The Descent of Man

they leave fewer, less vigorous, or no offspring.
In regard to structures acquired through ordinary
or natural selection, there is in most cases,
as long as the conditions of life remain the same,
a limit to the amount of advantageous modification
in relation to certain special purposes;
but in regard to structures adapted to make
one male victorious over another, either in fighting
or in charming the female, there is no definite
limit to the amount of advantageous modification;
so that as long as the proper variations
arise the work of sexual selection will go on.
This circumstance may partly account for the
frequent and extraordinary amount of variability
presented by secondary sexual characters.
Nevertheless, natural selection will determine
that such characters shall not be acquired by
the victorious males, if they would be highly
injurious, either by expending too much of
their vital powers, or by exposing them to any
great danger. The development, however, of
certain structures—of the horns, for instance, in