My dear Wallace

The offer of your valuable notes is most generous, but it w^d vex me to take so much from you, as it is certain that you c^d work up the subject very much better than I could. Therefore I earnestly & without any reservation hope that you will proceed with y^r paper, so that I return y^r notes.²

You seem already to have well investigated the subject. I confess on receiving yr note that I felt rather flat at my recent work being almost thrown away, but I did not intend to shew this feeling.³ As a proof how little advance I had made on the subject, I may mention that though I had been collecting facts on the colouring, & other sexual differences in mammals, your explanation with respect to the females had not occurred to me. I am surprized at my own stupidity, but I have long recognized how much clearer & deeper your insight into matters is than mine. I do not know how far you have attended to the laws of inheritance, so what follows may be obvious to you. I have begun my discussion on sexual selection by shewing that new characters often appear in one sex & are transmitted to that sex alone, & that from some unknown cause such characters apparently appear oftener in the male than in the female. Secondly characters may be developed & be confined to the male, & long afterwards be transferred to the female. 3^rdly characters may arise in either sex & be transmitted to both sexes, either in an equal or unequal degree.⁴ In this latter case I have supposed that the survival of the fittest has come into play with female birds & kept the female dull-coloured.⁵ With respect to the absence of spurs in female gallinaceous birds, I presume that they w^d be in the way during incubation; at least I have got the case of a German breed of fowls in which the hens were spurred, & were found to disturb & break their eggs much.⁶

With respect to the females of deer not having horns, I presume it is to save the loss of organized matter.⁷

In y^r note you speak of sexual selection & protection as sufficient to account for the colouring of all animals, but it seems to me doubtful how far this will come into play with some of the lower animals, such as sea anemones, some corals &c &c—⁸

On the other hand Häckel has recently well shewn that the transparency & absence of colour in the lower oceanic animals, belonging to the most different classes, may be well accounted for on the principle of protection.⁹

Some time or other I sh^d like much to know where y^r paper on the nests of birds has appeared, & I shall be extremely anxious to read y^r paper in the West. Rev. Your paper on the sexual colouring of birds will I have no doubt be very striking.¹⁰

Forgive me, if you can, for a touch of illiberality about y^r paper & believe me yrs very sincerely | Ch. Darwin