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Darwin Correspondence Project

To A. R. Wallace   15 April [1868]1

Down. | Bromley. | Kent. S.E.

Ap. 15th

My dear Wallace

I have been deeply interested by your admirable article on Birds’ nests.—2 I am delighted to see that we really differ very little,—not more than two men almost always will—

You do not lay much or any stress on new characters spontaneously appearing in one sex (generally the male) & being transmitted exclusively, or more commonly only in excess, to that sex.— I on the other hand formerly paid far too little attention to protection. I had only a glimpse of the truth. But even now I do not go quite as far as you.— I cannot avoid thinking rather more than you do about the exceptions in nesting to the rule, especially the partial exceptions, i.e when there is some little difference between the sexes in species which build concealed nests.3

I am not quite satisfied about the incubating males: there is so little difference in conspicuousness between the sexes.—4 I wish with all my heart I could could go the whole length with you.— You seem to think that male birds probably select the most beautiful females; I must feel some doubt on this head, for I can find no evidence of it.5 Though I am writing so carping a note, I admire the article thoroughily.—

And now I want to ask a question.— When female Butterflies are more brilliant than their males you believe that they have in most cases or in all cases been rendered brilliant so as to mimic some other species & thus escape danger.6 But can you account for the males not having been rendered equally brilliant & equally protected. Although it may be most for the welfare of the species that the female should be protected, yet it would be some advantage, certainly no disadvantage, for the unfortunate male to enjoy an equal immunity from danger. For my part, I should say that the female alone had happened to vary in the right manner, & that the beneficial variations had been transmitted to the same sex alone.— Believing in this, I can see no improbability (but from analogy of domestic animals a strong probability) that variations leading to beauty must often have occurred in the males alone, & been transmitted to that sex alone. Thus I shd account in many cases for the greater beauty of the male over the female, without the need of the protective principle.— I shd. be grateful for an answer on this point.

I hope that your Eastern Book progresses well—7

My dear Wallace | Yours sincerely | C. Darwin


The year is established by the reference to A. R. Wallace 1868 (see n. 2, below).
CD refers to Wallace’s paper ‘A theory of birds’ nests’, which appeared in the April 1868 issue of Journal of Travel and Natural History (A. R. Wallace 1868).
Wallace had argued that birds with both sexes brightly coloured built concealed nests while those with only one of the sexes brightly coloured built open nests (A. R. Wallace 1868, p. 78).
Wallace had given examples of birds in which the female was more brightly coloured than the male and noted that in these rare cases the male incubated the eggs (A. R. Wallace 1868, pp. 83–4).
CD probably refers to a passage where Wallace states that ‘the normal action of ‘sexual selection’ is to develop colour and beauty in both sexes, by the preservation and multiplication of all varieties of colour in either sex which are pleasing to the other’ (A. R. Wallace 1868, p. 82).
See, for example, A. R. Wallace 1866 and [A. R. Wallace] 1867b, pp. 24–5.
CD refers to The Malay Archipelago (A. R. Wallace 1869). CD had encouraged Wallace to write the book (see letter from A. R. Wallace, 7 February 1868, n. 4, and letter to A. R. Wallace, 22 February [1868]).


Wallace, Alfred Russel. 1868. A theory of birds’ nests: shewing the relation of certain sexual differences of colour in birds to their mode of nidification. Journal of Travel and Natural History 1 (1868–9): 73–89.


Admires ARW’s "Theory of birds’ nests" [J. Travel & Nat. Hist. 1 (1868): 73].

Discusses their respective views on birds’ nests, sexual selection, and protection.

Asks why, if brilliant colours of female butterflies are result of protective mimicry, do not males become equally brilliant? CD believes variation in females alone accounts for it, rather than protection.

Letter details

Letter no.
Charles Robert Darwin
Alfred Russel Wallace
Sent from
Source of text
The British Library (Add MS 46434: 133–5)
Physical description
6pp ††

Please cite as

Darwin Correspondence Project, “Letter no. 6121,” accessed on 18 September 2021,

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