We begin printing this week.—Yours very faithfully,
ALFRED R. WALLACE.
P.S.—Pray don't distress yourself on this subject. It will all come right in the end, and after all it is only an episode in your great work.—A.R.W.
9 St. Mark's Crescent, N.W. October 4, 1868.
Dear Darwin,—I should have answered your letter before, but have been very busy reading over my MSS. the last time before going to press, drawing maps, etc. etc.
Your first question cannot be answered, because we have not, in individual cases of slight sexual difference, sufficient evidence to determine how much of that difference is due to sexual selection acting on the male, how much to natural selection (protective) acting on the female, or how much of the difference may be due to inherited differences from ancestors who lived under different conditions. On your second question I can give an opinion. I do think the [pg 230]females of the Gallinaceæ you mention have been either modified; or prevented from acquiring much of the brighter plumage of the males, by the need of protection. I know that Gallus bankiva frequents drier and more open situations than Pavo muticus, which in Java is found among grassy and leafy vegetation corresponding with the colours of the two females. So the Argus pheasants, male and female, are, I feel sure, protected by their tints corresponding to dead leaves of the dry lofty forests in which they dwell; and the female of the gorgeous fire-back pheasant, Lophura viellottii, is of a very similar rich brown colour.
These and many other colours of female birds seem to me exactly analogous to the colours of both sexes in such groups as the snipes, woodcocks, plovers, 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.