To A. R. Wallace   6 October [1868]¹

My dear Wallace

Your letter is very valuable to me & in every way very kind. I will not inflict a long answer, but only answer your queries.²

There are breeds (viz Hamburgh) in which both sexes differ much from each other & from both sexes of G. bankiva; & both sexes are kept constant by selection.—

The comb of Spanish ♂ has been ordered to be upright & that of Spanish ♀ to lop over, & this has been effected. There are sub-breeds of Game Fowl, with ♀^s very distinct & ♂^s almost identical; but this apparently is result of spontaneous variation without special selection.—³

I am very glad to hear of case of ♀^s Birds of Paradise.—⁴

I have never in the least doubted possibility of modifying female birds alone for protection; & I have long believed it for Butterflies: I have wanted only evidence for the females alone of Birds, having had their colour modified for protection.

But then I believe, that the variations by which a female bird or butterfly could get or has got protective colouring have probably from the first been variations limited in their transmission to the female sex;—& so with the variations of the male, where the male is more beautiful than the female, I believe the variations were sexually limited in their transmission to the males.⁵

I am delighted to hear that you have been hard at work on your M.S.⁶

Yours most sincerely | Ch. Darwin