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Darwin Correspondence Project

From A. R. Wallace   4 October 1868

9 St. Mark’s Crescent | N.W.

Octr. 4th. 1868.

Dear Darwin

I should have answered your letter before, but I have been very busy reading over my MSs. the last time before going to press, drawing Maps &c &c.1

Your first question can not be answered, because we have not in individual cases of slight sexual difference, sufficient evidence to determine how much of that difference is due to sexual selection acting on the male,—how much to natural selection (protective) acting on the female;—or how much of the difference may be due to inherited differences from ancestors who lived under different conditions.2

On your second question I can give an opinion. I do think the females of the Gallinaceæ you mention have been either modified, or prevented from acquiring much of the brighter plumage of the male, by the need of protection. I know that Gallus bankiva frequents drier & more open situations than, Pavo muticus which in Java is found among grassy & leafy vegetation,—corresponding with the colours of the two females.3 So the Argus pheasants ♂ & ♀. are I feel sure protected by their tails corresponding to dead leaves of the dry lofty forests in which they dwell; and the female of the gorgeous fire-back pheasant, Lophura vielottii, is of a very similar rich brown colour.4

These and many other colours of female birds seem to me exactly analogous to the colours of both sexes in such groups as the snipes, woodcocks, plovers, ptarmigan, desert birds, arctic animals, green birds in leafy tropical jungles. If the colours of all such species are protective when both sexes are so coloured, I cannot believe that exactly analogous and often exactly similar colours, are not protective when the females only possess them.

If the females in these cases derive their colour from inheritance and from partial transmission of sexually selected male colours,—then these colours have no relation to the environment, which I cannot conceive possible.

I do not see how any difficulty as to transmission can have weight, in the face of the facts of dimorphism, where distinct colours and distinct forms are transmitted to the offspring of one female.

Again you have yourself laid down the principle that—“sexual selection is less rigorous than natural selection”.5 Then what is to prevent the female being selected for protection,—if she requires it,—while the male is selected for brilliant colour because he requires it and does not so much require protection.

The one case of the African Papilio merope seems to me to be inconsistent with your theory and to prove mine. In different localities in South & Trop. Africa it has distinct forms of females (three or four) each mimicking a Danais found in that locality, while the male remains almost unchanged. But in Madagascar where the conditions are certainly very different, the female is exactly like the male! yet otherwise hardly distinguishable as a species.6 These different forms can not be transmitted from a common ancestor nor partially transferred from the male from whom they totally differ, & they seem to me to prove that females can be easily modified for protection independently of the males.

I presume artificial selection has never been applied to hen birds only, but I have no doubt that a breed might be obtained in which the cocks remained with the ordinary characters of the Gallus bankiva while the hens were modified in colour. Does not any case of this kind exist in fowls?

In like manner could not the cock be bred for certain feathers in tail or hackles,—& the hen for certain other feathers? At all events such cases do exist in nature in insects if not in birds.

It is a curious case of the two birds of paradise P. apoda & P. papuana, for the females actually differ more than the males. The female of P. papuana is pure white beneath, whereas in apoda she is all deep brown like the male.7 Here must have been some separate selecting power acting on the female and it proves that the female may be modified in an altogether different way from that in which sexual selection has modified the male in the whole group.

Have you ever thought of the red wax-tips on wings of Bombycilla, a very sexual-looking character yet occurring also in the female;—because it beautifully imitates the red fructifications of lichens, & the nest is generally made of lichens, & the bird’s back is a licheny colour.—8

I cannot accept your explanation of the coincidence of hidden or covered nest with gay females,—that the habits have altered in consequence of the danger of the gay colour.9 Throughout all nature we find colour varying rapidly & continually adapted for protection & even for the pleasure of females. And if the need of protection has been powerful enough to change the females of a white Pieris into a variety of colours & a definite pattern, to imitate a Heliconia,—much more easy would it be, merely to tone down brighter colours into obscure tints.10

I am sorry to find that our difference of opinion on this point is a source of anxiety to you.11 Pray do not let it be so. The truth will come out at last, and our difference may be the means of setting others to work who may set us both right.

After all, this question is only an episode (though an important one) in the great question of the “Origin of Species,” and whether you or I are right will not at all affect the main doctrine,—that is one comfort.

I hope you will publish your treatise on “Sexual selection” as a separate book as soon as possible,12 & then while you are going on with your other work, there will no doubt be found some one to battle with me over your facts, on this hard problem.

With best wishes & kind regards to Mrs. Darwin & all your family | Believe me Dear Darwin | Yours very faithfully | Alfred R. Wallace—

C. Darwin Esq.

CD annotations

4.3 If the colours … possess them. 4.6] scored blue crayon
4.3 If the colours … protection. 7.4] crossed pencil
5.1 If the females … possible. 5.3] ‘No— inheritance for a ground Bird’ blue crayon
7.2 Then … it,— 7.3] scored blue crayon
8.8 & they seem … males. 8.9] double scored blue crayon; scoring del blue crayon
9.1 I presume … in birds. 10.3] crossed pencil
9.4 Does … fowls?] ‘yes’ added, scored blue crayon; all del blue crayon
10.1 In … feathers? 10.2] ‘yes’ added, scored blue crayon; all del blue crayon
11.2 The female … male. 11.3] double scored blue crayon
12.1 Have … colour.— 12.4] scored blue crayon; scoring del blue crayon
14.1 I am … problem. 16.3] scored blue crayon

Footnotes

See letter to A. R. Wallace, 23 September [1868]. Wallace also refers to the manuscript of his Malay Archipelago (A. R. Wallace 1869). Wallace wrote a draft of this letter dated 27 September (DAR 106: B83–5). See also A. R. Wallace 1905, 2: 18–20.
CD had asked whether the slightly less vivid colours of some female birds were acquired for protection (see letter to A. R. Wallace, 23 September [1868]).
CD had asked why he should believe that the similarities of some female birds, including Gallus bankiva and the peahen, were due to their protective advantage even though they lived under different conditions (see letter to A. R. Wallace, 23 September [1868]). The old order Gallinaceae is roughly equivalent to the modern order Galliformes. Pavo muticus is the green peafowl; Gallus bankiva is now G. gallus, the red junglefowl.
Wallace may refer to the crested argus and great argus, both in the pheasant family; see Birds of the world 2: 550–1. Wallace discussed the protective coloration of what he called the great argus pheasant in A. R. Wallace 1869, 1: 51–2. Wallace also refers to what is now the crested fireback or Viellot’s fireback, Lophura ignita.
Wallace presented this case in A. R. Wallace 1879, pp. 288–90. Papilio merope is a synonym of P. dardanus; for the different female forms, see Van Son 1949, pp. 6–9.
In Descent 2: 192–3, CD mentioned that the females of Paradisea apoda and P. papuana differed from each other in colour more than did the respective males; he cited A. R. Wallace 1869, 2: 394 for the information. The genus is now spelled Paradisaea, and P. papuana is now P. minor, the lesser bird of paradise.
In Descent 2: 179–80, CD referred to Bombycilla carolinensis (now B. cedrorum, the cedar waxwing). It was one of a number of examples he gave where females acquired late in life characters ‘proper to the male’, and where he believed protection could hardly have come into play. He thought the phenomenon could only be accounted for by the ‘laws of inheritance’.
See Descent 2: 171. No letter has been found in which CD raised this argument with Wallace; they may have discussed it when they met in September (see letter to J. D. Hooker, [8–10 September 1868] and n. 8).
The descent of man, and selection in relation to sex (Descent) was published in 1871.

Summary

Sexual differences in coloration. Sexual selection versus natural selection as explanations. ARW continues to argue against sexual selection, saying that natural selection, in keeping the female dull for protection, would account for differences in sexual colouring more effectively than inheritance and partial transmission of sexually selected male colours. Colours of female birds of paradise. Protective coloration. Disagrees with CD on coincidence of hidden nests and bright colours of females.

Letter details

Letter no.
DCP-LETT-6408
From
Alfred Russel Wallace
To
Charles Robert Darwin
Sent from
London, St Mark’s Crescent, 9
Source of text
DAR 106: B68–69
Physical description
8pp †† & draft

Please cite as

Darwin Correspondence Project, “Letter no. 6408,” accessed on 20 September 2019, https://www.darwinproject.ac.uk/letter/DCP-LETT-6408.xml

Also published in The Correspondence of Charles Darwin, vol. 16

letter