se abnormal cases the colour happened to
vary in the female alone, and was transmitted to females alone, and that
her variations have been selected through the admiration of the male.

It is a very interesting subject, but I shall not be able to go on with
it for the next five or six months, as I am fully employed in correcting
dull proof-sheets. When I return to the work I shall find it much better
done by you than I could have succeeded in doing.

It is curious how we hit on the same ideas. I have endeavoured to show
in my MS. discussion that nearly the same principles account for young
birds not being gaily coloured in many cases, but this is too complex a
point for a note.

On reading over your letter again, and on further reflection, I do not
think (as far as I remember my words) that I expressed myself nearly
strongly enough on the value and beauty of your generalisation (429/4.
See Letter 203, Volume I.), viz., that all birds in which the female
is conspicuously or brightly coloured build in holes or under domes. I
thought that this was the explanation in many, perhaps most cases, but
do not think I should ever have extended my view to your generalisation.
Forgive me troubling you with this P.S.

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