To A. R. Wallace 29 April 1
Down. | Bromley. | Kent. S.E.
I have been greatly interested by your letter, but your view is not new to me.2 If you will look at p. 240 of 4th Ed. of Origin you will find it very briefly given with two extreme examples of the Peacock & Black grouse.3 A more general statement is given at p. 101 or at p. 89 of the 1st Ed., for I have long entertained this view, though I have never had space to develope it.4 But I had not sufficient knowledge to generalize as far as you do about colouring & nesting. In your paper perhaps you will just allude to my scanty remark in the 4th Ed, because in my Essay upon Man I intend to discuss the whole subject of sexual selection, explaining as I believe it does much with respect to man.5 I have collected all my old notes & partly written my discussion & it wd be flat work for me to give the leading idea as exclusively from you. But as I am sure from your greater knowledge of ornithology & Entomology that you will write a much better discussion than I cd, your paper will be of great use to me.
Nevertheless I must discuss the subject fully in my essay on man. When we met at the Zoolog. Soc. & I asked you about the sexual differences in kingfishers I had this subject in view; as I had when I suggested to Bates the difficulty about gaudy caterpillars which you have so admirably, (as I believe it will prove) explained.6 I have got one capital case (genus forgotten) of a Mexican bird in which the female has long tailed plumes & which consequently builds a different nest from all her allies.7 With respect to certain female birds being more brightly coloured than the males, & the latter incubating I have gone a little into the subject & cannot say that I am fully satisfied.8 I remember mentioning to you the case of Rhynchæa, but its nesting seems unknown.9 In some other cases the difference in brightness seemed to me hardly sufficiently accounted for by the principle of protection.
At the Falkland I’s there is a Carrion hawk in which the female (as I ascertained by dissection) is the brightest coloured, & I doubt whether protection will here apply; but I wrote several months ago to the Falklands to make enquiries10
The conclusion to which I have been leaning is that in some of these abnormal cases the colour happened to vary in the female alone, & was transmitted to females alone, & that her variations have been selected through the admiration of the male.—11
It is a very interesting subject but I shall not be able to go on with it for the next 5 or 6 months, as I am fully employed in correcting dull proof sheets;12 when I return to the work I shall find it much better done by you than I cd have succeeded in doing.
With many thanks for your very interesting note | believe me dear Wallace | yours very sincerely | Ch. Darwin
It is curious, how we hit on the same ideas.—
I have endeavoured and show in my M.S. discussion that nearly the same principles account for young birds not being gaily coloured, in many cases,—but this is too complex a point for a note.—13
Down.— Ap 29th.
My dear Wallace
On reading over your letter again & on further reflexion, I do not think (as far as I remember my words) that I expressed myself nearly strongly enough on the value & beauty of your generalisation, viz that all Birds, in which the female is conspicuously or brightly coloured, build in holes or under domes. I thought that this was the explanation in many, perhaps most cases, but do not think I shd. ever have extended my view to your generalisation.— Forgive me troubling you with this. P.S.
yours | C. Darwin
Comments on ARW’s view of colouring in relation to sexual selection and protection. It is not new to CD. Hopes to discuss subject fully in his "Essay on Man" [Descent]. As to the problem of brightly coloured females, CD is not satisfied that it is due to males taking over incubation. Admires "value and beauty" of ARW’s generalisations.
Please cite as
Darwin Correspondence Project, “Letter no. 5517,” accessed on 25 September 2016, http://www.darwinproject.ac.uk/DCP-LETT-5517