The Descent of Man

Many analogous cases could be adduced; those
for instance of the plumes on the head being
generally longer in the male than in the female,
sometimes of equal length in both sexes, and
occasionally absent in the female,— these several
cases occurring in the same group of birds.
It would be difficult to account for such a difference
between the sexes by the female having
been benefited by possessing a slightly shorter
crest than the male, and its consequent diminution
or complete suppression through natural
selection. But I will take a more favourable case,
namely the length of the tail. The long train
of the peacock would have been not only inconvenient
but dangerous to the peahen during
the period of incubation and whilst accompanying
her young. Hence there is not the least a
priori improbability in the development of her
tail having been checked through natural selection.
But the females of various pheasants,
which apparently are exposed on their open
nests to as much danger as the peahen, have