we are wise enough, consider social changes. In short, we must abandon the idea that we can understand the history of any science as such, without reference to contemporary evolution in other departments of activity.
While there were many evolutionists before Darwin, few of them were expert naturalists and few were known outside a small circle; what was of much more importance was that the genetic view of nature was insinuating itself in regard to other than biological orders of facts, here a little and there a little, and that the scientific spirit had ripened since the days when Cuvier laughed Lamarck out of court. How was it that Darwin succeeded where others had failed? Because, in the first place, he had clear visions–“pensees de la jeunesse, executees par l’age mur”–which a University curriculum had not made impossible, which the “Beagle” voyage made vivid, which an unrivalled British doggedness made real–visions of the web of life, of the fountain of change within the organism, of the struggle for existence and its winnowing, and of the spreading genealogical tree. Because, in the second place, he put so much grit into the verification of his visions, putting them to the proof in an argument which is of its kind–direct demonstration being out of the question–quite unequalled. Because, in the third place, he broke down the opposition which the most scientific had felt to the seductive modal formula of evolution by bringing forward a more plausible theory of the process than had been previously suggested. Nor can one forget, since questions of this magnitude are human and not merely academic, that he wrote so that all men could understand.
AS REGARDS THE FACTORS OF EVOLUTION.
It is admitted by all who are acquainted with the history of biology that the general idea of organic evolution as expressed in the Doctrine of Descent was quite familiar to Darwin’s grandfather, and to others before and after him, as we have briefly indicated. It must also be admitted that some of these pioneers of evolutionism did more than apply the evolution- idea as a modal formula of becoming, they began to inquire into the factors in the process. Thus there were pre-Darwinian theories of evolution, and to these we must now briefly refer. (See Prof. W.A. Locy’s “Biology and its Makers”. New York, 1908. Part II. “The Doctrine of Organic Evolution”.
In all biological thinking we have to work with the categories Organism– Function–Environment, and theories of evolution may be classified in relation to these. To some it has always seemed that the fundamental fact is the living organism,–a creative agent, a striving will, a changeful Proteus, selecting its environment, adjusting itself to it, self- differentiating and self-adaptive. The necessity of recognising the importance of the organism is admitted by all Darwinians who start with inborn variations, but it is open to question whether the whole truth of what we might call the Goethian position is exhausted in the postulate of inherent variability.
To others it has always seemed that the emphasis should be laid on Function,–on use and disuse, on doing and not doing. Practice makes perfect; c’est a force de forger qu’on devient forgeron. This is one of the fundamental ideas of Lamarckism; to some extent it met with Darwin’s approval; and it finds many supporters to-day. One of the ablest of these –Mr Francis Darwin–has recently given strong reasons for combining a modernised Lamarckism with what we usually regard as sound Darwinism. (Presidential Address to the British Association meeting at Dublin in 1908.)
To others it has always seemed that the emphasis should be laid on the Environment, which wakes the organism to action, prompts it to change, makes dints upon it, moulds it, prunes it, and finally, perhaps, kills it. It is again impossible to doubt that there is truth in this view, for even if environmentally induced “modifications” be not transmissible, environmentally induced “variations” are; and even if the direct influence of the environment be less important than many enthusiastic supporters of this view–may we call them Buffonians–think, there remains the indirect influence which Darwinians in part rely on,–the eliminative process. Even if the extreme view be held that the only form of discriminate elimination that counts is inter-organismal competition, this might be included under the rubric of the animate environment.
In many passages Buffon (See in particular Samuel Butler, “Evolution Old and New”, London, 1879; J.L. de Lanessan, “Buffon et Darwin”, “Revue Scientifique”, XLIII. pages 385-391, 425-432, 1889.) definitely suggested that environmental influences–especially of climate and food–were directly productive of changes in organisms, but he did not discuss the question of the transmissibility of the modifications so induced, and it is difficult to gather from his inconsistent writings what extent of transformation he really believed in. Prof. Osborn says of Buffon: “The struggle for existence, the elimination of the least-perfected species, the contest between the fecundity of certain species and their constant destruction, are all clearly expressed in various passages.” He quotes two of these (op. cit. page 136.):
“Le cours ordinaire de la nature vivante, est en general toujours constant, toujours le meme; son mouvement, toujours regulier, roule sur deux points inebranlables: l’un, la fecondite sans bornes donnee a toutes les especes; l’autre, les obstacles sans nombre qui reduisent cette fecondite a une mesure determinee et ne laissent en tout temps qu’a peu pres la meme quantite d’individus de chaque espece”…”Les especes les moins parfaites, les plus delicates, les plus pesantes, les moins agissantes, les moins armees, etc., ont deja disparu ou disparaitront.”
Erasmus Darwin (See Ernst Krause and Charles Darwin, “Erasmus Darwin”, London, 1879.) had a firm grip of the “idea of the gradual formation and improvement of the Animal world,” and he had his theory of the process. No sentence is more characteristic than this: “All animals undergo transformations which are in part produced by their own exertions, in response to pleasures and pains, and many of these acquired forms or propensities are transmitted to their posterity.” This is Lamarckism before Lamarck, as his grandson pointed out. His central idea is that wants stimulate efforts and that these result in improvements, which subsequent generations make better still. He realised something of the struggle for existence and even pointed out that this advantageously checks the rapid multiplication. “As Dr Krause points out, Darwin just misses the connection between this struggle and the Survival of the Fittest.” (Osborn op. cit. page 142.)
Lamarck (1744-1829) (See E. Perrier “La Philosophie Zoologique avant Darwin”, Paris, 1884; A. de Quatrefages, “Darwin et ses Precurseurs Francais”, Paris, 1870; Packard op. cit.; also Claus, “Lamarck als Begrunder der Descendenzlehre”, Wien, 1888; Haeckel, “Natural History of Creation”, English translation London, 1879; Lang “Zur Charakteristik der Forschungswege von Lamarck und Darwin”, Jena, 1889.) seems to have thought out his theory of evolution without any knowledge of Erasmus Darwin’s which it closely resembled. The central idea of his theory was the cumulative inheritance of functional modifications. “Changes in environment bring about changes in the habits of animals. Changes in their wants necessarily bring about parallel changes in their habits. If new wants become constant or very lasting, they form new habits, the new habits involve the use of new parts, or a different use of old parts, which results finally in the production of new organs and the modification of old ones.” He differed from Buffon in not attaching importance, as far as animals are concerned, to the direct influence of the environment, “for environment can effect no direct change whatever upon the organisation of animals,” but in regard to plants he agreed with Buffon that external conditions directly moulded them.
Treviranus (1776-1837) (See Huxley’s article “Evolution in Biology”, “Encyclopaedia Britannica” (9th edit.), 1878, pages 744-751, and Sully’s article, “Evolution in Philosophy”, ibid. pages 751-772.), whom Huxley ranked beside Lamarck, was on the whole Buffonian, attaching chief importance to the influence of a changeful environment both in modifying and in eliminating, but he was also Goethian, for instance in his idea that species like individuals pass through periods of growth, full bloom, and decline. “Thus, it is not only the great catastrophes of Nature which have caused extinction, but the completion of cycles of existence, out of which new cycles have begun.” A characteristic sentence is quoted by Prof. Osborn: “In every living being there exists a capability of an endless variety of form-assumption; each possesses the power to adapt its organisation to the changes of the outer world, and it is this power, put into action by the change of the universe, that has raised the simple zoophytes of the primitive world to continually higher stages of organisation, and has introduced a countless variety of species into animate Nature.”
Goethe (1749-1832) (See Haeckel, “Die Naturanschauung von Darwin, Goethe und Lamarck”, Jena, 1882.), who knew Buffon’s work but not Lamarck’s, is peculiarly interesting as one of the first to use the evolution-idea as a guiding hypothesis, e.g. in the interpretation of vestigial structures in man, and to realise that organisms express an attempt to make a compromise between specific inertia and individual change. He gave the finest expression that science has yet known–if it has known it–of the kernel- idea of what is called “bathmism,” the idea of an “inherent growth-force”– and at the same time he held that “the way of life powerfully reacts upon all form” and that the orderly growth of form “yields to change from externally acting causes.”
Besides Buffon, Erasmus Darwin, Lamarck, Treviranus, and Goethe, there were other “pioneers of evolution,” whose views have been often discussed and appraised. Etienne Geoffroy Saint-Hilaire (1772-1844), whose work Goethe so much admired, was on the whole Buffonian, emphasising the direct action of the changeful milieu. “Species vary with their environment, and existing species have descended by modification from earlier and somewhat simpler species.” He had a glimpse of the selection idea, and believed in mutations or sudden leaps–induced in the embryonic condition by external influences. The complete history of evolution-theories will include many instances of guesses at truth which were afterwards substantiated, thus the geographer von Buch (1773-1853) detected the importance of the Isolation factor on which Wagner, Romanes, Gulick and others have laid great stress, but we must content ourselves with recalling one other pioneer, the author of the “Vestiges of Creation” (1844), a work which passed through ten editions in nine years and certainly helped to harrow the soil for Darwin’s sowing. As Darwin said, “it did excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views.” (“Origin of Species” (6th edition), page xvii.) Its author, Robert Chambers (1802- 1871) was in part a Buffonian–maintaining that environment moulded organisms adaptively, and in part a Goethian–believing in an inherent progressive impulse which lifted organisms from one grade of organisation to another.
AS REGARDS NATURAL SELECTION.
The only thinker to whom Darwin was directly indebted, so far as the theory of Natural Selection is concerned, was Malthus, and we may once more quote the well-known passage in the Autobiography: “In October, 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement ‘Malthus on Population’, and being well prepared to appreciate the struggle for existence which everywhere goes on from long- continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.” (“The Life and Letters of Charles Darwin”, Vol. 1. page 83. London, 1887.)
Although Malthus gives no adumbration of the idea of Natural Selection in his exposition of the eliminative processes which go on in mankind, the suggestive value of his essay is undeniable, as is strikingly borne out by the fact that it gave to Alfred Russel Wallace also “the long-sought clue to the effective agent in the evolution of organic species.” (A.R. Wallace, “My Life, A Record of Events and Opinions”, London, 1905, Vol. 1. page 232.) One day in Ternate when he was resting between fits of fever, something brought to his recollection the work of Malthus which he had read twelve years before. “I thought of his clear exposition of ‘the positive checks to increase’–disease, accidents, war, and famine–which keep down the population of savage races to so much lower an average than that of more civilized peoples. It then occurred to me that these causes or their equivalents are continually acting in the case of animals also; and as animals usually breed much more rapidly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since they evidently do not increase regularly from year to year, as otherwise the world would long ago have been densely crowded with those that breed most quickly. Vaguely thinking over the enormous and constant destruction which this implied, it occurred to me to ask the question, Why do some die and some live? And the answer was clearly, that on the whole the best fitted live. From the effects of disease the most healthy escaped; from enemies the strongest, the swiftest, or the most cunning; from famine the best hunters or those with the best digestion; and so on. Then it suddenly flashed upon me that this self- acting process would necessarily IMPROVE THE RACE, because in every generation the inferior would inevitably be killed off and the superior would remain–that is, THE FITTEST WOULD SURVIVE.” (Ibid. Vol. 1. page 361.) We need not apologise for this long quotation, it is a tribute to Darwin’s magnanimous colleague, the Nestor of the evolutionist camp,–and it probably indicates the line of thought which Darwin himself followed. It is interesting also to recall the fact that in 1852, when Herbert Spencer wrote his famous “Leader” article on “The Development Hypothesis” in which he argued powerfully for the thesis that the whole animate world is the result of an age-long process of natural transformation, he wrote for “The Westminster Review” another important essay, “A Theory of Population deduced from the General Law of Animal Fertility”, towards the close of which he came within an ace of recognising that the struggle for existence was a factor in organic evolution. At a time when pressure of population was practically interesting men’s minds, Darwin, Wallace, and Spencer were being independently led from a social problem to a biological theory. There could be no better illustration, as Prof. Patrick Geddes has pointed out, of the Comtian thesis that science is a “social phenomenon.”
Therefore, as far more important than any further ferreting out of vague hints of Natural Selection in books which Darwin never read, we would indicate by a quotation the view that the central idea in Darwinism is correlated with contemporary social evolution. “The substitution of Darwin for Paley as the chief interpreter of the order of nature is currently regarded as the displacement of an anthropomorphic view by a purely scientific one: a little reflection, however, will show that what has actually happened has been merely the replacement of the anthropomorphism of the eighteenth century by that of the nineteenth. For the place vacated by Paley’s theological and metaphysical explanation has simply been occupied by that suggested to Darwin and Wallace by Malthus in terms of the prevalent severity of industrial competition, and those phenomena of the struggle for existence which the light of contemporary economic theory has enabled us to discern, have thus come to be temporarily exalted into a complete explanation of organic progress.” (P. Geddes, article “Biology”, “Chambers’s Encyclopaedia”.) It goes without saying that the idea suggested by Malthus was developed by Darwin into a biological theory which was then painstakingly verified by being used as an interpretative formula, and that the validity of a theory so established is not affected by what suggested it, but the practical question which this line of thought raises in the mind is this: if Biology did thus borrow with such splendid results from social theory, why should we not more deliberately repeat the experiment?
Darwin was characteristically frank and generous in admitting that the principle of Natural Selection had been independently recognised by Dr W.C. Wells in 1813 and by Mr Patrick Matthew in 1831, but he had no knowledge of these anticipations when he published the first edition of “The Origin of Species”. Wells, whose “Essay on Dew” is still remembered, read in 1813 before the Royal Society a short paper entitled “An account of a White Female, part of whose skin resembles that of a Negro” (published in 1818). In this communication, as Darwin said, “he observes, firstly, that all animals tend to vary in some degree, and, secondly, that agriculturists improve their domesticated animals by selection; and then, he adds, but what is done in this latter case ‘by art, seems to be done with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit.'” (“Origin of Species” (6th edition) page xv.) Thus Wells had the clear idea of survival dependent upon a favourable variation, but he makes no more use of the idea and applies it only to man. There is not in the paper the least hint that the author ever thought of generalising the remarkable sentence quoted above.
Of Mr Patrick Matthew, who buried his treasure in an appendix to a work on “Naval Timber and Arboriculture”, Darwin said that “he clearly saw the full force of the principle of natural selection.” In 1860 Darwin wrote–very characteristically–about this to Lyell: “Mr Patrick Matthew publishes a long extract from his work on “Naval Timber and Arboriculture”, published in 1831, in which he briefly but completely anticipates the theory of Natural Selection. I have ordered the book, as some passages are rather obscure, but it is certainly, I think, a complete but not developed anticipation. Erasmus always said that surely this would be shown to be the case some day. Anyhow, one may be excused in not having discovered the fact in a work on Naval Timber.” (“Life and Letters” II. page 301.)
De Quatrefages and De Varigny have maintained that the botanist Naudin stated the theory of evolution by natural selection in 1852. He explains very clearly the process of artificial selection, and says that in the garden we are following Nature’s method. “We do not think that Nature has made her species in a different fashion from that in which we proceed ourselves in order to make our variations.” But, as Darwin said, “he does not show how selection acts under nature.” Similarly it must be noted in regard to several pre-Darwinian pictures of the struggle for existence (such as Herder’s, who wrote in 1790 “All is in struggle…each one for himself” and so on), that a recognition of this is only the first step in Darwinism.
Profs. E. Perrier and H.F. Osborn have called attention to a remarkable anticipation of the selection-idea which is to be found in the speculations of Etienne Geoffroy St Hilaire (1825-1828) on the evolution of modern Crocodilians from the ancient Teleosaurs. Changing environment induced changes in the respiratory system and far-reaching consequences followed. The atmosphere, acting upon the pulmonary cells, brings about “modifications which are favourable or destructive (‘funestes’); these are inherited, and they influence all the rest of the organisation of the animal because if these modifications lead to injurious effects, the animals which exhibit them perish and are replaced by others of a somewhat different form, a form changed so as to be adapted to (a la convenance) the new environment.”
Prof. E.B. Poulton (“Science Progress”, New Series, Vol. I. 1897. “A Remarkable Anticipation of Modern Views on Evolution”. See also Chap. VI. in “Essays on Evolution”, Oxford, 1908.) has shown that the anthropologist James Cowles Prichard (1786-1848) must be included, even in spite of himself, among the precursors of Darwin. In some passages of the second edition of his “Researches into the Physical History of Mankind” (1826), he certainly talks evolution and anticipates Prof. Weismann in denying the transmission of acquired characters. He is, however, sadly self- contradictory and his evolutionism weakens in subsequent editions–the only ones that Darwin saw. Prof. Poulton finds in Prichard’s work a recognition of the operation of Natural Selection. “After enquiring how it is that ‘these varieties are developed and preserved in connection with particular climates and differences of local situation,’ he gives the following very significant answer: ‘One cause which tends to maintain this relation is obvious. Individuals and families, and even whole colonies, perish and disappear in climates for which they are, by peculiarity of constitution, not adapted. Of this fact proofs have been already mentioned.'” Mr Francis Darwin and Prof. A.C. Seward discuss Prichard’s “anticipations” in “More Letters of Charles Darwin”, Vol. I. page 43, and come to the conclusion that the evolutionary passages are entirely neutralised by others of an opposite trend. There is the same difficulty with Buffon.
Hints of the idea of Natural Selection have been detected elsewhere. James Watt (See Prof. Patrick Geddes’s article “Variation and Selection”, “Encyclopaedia Britannica (9th edition) 1888.), for instance, has been reported as one of the anticipators (1851). But we need not prolong the inquiry further, since Darwin did not know of any anticipations until after he had published the immortal work of 1859, and since none of those who got hold of the idea made any use of it. What Darwin did was to follow the clue which Malthus gave him, to realise, first by genius and afterwards by patience, how the complex and subtle struggle for existence works out a natural selection of those organisms which vary in the direction of fitter adaptation to the conditions of their life. So much success attended his application of the Selection-formula that for a time he regarded Natural Selection as almost the sole factor in evolution, variations being pre- supposed; gradually, however, he came to recognise that there was some validity in the factors which had been emphasized by Lamarck and by Buffon, and in his well-known summing up in the sixth edition of the “Origin” he says of the transformation of species: “This has been effected chiefly through the natural selection of numerous successive, slight, favourable variations; aided in an important manner by the inherited effects of the use and disuse of parts; and in an unimportant manner, that is, in relation to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us in our ignorance to arise spontaneously.”
To sum up: the idea of organic evolution, older than Aristotle, slowly developed from the stage of suggestion to the stage of verification, and the first convincing verification was Darwin’s; from being an a priori anticipation it has become an interpretation of nature, and Darwin is still the chief interpreter; from being a modal interpretation it has advanced to the rank of a causal theory, the most convincing part of which men will never cease to call Darwinism.
III. THE SELECTION THEORY
By August Weismann.
Professor of Zoology in the University of Freiburg (Baden).
I. THE IDEA OF SELECTION.
Many and diverse were the discoveries made by Charles Darwin in the course of a long and strenuous life, but none of them has had so far-reaching an influence on the science and thought of his time as the theory of selection. I do not believe that the theory of evolution would have made its way so easily and so quickly after Darwin took up the cudgels in favour of it, if he had not been able to support it by a principle which was capable of solving, in a simple manner, the greatest riddle that living nature presents to us,–I mean the purposiveness of every living form relative to the conditions of its life and its marvellously exact adaptation to these.
Everyone knows that Darwin was not alone in discovering the principle of selection, and that the same idea occurred simultaneously and independently to Alfred Russel Wallace. At the memorable meeting of the Linnean Society on 1st July, 1858, two papers were read (communicated by Lyell and Hooker) both setting forth the same idea of selection. One was written by Charles Darwin in Kent, the other by Alfred Wallace in Ternate, in the Malay Archipelago. It was a splendid proof of the magnanimity of these two investigators, that they thus, in all friendliness and without envy, united in laying their ideas before a scientific tribunal: their names will always shine side by side as two of the brightest stars in the scientific sky.
But it is with Charles Darwin that I am here chiefly concerned, since this paper is intended to aid in the commemoration of the hundredth anniversary of his birth.
The idea of selection set forth by the two naturalists was at the time absolutely new, but it was also so simple that Huxley could say of it later, “How extremely stupid not to have thought of that.” As Darwin was led to the general doctrine of descent, not through the labours of his predecessors in the early years of the century, but by his own observations, so it was in regard to the principle of selection. He was struck by the innumerable cases of adaptation, as, for instance, that of the woodpeckers and tree-frogs to climbing, or the hooks and feather-like appendages of seeds, which aid in the distribution of plants, and he said to himself that an explanation of adaptations was the first thing to be sought for in attempting to formulate a theory of evolution.
But since adaptations point to CHANGES which have been undergone by the ancestral forms of existing species, it is necessary, first of all, to inquire how far species in general are VARIABLE. Thus Darwin’s attention was directed in the first place to the phenomenon of variability, and the use man has made of this, from very early times, in the breeding of his domesticated animals and cultivated plants. He inquired carefully how breeders set to work, when they wished to modify the structure and appearance of a species to their own ends, and it was soon clear to him that SELECTION FOR BREEDING PURPOSES played the chief part.
But how was it possible that such processes should occur in free nature? Who is here the breeder, making the selection, choosing out one individual to bring forth offspring and rejecting others? That was the problem that for a long time remained a riddle to him.
Darwin himself relates how illumination suddenly came to him. He had been reading, for his own pleasure, Malthus’ book on Population, and, as he had long known from numerous observations, that every species gives rise to many more descendants than ever attain to maturity, and that, therefore, the greater number of the descendants of a species perish without reproducing, the idea came to him that the decision as to which member of a species was to perish, and which was to attain to maturity and reproduction might not be a matter of chance, but might be determined by the constitution of the individuals themselves, according as they were more or less fitted for survival. With this idea the foundation of the theory of selection was laid.
In ARTIFICIAL SELECTION the breeder chooses out for pairing only such individuals as possess the character desired by him in a somewhat higher degree than the rest of the race. Some of the descendants inherit this character, often in a still higher degree, and if this method be pursued throughout several generations, the race is transformed in respect of that particular character.
NATURAL SELECTION depends on the same three factors as ARTIFICIAL SELECTION: on VARIABILITY, INHERITANCE, and SELECTION FOR BREEDING, but this last is here carried out not by a breeder but by what Darwin called the “struggle for existence.” This last factor is one of the special features of the Darwinian conception of nature. That there are carnivorous animals which take heavy toll in every generation of the progeny of the animals on which they prey, and that there are herbivores which decimate the plants in every generation had long been known, but it is only since Darwin’s time that sufficient attention has been paid to the facts that, in addition to this regular destruction, there exists between the members of a species a keen competition for space and food, which limits multiplication, and that numerous individuals of each species perish because of unfavourable climatic conditions. The “struggle for existence,” which Darwin regarded as taking the place of the human breeder in free nature, is not a direct struggle between carnivores and their prey, but is the assumed competition for survival between individuals OF THE SAME species, of which, on an average, only those survive to reproduce which have the greatest power of resistance, while the others, less favourably constituted, perish early. This struggle is so keen, that, within a limited area, where the conditions of life have long remained unchanged, of every species, whatever be the degree of fertility, only two, ON AN AVERAGE, of the descendants of each pair survive; the others succumb either to enemies, or to disadvantages of climate, or to accident. A high degree of fertility is thus not an indication of the special success of a species, but of the numerous dangers that have attended its evolution. Of the six young brought forth by a pair of elephants in the course of their lives only two survive in a given area; similarly, of the millions of eggs which two thread-worms leave behind them only two survive. It is thus possible to estimate the dangers which threaten a species by its ratio of elimination, or, since this cannot be done directly, by its fertility.
Although a great number of the descendants of each generation fall victims to accident, among those that remain it is still the greater or lesser fitness of the organism that determines the “selection for breeding purposes,” and it would be incomprehensible if, in this competition, it were not ultimately, that is, on an average, the best equipped which survive, in the sense of living long enough to reproduce.
Thus the principle of natural selection is THE SELECTION OF THE BEST FOR REPRODUCTION, whether the “best” refers to the whole constitution, to one or more parts of the organism, or to one or more stages of development. Every organ, every part, every character of an animal, fertility and intelligence included, must be improved in this manner, and be gradually brought up in the course of generations to its highest attainable state of perfection. And not only may improvement of parts be brought about in this way, but new parts and organs may arise, since, through the slow and minute steps of individual or “fluctuating” variations, a part may be added here or dropped out there, and thus something new is produced.
The principle of selection solved the riddle as to how what was purposive could conceivably be brought about without the intervention of a directing power, the riddle which animate nature presents to our intelligence at every turn, and in face of which the mind of a Kant could find no way out, for he regarded a solution of it as not to be hoped for. For, even if we were to assume an evolutionary force that is continually transforming the most primitive and the simplest forms of life into ever higher forms, and the homogeneity of primitive times into the infinite variety of the present, we should still be unable to infer from this alone how each of the numberless forms adapted to particular conditions of life should have appeared PRECISELY AT THE RIGHT MOMENT IN THE HISTORY OF THE EARTH to which their adaptations were appropriate, and precisely at the proper place in which all the conditions of life to which they were adapted occurred: the humming-birds at the same time as the flowers; the trichina at the same time as the pig; the bark-coloured moth at the same time as the oak, and the wasp-like moth at the same time as the wasp which protects it. Without processes of selection we should be obliged to assume a “pre-established harmony” after the famous Leibnitzian model, by means of which the clock of the evolution of organisms is so regulated as to strike in exact synchronism with that of the history of the earth! All forms of life are strictly adapted to the conditions of their life, and can persist under these conditions alone.
There must therefore be an intrinsic connection between the conditions and the structural adaptations of the organism, and, SINCE THE CONDITIONS OF LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE ADAPTATIONS MUST BE CALLED FORTH BY THE CONDITIONS.
The selection theory teaches us how this is conceivable, since it enables us to understand that there is a continual production of what is non- purposive as well as of what is purposive, but the purposive alone survives, while the non-purposive perishes in the very act of arising. This is the old wisdom taught long ago by Empedocles.
II. THE LAMARCKIAN PRINCIPLE.
Lamarck, as is well known, formulated a definite theory of evolution at the beginning of the nineteenth century, exactly fifty years before the Darwin- Wallace principle of selection was given to the world. This brilliant investigator also endeavoured to support his theory by demonstrating forces which might have brought about the transformations of the organic world in the course of the ages. In addition to other factors, he laid special emphasis on the increased or diminished use of the parts of the body, assuming that the strengthening or weakening which takes place from this cause during the individual life, could be handed on to the offspring, and thus intensified and raised to the rank of a specific character. Darwin also regarded this LAMARCKIAN PRINCIPLE, as it is now generally called, as a factor in evolution, but he was not fully convinced of the transmissibility of acquired characters.
As I have here to deal only with the theory of selection, I need not discuss the Lamarckian hypothesis, but I must express my opinion that there is room for much doubt as to the cooperation of this principle in evolution. Not only is it difficult to imagine how the transmission of functional modifications could take place, but, up to the present time, notwithstanding the endeavours of many excellent investigators, not a single actual proof of such inheritance has been brought forward. Semon’s experiments on plants are, according to the botanist Pfeffer, not to be relied on, and even the recent, beautiful experiments made by Dr Kammerer on salamanders, cannot, as I hope to show elsewhere, be regarded as proof, if only because they do not deal at all with functional modifications, that is, with modifications brought about by use, and it is to these ALONE that the Lamarckian principle refers.
III. OBJECTIONS TO THE THEORY OF SELECTION.
(a) Saltatory evolution.
The Darwinian doctrine of evolution depends essentially on THE CUMULATIVE AUGMENTATION of minute variations in the direction of utility. But can such minute variations, which are undoubtedly continually appearing among the individuals of the same species, possess any selection-value; can they determine which individuals are to survive, and which are to succumb; can they be increased by natural selection till they attain to the highest development of a purposive variation?
To many this seems so improbable that they have urged a theory of evolution by leaps from species to species. Kolliker, in 1872, compared the evolution of species with the processes which we can observe in the individual life in cases of alternation of generations. But a polyp only gives rise to a medusa because it has itself arisen from one, and there can be no question of a medusa ever having arisen suddenly and de novo from a polyp-bud, if only because both forms are adapted in their structure as a whole, and in every detail to the conditions of their life. A sudden origin, in a natural way, of numerous adaptations is inconceivable. Even the degeneration of a medusoid from a free-swimming animal to a mere brood- sac (gonophore) is not sudden and saltatory, but occurs by imperceptible modifications throughout hundreds of years, as we can learn from the numerous stages of the process of degeneration persisting at the same time in different species.
If, then, the degeneration to a simple brood-sac takes place only by very slow transitions, each stage of which may last for centuries, how could the much more complex ASCENDING evolution possibly have taken place by sudden leaps? I regard this argument as capable of further extension, for wherever in nature we come upon degeneration, it is taking place by minute steps and with a slowness that makes it not directly perceptible, and I believe that this in itself justifies us in concluding that THE SAME MUST BE TRUE OF ASCENDING evolution. But in the latter case the goal can seldom be distinctly recognised while in cases of degeneration the starting-point of the process can often be inferred, because several nearly related species may represent different stages.
In recent years Bateson in particular has championed the idea of saltatory, or so-called discontinuous evolution, and has collected a number of cases in which more or less marked variations have suddenly appeared. These are taken for the most part from among domesticated animals which have been bred and crossed for a long time, and it is hardly to be wondered at that their much mixed and much influenced germ-plasm should, under certain conditions, give rise to remarkable phenomena, often indeed producing forms which are strongly suggestive of monstrosities, and which would undoubtedly not survive in free nature, unprotected by man. I should regard such cases as due to an intensified germinal selection–though this is to anticipate a little–and from this point of view it cannot be denied that they have a special interest. But they seem to me to have no significance as far as the transformation of species is concerned, if only because of the extreme rarity of their occurrence.
There are, however, many variations which have appeared in a sudden and saltatory manner, and some of these Darwin pointed out and discussed in detail: the copper beech, the weeping trees, the oak with “fern-like leaves,” certain garden-flowers, etc. But none of them have persisted in free nature, or evolved into permanent types.
On the other hand, wherever enduring types have arisen, we find traces of a gradual origin by successive stages, even if, at first sight, their origin may appear to have been sudden. This is the case with SEASONAL DIMORPHISM, the first known cases of which exhibited marked differences between the two generations, the winter and the summer brood. Take for instance the much discussed and studied form Vanessa (Araschnia) levana-prorsa. Here the differences between the two forms are so great and so apparently disconnected, that one might almost believe it to be a sudden mutation, were it not that old transition-stages can be called forth by particular temperatures, and we know other butterflies, as for instance our Garden Whites, in which the differences between the two generations are not nearly so marked; indeed, they are so little apparent that they are scarcely likely to be noticed except by experts. Thus here again there are small initial steps, some of which, indeed, must be regarded as adaptations, such as the green-sprinkled or lightly tinted under-surface which gives them a deceptive resemblance to parsley or to Cardamine leaves.
Even if saltatory variations do occur, we cannot assume that these HAVE EVER LED TO FORMS WHICH ARE CAPABLE OF SURVIVAL UNDER THE CONDITIONS OF WILD LIFE. Experience has shown that in plants which have suddenly varied the power of persistence is diminished. Korschinksky attributes to them weaknesses of organisation in general; “they bloom late, ripen few of their seeds, and show great sensitiveness to cold.” These are not the characters which make for success in the struggle for existence.
We must briefly refer here to the views–much discussed in the last decade –of H. de Vries, who believes that the roots of transformation must be sought for in SALTATORY VARIATIONS ARISING FROM INTERNAL CAUSES, and distinguishes such MUTATIONS, as he has called them, from ordinary individual variations, in that they breed true, that is, with strict inbreeding they are handed on pure to the next generation. I have elsewhere endeavoured to point out the weaknesses of this theory (“Vortrage uber Descendenztheorie”, Jena, 1904, II. 269. English Translation London, 1904, II. page 317.), and I am the less inclined to return to it here that it now appears (See Poulton, “Essays on Evolution”, Oxford, 1908, pages xix-xxii.) that the far-reaching conclusions drawn by de Vries from his observations on the Evening Primrose, Oenothera lamarckiana, rest upon a very insecure foundation. The plant from which de Vries saw numerous “species”–his “mutations”–arise was not, as he assumed, a WILD SPECIES that had been introduced to Europe from America, but was probably a hybrid form which was first discovered in the Jardin des Plantes in Paris, and which does not appear to exist anywhere in America as a wild species.
This gives a severe shock to the “Mutation theory,” for the other ACTUALLY WILD species with which de Vries experimented showed no “mutations” but yielded only negative results.
Thus we come to the conclusion that Darwin (“Origin of Species” (6th edition), pages 176 et seq.) was right in regarding transformations as taking place by minute steps, which, if useful, are augmented in the course of innumerable generations, because their possessors more frequently survive in the struggle for existence.
(b) SELECTION-VALUE OF THE INITIAL STEPS.
Is it possible that the significant deviations which we know as “individual variations” can form the beginning of a process of selection? Can they decide which is to perish and which to survive? To use a phrase of Romanes, can they have SELECTION-VALUE?
Darwin himself answered this question, and brought together many excellent examples to show that differences, apparently insignificant because very small, might be of decisive importance for the life of the possessor. But it is by no means enough to bring forward cases of this kind, for the question is not merely whether finished adaptations have selection-value, but whether the first beginnings of these, and whether the small, I might almost say minimal increments, which have led up from these beginnings to the perfect adaptation, have also had selection-value. To this question even one who, like myself, has been for many years a convinced adherent of the theory of selection, can only reply: WE MUST ASSUME SO, BUT WE CANNOT PROVE IT IN ANY CASE. It is not upon demonstrative evidence that we rely when we champion the doctrine of selection as a scientific truth; we base our argument on quite other grounds. Undoubtedly there are many apparently insignificant features, which can nevertheless be shown to be adaptations– for instance, the thickness of the basin-shaped shell of the limpets that live among the breakers on the shore. There can be no doubt that the thickness of these shells, combined with their flat form, protects the animals from the force of the waves breaking upon them,–but how have they become so thick? What proportion of thickness was sufficient to decide that of two variants of a limpet one should survive, the other be eliminated? We can say nothing more than that we infer from the present state of the shell, that it must have varied in regard to differences in shell-thickness, and that these differences must have had selection-value, –no proof therefore, but an assumption which we must show to be convincing.
For a long time the marvellously complex RADIATE and LATTICE-WORK skeletons of Radiolarians were regarded as a mere outflow of “Nature’s infinite wealth of form,” as an instance of a purely morphological character with no biological significance. But recent investigations have shown that these, too, have an adaptive significance (Hacker). The same thing has been shown by Schutt in regard to the lowly unicellular plants, the Peridineae, which abound alike on the surface of the ocean and in its depths. It has been shown that the long skeletal processes which grow out from these organisms have significance not merely as a supporting skeleton, but also as an extension of the superficial area, which increases the contact with the water-particles, and prevents the floating organisms from sinking. It has been established that the processes are considerably shorter in the colder layers of the ocean, and that they may be twelve times as long (Chun, “Reise der Valdivia”, Leipzig, 1904.) in the warmer layers, thus corresponding to the greater or smaller amount of friction which takes place in the denser and less dense layers of the water.
The Peridineae of the warmer ocean layers have thus become long-rayed, those of the colder layers short-rayed, not through the direct effect of friction on the protoplasm, but through processes of selection, which favoured the longer rays in warm water, since they kept the organism afloat, while those with short rays sank and were eliminated. If we put the question as to selection-value in this case, and ask how great the variations in the length of processes must be in order to possess selection-value; what can we answer except that these variations must have been minimal, and yet sufficient to prevent too rapid sinking and consequent elimination? Yet this very case would give the ideal opportunity for a mathematical calculation of the minimal selection-value, although of course it is not feasible from lack of data to carry out the actual calculation.
But even in organisms of more than microscopic size there must frequently be minute, even microscopic differences which set going the process of selection, and regulate its progress to the highest possible perfection.
Many tropical trees possess thick, leathery leaves, as a protection against the force of the tropical rain drops. The DIRECT influence of the rain cannot be the cause of this power of resistance, for the leaves, while they were still thin, would simply have been torn to pieces. Their toughness must therefore be referred to selection, which would favour the trees with slightly thicker leaves, though we cannot calculate with any exactness how great the first stages of increase in thickness must have been. Our hypothesis receives further support from the fact that, in many such trees, the leaves are drawn out into a beak-like prolongation (Stahl and Haberlandt) which facilitates the rapid falling off of the rain water, and also from the fact that the leaves, while they are still young, hang limply down in bunches which offer the least possible resistance to the rain. Thus there are here three adaptations which can only be interpreted as due to selection. The initial stages of these adaptations must undoubtedly have had selection-value.
But even in regard to this case we are reasoning in a circle, not giving “proofs,” and no one who does not wish to believe in the selection-value of the initial stages can be forced to do so. Among the many pieces of presumptive evidence a particularly weighty one seems to me to be THE SMALLNESS OF THE STEPS OF PROGRESS which we can observe in certain cases, as for instance in leaf-imitation among butterflies, and in mimicry generally. The resemblance to a leaf, for instance of a particular Kallima, seems to us so close as to be deceptive, and yet we find in another individual, or it may be in many others, a spot added which increases the resemblance, and which could not have become fixed unless the increased deceptiveness so produced had frequently led to the overlooking of its much persecuted possessor. But if we take the selection-value of the initial stages for granted, we are confronted with the further question which I myself formulated many years ago: How does it happen THAT THE NECESSARY BEGINNINGS OF A USEFUL VARIATION ARE ALWAYS PRESENT? How could insects which live upon or among green leaves become all green, while those that live on bark become brown? How have the desert animals become yellow and the Arctic animals white? Why were the necessary variations always present? How could the green locust lay brown eggs, or the privet caterpillar develop white and lilac-coloured lines on its green skin?
It is of no use answering to this that the question is wrongly formulated (Plate, “Selektionsprinzip u. Probleme der Artbildung” (3rd edition), Leipzig, 1908.) and that it is the converse that is true; that the process of selection takes place in accordance with the variations that present themselves. This proposition is undeniably true, but so also is another, which apparently negatives it: the variation required has in the majority of cases actually presented itself. Selection cannot solve this contradiction; it does not call forth the useful variation, but simply works upon it. The ultimate reason why one and the same insect should occur in green and in brown, as often happens in caterpillars and locusts, lies in the fact that variations towards brown presented themselves, and so also did variations towards green: THE KERNEL OF THE RIDDLE LIES IN THE VARYING, and for the present we can only say, that small variations in different directions present themselves in every species. Otherwise so many different kinds of variations could not have arisen. I have endeavoured to explain this remarkable fact by means of the intimate processes that must take place within the germ-plasm, and I shall return to the problem when dealing with “germinal selection.”
We have, however, to make still greater demands on variation, for it is not enough that the necessary variation should occur in isolated individuals, because in that case there would be small prospect of its being preserved, notwithstanding its utility. Darwin at first believed, that even single variations might lead to transformation of the species, but later he became convinced that this was impossible, at least without the cooperation of other factors, such as isolation and sexual selection.
In the case of the GREEN CATERPILLARS WITH BRIGHT LONGITUDINAL STRIPES, numerous individuals exhibiting this useful variation must have been produced to start with. In all higher, that is, multicellular organisms, the germ-substance is the source of all transmissible variations, and this germ-plasm is not a simple substance but is made up of many primary constituents. The question can therefore be more precisely stated thus: How does it come about that in so many cases the useful variations present themselves in numbers just where they are required, the white oblique lines in the leaf-caterpillar on the under surface of the body, the accompanying coloured stripes just above them? And, further, how has it come about that in grass caterpillars, not oblique but longitudinal stripes, which are more effective for concealment among grass and plants, have been evolved? And finally, how is it that the same Hawk-moth caterpillars, which to-day show oblique stripes, possessed longitudinal stripes in Tertiary times? We can read this fact from the history of their development, and I have before attempted to show the biological significance of this change of colour. (“Studien zur Descendenz-Theorie” II., “Die Enstehung der Zeichnung bei den Schmetterlings-raupen,” Leipzig, 1876.)
For the present I need only draw the conclusion that one and the same caterpillar may exhibit the initial stages of both, and that it depends on the manner in which these marking elements are INTENSIFIED and COMBINED by natural selection whether whitish longitudinal or oblique stripes should result. In this case then the “useful variations” were actually “always there,” and we see that in the same group of Lepidoptera, e.g. species of Sphingidae, evolution has occurred in both directions according to whether the form lived among grass or on broad leaves with oblique lateral veins, and we can observe even now that the species with oblique stripes have longitudinal stripes when young, that is to say, while the stripes have no biological significance. The white places in the skin which gave rise, probably first as small spots, to this protective marking could be combined in one way or another according to the requirements of the species. They must therefore either have possessed selection-value from the first, or, if this was not the case at their earliest occurrence, there must have been SOME OTHER FACTORS which raised them to the point of selection-value. I shall return to this in discussing germinal selection. But the case may be followed still farther, and leads us to the same alternative on a still more secure basis.
Many years ago I observed in caterpillars of Smerinthus populi (the poplar hawk-moth), which also possess white oblique stripes, that certain individuals showed RED SPOTS above these stripes; these spots occurred only on certain segments, and never flowed together to form continuous stripes. In another species (Smerinthus tiliae) similar blood-red spots unite to form a line-like coloured seam in the last stage of larval life, while in S. ocellata rust-red spots appear in individual caterpillars, but more rarely than in S. Populi, and they show no tendency to flow together.
Thus we have here the origin of a new character, arising from small beginnings, at least in S. tiliae, in which species the coloured stripes are a normal specific character. In the other species, S. populi and S. ocellata, we find the beginnings of the same variation, in one more rarely than in the other, and we can imagine that, in the course of time, in these two species, coloured lines over the oblique stripes will arise. In any case these spots are the elements of variation, out of which coloured lines MAY be evolved, if they are combined in this direction through the agency of natural selection. In S. populi the spots are often small, but sometimes it seems as though several had united to form large spots. Whether a process of selection in this direction will arise in S. populi and S. ocellata, or whether it is now going on cannot be determined, since we cannot tell in advance what biological value the marking might have for these two species. It is conceivable that the spots may have no selection- value as far as these species are concerned, and may therefore disappear again in the course of phylogeny, or, on the other hand, that they may be changed in another direction, for instance towards imitation of the rust- red fungoid patches on poplar and willow leaves. In any case we may regard the smallest spots as the initial stages of variation, the larger as a cumulative summation of these. Therefore either these initial stages must already possess selection-value, or, as I said before: THERE MUST BE SOME OTHER REASON FOR THEIR CUMULATIVE SUMMATION. I should like to give one more example, in which we can infer, though we cannot directly observe, the initial stages.
All the Holothurians or sea-cucumbers have in the skin calcareous bodies of different forms, usually thick and irregular, which make the skin tough and resistant. In a small group of them–the species of Synapta–the calcareous bodies occur in the form of delicate anchors of microscopic size. Up till 1897 these anchors, like many other delicate microscopic structures, were regarded as curiosities, as natural marvels. But a Swedish observer, Oestergren, has recently shown that they have a biological significance: they serve the footless Synapta as auxiliary organs of locomotion, since, when the body swells up in the act of creeping, they press firmly with their tips, which are embedded in the skin, against the substratum on which the animal creeps, and thus prevent slipping backwards. In other Holothurians this slipping is made impossible by the fixing of the tube-feet. The anchors act automatically, sinking their tips towards the ground when the corresponding part of the body thickens, and returning to the original position at an angle of 45 degrees to the upper surface when the part becomes thin again. The arms of the anchor do not lie in the same plane as the shaft, and thus the curve of the arms forms the outermost part of the anchor, and offers no further resistance to the gliding of the animal. Every detail of the anchor, the curved portion, the little teeth at the head, the arms, etc., can be interpreted in the most beautiful way, above all the form of the anchor itself, for the two arms prevent it from swaying round to the side. The position of the anchors, too, is definite and significant; they lie obliquely to the longitudinal axis of the animal, and therefore they act alike whether the animal is creeping backwards or forwards. Moreover, the tips would pierce through the skin if the anchors lay in the longitudinal direction. Synapta burrows in the sand; it first pushes in the thin anterior end, and thickens this again, thus enlarging the hole, then the anterior tentacles displace more sand, the body is worked in a little farther, and the process begins anew. In the first act the anchors are passive, but they begin to take an active share in the forward movement when the body is contracted again. Frequently the animal retains only the posterior end buried in the sand, and then the anchors keep it in position, and make rapid withdrawal possible.
Thus we have in these apparently random forms of the calcareous bodies, complex adaptations in which every little detail as to direction, curve, and pointing is exactly determined. That they have selection-value in their present perfected form is beyond all doubt, since the animals are enabled by means of them to bore rapidly into the ground and so to escape from enemies. We do not know what the initial stages were, but we cannot doubt that the little improvements, which occurred as variations of the originally simple slimy bodies of the Holothurians, were preserved because they already possessed selection-value for the Synaptidae. For such minute microscopic structures whose form is so delicately adapted to the role they have to play in the life of the animal, cannot have arisen suddenly and as a whole, and every new variation of the anchor, that is, in the direction of the development of the two arms, and every curving of the shaft which prevented the tips from projecting at the wrong time, in short, every little adaptation in the modelling of the anchor must have possessed selection-value. And that such minute changes of form fall within the sphere of fluctuating variations, that is to say, THAT THEY OCCUR is beyond all doubt.
In many of the Synaptidae the anchors are replaced by calcareous rods bent in the form of an S, which are said to act in the same way. Others, such as those of the genus Ankyroderma, have anchors which project considerably beyond the skin, and, according to Oestergren, serve “to catch plant- particles and other substances” and so mask the animal. Thus we see that in the Synaptidae the thick and irregular calcareous bodies of the Holothurians have been modified and transformed in various ways in adaptation to the footlessness of these animals, and to the peculiar conditions of their life, and we must conclude that the earlier stages of these changes presented themselves to the processes of selection in the form of microscopic variations. For it is as impossible to think of any origin other than through selection in this case as in the case of the toughness, and the “drip-tips” of tropical leaves. And as these last could not have been produced directly by the beating of the heavy rain-drops upon them, so the calcareous anchors of Synapta cannot have been produced directly by the friction of the sand and mud at the bottom of the sea, and, since they are parts whose function is PASSIVE the Lamarckian factor of use and disuse does not come into question. The conclusion is unavoidable, that the microscopically small variations of the calcareous bodies in the ancestral forms have been intensified and accumulated in a particular direction, till they have led to the formation of the anchor. Whether this has taken place by the action of natural selection alone, or whether the laws of variation and the intimate processes within the germ-plasm have cooperated will become clear in the discussion of germinal selection. This whole process of adaptation has obviously taken place within the time that has elapsed since this group of sea-cucumbers lost their tube-feet, those characteristic organs of locomotion which occur in no group except the Echinoderms, and yet have totally disappeared in the Synaptidae. And after all what would animals that live in sand and mud do with tube-feet?
Darwin pointed out that one of the essential differences between artificial and natural selection lies in the fact that the former can modify only a few characters, usually only one at a time, while Nature preserves in the struggle for existence all the variations of a species, at the same time and in a purely mechanical way, if they possess selection-value.
Herbert Spencer, though himself an adherent of the theory of selection, declared in the beginning of the nineties that in his opinion the range of this principle was greatly over-estimated, if the great changes which have taken place in so many organisms in the course of ages are to be interpreted as due to this process of selection alone, since no transformation of any importance can be evolved by itself; it is always accompanied by a host of secondary changes. He gives the familiar example of the Giant Stag of the Irish peat, the enormous antlers of which required not only a much stronger skull cap, but also greater strength of the sinews, muscles, nerves and bones of the whole anterior half of the animal, if their mass was not to weigh down the animal altogether. It is inconceivable, he says, that so many processes of selection should take place SIMULTANEOUSLY, and we are therefore forced to fall back on the Lamarckian factor of the use and disuse of functional parts. And how, he asks, could natural selection follow two opposite directions of evolution in different parts of the body at the same time, as for instance in the case of the kangaroo, in which the forelegs must have become shorter, while the hind legs and the tail were becoming longer and stronger?
Spencer’s main object was to substantiate the validity of the Lamarckian principle, the cooperation of which with selection had been doubted by many. And it does seem as though this principle, if it operates in nature at all, offers a ready and simple explanation of all such secondary variations. Not only muscles, but nerves, bones, sinews, in short all tissues which function actively, increase in strength in proportion as they are used, and conversely they decrease when the claims on them diminish. All the parts, therefore, which depend on the part that varied first, as for instance the enlarged antlers of the Irish Elk, must have been increased or decreased in strength, in exact proportion to the claims made upon them,–just as is actually the case.
But beautiful as this explanation would be, I regard it as untenable, because it assumes the TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS (so- called “acquired” characters), and this is not only undemonstrable, but is scarcely theoretically conceivable, for the secondary variations which accompany or follow the first as correlative variations, occur also in cases in which the animals concerned are sterile and THEREFORE CANNOT TRANSMIT ANYTHING TO THEIR DESCENDANTS. This is true of WORKER BEES, and particularly of ANTS, and I shall here give a brief survey of the present state of the problem as it appears to me.
Much has been written on both sides of this question since the published controversy on the subject in the nineties between Herbert Spencer and myself. I should like to return to the matter in detail, if the space at my disposal permitted, because it seems to me that the arguments I advanced at that time are equally cogent to-day, notwithstanding all the objections