never have been modified to bring the female into harmony with the
environment. "Sexual selection is less rigorous than Natural Selection,"
and will therefore be subordinate to it.

I think the case of female Pieris pyrrha proves that females alone can
be greatly modified for protection. (450/1. My latest views on this
subject, with many new facts and arguments, will be found in the later
editions of my "Darwinism," Chapter X. (A.R.W.))

LETTER 451. A.R. WALLACE TO CHARLES DARWIN.

(451/1. On October 4th, 1868, Mr. Wallace wrote again on the same
subject without adding anything of importance to his arguments of
September 27th. We give his final remarks:--)

October 4th, 1868.

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 some one to battle with me
over your facts on this hard problem.

LETTER 452. TO A.R. WALLACE. Down, October 6th [1868].

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. Hamburg) in which both sexes differ much from each other
and from both sexes of Gallus bankiva; and both sexes are kept constant
by selection. The comb of the Spanish male has been ordered to be
upright, and that of Spanish female to lop over, and this has been
effected. There are sub-breeds of game fowl, with females very distinct
and males almost identical; but this, apparently, is the result of
spontaneous variation, without special selection. I am very glad to hear
of case of female Birds of Paradise.

I have never in the least doubted possibility of modifying female birds
alone for protection, and I have long believed it for butterflies. I
have wanted only evidence for the female 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 h