The Descent of Man

ornament, for producing various sounds, and
for fighting together, have been transmitted to
the males alone or to both sexes, either permanently,
or periodically during certain seasons of
the year. Why various characters should have
been transmitted sometimes in one way and
sometimes in another, is not in most cases
known; but the period of variability seems often
to have been the determining cause. When
the two sexes have inherited all characters in
common they necessarily resemble each other;
but as the successive variations may be differently
transmitted, every possible gradation
may be found, even within the same genus,
from the closest similarity to the widest dissimilarity
between the sexes. With many closelyallied
species, following nearly the same habits
of life, the males have come to differ from each
other chiefly through the action of sexual selection;
whilst the females have come to differ
chiefly from partaking more or less of the characters
thus acquired by the males. The effects,