CHAPTER XI.

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

[Sidenote: 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.

As has been indicated above, Darwin suggested a cause of variation in the direct effect of changed external conditions on the reproductive system.

In comparing the two essays it is not unnatural to conclude, as Professor Osborn has done (“From the Greeks to Darwin,” 1894, p. 245), that the two writers held different views upon the material utilised by natural selection in the production of new species, Darwin relying upon the usual slight differences which separate individuals and upon variations in single characters, Wallace upon fully formed varieties--viz. individuals which departed conspicuously from the type of the species, and which may exist singly or in considerable numbers side by side with the parent form.

Professor Osborn’s actual words are as follows:--

“Darwin dwells upon _variations in single characters_, as taken hold of by Selection; Wallace mentions variations, but dwells upon _full-formed varieties_, as favourably or unfavourably adapted. It is perfectly clear that with Darwin the struggle is so intense that the chance of survival of each individual turns upon a single and even slight variation. With Wallace, varieties are already presupposed by causes which he does not discuss, a change in the environment occurs, and those varieties which happen to be adapted to it survive. There is really a wide gap between these two statements and applications of the theory.”

Further consideration tends to obliterate this supposed distinction. Although Wallace used the term “variety” as contrasted with “species,” the whole context proves that he, equally with Darwin, recognised the importance of individual variations and of variations in single characters. This becomes clear when we remember his argument about the neck of the giraffe, the changes of colour and hairiness, the shorter legs of the antelope, and the less powerful wings of the passenger pigeon. Wallace has kindly written to me (May 12th, 1896) stating the case as I have given it, and he further explains--

“I used the term ‘varieties’ because ‘varieties’ were alone recognised at that time, individ^l variability being ignored or thought of _no importance_. My ‘varieties’ therefore included ‘individual variations.’”

On the other hand, Darwin certainly included large single variations (in other words, “varieties”) as well as ordinary individual differences, among the material for natural selection, and he did not abandon the former until he was convinced by the powerful reasoning of Fleeming Jenkin (_North British Review_, June, 1867), who argued that single large differences of a sudden and conspicuous kind (Darwin’s “variations”) would certainly be swamped by intercrossing. Upon this review of the “Origin” Francis Darwin says (“Life and Letters”)--

“It is not a little remarkable that the criticisms which my father, as I believe, felt to be the most valuable ever made on his views should have come, not from a professed naturalist but from a Professor of Engineering.”

After reading this review, Darwin wrote to Wallace (January 22nd, 1869):--

“I always thought individual differences more important than single variations, but now I have come to the conclusion that they are of paramount importance, and in this I believe I agree with you. Fleeming Jenkin’s arguments have convinced me.”

The ambiguity of this sentence evidently misled Wallace into believing that the single variations were considered of paramount importance. Darwin therefore wrote again (February 2nd):--

“I must have expressed myself atrociously; I meant to say exactly the reverse of what you have understood. F. Jenkin argued in the ‘North British Review’ (June 1867) against single variations ever being perpetuated, and has convinced me, though not in quite so broad a manner as here put. I always thought individual differences more important; but I was blind and thought single variations might be preserved much oftener than I now see is possible or probable. I mentioned this in my former note merely because I believed that you had come to a similar conclusion, and I like much to be in accord with you. I believe I was mainly deceived by single variations offering such simple illustrations, as when man selects.”

From these two letters to Wallace we see that the latter was the first to give up the larger variations in favour of ordinary individual differences.

Darwin also wrote to Victor Carus on May 4th, 1869:--

“I have been led to ... infer that single variations are even of less importance, in comparison with individual differences, than I formerly thought.”

There has been much misconception on this point, and a theory of evolution by the selection of large single variations--a view held by many, but not by Darwin--has been passed off as the Darwinian theory of natural selection. It is surprising that this old mistake should have been repeated at so recent a date, and on so important an occasion as the Presidential Address to the British Association at Oxford on August 8th, 1894, and that so ill-aimed a criticism should have been quoted with approval in a leading article in the _Times_ of the following day. The following extracts from Lord Salisbury’s address unfortunately leave no doubt on the matter:

[Sidenote: LORD SALISBURY’S CRITICISM.]

“What is to secure that the two individuals of opposite sexes in the primeval forest, who have been both accidentally blessed with the same advantageous variation shall meet, and transmit by inheritance that variation to their successors?... The biologists do well to ask for an immeasurable expanse of time, if the occasional meetings of advantageously varied couples from age to age are to provide the pedigree of modifications which unite us to our ancestor the jelly-fish.... There would be nothing but mere chance to secure that the advantageously varied bridegroom at one end of the wood should meet the bride, who by a happy contingency had been advantageously varied in the same direction at the same time at the other end of the wood. It would be a mere chance if they ever knew of each other’s existence--a still more unlikely chance that they should resist on both sides all temptations to a less advantageous alliance. But unless they did so, the new breed would never even begin, let alone the question of its perpetuation after it had begun.”

It is of interest to reproduce Lord Salisbury’s words in close proximity to Darwin’s real statements on the subject, as shown in the letters to his friends--statements which are also expressed in many places in his published works.

The joint paper was read before the Linnean Society on July 1st, 1858, about a fortnight after Wallace’s essay had been received by Darwin. There was no discussion, but the interest and excitement at the meeting were very great, owing in large part to the influential support with which the new theory came before the scientific world. Darwin appreciated the importance of this support at its true value, for he wrote to Hooker, July 5th:--

“You must know that I look at it, as very important, for the reception of the view of species not being immutable, the fact of the greatest Geologist and Botanist in England taking _any sort of interest_ in the subject: I am sure it will do much to break down prejudices.”

In the following January Darwin received a letter from Wallace, and his reply (on the 25th) shows how much relieved and pleased he was at its generous spirit. Alluding to Lyell’s and Hooker’s action in his “Autobiography” Darwin says:--“I was at first very unwilling to consent, as I thought Mr. Wallace might consider my doing so unjustifiable, for I did not then know how generous and noble was his disposition.” It was this letter which conveyed the knowledge to him and set his mind at rest on the subject.

Thus ended one of the most interesting and memorable episodes in the history of science. It was sufficiently remarkable that two naturalists in widely-separated lands should have independently arrived at the theory which was to be the turning-point in the history of biology and of many other sciences--although such simultaneous discoveries have been known before; it was still more remarkable that one of the two should unknowingly have chosen the other to advise him upon the theory which was to be for ever associated with both their names. It was a magnificent answer to those who believed that the progress of scientific discovery implies continual jealousy and bitterness, that the conditions attending the first publication of the theory of natural selection were the beginning of a life-long friendship and of mutual confidence and esteem.[F]

[Sidenote: FRIENDSHIP WITH WALLACE.]

It is justifiable to speak of this episode as the _beginning_ of Darwin’s and Wallace’s friendship, for the latter writes (February, 1895):--

“I had met him _once_ only for a few minutes at the Brit. Mus. before I went to the East.”

Later on Darwin, in his letters to Wallace, more than once alluded to the simultaneous publication of their essays. Thus he wrote, April 18th, 1869, congratulating Wallace on his article in the _Quarterly Review_ for that month:--

“I was also much pleased at your discussing the difference between our views and Lamarck’s. One sometimes sees the odious expression, ‘Justice to myself compels me to say,’ &c., but you are the only man I ever heard of who persistently does himself an injustice, and never demands justice. Indeed, you ought in the review to have alluded to your paper in the ‘Linnean Journal,’ and I feel sure all our friends will agree in this. But you cannot ‘Burke’ yourself however much you may try, as may be seen in half the articles which appear.”

And again, on April 20th of the following year, he wrote:--

“I hope it is a satisfaction to you to reflect--and very few things in my life have been more satisfactory to me--that we have never felt any jealousy towards each other, though in one sense rivals. I believe that I can say this of myself with truth, and I am absolutely sure that it is true of you.”