overs, ptarmigan, desert birds, Arctic animals, greenbirds.

[The second page of this letter has been torn off. This letter and that
of September 27 appear both to answer the same letter from Darwin. The
last page of this or of another letter was placed with it in the
portfolio of letters; it is now given.]

I am sorry to find that our difference of opinion on this point is a
source of anxiety to you.

Pray do not let it be so. The truth will come out at last, and our
difference may be the means of setting others to work who may set us
both right.

After all, this question is only an episode (though an important one) in
the great question of the origin of species, and whether you or I are
right will not at all affect the main doctrine--that is one comfort.

I hope you will publish your treatise on Sexual Selection as a separate
book as soon as possible, and then while you are going on with your
other work, there will no doubt be found someone to battle with me over
your facts, on this hard problem.

With best wishes and kind regards to Mrs. Darwin and all your family,
believe me, dear Darwin, yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Down, Bromley, Kent, S.E. October 6, 1868._

My dear Wallace,--Your letter is very valuable to me, and in every way
very kind. I will not inflict a long answer, but only answer your
queries. There are breeds (viz. Hamburgh) in which both sexes differ
much from each other and from both sexes of _G. bankiva_; and both sexes
are kept constant by selection.

The comb of Spanish [male symbol] has been ordered to be upright and
that of Spanish [female symbol] to lop over, and this has been effected.
There are sub-breeds of game fowl, with [female symbol]s very distinct
and [male symbol]s almost identical; but this apparently is the result
of spontaneous variation without special selection.

I am very glad to hear of the case of [female symbol] birds of paradise.

I have never in the least doubted the possibility of modifying female
birds _alone_ for protection; and I have long believed it for
butterflies: I have wanted only evidence for the females alone of birds
having had their colours 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; and so with the
v