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.
Down. | Bromley. | Kent. S.E.
I have been greatly interested by your letter, but your view is not new to me. If you will look at p. 240 of
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. 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. 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. I remember mentioning to you the case of Rhynchæa, but its nesting seems unknown. 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 enquiries
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.—
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; when I return to the work I shall find it much
better done by you than I c
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.—
Down.— Ap 29
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 sh
yours | C. Darwin
- f1 5517.f1The year is established by the relationship between this letter and the letter from A. R. Wallace, 1 May 1867.
- f2 5517.f2CD refers to the letter from A. R. Wallace, 26 April , and to Wallace's view that the brightness of the plumage of female birds was influenced by whether they sat on eggs in a covered or an open situation.
- f3 5517.f3In Origin 4th ed., pp. 240--1, in a paragraph on how the beauty of many male animals was acquired as a result of selection by the females, CD wrote:
We can sometimes plainly see the proximate cause of the transmission of ornaments to the males alone; for a pea-hen with the long tail of the male bird would be badly fitted to sit on her eggs, and a coal-black female capercailzie would be far more conspicuous on her nest and more exposed to danger than in her present modest attire.
- f4 5517.f4In Origin, p. 89, in a section on sexual selection, CD wrote:
I strongly suspect that some well-known laws with respect to the plumage of male and female birds, in comparison with the plumage of the young, can be explained on the view of plumage having been chiefly modified by sexual selection, acting when the birds have come to the breeding age or during the breeding season; the modifications thus produced being inherited at corresponding ages or seasons, either by the males alone, or by the males and females; but I have not space here to enter on this subject.The same passage appears in Origin 4th ed., p. 101.
- f5 5517.f5Wallace had written a paper on mimicry for the Westminster Review ([A. R. Wallace] 1867a), and published an article on bird coloration and nesting habits in the Journal of Travel and Natural History (A. R. Wallace 1868--9). Wallace cited the fourth edition of Origin in general in [A. R. Wallace] 1867a, but not specifically in connection with the nesting habits of birds, which he discussed on pp. 38--9. In A. R. Wallace 1868--9, Wallace wrote (pp. 77--8):
The sexual differences of colour and plumage in birds are very remarkable and have attracted much attention; and in the case of polygamous birds have been well explained by Mr Darwin's principle of sexual selection … but this theory does not throw any light on the causes which have made the female toucan, bee-eater, parroquet, macaw and tit, in almost every case as gay and brilliant as the male.CD's material on sexual selection for his `Essay upon Man' was published as Descent in 1871: CD had first intended to publish the material as a chapter in Variation but later decided to publish it separately (see letter to J. D. Hooker, 8 February  and n. 16). Sexual selection among animals, including humans, was discussed in the second part of the first volume and in the second volume of Descent.
- f6 5517.f6CD had visited London from 13 to 21 February 1867 (CD's `Journal' (Correspondence vol. 15, Appendix II)), but evidently did not see Wallace then (see letter to A. R. Wallace, 23 February 1867). He was also in London from 22 to 29 November 1866 (Correspondence vol. 14, Appendix II), and visited the Zoological Gardens (Correspondence vol. 14, letter to Edward Blyth, 10 December ). Henry Walter Bates had referred CD to Wallace for an answer to the question why some caterpillars were brightly coloured; see letter to A. R. Wallace, 23 February 1867, and letter from A. R. Wallace, 24 February .
- f7 5517.f7The Mexican bird (if it existed) has not been identified. CD may have been thinking of Menura superba, a lyre-bird of Australia, in which both sexes had long tails, and built a domed nest, which CD said was an anomaly in so large a bird (see Descent 2: 164--5).
- f8 5517.f8In the section on colour and nidification among birds in Descent (Descent 2: 167), CD wrote that in one bird species that built open nests, the male sat on the eggs and was brightly coloured.
- f9 5517.f9See letter to Alfred Newton, 19 January . CD discussed Rhynchaea (now Rostratula), the painted snipe, in Descent 2: 202--3, pointing out that the female was more brightly coloured than the male, and that there was reason to believe that the male sat on the eggs.
- f10 5517.f10CD had given this information in Birds, p. 16, and repeated it in Descent 2: 205--6. CD's letter to the Falkland Islands has not been found. See also letter to Alfred Newton, 4 March  and n. 3.
- f11 5517.f11See also Descent 2: 207--8.
- f12 5517.f12CD was correcting the proof-sheets of Variation (see `Journal' (Correspondence vol. 15, Appendix II)).
- f13 5517.f13In Descent, CD argued that most juvenile birds were dull coloured, and that many males and some females acquired bright colours through sexual selection. These colours, being acquired late in life, tended not to be transmitted to the opposite sex, and any tendency for them to be transmitted to the same sex would have been eliminated because it was dangerous for young birds to be brightly coloured. (See Descent 2: 196, 200, 222.)