LETTER 430. TO A.R. WALLACE.
Down, May 5th [1867].

The offer of your valuable notes is most generous, but it would vex me to
take so much from you, as it is certain that you could work up the subject
very much better than I could. Therefore I earnestly, and without any
reservation, hope that you will proceed with your paper, so that I return
your notes. You seem already to have well investigated the subject. I
confess on receiving your note that I felt rather flat at my recent work
being almost thrown away, but I did not intend to show this feeling. 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, and other sexual
differences in mammals, your explanation with respect to the females had
not occurred to me. I am surprised at my own stupidity, but I have long
recognised how much clearer and 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 showing that new characters often appear in one sex and
are transmitted to that sex alone, and that from some unknown cause such
characters apparently appear oftener in the male than in the female.
Secondly, characters may be developed and be confined to the male, and long
afterwards be transferred to the female. Thirdly, characters may arise in
either sex and be transmitted to both sexes, either in an equal or unequal
degree. In this latter case I have supposed that the survival of the
fittest has come into play with female birds and kept the female
dull-coloured. With respect to the absence of spurs in the female
gallinaceous birds, I presume that they would be in the way during
incubation; at least I have got the case of a German breed of fowls in