protection.

To answer your first question is most difficult, if not impossible, because
we have no sufficient evidence in individual cases of slight sexual
difference, to determine whether the male alone has acquired his superior
brightness by sexual selection, or the female been made duller by need of
protection, or whether the two causes have acted. Many of the sexual
differences of existing species may be inherited differences from parent
forms, which existed under different conditions and had greater or less
need of protection.

I think I admitted before, the general tendency (probably) of males to
acquire brighter tints. Yet this cannot be universal, for many female
birds and quadrupeds have equally bright tints.

To your second question I can reply more decidedly. I do think the females
of the Gallinaceae you mention have been modified or been prevented from
acquiring the brighter plumage of the male, by need of protection. I know
that the Gallus bankiva frequents drier and more open situations than the
pea-hen of Java, which is found among grassy and leafy vegetation,
corresponding with the colours of the two. So the Argus pheasant, male and
female, are, I feel sure, protected by their tints corresponding to the
dead leaves of the lofty forest in which they dwell, and the female of the
gorgeous fire-back pheasant Lophura viellottii is of a very similar rich
brown colour.

I do not, however, at all think the question can be settled by individual
cases, but by only large masses of facts. The colours of the mass of
female birds seem to me strictly analogous to the colours of both sexes of
snipes, woodcocks, plovers, etc., which are undoubtedly protective.