Dear Darwin,—Many thanks for your long letter. I thought you might have had some notes or memories of conversations, to show in a general way what the 'line' would have been.[63] If so, of course I should not have said that my sayings were inspired, but should myself have known that I was not going astray.
The line I am going to take is:
1st. Even assuming, for sake of argument, that heightened colour is correlated with increased vigour, Wallace everywhere fails to distinguish between brilliancy and ornament; yet it is the disposition of colours in patterns, &c., that is the chief thing to be explained.
2nd. In many cases (e.g. peacock's tail) the pattern is only revealed when unfolded during courtship. Besides natural selection could not be such a fool as to develope large (physiologically expressive) and weighty (impeding flight) structures like this—stags' antlers, &c., merely as correlates of vigour.
3rd. There is not much in Wallace's merely negative difficulty about our not knowing what goes on in the mind of a hen, when we set against that difficulty the positive fact that we can see what does go on in the mind of a cock—display, antics, song, &c.
4th. To say that 'each bird finds a mate under any circumstances' is merely to beg the whole question.
5th. There remains Wallace's jealousy of natural selection. He will not have any other 'factor,' and therefore says natural selection must eat up sexual selection like the lean kine have the fat kine. But natural selection alone does not explain all the phenomena of sexual colouring, courtship, &c., and sexual selection is exactly the theory that does. Wallace's jealousy, therefore, is foolish and inimical to natural selection theory itself, by forcing it into explanations which are plainly false.
My own belief is, that what Lankester calls the 'pure Darwinians' are doing the same thing in another direction. By endeavouring, with Wallace and Weismann, to make natural selection all in all as the sole cause of adaptive structure, and expressly discarding the Darwinian recognition of use and disuse. I think they are doing harm to natural selection theory itself. Moreover, because I do not see any sufficient reason as yet to budge from the real Darwinian standpoint (Weismann has added nothing to the facts which were known to Charles Darwin), the post-Darwinians accuse me of moving away from Darwinian principles. But it is they who are moving, and, because they see a change in our relative positions, affirm that it is I. In point of fact, my position has never varied in the least, and my confession of faith would still follow, in every detail, that given on p. 421 of 'Origin,' 6th ed., which, it seems to me, might also be regarded as prophetic no less than retrospective.
If I did not say all this in my paper in physiological selection, it is only because I never conceived the possibility of my being accused of trying to undermine natural selection; and, therefore, I only stated as briefly as possible what my relations were to it. Yet it seems to me that this statement was clear enough if Wallace had not come down with his preposterous 'Romanes versus Darwin.' At all events, it is not in my power—or, I believe, in that of anybody else—to express more strongly than I now have in 'Nature,' in answer to Dyer, what I do hold about natural selection in its relation to physiological selection, sexual selection, and other subordinate principles. Of course, if there were a debate on these lines at the B.A., I should get my part of it published somewhere. As far as I can honestly see, my 'position' is absolutely identical with that in last editions of 'Origin' and 'Descent,' with, perhaps, a 'tendency' to lay more stress on levelling influence of Panmixia.
Re physiological selection. I have sent Correvon, of Geneva, £50 to help in founding a garden in the Alps, which will have the proud distinction of being the highest garden in the world. He is a splendid man for his knowledge of Alpine flora, and besides, is strongly bitten with a desire to test physiological selection. Of course I shall do the hybridising experiments myself, but he will collect the material from the different mountains—i.e. nearly allied species, topographically separated, and therefore, I hope, mutually fertile. The converse experiments of nearly allied species on common areas may be tried in England.