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can understand that to get the full benefit of this protection they should be easily recognized, should have some outward character by which birds would soon learn to know them and thus let them alone; because if birds could not tell the eatable from the uneatable till they had seized and tasted them, the protection would be of no avail, a growing caterpillar being so delicate that a wound is certain death. If, therefore, the eatable caterpillars derive a partial protection from their obscure and imitative colouring, then we can understand that it would be an advantage to the uneatable kinds to be well distinguished from them by bright and conspicuous colours.

"I may add that this question has an important bearing on the whole theory of the origin of the colours of animals, and especially of insects. I hope many of your readers may be thereby induced to make such observations as I have indicated, and if they will kindly send me their notes at the end of the summer, or earlier, I will undertake to compare and tabulate the whole, and to make known the results, whether they confirm or refute the theory here indicated.

"ALFRED R. WALLACE. “9, St. Mark's Crescent, Regent's Park, N.W.,

“March, 1867."

This letter brought me only one reply, from a gentleman in Cumberland, who informed me that the common “gooseberry” caterpillar, which is the lava of the magpie moth (Abraras grossulariata), is refused by young pheasants, partridges, and wild ducks, as well as sparrows and finches, and that all birds to whom he offered it rejected it with evident dread and abhorrence. But in 1869 two entomologists, Mr. Jenner Weir and Mr. A. G. Butler, gave an account of their two seasons' experiments and observations with several of our most gaily-coloured caterpillars, and with a considerable variety of birds, and also with lizards, frogs, and spiders, confirming my explanation in a most remarkable manner. An account of these experiments is given in the second and all later editions of my book on “Natural Selection ;” but it

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is more fully treated in my “Darwinism," chap. ix., under the heading "Warning Colours among Insects,” and it has thus led to the establishment of a general principle which is very widely applicable, and serves to explain a not inconsiderable proportion of the colours and markings in the animal world. It is, of course, only a wider application of the same fundamental fact by which Bates had already explained the purpose of “mimicry" among insects, and it is a matter of surprise to me that neither Bates himself nor Darwin had seen the probability of the occurrence of inedibility in the larvæ as well as in the perfect insects.

In the year 1870 Mr. A. W. Bennett read a paper before Section D. of the British Association at Liverpool, entitled “The Theory of Natural Selection from a Mathematical Point of View," and this paper was printed in full in Nature of November 10, 1870. To this I replied on November 17, and my reply so pleased Mr. Darwin that he at once wrote to me as follows:

“ Down, November 22. “MY DEAR WALLACE,

“I must ease myself by writing a few words to say how much I and all in this house admire your article in Nature. You are certainly an unparalleled master in lucidly stating a case and in arguing. Nothing ever was better done than your argument about the term Origin of Species, and about much being gained if we know nothing about precise cause of each variation."

At the end of the letter he says something about the progress of his great work, “The Descent of Man."

“I have finished ist vol. and am half-way through proofs of 2nd vol. of my confounded book, which half kills me by fatigue, and which I fear will quite kill me in your good estimation.

"If you have leisure, I should much like a little news of you and your doings and your family,

“Ever yours very sincerely,

" CH. DARWIN."

The above remark, “kill me in your good estimation," refers to his views on the mental and moral nature of man being very different from mine, this being the first important question as to which our views had diverged. But I never had the slightest feeling of the kind he supposed, looking upon the difference as one which did not at all affect our general agreement, and also as being one on which no one could dogmatize, there being much to be said on both sides, The last paragraph shows the extreme interest he took in the personal affairs of all his friends.

As my article of which he thought so highly is buried in an early volume of Nature, I will here reproduce the rather long paragraph which so specially interested him. It is as follows:

"The first objection brought forward (and which had been already advanced by the Duke of Argyll) is, that the very title of Mr. Darwin's celebrated work is a misnomer, and that the real 'origin of species ’ is that spontaneous tendency to variation which has not yet been accounted for. Mr. Bennett further remarks that, throughout my volume of 'Essays,' I appear to be unconscious that the theory I advocate does not go to the root of the matter. It is true that I am 'unconscious' of anything of the kind, for I maintain, and am prepared to prove, that the theory, if true, does go to the very root of the question of the 'origin of species.' The objection, which from its being so often made, and now again brought forward, is evidently thought to be an important one, is founded on a misapprehension of the right meaning of words. It ignores the fact that the word 'species' denotes something more than ‘variety' or 'individual. A species is an organic form (or group) which, for periods of great and indefinite length, as compared with the duration of human life, fluctuates only within narrow limits. But the spontaneous tendency to variation' is altogether antagonistic to such comparative stability, and would, if unchecked, entirely destroy all 'species.' Abolish, if possible, selection and survival of the fittest, so that every spontaneous variation should survive in equal proportion with all others, and the result must inevitably be an endless variety of unstable forms

no one of which would answer to what we mean by the word 'species. No other cause but selection has yet been discovered capable of perpetuating and giving stability to some forms, and causing the disappearance of others, and therefore Mr. Darwin's book, if there is any truth in it at all, has a logical claim to its title. It shows how 'species,' or stable forms, are produced out of unstable spontaneous variations, which is certainly to trace their origin.' The distinction of 'species' and 'individual' is equally important. A horse, or a number of horses, as such, do not constitute a 'species.' It is the comparative permanence of the form as distinguished from the ass, quagga, zebra, tapir, camel, etc., that makes them one.

Were there a mass of intermediate forms connecting all these animals by fine gradations, and hardly a dozen individuals alike—as would probably be the case had selection not acted—there might be a few horses, but there would be no such thing as a species of horse. That could only be produced by some power capable of eliminating intermediate forms as they arose, and preserving all of the true horse type ; and such a power was first shown to exist by Mr. Darwin. The origin of varieties and individuals is one thing, the origin of species another."

It is a remarkable thing that this very simple preliminary misunderstanding of the very meaning of the term "species continued to appear year after year in most of the criticisms of the theory of natural selection. It was put forward both by mere literary critics and also by naturalists, and was in many cases adduced as a discovery which completely overthrew the whole of Darwin's work. So frequent was it that twenty years later, when writing my "Darwinism," I found it necessary to devote the first chapter to a thorough explanation of this point, under the heading, "What are ‘Species,' and what is meant by their 'Origin'?" and I think I may feel confident that to those who have read that work this particular purely imaginary difficulty will no longer exist.

Soon after the “Descent of Man" appeared, I wrote to Darwin, giving my impressions of the first volume, to which he replied (January 30, 1871). This letter is given in the

“Life and Letters ” (iii. p. 134), but I will quote two short passages expressing his kind feelings towards myself. He begins, “Your note has given me very great pleasure, chiefly because I was so anxious not to treat you with the least disrespect, and it is so difficult to speak fairly when differing from any one.

If I had offended you, it would have grieved me more than you will readily believe.” And the conclusion is, "Forgive me for scribbling at such length. You have put me quite in good spirits; I did so dread having been unintentionally unfair towards your views. I hope earnestly the second volume will escape as well. I care now very little what others say. As for our not agreeing, really, in such complex subjects, it is almost impossible for two men who arrive independently at their conclusions to agree fully ; it would be unnatural for them to do so."

I reviewed “The Descent," in The Academy, early in March, and Darwin wrote to me on the 16th, expressing his gratification at its whole tone and matter, and then, referring to the differences between us, making what was then a good point against me—that my objections to sexual selection having produced certain results in man, had not much force if, as he believed, I admitted that the plumes of the birds of paradise had been thus gained. At that time, though I had begun to doubt, I had not definitely rejected the whole of that part of "sexual selection” depending on female preference for certain colours and ornaments.

On July 9, 1871, he wrote me a long letter, chiefly about Mr. Mivart's criticisms and accusations in his book on “The Genesis of Species," and again in a severe article in the Quarterly Review. These he proposed replying to in a new edition of the “Origin,” but the incident worried him a good deal. In a postscript he says, "I quite agree with what you say, that Mivart fully intends to be honourable, but he seems to me to have the mind of a most able lawyer retained to plead against us, and especially against me. God knows whether my strength and spirit will last out to write a chapter versus Mivart and others; I do so hate controversy, and feel I shall do it so badly."

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