atural
selection; seeing that it expresses the natural advantages of brute
force in the struggling of rival animals, and so frequently results in
_death of the less fitted_, as distinguished from a mere failure to
propagate. Now against this doctrine of the law of battle, and the
consequences to which it leads in the superior fighting powers of male
animals, no objection has been raised in any quarter. It is only with
regard to the other aspect of the theory of sexual selection--or that
which is concerned with the superior embellishment of male animals--that
any difference of opinion obtains. I will now proceed to give the main
arguments on both sides of this question, beginning with a _resume_ of
the evidences in favour of sexual selection.

In the first place, the fact that secondary sexual characters of the
embellishing kind are so generally restricted to the male sex in itself
seems to constitute very cogent proof that, in some way or another, such
characters are connected with the part which is played by the male in
the act of propagation. Moreover, secondary sexual characters of this
kind are of quite as general occurrence as are those of the other kind
which have to do with rivalry in battle; and the former are usually of
the more elaborate description. Therefore, as there is no doubt that
secondary sexual characters of the one order have an immediate purpose
to serve in the act of propagation, we are by this close analogy
confirmed in our surmise that secondary sexual characters of the other,
and still more elaborate, order are likewise so concerned. Moreover,
this view of their meaning becomes still further strengthened when we
take into consideration the following facts. Namely, (_a_) secondary
sexual characters of the embellishing kind are, as a rule, developed
only at maturity; and most frequently during only a part of the year,
which is invariably the breeding season: (_b_) they are always more or
less seriously affected by emasculation: (_c_) they are always, and
only, displayed in perfection during the act of courtship: (_d_) then,
however, they are displayed with the most elaborate pains; yet always,
and only, before the females: (_e_) they appear, at all events in many
cases, to have the effect of charming the females into a performance of
the sexual act; while it is certain that in many cases, both among
quadrupeds and birds, individuals of the one sex are capable of feeling
a strong antipathy against,