The Project Gutenberg eBook, Charles Darwin and the Theory of Natural Selection, by Sir Edward Bagnall Poulton

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THE CENTURY SCIENCE SERIES

Edited by SIR HENRY E. ROSCOE, D.C.L., LL.D., F.R.S.

CHARLES DARWIN
AND THE
THEORY OF NATURAL SELECTION

The Century Science Series.

EDITED BY

SIR HENRY E. ROSCOE, D.C.L., F.R.S.

John Dalton and the Rise of Modern Chemistry.

By Sir Henry E. Roscoe, F.R.S., &c.

Major Rennell, F.R.S., and the Rise of Modern English Geography.

By Sir Clements R. Markham, C.B., F.R.S., President of the Royal Geographical Society.

Justus von Liebig: his Life and Work (1803–1873).

By W. A. Shenstone, F.I.C., Lecturer on Chemistry in Clifton College.

The Herschels and Modern Astronomy.

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Charles Lyell and Modern Geology.

By Professor T. G. Bonney, F.R.S., &c.

James Clerk Maxwell and Modern Physics.

By R. T. Glazebrook, F.R.S., Fellow of Trinity College, Cambridge.

Humphry Davy, Poet and Philosopher.

By T. E. Thorpe, LL.D., F.R.S.

Charles Darwin and the Theory of Natural Selection.

By Edward B. Poulton, M.A., F.R.S., Hope Professor of Zoology at the University of Oxford, &c.

In Preparation.

Michael Faraday: his Life and Work.

By Professor Silvanus P. Thompson, F.R.S.

Pasteur: his Life and Work.

By M. Armand Ruffer, M.D., Director of the British Institute of Preventive Medicine.

Hermann von Helmholtz.

By A. W. Rücker, F.R.S., Professor of Physics in the Royal College of Science, London.

CASSELL & COMPANY, Limited, London; Paris & Melbourne.

Photo by Mr. James C. Christie, F.G.S., Glasgow.

STATUE OF CHARLES DARWIN.

(By Boehm.)

CENTRAL HALL OF THE BRITISH MUSEUM OF NATURAL HISTORY.

THE CENTURY SCIENCE SERIES

Charles Darwin
AND THE
THEORY OF NATURAL SELECTION

BY
EDWARD B. POULTON
M.A., F.R.S., F.G.S., F.L.S., ETC.

HOPE PROFESSOR OF ZOOLOGY AT THE UNIVERSITY OF OXFORD
CORRESP. MEMB. OF THE NEW YORK ACADEMY OF SCIENCES
CORRESP. MEMB. OF THE BOSTON SOCIETY OF NAT. HIST.

CASSELL and COMPANY, Limited
LONDON, PARIS & MELBOURNE
1896
ALL RIGHTS RESERVED

INTRODUCTION

In the following pages I have tried to express a sense of the greatness of my subject by simplicity and directness of statement. The limits of the work necessarily prevented any detailed treatment, the subject of the work prevented originality. We have had the great “Life and Letters” with us for nine years, and this I have used as a mine, extracting what I believed to be the statements of chief importance for the work in hand, and grouping them so as to present what I hope is a connected account of Darwin’s life, when considered in relation to his marvellous work; and especially to the great central discovery of Natural Selection and its exposition in the “Origin of Species.”

In addition to the invaluable volumes which we owe to the industry, taste, and skill of Francis Darwin, an immense number of other works have been consulted. We live in an age of writing, and of speeches and addresses; and the many sides of Darwin’s life and work have again and again inspired the ablest men of our time to write and speak their best—a justification for the freedom with which quotations are spread over the following pages.

It is my pleasant duty to express my hearty thanks to many kind friends who have helped in the production of this little work. Mr. Francis Darwin has kindly permitted the use of many of Darwin’s letters, which have not as yet been published, and he has given me valuable information and criticism on many points. I have also gained much by discussion and correspondence with my friends Dr. A. R. Wallace, Professor E. Ray Lankester, and Professor Meldola. The latter has freely given me the use of his valuable series of letters; and I owe to my friend, Mr. Rowland H. Wedgwood, the opportunity of publishing a single letter of very great interest.

The greater part of the volume formed the subject of two short courses of lectures delivered in the Hope Department of the Oxford University Museum in Michaelmas Term 1894 and Lent Term 1895.

Edward B. Poulton.

Oxford, October, 1896.

CONTENTS

Charles Darwin
AND THE
THEORY OF NATURAL SELECTION.

CHAPTER I.
THE SECRET OF DARWIN’S GREATNESS.

Charles Robert Darwin was born at Shrewsbury on February 12th, 1809, the year which witnessed the birth of Alfred Tennyson, W. E. Gladstone, and Abraham Lincoln.

Oliver Wendell Holmes, born in the same year, delighted to speak of the good company in which he came into the world. On January 27th, 1894, I had the great pleasure of sitting next to him at a dinner of the Saturday Club in Boston, and he then spoke of the subject with the same enthusiasm with which he deals with it in his writings; mentioning the four distinguished names, and giving a brief epigrammatic description of each with characteristic felicity. Dr. Holmes further said that he remembered with much satisfaction an occasion on which he was able to correct Darwin on a matter of scientific fact. He could not remember the details, but we may hope for their ultimate recovery, for he said that Darwin had written a courteous reply accepting the correction.

HIS FAMILY.

Charles Darwin’s grandfather, Erasmus Darwin (1731–1802), was a man of great genius. He speculated upon the origin of species, and arrived at views which were afterwards independently enunciated by Lamarck. He resembled this great zoologist in fertility of imagination, and also in the boldness with which he put forward suggestions, many of which were crude and entirely untested by an appeal to facts. The poetical form in which a part of his work was written was, doubtless, largely due to the traditions and customs of the age in which he lived.

Robert Waring (1766–1848), the father of Charles Darwin, was the second son of Erasmus. He married a daughter of the great Josiah Wedgwood. Although his mother died when he was only eight years old, and Darwin remembered very little of her, there is evidence that she directed his attention to Nature (“Autobiography,” p. 28, footnote). Dr. Darwin followed his father’s profession, commencing a very successful medical practice at Shrewsbury before he was twenty-one. He was a man of great penetration, especially in the discernment of character—a power which was of the utmost value to him in his profession. Dr. Darwin had two sons and four daughters: Charles was the younger son and fourth child, his brother Erasmus being the third.

Even in this mere outline there is evidence of hereditary genius in the Darwin family—evidence which becomes irresistible when all available details of every member of the family are brought together, as they are in the great “Life and Letters.” When it is further remembered that two of Charles Darwin’s sons have achieved distinction as scientific investigators, it will be admitted that the history of the family affords a most striking example of hereditary intellectual power.

There is nothing in this history to warrant the belief that the nature and direction of hereditary genius receive any bias from the line of intellectual effort pursued by a parent. We recognise the strongest evidence for hereditary capacity, but none at all for the transmission of results which follow the employment of capacity. Thus Erasmus inherited high intellectual power, with a bias entirely different from that of his younger brother Charles—his interests being literary and artistic rather than scientific. The wide difference between the brothers seems to have made a great impression upon Charles, for he wrote:—

“Our minds and tastes were, however, so different, that I do not think I owe much to him intellectually. I am inclined to agree with Francis Galton in believing that education and environment produce only a small effect on the mind of anyone, and that most of our qualities are innate” (“Life and Letters,” 1887, p. 22).

Equally significant is the fact that Professor George Darwin’s important researches in mathematics have been applied to astronomy—subjects which were not pursued by his father.

CHARACTER AND POWERS.

It appears probable that Charles Darwin’s unique power was largely due to the inheritance of the imagination of his grandfather combined with the acute observation of his father. Although he possessed an even larger share of both these qualities than his predecessors, it is probable that he owed more to their co-operation than to the high degree of their development.

It is a common error to suppose that the intellectual powers which make the poet or the historian are essentially different from those which make the man of science. Powers of observation, however acute, could never make a scientific discoverer; for discovery requires the creative effort of the imagination. The scientific man does not stumble upon new facts or conclusions by accident; he finds what he looks for. The problem before him is essentially similar to that of the historian who tries to create an accurate and complete picture of an epoch out of scattered records of contemporary impressions more or less true, and none wholly true. Fertility of imagination is absolutely essential for that step from the less to the more perfectly known which we call discovery.

But fertility of imagination alone is insufficient for the highest achievement in poetry, history, or science; for in all these subjects the strictest self-criticism and the soundest judgment are necessary in order to ensure that the results are an advance in the direction of the truth. A delicately-adjusted balance between the powers of imagination and the powers which hold imagination in check, is essential in the historian who is to provide us with a picture of a past age, which explains the mistaken impression gained by a more or less prejudiced observer who saw but a small part of it from a limited standpoint, and has handed down his impression to us. A poem which sheds new light upon the relation between mind and mind, requires to be tested and controlled by constant and correct observation, like a hypothesis in the domain of the natural sciences.

It is probable, then, that the secret of Darwin’s strength lay in the perfect balance between his powers of imagination and those of accurate observation, the creative efforts of the one being ever subjected to the most relentless criticism by the employment of the other. We shall never know, I have heard Professor Michael Foster say, the countless hypotheses which passed through the mind of Darwin, and which, however wild and improbable, were tested by an appeal to Nature, and were then dismissed for ever.

Darwin’s estimate of his own powers is given with characteristic candour and modesty in the concluding paragraph of his “Autobiography” (“Life and Letters,” 1887, p. 107):—

“Therefore 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.”

We also know from other sources that Darwin looked upon the creative powers as essential to scientific progress. Thus he wrote to Wallace in 1857: “I am a firm believer that without speculation there is no good and original observation.” He also says in the “Autobiography”: “I have steadily endeavoured to keep my mind free so as to give up any hypothesis, however much beloved (and I cannot resist forming one on every subject), as soon as facts are shown to be opposed to it.”

VALUE OF HYPOTHESIS.

I have thought it worth while to insist thus strongly on the high value attached by Darwin to hypothesis, controlled by observation, in view of certain recent attacks upon this necessary weapon for scientific advance. Thus Bateson, in his “Materials for the Study of Variation” (London, 1894), p. 7, says: “In the old time the facts of Nature were beautiful in themselves and needed not the rouge of speculation to quicken their charm, but that was long ago before Modern Science was born.” The author does not specify the period in the history of science when discovery proceeded without hypothesis. A study of the earlier volumes of the Philosophical Transactions reveals a far greater interest in speculation than in the facts of Nature. We can hardly call those ages anything but speculative which received with approval the suggestions that geese were developed from barnacles which grew upon trees; that swallows hibernated at the bottom of lakes; that the Trade-winds were due to the breath of a sea-weed. Bateson’s statement requires to be reversed in order to become correct. Modern science differs from the science of long ago in its greater attention to the facts of Nature and its more rigid control over the tendency to hypothesis; although hypothesis remains, and must ever remain, as the guide and inspirer of observation and the discovery of fact.[A] Although Darwin has kindled the imagination of hundreds of workers, and has thus been the cause of an immense amount of speculation, science owes him an even larger debt for the innumerable facts discovered under the guidance of this faculty.

CHAPTER II.
BOYHOOD—EDINBURGH—CAMBRIDGE (1817–31).

Of Darwin’s boyhood and school-life we only know the facts given in his brief “Autobiography,” written when he was sixty-seven, together with those collected by his son Francis and appended in the form of notes. He first went to Mr. Case’s day-school in Shrewsbury in 1817, the year of his mother’s death. At this time, although only eight years old, his interest in natural history and in collecting was well established. “The passion for collecting, which leads a man to be a systematic naturalist, a virtuoso, or a miser, was very strong in me, and was clearly innate, as none of my sisters or brother had this taste.”

In the following year he went to Dr. Butler’s school in Shrewsbury, where he remained seven years. He does not appear to have profited much by the classical instruction which at that time received almost exclusive attention. His interest seems to have been chiefly concentrated upon sport; but whenever a subject attracted him he worked hard at it, and it is probable that he would have conveyed a very different impression of his powers to the masters and his father if scientific subjects had been taught, as they are now to a moderate extent in many schools.

That he was a keen observer for his age is clear from the fact that, when he was only ten, he was much interested and surprised to notice that the insects he found on the Welsh coast were different from those in Shropshire. His most valuable education was received out of school hours—collecting, and working at chemistry with his brother Erasmus, although this latter study drew down upon him the rebukes of Dr. Butler for wasting time on such useless subjects.

AT EDINBURGH.

He was removed from school early, and in 1825 went to Edinburgh to study medicine—a subject for which he seemed to be unfitted by nature. The methods of instruction by lectures did not benefit him; he was disgusted at dissection, and could not endure to witness an operation. And yet here it was evident, as it became afterwards at Cambridge, that Darwin—although seeming to be by no means above the average when judged by ordinary standards—possessed in reality a very remarkable and attractive personality. There can be no other explanation of the impression he made upon distinguished men who were much older than himself, and the friendships he formed with those of his own age who were afterwards to become eminent.

Thus at Edinburgh he was well acquainted with Dr. Grant and Mr. Macgillivray, the curator of the museum, and worked at marine zoology in company with the former. Here, too, in 1826, he made his first scientific discovery, and read a paper before the Plinian Society, proving that so-called eggs of Flustra were in reality free-swimming larvæ. And it is evident from his “Autobiography” that he took every opportunity of hearing and learning about scientific subjects.

Darwin’s love of sport remained as keen as ever at this period and at Cambridge, and he speaks with especial enthusiasm of his visits in the autumn to Maer, the home of his uncle, Josiah Wedgwood, who afterwards exerted so important an influence upon his life.

AT CAMBRIDGE.

After Darwin had been at Edinburgh for two sessions, his father realised that he did not like the thought of the medical profession, and suggested that he should become a clergyman. With this intention he was sent to Cambridge in the beginning of 1828, after spending some months in recovering the classics he had learnt at school.

He joined Christ’s College, and passed his final examination in January, 1831, being tenth in the list of those who do not seek honours. The immense, and in many respects disastrous, development of the competitive examination system since that time has almost banished from our universities the type of student represented by Darwin—the man who takes the easiest road to a degree and obtains it with the minimum of effort, but who all the time is being benefited by residence, studying, without any thought of examinations, the subjects which are of special interest to him, and seeking personal contact with older men who have reached the highest eminence in those subjects.

He seems to have led a somewhat double life at Cambridge, his intense love of sport taking him into a pleasure-loving set, while his intellectual interests made him the intimate friend of Whitley, who became Senior Wrangler, and of Professor Henslow, to whom he was introduced by his second cousin, W. Darwin Fox, who also first interested him in entomology. He became so keen a collector of beetles that his successes and experiences in this direction seem to have impressed him more deeply than anything else at Cambridge. Entomology, and especially beetles, form the chief subject of those of his Cambridge letters which have been recovered.

Darwin’s friendship with Henslow, which was to have a most important effect on his life, very soon deepened. They often went long walks together, so that he was called “the man who walks with Henslow.” This fact and the subsequent rapidly formed intimacy with Professor Adam Sedgwick, indicate that he was remarkable among the young men of his standing.

One of his undergraduate friends, J. M. Herbert, afterwards County Court Judge for South Wales, retained the most vivid recollection of Darwin at Cambridge, and contributed the following impression of his character to the “Life and Letters”:—

“It would be idle for me to speak of his vast intellectual powers ... but I cannot end this cursory and rambling sketch without testifying, and I doubt not all his surviving college friends would concur with me, that he was the most genial, warm-hearted, generous and affectionate of friends; that his sympathies were with all that was good and true; and that he had a cordial hatred for everything false, or vile, or cruel, or mean, or dishonourable. He was not only great, but pre-eminently good, and just, and loveable.”

Two books greatly influenced Darwin—Herschel’s “Introduction to the Study of Natural Philosophy,” which, he said, “stirred up in me a burning zeal to add even the most humble contribution to the noble structure of Natural Science”; and Humboldt’s “Personal Narrative,” which roused in him the longing to travel—a desire which was soon afterwards gratified by his voyage in the Beagle.

“Upon the whole,” he says, “the three years which I spent at Cambridge were the most joyful in my happy life; for I was then in excellent health, and almost always in high spirits.”

After passing his last examination, Darwin had still two terms’ residence to keep, and was advised by Henslow to study geology. To this end Henslow asked Sedgwick to allow Darwin to go with him on a geological excursion in North Wales in August, 1831. He thus gained experience which was of the utmost value during the voyage of the Beagle.

CHAPTER III.
VOYAGE OF THE “BEAGLE” (1831–36).

About the time of the excursion with Sedgwick (the exact date is uncertain) Professor Henslow received a letter from George Peacock (formerly Dean of Ely and Lowndean Professor of Astronomy at Cambridge) stating that he had the offer to recommend a young man as naturalist to accompany Captain Fitzroy on a surveying expedition to many parts of the world. Leonard Jenyns (afterwards Blomefield) was evidently considered to be the most suitable person for the position, but he was unable to accept it. Henslow at once wrote (August 24th, 1831) to Darwin, and advised him to do his utmost to obtain the position, and Darwin found the letter waiting for him on his return home after the geological excursion with Sedgwick. As his father greatly disliked the idea, Darwin at once wrote (August 30th) and declined, and the next day went to Maer to be ready for the shooting on September 1st. Here, however, his uncle, Josiah Wedgwood, took a very different view from that adopted by his father, with the result that both he and Darwin wrote (August 31st) to Shrewsbury and reopened the question. Darwin’s letter shows the most touching deference to his father’s wishes, and the gravest apprehension lest he should be rendered “uncomfortable” or “uneasy” by any further suggestion as to the possibility of the voyage, although his father had said, “If you can find any man of common-sense who advises you to go, I will give my consent.” We also learn from the “Autobiography” that his uncle sent for him whilst out shooting and drove him the thirty miles to Shrewsbury, in order that they might talk with his father, who then at once consented. This must have been on September 1st, 1831.

From this time until he went to Plymouth, on October 24th—the final start was not until December 27th—his letters show that he had a very busy time making purchases and preparing for the voyage. These letters breathe the warmest affection to the members of his family and his friends, together with the keenest enthusiasm for Captain Fitzroy, the ship, and the voyage.

The voyage of the Beagle lasted from December 27th, 1831, to October 2nd, 1836. Darwin says that it was “by far the most important event in my life, and has determined my whole career.... I have always felt that I owe to the voyage the first real training or education of my mind” (l. c., p. 61). He attributes the greatest share in this training to geology, among the special sciences, because of the reasoning involved in making out the structure of a new and unknown district; but he considers that the habits of “energetic industry and of concentrated attention” which he then acquired were of the utmost importance, and the secret of all his success in science. He tells us that the love of sport was present at first in all its keenness, but that he gradually abandoned it for scientific work.

Among his numerous observations and discoveries during the voyage, those which appear to stand out in his mind so that he quotes them in his “Autobiography” are—the explanation of the forms of coral islands, the geological structure of St. Helena and other islands, and the relations between the animals and plants of the several Galapagos islands to each other and to those of South America. His letters and the collections which he sent home attracted much attention; and Sedgwick told Dr. Darwin that his son would take a place among the leading scientific men. When Darwin heard this from his sisters, he says, “I clambered over the mountains of Ascension with a bounding step, and made the volcanic rocks resound under my geological hammer.” His letters during the voyage are full of enthusiasm and of longing to return to his family and friends.

There was the same conflict between the naval and scientific departments of the Beagle on the untidiness of the decks which was afterwards repeated on the Challenger, where I have been told that one of the naval authorities used to say, with resigned disgust, “Oh, no, we’re not a man-of-war, we’re only a —— dredger!”

In the course of the voyage the following countries and islands were visited in the order given:—The Cape de Verde Islands, St. Paul’s Rocks, Fernando Noronha, South America (including the Galapagos Archipelago, the Falkland Islands, and Tierra del Fuego), Tahiti, New Zealand, Australia, Tasmania, Keeling Island, Maldive Coral Atolls, Mauritius, St. Helena, Ascension. Brazil was then visited again for a short time, the Beagle touching at the Cape de Verde Islands and the Azores on the voyage home.

Darwin says, concerning the intellectual effect of his work during the voyage:—

“That my mind became developed through my pursuits during the voyage is rendered probable by a remark made by my father, who was the most acute observer whom I ever saw, of a sceptical disposition, and far from being a believer in phrenology; for on first seeing me after the voyage he turned round to my sisters, and exclaimed, ‘Why the shape of his head is quite altered!’” (l. c., pp. 63, 64).

CHAPTER IV.
CAMBRIDGE—LONDON—WORK UPON THE COLLECTIONS—MARRIAGE—GEOLOGICAL WORK—JOURNAL OF THE VOYAGE—CORAL REEFS—FIRST RECORDED THOUGHTS ON EVOLUTION (1837–42).

Darwin reached England October 2nd, 1836, and was home at Shrewsbury October 5th (according to his Letters; the 4th is the date given by Francis Darwin in the “Life and Letters”). The two years and three months which followed he describes as the most active ones he ever spent. After visiting his family, he stayed three months in Cambridge, working at his collection of rocks, writing his “Naturalist’s Voyage,” and one or two scientific papers. He then (March 7th, 1837) took lodgings in 36, Great Marlborough Street, London, where he remained until his marriage, January 29th, 1839. The apathy of scientific men—even those in charge of museums—caused him much depression, and he found great difficulty in getting specialists to work out his collections, although the botanists seem to have been keener than the zoologists.

The commencement of his London residence is of the deepest interest, as the time at which he began to reflect seriously on the origin of species. Thus he says in the “Autobiography”:—“In July 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.” Furthermore, his pocket-book for 1837 contained the words:—“In July opened first note-book on Transmutation of Species. Had been greatly struck from about the month of previous March” (he was then just over twenty-eight years old) “on character of South American fossils, and species on Galapagos Archipelago. These facts (especially latter) origin of all my views.” It is, perhaps, worth while to explain in greater detail the nature of this evidence which appealed so strongly to Darwin’s mind. The Edentata (sloths, ant-eaters, armadilloes, etc.) have their metropolis in South America, and in the later geological formations of this country the skeletons of gigantic extinct animals of the same order (Megatherium, Mylodon, Glyptodon, etc.) are found; and Darwin was doubtless all the more impressed by discovering such remains for himself. In his “Autobiography” he says: “During the voyage of the Beagle I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on existing armadilloes;...”

Darwin was thus led to conclude that there was some genetic connection between the animals which have succeeded each other in the same district; for in a theory of destructive cataclysms, followed by re-creations—or, indeed, in any theory of special creation—there seemed no adequate reason why the successive forms should belong to the same order. In his “Naturalist’s Voyage Round the World” he says, speaking of this subject: “This wonderful relationship in the same continent between the dead and the living will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts” (p. 173 in the third edition).

THE GALAPAGOS.

The other class of evidence which impressed him even more strongly was afforded by the relations between the animals and plants of the several islands of the Galapagos Archipelago and between those of the Archipelago and of South America, nearly 600 miles to the East. Although the inhabitants of the separate islands show an astonishing amount of peculiarity, the species are nearly related, and also exhibit American affinities. Concerning this, Darwin writes in his “Voyage” (p. 398 in the third edition): “Reviewing the facts here given, one is astonished at the amount of creative force—if such an expression may be used—displayed on these small, barren, and rocky islands; and still more so at its diverse and yet analogous action on points so near each other.” Here, too, the facts were unintelligible on a theory of separate creation of species, but were at once explained if we suppose that the inhabitants were the modified descendants of species which had migrated from South America—the migrations to the Archipelago and between the separate islands being rendered extremely rare from the depth of the sea, the direction of the currents, and the absence of gales. In this way time for specific modification was provided before the partially modified form could interbreed with the parent species and thus lose its own newly-acquired characteristics.

Although Darwin made these observations on the Beagle, they required, as Huxley has suggested (Obituary [1888], “Darwiniana”: Collected Essays, vol. ii., pp. 274–275. London, 1893), careful and systematic working out before they could be trusted as a basis on which to speculate; and this could not be done until the return home. The following letter written by Darwin to Dr. Otto Zacharias in 1877 confirms this opinion. It was sent to Huxley by Francis Darwin, and is printed in “Darwiniana” (l. c., p. 275):—

“When I was on board the ‘Beagle,’ I believed in the permanence of species, but, as far as I can remember, vague doubts occasionally flitted across my mind. On my return home 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, so that in July, 1837, I opened a note-book to record any facts which might bear on the question. But I did not become convinced that species were mutable until I think two or three years had elapsed.”

It is interesting to note that both the lines of evidence which appealed to Darwin so strongly, point to evolution, but not to any causes of evolution. The majority of mankind were only convinced of this process when some conception as to its causes had been offered to them; Darwin took the more logical course of first requiring evidence that the process takes place, and then inquiring for its causes.

EARLY NOTES ON SPECIES.

The first indication of these thoughts in any of his published letters is in one to his cousin Fox written in June, 1838, in which, after alluding to some questions he had previously asked about the crossing of animals, he says, “It is my prime hobby, and I really think some day I shall be able to do something in that most intricate subject—species and varieties.”

He is rather more definite in a letter to Sir Charles Lyell, written September 13th in the same year:—

“I have lately been sadly tempted to be idle—that is, as far as pure geology is concerned—by the delightful number of new views which have been coming in thickly and steadily,—on the classification and affinities and instincts of animals—bearing on the question of species. Note-book after note-book has been filled with facts which begin to group themselves clearly under sub-laws.”

On February 16th, 1838, he was appointed Secretary of the Geological Society, a position which he retained until February 1st, 1841. During these two years after the voyage he saw much of Sir Charles Lyell, whose teachings had been of the greatest help to him during the voyage, and whose method of appealing to natural causes rather than supernatural cataclysms undoubtedly had a most important influence on the development of Darwin’s mind. This influence he delighted to acknowledge, dedicating to Lyell the second edition of his “Voyage,” “as an acknowledgment that the chief part of whatever scientific merit this ‘Journal’ and the other works of the author may possess has been derived from studying the well-known and admirable ‘Principles of Geology.’”

EARLY WORKS.

At this period he finished his “Journal,” which was published in 1839 as Vol. III. of the “Narrative of the Surveying Voyages of Her Majesty’s Ships Adventure and Beagle.” A second edition was published in a separate form in 1845 as the “Journal of Researches into the Natural History and Geology of the Countries visited during the Voyage of H.M.S. Beagle round the World, under the command of Captain Fitz-Roy, R.N.”; and a third edition—but very slightly altered—in 1860, under the title “A Naturalist’s Voyage: Journal of Researches, etc.” This book is generally admitted to deserve above all others the generous description which Darwin gave to Sir Joseph Hooker of Belt’s admirable “Naturalist in Nicaragua”—as “the best of all Natural History journals which have ever been published.”

A comparison between the first and second editions indicates, but by no means expresses, his growing convictions on evolution and natural selection. Natural selection he had not discovered when the MS. of the first edition was complete; and if we had no further evidence we could not, from any passage in the work, maintain that he was convinced of evolution. His great caution in dealing with so tremendous a problem explains why the second edition does not reflect the state of his mind at the time of its publication. He tells us (“Autobiography”) that in the preparation of this second edition he “took much pains,” and we may feel confident that much of this care was given to the decision as to how much he should reveal and how much withhold of the thoughts which were occupying his mind, and the conclusions to which he had at that time arrived. That he did attribute much importance to the evolutionary passages added in the second edition is shown by his letter to Lyell (July, 1845), in which he alludes to some of them, and specially asks Lyell to read the pages on the causes of extinction.

He also edited and superintended the “Zoology of the Voyage of H.M.S. Beagle,” the special parts of which were written by various eminent systematists, and appeared separately between 1839 and 1843.

He also read several papers before the Geological Society, including two (1838 and 1840) on the Formation of Mould by the Action of Earth-Worms—a subject to which he returned, and upon which his last volume (published in 1881) was written. He also read a paper on the Parallel Roads of Glen Roy before the Royal Society (published in the Phil. Trans., 1839). These wonderful parallel terraces are now admitted to be due to the changes of level in a lake following those of an ice-barrier at the mouth of the valley. At the time Darwin studied them, the terraces were believed to have been formed by a lake dammed back by a barrier of rock and alluvium; this he proved to be wrong, and as no other barrier was then available—for the evidences of glaciation had not then been discovered by Agassiz—he was driven, on the method of exclusion, to the action of the sea. Upon this subject he says, in the “Autobiography,” “My error has been a good lesson to me never to trust in science to the principle of exclusion.”

On January 29th, 1839, he married his cousin, Emma Wedgwood, the daughter of Josiah Wedgwood, of Maer. They resided at 12, Upper Gower Street until September 14th, 1842, when they settled at Down.

The few graceful and touching words in which Francis Darwin, in the “Life and Letters,” alludes to his father’s married life show how deep is the debt of gratitude which the world owes to Mrs. Darwin; for without her constant and loving care it would have been impossible for Darwin to have accomplished his life-work.

ON CORAL REEFS.

During these years in London his health broke down many times; so that he says, in the “Autobiography”: “I did less scientific work, though I worked as hard as I possibly could, than during any other equal length of time in my life.” He chiefly worked at his book on “The Structure and Distribution of Coral Reefs,” published in 1842 (second edition in 1874). This work contains an account of Darwin’s well-known theory upon the origin of the various coral formations—fringing reefs, barrier reefs, and atolls—by the upward growth of the reef keeping pace with the gradual sinking of the island upon which it is based, so that the living corals always remain at the surface under the most favourable conditions, while beneath them is an ever-thickening reef formed of dead coral, until at length, by continuing this process, the climax is reached in the atoll, in which the original island has altogether disappeared beneath the surface of a central lagoon enclosed in a ring formed by the living edge of the reef. This theory, after being accepted for many years, has recently been disputed, chiefly as the result of the observations made on the Challenger expedition. It is contended by Dr. John Murray “that it is not necessary to call in subsidence to explain any of the characteristic features of barrier reefs or atolls, and that all these features would exist alike in areas of slow elevation, of rest, or of slow subsidence” (Nature, August 12th, 1880, p. 337). It cannot be said that this controversy is yet settled, or that the supporters of either theory have proved that the other does not hold—at any rate, in certain cases.

Among his geological papers written at this time was one describing the glacial phenomena observed during a tour in North Wales. This paper (Philosophical Magazine, 1842, p. 352) is placed by Sir Archibald Geikie “almost at the top of the long list of English contributions to the history of the Ice Age.”

At this time, too, he was reflecting and collecting evidence for the great work of his life. Thus in January, 1841, he writes to his cousin, Darwin Fox, asking for “all kinds of facts about ‘Varieties and Species.’”

CHAPTER V.
DOWN—GEOLOGY OF THE VOYAGE—WORK ON CIRRIPEDES (1842–54).

From September 14th, 1842, until his death, Darwin resided at Down, living a very retired life, and almost exclusively engaged in his scientific researches. Although Down is only twenty miles from London, it is three miles from the nearest railway station (Orpington), and is only now for the first time receiving a telegraph office. A home in such a place enabled Darwin to pursue his work without interruption, remaining, at the same time, within easy reach of all the advantages of London. Here, too, he had no difficulty in avoiding social engagements, which always injured his very precarious health, and thus interfered with work; although, at the same time, he could entertain in his own house at such times as he felt able to do so.

In 1844, and again in 1846, he published works on the geology of the voyage of the Beagle; the first on the Volcanic Islands visited, the second on South America. A second edition, in which both were combined in a single work, appeared in 1876. He seemed somewhat disappointed at the small amount of attention they at first attracted, and wrote with much humour to J. M. Herbert:—“I have long discovered that geologists never read each other’s works, and that the only object in writing a book is a proof of earnestness, and that you do not form your opinions without undergoing labour of some kind.” All geologists were, nevertheless, soon agreed in attaching the highest value to these researches.

ON CIRRIPEDES.

From this time forward his work was almost exclusively zoological. The four monographs on the Cirripedia, recent and fossil, occupied eight years—from October, 1846, to October, 1854. The works on the recent forms were published by the Ray Society (1851 and 1854), and those on the fossil forms by the Palæontographical Society (1851 and 1854). These researches grew directly out of his observations on the Beagle, but it is evident that they reached far greater dimensions than he had at first intended. Thus, at the very beginning of the work, he wrote (October, 1846) to Hooker:—

“I am going to begin some papers on the lower marine animals, which will last me some months, perhaps a year, and then I shall begin looking over my ten-year-long accumulation of notes on species and varieties, which, with writing, I dare say will take me five years, and then, when published, I dare say I shall stand infinitely low in the opinion of all sound Naturalists—so this is my prospect for the future.”

Darwin himself, at any rate towards the end of his life, when he wrote his “Autobiography,” doubted “whether this work was worth the consumption of so much time,” although admitting that it was of “considerable value” when he had “to discuss in the ‘Origin of Species’ the principles of a natural classification.” Sir Joseph Hooker remembers that Darwin at an earlier time “recognised three stages in his career as a biologist: the mere collector at Cambridge; the collector and observer in the Beagle and for some years afterwards; and the trained naturalist after, and only after, the Cirripede work” (Letter to F. Darwin).

Professor Huxley considers that just as by Darwin’s practical experience of physical geography, geology, etc., on the Beagle, “he knew of his own knowledge the way in which the raw materials of these branches of science are acquired, and was, therefore, a most competent judge of the speculative strain they would bear,” so his Cirripede work fitted him for his subsequent speculations upon the deepest biological problems. “It was a piece of critical self-discipline, the effect of which manifested itself in everything your father wrote afterwards, and saved him from endless errors of detail” (Letter to F. Darwin, “Life and Letters”). The history of Darwin’s career has often been used as an argument against those who, not having passed through a similar training as regards systematic zoological work, have ventured to concern themselves with the problems of evolution. Professor Meldola has recently treated of this subject in his interesting presidential address to the Entomological Society (1896). He says:—

“It used formerly to be asserted that he only is worthy of attention who has done systematic, i.e. taxonomic, work. I do not know whether this view is still entertained by entomologists; if so, I feel bound to express my dissent. It has been pointed out that the great theorisers have all done such work—that Darwin monographed the Cirripedia, and Huxley the oceanic Hydrozoa, and it has been said that Wallace’s and Bates’s contributions in this field have been their biological salvation. I yield to nobody in my recognition of the value and importance of taxonomic work, but the possibilities of biological investigation have developed to such an extent since Darwin’s time that I do not think this position can any longer be seriously maintained. It must be borne in mind that the illustrious author of the ‘Origin of Species’ had none of the opportunities for systematic training in biology which any student can now avail himself of. To him the monographing of the Cirripedia was, as Huxley states in a communication to Francis Darwin, ‘a piece of critical self-discipline,’ and there can be no reasonable doubt that this value of systematic work will be generally conceded. That this kind of work gives the sole right to speculate at the present time is, however, quite another point.”

Meldola then goes on to argue that the systematic work of those who know nothing of the living state of the species they are describing does not specially fit them for theorising, and he concludes by quoting the following passage from a letter recently received from A. R. Wallace:—

“I do not think species-describing is of any special use to the philosophical generaliser, but I do think the collecting, naming, and classifying some extensive group of organisms is of great use, is, in fact, almost essential to any thorough grasp of the whole subject of the evolution of species through variation and natural selection. I had described nothing when I wrote my papers on variation, etc. (except a few fishes and palms from the Amazon), but I had collected and made out species very largely and had seen to some extent how curiously useful and protective their forms and colours often were, and all this was of great use to me.”

Towards the end of this long period of hard taxonomic labour, we know from Darwin’s letters that he was extremely tired of the work; but with marvellous resolution—and in spite of the trouble of his health, which was perhaps worse than at any other time—he clung to and carried through this stupendous task, although all the time attracted away from it by the weightier problems which he could never thrust aside after they had once made their claim upon him.

ON NAMING SPECIES.

Darwin was evidently greatly disconcerted at the task of making out those special difficulties which man has added to the difficulties of Nature herself—the disheartening tangle of nomenclature. He thought that the custom of appending the name of the systematist after that of the species or genus he had named was injurious to the interests of science—inducing men to name quickly rather than describe accurately. Some of his remarks on this subject indicate the state of his mind. Thus he wrote to Hooker, October 6th, 1848:—

“I have lately been trying to get up an agitation ... against the practice of Naturalists appending for perpetuity the name of the first describer to species. I look at this as a direct premium to hasty work, to naming instead of describing. A species ought to have a name so well known that the addition of the author’s name would be superfluous, and ... empty vanity.... Botany, I fancy, has not suffered so much as zoology from mere naming; the characters, fortunately, are more obscure.... Why should Naturalists append their own names to new species, when Mineralogists and chemists do not do so to new substances?”

And again he wrote to Hugh Strickland, January 29th, 1849:—

“I have come to a fixed opinion that the plan of the first describer’s name, being appended for perpetuity to a species, has been the greatest curse to Natural History.... I feel sure as long as species-mongers have their vanity tickled by seeing their own names appended to a species, because they miserably described it in two or three lines, we shall have the same vast amount of bad work as at present, and which is enough to dishearten any man who is willing to work out any branch with care and time.”

And in another letter (February 4th) to the same correspondent:—

“In mineralogy I have myself found there is no rage to merely name; a person does not take up the subject without he intends to work it out, as he knows that his only claim to merit rests on his work being ably done, and has no relation whatever to naming.... I do not think more credit is due to a man for defining a species, than to a carpenter for making a box. But I am foolish and rabid against species-mongers, or rather against their vanity; it is useful and necessary work which must be done; but they act as if they had actually made the species, and it was their own property.”

A little later in the same year (1849) his health seems to have determined him to give up the crusade, for he writes to Hooker (April 29th):—

“With health and vigour, I would not have shewn a white feather, [and] with aid of half-a-dozen really good Naturalists, I believe something might have been done against the miserable and degrading passion of mere species naming.”

Anyone whose researches have been among the species of any much-worked and much-collected zoological group will quite agree that synonymy is, as Darwin found it, heart-breaking work; and although there may be good reasons why the system of appending the describer’s name must be retained, such a protest as that raised in these letters cannot fail to do good in drawing attention to an abuse which is only too common, and which introduces unnecessary difficulty and gratuitous confusion into the study of Nature.

DEATH OF HIS FATHER.

His father, Dr. Darwin, died November 13th, 1848, at the age of eighty-three, when he was so much out of health that he was unable to attend the funeral. In 1851 he lost his little daughter Annie, who died at Malvern, April 23rd. A few days after her death he wrote a most affecting account of her—a composition of great beauty and pathos.

CHAPTER VI.
THE GROWTH OF THE “ORIGIN OF SPECIES” (1837–58).

In dealing with this subject in his “Autobiography,” Darwin tells us of his reflections whilst on the voyage of the Beagle, and here mentions another observation which deeply impressed him in addition to those which he again repeats, on the relation between the living and the dead in the same area and on the productions of the Galapagos Archipelago—viz. “the manner in which closely allied animals replace one another in proceeding southwards over the continent” (of South America). On the theory of separate creation the existence of such representative species received no explanation, although it became perfectly intelligible on the theory that a single species may be modified into distinct, although nearly related, species in the course of its range over a wide geographical area. Here, too, the evidence is in favour of evolution simply, and does not point to any cause of evolution.

He also implies that even at this time he regarded the beautiful adaptations or contrivances of nature by which organisms are fitted to their habits of life—“for instance, a woodpecker or a tree-frog to climb trees, or a seed for dispersal by hooks or plumes”—as the most striking and important phenomena of the organic world, and the one great difficulty in the path of any naturalist who should attempt to supply a motive force for evolution. And he regarded the previous attempts at an explanation—the direct action of surroundings and the will of the organism—as inadequate because they could not account for such adaptations.

Therefore being convinced of evolution, but as yet unprovided with a motive cause which in any way satisfied him, he began in July, 1837, shortly after his return home from the Beagle, to collect all facts which bore upon the modifications which man has induced in the animals and plants which he has subjugated, following, as he tells us, the example of Lyell in geology. He goes on to say in his “Autobiography”:—

“I soon perceived that selection was the key-stone of man’s success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me.”

COLLECTION OF NOTES.

We see indications in the extracts from his note-book at this period (viz. between July, 1837, and February, 1838), and before he had arrived at the conception of Natural Selection, that he had the idea of “laws of change” affecting species to some extent like the laws of change which compel the individuals of every species to work out their own development, the extinction of the one corresponding in a measure to the death of the other. Thus he says, “It is a wonderful fact, horse, elephant, and mastodon dying out about the same time in such different quarters. Will Mr. Lyell say that some [same?] circumstance killed it over a tract from Spain to South America? Never.” We know that a few months later he would have himself accepted the view he imputes to Lyell, and would have regarded the extinction as due to some circumstance affecting the competition for food or some other relationship with the organic life of the same district. It is probable that the above quotation from his Diary was written in connection with the conclusion of Chapter IX. of the first edition of the “Journal of the Voyage” (pp. 211, 212); for the latter is a fuller exposition of the same argument.[B]

“One is tempted to believe,” he says, “in such simple relations, as variation of climate and food, or introduction of enemies, or the increased numbers of other species, as the cause of the succession of races. But it may be asked whether it is probable that [“than” is an evident misprint in the original] any such cause should have been in action during the same epoch over the whole northern hemisphere, so as to destroy the Elephas primigenius on the shores of Spain, on the plains of Siberia, and in Northern America.... These cases of extinction forcibly recall the idea (I do not wish to draw any close analogy) of certain fruit-trees, which, it has been asserted, though grafted on young stems, planted in varied situations, and fertilized by the richest manures, yet at one period have all withered away and perished. A fixed and determined length of life has in such cases been given to thousands and thousands of buds (or individual germs), although produced in long succession.”

He then concludes that the animals of one species, although “each individual appears nearly independent of its kind,” may be bound together by common laws. He ends by arguing that the adaptations of animals confined to certain areas cannot be related to the peculiarities of climate or country, because other animals introduced by man are often so much more successful than the aborigines. As to the causes of extinction, “all that at present can be said with certainty is that, as with the individual, so with the species, the hour of life has run its course, and is spent.”

EARLY VIEWS.

At this time he had the conception—as we see in the succeeding extracts from his Diary—of species being so constituted that they must give rise to other species; or, if not, that they must die out, just as an individual dies unrepresented if it has no offspring; that change—and evidently change in some fixed direction—or extinction, is inevitable in the history of a species after a certain period of time. With this view, which presented much resemblance to that of the author of the “Vestiges,” and which seemed uppermost in his mind at this time, there are traces of others. Thus in one extract the “wish of parents” was thought of as a very doubtful explanation of adaptation, while in another we meet a tolerably clear indication of natural selection, a variety which is not well adapted being doomed to extinction, while a favourable one is perpetuated, the death of a species being regarded as “a consequence ... of non-adaptation of circumstances.”

It seems certain that for fifteen months after July, 1837, he was keenly considering the various causes of evolution which were suggested to him by the facts of nature, and that some general idea of natural selection presented itself to him at times, although without any of the force and importance it assumed in his mind at a later time.

In October, 1838, he read “Malthus on Population,” and as he says:—

“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 a theory by which to work.”

SKETCH OF THE “ORIGIN.”

In June, 1842, he wrote a brief account of the theory, occupying thirty-five pages. In Lyell’s and Hooker’s introduction to the joint paper by Darwin and Wallace in the Linnean Society’s Journal (1858) it is stated that the first sketch was made in 1839, but Francis Darwin shows (“Life and Letters,” 1887, Vol. II. pp. 11, 12) that in all probability this is an error—a note of Darwin’s referring to the first complete grasp of the theory after reading Malthus, being mistaken for a reference to the first written account.

In 1844 the sketch was enlarged to a written essay occupying 231 pages folio—“a surprisingly complete presentation of the argument afterwards familiar to us in the ‘Origin of Species’” published fifteen years later. Professor Huxley, after reading this essay, observed that “much more weight is attached to the influence of external conditions in producing variation, and to the inheritance of acquired habits than in the ‘Origin,’” while Professor Newton pointed out that the remarks on the migration of birds anticipate the views of later writers.[C]

The explanation of divergence of species during modification (divergence of character) had not then occurred to him, and he tells us in the “Autobiography”:—

“I can remember the very spot in the road, whilst in my carriage, when to my joy the solution occurred to me; and this was long after I had come to Down. The solution, as I believe, is that the modified offspring of all dominant and increasing forms tend to become adapted to many and highly diversified places in the economy of nature.”

A good example of this tendency is seen in the relations of three great vertebrate classes—mammals, birds, and fishes—to the environments for which they are respectively fitted: earth, air, and water. Competition is most severe between forms most nearly alike, and hence some measure of relief from competition is afforded when certain members of each of these classes enter the domain of one of the others. Hence, we observe that although mammals as a whole are terrestrial, a small minority are aërial and aquatic; although birds are aërial, a minority are terrestrial and aquatic; although fishes are aquatic, a minority tend to be, at any rate largely, terrestrial and aërial.

Huxley considered it “curious that so much importance should be attached to this supplementary idea. It seems obvious that the theory of the origin of species by natural selection necessarily involves the divergence of the forms selected” (“Obituary,” 1888, reprinted in “Darwiniana,” 1893; see pp. 280, 281). But Darwin showed that divergence might be a great advantage in itself, and would then be directly (and not merely incidentally and indirectly) encouraged and increased by natural selection.

RESOLVE TO PUBLISH.

As soon as the 1844 sketch was finished, Darwin wrote a letter (July 5th) as his “solemn and last request” that his wife would, in the case of his death, devote £400, or if necessary £500, in publishing it, and would take trouble in promoting it. He suggests Lyell as the best editor, then Edward Forbes, then Henslow (“quite the best in many respects”), then Hooker (“would be very good”), then Strickland. After Strickland he had thought of Owen as “very good,” but added, “I presume he would not undertake such a work.” If no editor could be obtained, he requested that the essay should be published as it was—stating that it was not intended for publication in its present form. In August, 1854, he wrote on the back of the letter: “Hooker by far best man to edit my Species volume.”

All this shows how certain he felt that he was on firm ground, and that his theory of natural selection was of vast importance to science. This same strong conviction appears clearly in the first edition of the “Origin,” and is undoubtedly one of the secrets of its power to move the minds of men. Although the author is above all others fair-minded; although he is most keen to discover and to bring forward all opposing evidence, and to criticise most minutely everything favourable; nevertheless, looking at the evidence as a whole, he has no doubt as to its bearing, and feels, and shows that he feels, a magnificent confidence in the truth and the importance of his theory.

CHAPTER VII.
GROWTH OF THE “ORIGIN” (continued)—CORRESPONDENCE WITH FRIENDS.

The great periods of Darwin’s scientific career are marked by intimate friendships, which must be taken into account in attempting to trace his mental development. Henslow was his intimate friend at Cambridge and during the voyage of the Beagle. The influence of Lyell, through his writings, was of the utmost importance during the voyage, and was deepened by the close personal contact which took place on Darwin’s return. Sir Joseph Hooker was his most intimate friend during the growth of the “Origin of Species.”

Although Hooker met Darwin in 1839, their friendship did not begin until four years later, when the former returned from the Antarctic Expedition. On January 11th, 1844, Darwin wrote admitting his conclusions on the question of evolution:—“At last gleams of light have come,” he says, “and I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable” (“Life and Letters,” Vol. II. p. 23).

INQUIRIES AND EXPERIMENTS.

From this point onwards his letters, especially to Hooker, indicate the course he was following and the various problems he was considering as they arose. Thus we find that he had finished reading Wollaston’s “Insecta Maderensia” in 1855 (writing March 7th), and had been struck with the very large proportion of wingless beetles, and had interpreted the observation, viz. “that powers of flight would be injurious to insects inhabiting a confined locality, and expose them to be blown to the sea.” It is of great interest thus to witness the origin of a theory which has since been universally accepted, and has received confirmation from many parts of the world.

On April 11th of the same year he is experimenting on the powers of resistance to immersion in salt water possessed by seeds, and he writes an account of it to Hooker. The object of these experiments was to throw light on the means by which plants have been transported to islands.

In the same year began his correspondence with Asa Gray, who soon became one of his warmest friends. He had numerous questions to ask about the geographical range of plants, and in 1857 he wrote explaining in some detail the views at which he had arrived as to the causes of evolution.

My friend Rowland H. Wedgwood, a nephew of Darwin, has given me the following interesting letter to his father, which was written, he believes, probably before 1855. By kind permission, it is here published for the first time. The letter is of great interest, as throwing light upon his work, and also because of this early reference to Huxley:—

“Down, Sept. 5.

“My dear Harry,—I am very much obliged for the Columbine seed and for your note which made us laugh heartily.

“I had no idea what trouble the counting must have been, I had not the least conception that there would have been so many pods. I am very much interested on this point, and therefore to make assurance sure, I repeat your figures viz. 560 and 742 pods on two plants and 7200 on another. Does the latter number really mean pods and not seeds? Upon my life I am sorry to give so much trouble, but I should be VERY MUCH obliged for a few average size pods, put up separately that I may count the seeds in each pod: for though I counted the seeds in the pods sent before, I hardly dare trust them without counting more. Moreover I sadly want more seed itself for one of my experiments.

“The young cabbages are coming up already. Thank you much about the asparagus seeds; as it is so rare a plant, you are my only chance.

“We have been grieved to hear about poor Anne and Tom.—Your affect^te screw

“C. Darwin.

“Have you been acquainted with Mr. Huxley; I think you would find him a pleasant acquaintance. He is a very clever man.”

Mr. Francis Darwin believes that the asparagus and cabbage seeds were for the experiments to determine the time during which immersion in salt water could be endured. The object of such experiments was to throw light on the means by which plants are distributed over the earth’s surface. He also informs me that the use of the word “screw” is unique and incomprehensible.

Darwin tells us in the “Autobiography” that “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.’” This work he began on May 14th, and, after working steadily until June, 1858, had written about half the book, in ten chapters, when he received the celebrated letter from Wallace, which altered everything.

ON THE “ATLANTIS” THEORY.

At this period we get interesting evidence of his extraordinary insight in the strong protests he makes against the Atlantis hypothesis of Edward Forbes, and the other vast continental extensions which naturalists did not hesitate to make in order to explain the existence of species common to countries separated by wide tracts of the ocean. These lost continents were as generally accepted as they were freely proposed. And yet we find that, even then, one thinker far ahead of his time saw clearly enough—as the Challenger Expedition twenty years later proved beyond all doubt—that the geological evidence is against such extension, and that the means of distribution possessed by animals are such as to render the supposition unnecessary.

In June, 1856, he writes to Lyell: “My blood gets hot with passion and turns cold alternately at the geological strides, which many of your disciples are taking”; and after mentioning the extension of continents proposed by many leading naturalists, he says: “If you do not stop this, if there be a lower region for the punishment of geologists, I believe, my great master, you will go there. Why, your disciples in a slow and creeping manner beat all the old Catastrophists who ever lived! You will live to be the great chief of the Catastrophists.” Lyell wrote disagreeing on the subject of continental extension; and hence, on June 25th, 1856, Darwin replied in a long letter, giving in detail his reasons for rejecting the hypothesis. He argued (1) that the supposed extension of continents and fusion of islands would be vast changes, giving the earth a new aspect, but that recent and tertiary molluscs, etc., are distinct on opposite sides of the existing continents; so that, although he did not doubt great changes of level in parts of continents, he concluded that “fundamentally they stood as barriers to the sea where they now stand” ever since the appearance of living species; (2) that if a continent were nearly submerged, the last remaining peaks would by no means always be volcanic, as are, almost without exception, the oceanic islands; (3) that the amount of subsidence which took place in continental areas during the Silurian and Carboniferous periods—viz. during one tolerably uniform set of beings—would not be enough to account for the depth of the ocean over some parts of the site of the supposed submerged continents; (4) that the supposed extensions are not consistent with the absence of many groups of animals—e.g. mammals, frogs, etc.—from islands.

These arguments did not convince Lyell; and they have only received an almost universal acceptance after the confirmatory evidence afforded by the voyage of the Challenger. Dredgings over many parts of the ocean showed that all the continental deposits are collected on a fringing shelf not more than 200 miles wide, and that beyond this in the ocean bed proper an entirely different kind of deposit is accumulating, composed of the shells, bones, and teeth of swimming or floating organisms, or the products of their decomposition, of volcanic and cosmic dust, and the products—e.g. manganese dioxide—of the decomposition of these and of floating pumice. Hence, the depths of the ocean afford no indications of a lost continental area, but are covered by a peculiar deposit unknown among the rocks of continents which were formed in comparatively shallow water round and not far from coasts, or in land-locked or nearly land-locked seas like the Mediterranean.

EARLY CORRESPONDENCE.

On July 20th, 1856, he wrote to Asa Gray, giving some account of his views, and stating his belief in evolution, but only hinting at natural selection.

About this time we meet with evidence of the great difficulty with which Darwin’s ideas were thoroughly understood, even by his intimate friends, to whom he often wrote on the subject. Later on, when the “Origin of Species” was published, although the arguments in favour of natural selection were given in considerable detail, many years passed before the theory itself was understood by the great body of naturalists. This particular case of misunderstanding is of such great interest that it is desirable to consider it in detail.

In the origin of new species by natural selection, the stress of competition determines the survival of favourable individual variations, and these, when by the continued operation of the process they have become constant, are added to those pre-existing characters of the species which are inherited from a remote past, and are witnesses of the operation of natural selection from age to age under ever-changing conditions of competition and variation. It follows, therefore, that the origin of a species can only take place once; for it is infinitely improbable that the same variation would be independently submitted under the same conditions of competition, and added to the mass of inherited characters independently gained in two distinct lines by natural selection acting in the same manner upon the same variations in the same order through all ages. Not only is it inconceivable that the same species could arise by natural selection from distinct lines of ancestry, but it is extremely improbable that the same species could arise independently in more than one centre among the individuals of a changing species; for in this case, too, it is most unlikely that the same conditions of competition would co-exist with the same favourable variations in the areas inhabited by independent colonies of the same species.

EARLY CRITICISM.

Under other theories of evolution—direct action of environment, supposed inherited effects of use and disuse, etc.—an independent origin, even from quite distinct lines, would be probable; and we find, accordingly, that those who would advance such theories believe in what is called the “polyphyletic” origin of species (e.g. the horse), and in the principle of “convergence” carried far enough to produce the same complex character (e.g. vertebrate teeth) twice over without any genetic connection between the forms in which the character appears.

Under natural selection, however, such a result would be infinitely improbable, and hence this theory strongly supports, and indeed explains, the theory of “specific centres,” viz. that each species has arisen in one area only, and has spread from that into the other areas over which it now occurs. This view was strongly held by Lyell and Hooker after an exhaustive study of the facts then known as to the geographical distribution of plants and animals; and yet both of these distinguished naturalists seem to have feared that Darwin, in advancing a theory which was entirely consistent with their convictions and utterly inconsistent with any other views upon the same subject, was in some way undermining the conclusions at which they had arrived.

Thus Lyell wrote (July 25th, 1856) to Hooker:—

“I fear much that if Darwin argues that species are phantoms, he will also have to admit that single centres of dispersion are phantoms also, and that would deprive me of much of the value which I ascribe to the present provinces of animals and plants, as illustrating modern and tertiary changes in physical geography.”

And on August 5th of the same year Darwin replied to Hooker, who had apparently argued that the origin of species by direct action of climate, etc., would mean independent and multiple specific centres:—

“I see from your remarks that you do not understand my notions (whether or no worth anything) about modification; I attribute very little to the direct action of climate, etc. I suppose, in regard to specific centres, we are at cross purposes; I should call the kitchen garden in which the red cabbage was produced, or the farm in which Bakewell made the Shorthorn cattle, the specific centre of these species! And surely this is centralisation enough!”

As I have argued above, Darwin was all the time affording the strongest support to the theory of specific centres: support which was entirely wanting in the theory of separate creation, in which the origin of each species is wrapped in mystery, so that we can form no opinion as to whether it took place at one centre or at many.

At this time, when the views set forth in the “Origin” were gaining shape and expression, we cannot estimate too highly the value of the correspondence with Hooker. In after years, when the “Origin” had to stand the fire of adverse criticism, and at first of very general disapproval, it was of inestimable advantage that every idea contained in it should have been minutely discussed beforehand with one who was more critical and more learned than the greatest of those who afterwards objected. Darwin tells us in his “Autobiography”:—

“I think that I can say with truth that in after years, though I cared in the highest degree for the approbation of such men as Lyell and Hooker, who were my friends, I did not care much about the general public.”

But, although Darwin cared nothing for it, it is nevertheless true that the approbation of minds such as these was a sure indication of the general approbation of the intellect of the country, and of the world, which was to follow as soon as the new ideas were absorbed.

VALUE OF THE DISCUSSION.

And the value which Darwin himself placed on these discussions appears again and again in his letters. To take a single example, he writes to Hooker November 23rd, 1856:—

“I fear I shall weary you with letters, but do not answer this, for in truth and without flattery, I so value your letters, that after a heavy batch, as of late, I feel that I have been extravagant and have drawn too much money, and shall therefore have to stint myself on another occasion.”

CHAPTER VIII.
DARWIN AND WALLACE (1858).

The history of Darwin’s friendship with Alfred Russel Wallace is of quite unique interest, being brought about by the fact that both naturalists saw in evolution and its causes the great questions of the immediate future, and by the agreement in the interpretations which they independently offered. Wallace was collecting and observing in the Malay Archipelago, and wrote to Darwin as the one man most likely to sympathise with and understand his views and to offer valuable criticism.

In the “Annals and Magazine of Natural History” for 1855, Wallace published a paper “On the Law that has Regulated the Introduction of New Species,” and in this and a letter written from the Malay Archipelago Darwin recognised the similarity of their views, although the completeness of this agreement was to be brought before him with startling force a year after his sympathetic reply, written May 1st, 1857. He then wrote:—

“By your letter and even still more by your paper in the Annals, a year or more ago, I can plainly see that we have thought much alike and to a certain extent have come to similar conclusions. In regard to the Paper in the Annals, I agree to the truth of almost every word of your paper; and I dare say that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper; for it is lamentable how each man draws his own different conclusions from the very same facts.”

On December 22nd he replied to another letter from Wallace, again expressing agreement with all his conclusions except that upon the supposed continental extension to oceanic islands, on which, alluding to his previous discussion, he says:—

“You will be glad to hear that neither Lyell nor Hooker thought much of my arguments. Nevertheless, for once in my life, I dare withstand the almost preternatural sagacity of Lyell.”

And he concludes with the wish—

“May all your theories succeed, except that on Oceanic Islands, on which subject I will do battle to the death.”

He also said, as regards Wallace’s conclusions: “I believe I go much further than you; but it is too long a subject to enter on my speculative notions.”

WALLACE’S ESSAY.

Finally, on June 18th, 1858, Darwin received from Wallace a manuscript essay bearing the title “On the Tendency of Varieties to depart indefinitely from the Original Type.” Upon this essay he wanted Darwin’s opinion, and asked him, if he thought well of it, to forward it to Lyell. Darwin was startled to find in the essay a complete account of his own views. That very day he wrote to Lyell, enclosing the essay. In the letter he said:—

“Your words have come true with a vengeance—that I should be forestalled. You said this, when I explained to you here very briefly my views of ‘Natural Selection’ depending on the struggle for existence. I never saw a more striking coincidence; if Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract! Even his terms now stand as heads of my chapters.”

A few days later (June 25th) he again wrote to Lyell, saying—

“I should be extremely glad now to publish a sketch of my general views in about a dozen pages or so; but I cannot persuade myself that I can do so honourably. Wallace says nothing about publication, and I enclose his letter. But as I had not intended to publish any sketch, can I do so honourably, because Wallace has sent me an outline of his doctrine? I would far rather burn my whole book, than that he or any other man should think that I had behaved in a paltry spirit.”

He also asked Lyell to send the letter on to Hooker, “for then I shall have the opinion of my two best and kindest friends.” He was so much distressed at the idea of being unfair to Wallace that he wrote again the next day to put the case against himself in an even stronger light. This must have been one of the most trying times in Darwin’s life, for, in addition to the cause of trouble and perplexity described above, one of his children died of scarlet fever, and there was the gravest fear lest the others should be attacked.

BOTH ESSAYS PUBLISHED.

Thus appealed to, Lyell and Hooker took an extremely wise and fair course. They asked Darwin for an abstract of his work, and, accepting the whole responsibility, communicated it and Wallace’s essay in a joint paper to the Linnean Society, giving an account of the circumstances of the case in a preface, which took the form of a letter to the Secretary of the Society. In this letter they introduced to the Society “the results of the investigations of the indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace.”

“These gentlemen having, independently and unknown to one another, conceived the same very ingenious theory to account for the appearance and perpetuation of varieties and of specific forms on our planet, may both fairly claim the merit of being original thinkers in this important line of enquiry; but neither of them having published his views, though Mr. Darwin has for many years past been repeatedly urged by us to do so, and both authors having now unreservedly placed their papers in our hands, we think it would best promote the interests of science that a selection from them should be laid before the Linnean Society.”

After giving a list of these selections, they say of Wallace’s essay—

“This was written at Ternate[D] in February, 1858, for the perusal of his friend and correspondent Mr. Darwin, and sent to him with the expressed wish that it should be forwarded to Sir Charles Lyell, if Mr. Darwin thought it sufficiently novel and interesting. So highly did Mr. Darwin appreciate the value of the views therein set forth, that he proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace’s consent to allow the Essay to be published as soon as possible. Of this step we highly approved, provided Mr. Darwin did not withhold from the public, as he was strongly inclined to do (in favour of Mr. Wallace), the memoir which he had himself written on the same subject, and which, as before stated, one of us had perused in 1844, and the contents of which we had both of us been privy to for many years. On representing this to Mr. Darwin, he gave us permission to make what use we thought proper of his memoir, &c.; and in adopting our present course, of presenting it to the Linnean Society, we have explained to him that we are not solely considering the relative claims to priority of himself and his friend, but the interests of science generally; for we feel it to be desirable that views founded on a wide deduction from facts, and matured by years of reflection, should constitute at once a goal from which others may start, and that, while the scientific world is waiting for the appearance of Mr. Darwin’s complete work, some of the leading results of his labours, as well as those of his able correspondent, should together be laid before the public.”

The title of the joint paper was “On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection.” It was read July 1st, 1858.

CHAPTER IX.
DARWIN’S SECTION OF THE JOINT MEMOIR READ BEFORE THE LINNEAN SOCIETY JULY 1, 1858.

FIRST PUBLISHED ESSAY.

The first section of Darwin’s communication consisted of extracts from the Second Chapter of the First Part of his manuscript essay of 1844. The Part was entitled “The Variation of Organic Beings under Domestication, and in their Natural State,” and the Second Chapter was headed “On the Variation of Organic Beings in a State of Nature; on the Natural Means of Selection; on the Comparison of Domestic Races and True Species.” The extracts first deal with the tendency towards rapid multiplication and the consequent struggle for life. The average constancy of the numbers of individuals is traced to the average constancy of the amount of food, “whereas the increase of all organisms tends to be geometrical.” Practical illustrations are given in the enormous increase of the mice in La Plata during the drought which killed millions of cattle, and in the well-known and rapid increase of the animals and plants introduced by man into a new and favourable country.

The checks which operate when the country is stocked and the species reaches its average are most difficult to detect, but none the less certain. If any check is lightened in the case of any organism it will at once tend to increase. “Nature may be compared to a surface on which rest ten thousand sharp wedges touching each other and driven inward by incessant blows.” Darwin meant by this image to express that just as any single wedge would instantly rise above the rest when the blows on it were in any way lessened as compared with those on the other wedges, so it would be with the proportionate number of any species when the checks to which it is subjected are in any way relaxed.

If the external conditions alter, and the changes continue progressing, the inhabitants will be less well adapted than formerly. The changed conditions would act on the reproductive system and render the organisation plastic. Now, can it be doubted, from the struggle each individual has to obtain subsistence, that any minute variation in structure, habits, or instincts adapting that individual better to the new conditions would tell upon its vigour and health? “Yearly more are bred than can survive; the smallest grain in the balance, in the long run, must tell on which death shall fall, and which shall survive.” If this went on for a thousand generations who will deny its effect “when we remember what, in a few years, Bakewell effected in cattle, and Western in sheep, by this identical principle of selection?”

He gives an imaginary example of a canine animal preying on rabbits and hares. If the rabbits, constituting its chief food, gradually became rarer, and the hares more plentiful, the animal would be driven to try and catch more hares, and hence would be selected in the direction of speed and sharp eyesight. “I can see no more reason to doubt that these cases in a thousand generations would produce a marked effect, and adapt the form of the fox or dog to the catching of hares instead of rabbits, than that greyhounds can be improved by selection and careful breeding.” So also with plants having seeds with rather more down, leading to wider dissemination. Darwin here added this note: “I can see no more difficulty in this, than in the planter improving his varieties of the cotton plant. C. D. 1858.”

Then follows a brief sketch of sexual selection and a comparison with natural selection, and the conclusion is reached—“this kind of selection, however, is less vigorous than the other; it does not require the death of the less successful, but gives to them fewer descendants. The struggle falls, moreover, at a time of year when food is generally abundant, and perhaps the effect chiefly produced would be the modification of the secondary sexual characters, which are not related to the power of obtaining food, or to defence from enemies, but to fighting with or rivalling other males.”

The second section was entitled “Abstract of a Letter from C. Darwin, Esq., to Professor Asa Gray, Boston, U.S., dated Down, September 5th, 1857.” To this letter Darwin attached great importance as a convenient and brief account of the essentials of his theory, written and sent to Asa Gray many months before he received Wallace’s essay. A tolerably full abstract of the letter, which is itself a very brief abstract, is therefore printed below. The epitome here given is taken from the letter itself, and is in certain respects more full than that published in the Linnean Journal.

In the introductory parts Darwin explained that “the facts which kept me longest scientifically orthodox are those of adaptation—the pollen-masses in asclepias—the mistletoe, with its pollen carried by insects, and seed by birds—the woodpecker, with its feet and tail, beak and tongue, to climb the tree and secure insects. To talk of climate or Lamarckian habit producing such adaptations to other organic beings is futile. This difficulty I believe I have surmounted.” Having then stated that the reasons which induced him to accept evolution were “general facts in the affinities, embryology, rudimentary organs, geological history, and geographical distribution of organic beings,” he proceeds to give a brief account of his “notions on the means by which Nature makes her species.” The following is an abstract of the account he gives:—

SUMMARY OF THE ESSAY.

I. The success with which selection has been applied by man in making his breeds of domestic animals and plants: and this even in ancient times when the selection was unconscious, viz. when breeding was not thought of, but the most useful animals and plants were kept and the others destroyed. “Selection acts only by the accumulation of very slight or greater variations,” and man in thus accumulating “may be said to make the wool of one sheep good for carpets, and another for cloth, &c.”

II. Slight variations of all parts of the organism occur in nature, and if a being could select with reference to the whole structure, what changes might he not effect in the almost unlimited time of which geology assures us.

III. Animals increase so fast that, but for extermination, the earth would not hold the progeny of even the slowest breeding animal. Only a few in each generation can live; hence the struggle for life, which has never yet been sufficiently appreciated. “What a trifling difference must often determine which shall survive and which perish!” Thus is supplied the “unerring power” of “Natural Selection ... which selects exclusively for the good of each organic being.”

IV. If a country were changing the altered conditions would tend to cause variation, “not but what I believe most beings vary at all times enough for selection to act on.” Extermination would expose the remainder to “the mutual action of a different set of inhabitants, which I believe to be more important to the life of each being than mere climate.” In the infinite complexity of the struggle for life “I cannot doubt that during millions of generations individuals of a species will be born with some slight variation profitable to some part of its economy; such will have a better chance of surviving and propagating this variation, which again will be slowly increased by the accumulative action of natural selection; and the variety thus formed will either coexist with, or more commonly will exterminate its parent form.” Thus complex adaptations like those of woodpecker or mistletoe may be produced.

V. Numerous difficulties can be answered satisfactorily in time. The supposed changes are only very gradual, and very slow, “only a few undergoing change at any one time.” The imperfection of the geological record accounts for deficient direct evidence of change.

VI. Divergence during evolution will be an advantage. “The same spot will support more life if occupied by very diverse forms.” Hence during the increase of species into its offspring—varieties, or sub-species, or true species, the latter “will try (only few will succeed) to seize on as many and as diverse places in the economy of nature as possible,” and so will tend to “exterminate its less well-fitted parent.” This explains classification, in which the organic beings “always seem to branch and sub-branch like a tree from a common trunk; the flourishing twigs destroying the less vigorous—the dead and lost branches rudely representing extinct genera and families.”

In a postscript he says:—

“This little abstract touches only the accumulative power of natural selection, which I look at as by far the most important element in the production of new forms. The laws governing the incipient or primordial variation (unimportant except as the groundwork for selection to act on, in which respect it is all important), I shall discuss under several heads, but I can come, as you may well believe, only to very partial and imperfect conclusions.”

It is, I think, of especial interest to find Darwin at this early period arguing in a most convincing manner for the creative power of natural selection. The selective power becomes, by accumulation, of such paramount importance in the process, as compared with the variations, that, although these latter are absolutely essential, man may be said to make his domestic breeds and Nature her species. The man who argued thus had been through and had left behind the difficulty that, even now, is often raised—that “before anything can be selected it must be,” and therefore that selection is of small account as compared with variation.

CHAPTER X.
WALLACE’S SECTION OF THE JOINT MEMOIR READ BEFORE THE LINNEAN SOCIETY JULY 1, 1858.

The communication by Alfred Russel Wallace was entitled “On the Tendency of Varieties to depart indefinitely from the Original Type.” An abstract of it is given below.

WALLACE’S ESSAY.

Varieties produced in domesticity are more or less unstable, and often tend to return to the parent form. This is usually thought to be true for all varieties, and to be a strong argument for the original and permanent distinctness of species.

On the other hand, races forming “permanent or true varieties” are well known, and there are generally no means of determining which is the variety and which the original species. The hypothesis of a “permanent invariability of species” is satisfied by supposing that, while such varieties cannot diverge from the species beyond a certain fixed limit, they may return to it.

This argument is founded on the assumption that varieties in nature are in all respects identical with those of domestic animals. The object of the paper is to show that this is false, and “that there is a general principle in nature which will cause many varieties to survive the parent species and to give rise to successive variations departing further and further from the original type.” The same principle explains the tendency of domestic animals to return to the parent form.

“The life of wild animals is a struggle for existence.” To procure food and escape enemies are the primary conditions of existence, and determine abundance and rarity, frequently seen in closely allied species.

“Large animals cannot be so abundant as small ones; the carnivora must be less numerous than the herbivora,” eagles and lions than pigeons and antelopes. Fecundity has little or nothing to do with this. The least prolific animals would increase rapidly if unchecked. But wild animals do not increase beyond their average; hence there must be an immense amount of destruction. The abundance of species in individuals bears no relation whatever to their fertility. Thus the excessively abundant passenger pigeon of the United States lays only one or two eggs. Its abundance is explained by the widespread supply of food rendered available by its powers of flight. The food-supply “is almost the sole condition requisite for ensuring the rapid increase of a given species.” This explains why the sparrow is more abundant than the red-breast, why aquatic species of birds are specially numerous in individuals, why the wild cat is rarer than the rabbit. “So long as a country remains physically unchanged, the numbers of its animal population cannot materially increase.” If one species does so, others must diminish. In the immense amount of destruction the weakest must die, “while those that prolong their existence can only be the most perfect in health and vigour—those who are best able to obtain food regularly and to avoid their numerous enemies. It is, as we commenced by remarking, ‘a struggle for existence,’ in which the weakest and least perfectly organised must always succumb.”

This tendency must apply to species as well as individuals, the best adapted becoming abundant, the others scarce or even extinct. If we knew the whole of the conditions and powers of a species “we might be able even to calculate the proportionate abundance of individuals, which is the necessary result.”

Hence, first, the animal population of a country is generally stationary (due to food and other checks); second, comparative abundance or scarcity of individuals is entirely due to organisation and resulting habits, the varying measure of success in the struggle being balanced by a varying population in a given area.

Variations from type must nearly always affect habits or capacities. Even changes of colour may promote concealment, while changes in the limbs or any external organs would affect the mode of procuring food, etc. “An antelope with shorter or weaker legs must necessarily suffer more from the attacks of the feline carnivora”; the passenger pigeon with less powerful wings could not always procure sufficient food. Hence species thus modified would gradually diminish; but, on the other hand, if modified in the direction of increased powers, would become more numerous. Varieties will fall under these two classes—those which will never rival, and those which will eventually outnumber, the parent species. If, then, some alteration in conditions occurred making existence more difficult to a certain species, first the less favourable variety would suffer and become extinct, then the parent species, while the superior variety would alone remain, “and on a return to favourable circumstances would rapidly increase in numbers and occupy the place of the extinct species and variety.”

The superior variety would thus replace the species, to which it could not return, for the latter could never compete with the former. Hence a tendency to revert would be checked. But the superior variety, when established, would in time give rise to new varieties, some of which would become predominant. Hence progression and continued divergence would follow, but not invariably, for the criteria of success or failure would vary, and would sometimes render a race which was under other conditions the most favoured now the least so. Variations without any effect on the life-preserving powers might also occur. But it is contended that certain varieties must, on the average, tend to persist longer than the parent species, while the scale on which nature works is so vast that an average tendency must in the end attain its full result.

Comparing domestic with wild animals, the very existence of the latter depends upon their senses and physical powers. Not so with the former, which are defended and fed by man.

Any favourable variety of a domestic animal is utterly useless to itself; while any increase of the powers and faculties of wild animals is immediately available, creating, as it were, a new and superior animal.

Again, with domestic animals all variations have an equal chance, and those which would be extremely injurious in a wild state are, under the artificial conditions, no disadvantage. Our domestic breeds could never have come into existence in a wild state, and if turned wild “must return to something near the type of the original wild stock, or become altogether extinct.”[E]

Hence we cannot argue from domestic to wild animals, the conditions of life in the two being completely opposed.

Lamarck’s hypothesis of change produced by the attempts of animals to increase the development of their own organs has been often refuted, but the view here proposed depends upon the action of principles constantly working in nature. Retractile talons of falcons and cats have not been developed by volition, but by the survival of those which had the greatest facilities for seizing prey. The long neck of the giraffe was not produced by constant stretching, but by the success which any increase in the length of neck ensured to its possessors. Even colours, especially of insects, are explained in the same way, for among the varieties of many tints, those “having colours best adapted to concealment ... would inevitably survive the longest.” We can similarly explain deficiency of some organs with compensating development of others, “great velocity making up for the absence of defensive weapons,” etc. Varieties with an unbalanced deficiency could not long survive. The action of the principle is like the governor of a steam-engine, checking irregularities almost before they become evident. Such a view accords well with “the many lines of divergence from a central type”; the increasing efficiency of a particular organ in a series of allied species; the persistence of unimportant parts when important ones have changed; the “more specialised structure,” said by Owen to be characteristic of recent as compared with extinct forms.

Hence there is a tendency of certain classes of varieties to progress further and further from the original type, and there is no reason for assigning any limit to this progression. Such gradual changes “may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.”

Wallace’s Essay has been reprinted without any alteration in his “Essays on Natural Selection,” recently re-issued combined with “Tropical Nature.”

CHAPTER XI.
COMPARISON OF DARWIN’S AND WALLACE’S SECTIONS OF THE JOINT MEMOIR—RECEPTION OF THEIR VIEWS—THEIR FRIENDSHIP.

WALLACE AND DARWIN.

Comparing the essays of these two naturalists, we observe that Darwin here first makes public the phrase “natural selection,” Wallace the “struggle for existence”; although so closely do their lines of thought converge that Darwin, using practically the same words, speaks of the “struggle for life.” Both show, by examples, the tendency of all animals to multiply at an enormous rate, and both show that their tolerably constant numbers are due to the constant supply of food.

Both treat of domesticated animals, but in very different ways. Darwin uses them as the practical illustration of selection, and argues that if man by selection can make such forms, Nature can make her species by the same means. Wallace disposes of the argument that the reversion of domesticated varieties to the wild form is a proof of the permanent distinctness of species, by showing in some detail that the former are “abnormal, irregular, artificial.”

Neither of them draws any distinction between instinct and other qualities, but assumes that the former is, like the latter, operated upon by natural selection.

Wallace makes a special point of protective resemblances in the colours of insects, etc.

The important principle of “divergence of character,” and the relatively unimportant one of “sexual selection,” are both clearly explained by Darwin.

Neither writer speaks of the direct effect of external conditions—except as a cause of plasticity by Darwin—or the inherited effects of use and disuse. Lamarck is mentioned only to be dismissed by Wallace. The evolution of the giraffe’s long neck is explained by Wallace on the principle of natural selection, which is contrasted with Lamarck’s original explanation of the same character. This contrast, which has been so often drawn, was therefore originally contained in the first public statement of natural selection.