The Descent of Man

winter and summer, nearly the same plumage
as that possessed by the three first species during
the winter and in their immature state; and
this plumage, which is common to several distinct
species at different ages and seasons, probably
shews us how the progenitors of the genus
were coloured. In all these cases, the nuptial
plumage which we may assume was originally
acquired by the adult males during the
breeding-season, and transmitted to the adults
of both sexes at the corresponding season, has
been modified, whilst the winter and immature
plumages have been left unchanged.
The question naturally arises, how is it that in
these latter cases the winter plumage of both
sexes, and in the former cases the plumage of
the adult females, as well as the immature plumage
of the young, have not been at all affected?
The species which represent each other in
distinct countries will almost always have been
exposed to somewhat different conditions, but