The Descent of Man

The law of the equal transmission of characters
to both sexes, as far as colour and other ornaments
are concerned, has prevailed far more
extensively with mammals than with birds; but
weapons, such as horns and tusks, have often
been transmitted either exclusively or much
more perfectly to the males than to the females.
This is surprising, for, as the males generally
use their weapons for defence against enemies
of all kinds, their weapons would have been of
service to the females. As far as we can see,
their absence in this sex can be accounted for
only by the form of inheritance which has prevailed.
Finally, with quadrupeds the contest
between the individuals of the same sex, whether
peaceful or bloody, has, with the rarest exceptions,
been confined to the males; so that the
latter have been modified through sexual selection,
far more commonly than the females, either
for fighting with each other or for alluring
the opposite sex.