The Descent of Man

With birds it is difficult to decide by what standard
we ought to judge of the earliness or lateness
of the period of variation, whether by the
age in reference to the duration of life, or to the
power of reproduction, or to the number of
moults through which the species passes. The
moulting of birds, even within the same family,
sometimes differs much without any assignable
cause. Some birds moult so early, that nearly all
the body feathers are cast off before the first
wing-feathers are fully grown; and we cannot
believe that this was the primordial state of
things. When the period of moulting has been
accelerated, the age at which the colours of the
adult plumage are first developed will falsely
appear to us to be earlier than it really is. This
may be illustrated by the practice followed by
some bird-fanciers, who pull out a few feathers
from the breast of nestling bullfinches, and
from the head or neck of young goldpheasants,
in order to ascertain their sex; for in
the males, these feathers are immediately re-