The Descent of Man

an extraordinary amount of difference to identity
in colour between the two sexes.
But it may be asked whether the difference in
colour between the sexes may not be accounted
for by other means besides sexual selection.
Thus the males and females of the same species
of butterfly are in several cases known (26.
H.W. Bates, 'The Naturalist on the Amazons,'
vol. ii. 1863, p. 228. A.R. Wallace, in 'Transactions,
Linnean Society,' vol. xxv. 1865, p. 10.) to
inhabit different stations, the former commonly
basking in the sunshine, the latter haunting
gloomy forests. It is therefore possible that different
conditions of life may have acted directly
on the two sexes; but this is not probable (27.
On this whole subject see 'The Variation of
Animals and Plants under Domestication,'
1868, vol. ii. chap. xxiii.) as in the adult state
they are exposed to different conditions during
a very short period; and the larvae of both are
exposed to the same conditions. Mr. Wallace