were to become more familiar with the idea
of sexual selection, it would, I think, be accepted to a much greater
extent, and already it is fully and favourably accepted by many
competent judges." Darwin was able to speak thus because he was already
acquainted with an immense mass of facts, which, taken together,
yield overwhelming evidence of the validity of the principle of sexual
selection.

NATURAL SELECTION chooses out for reproduction the individuals that are
best equipped for the struggle for existence, and it does so at every
stage of development; it thus improves the species in all its stages and
forms. SEXUAL SELECTION operates only on individuals that are already
capable of reproduction, and does so only in relation to the attainment
of reproduction. It arises from the rivalry of one sex, usually the
male, for the possession of the other, usually the female. Its influence
can therefore only DIRECTLY affect one sex, in that it equips it
better for attaining possession of the other. But the effect may
extend indirectly to the female sex, and thus the whole species may be
modified, without, however, becoming any more capable of resistance
in the struggle for existence, for sexual selection only gives rise to
adaptations which are likely to give their possessor the victory over
rivals in the struggle for possession of the female, and which are
therefore peculiar to the wooing sex: the manifold "secondary sexual
characters." The diversity of these characters is so great that I cannot
here attempt to give anything approaching a complete treatment of them,
but I should like to give a sufficient number of examples to make the
principle itself, in its various modes of expression, quite clear.

One of the chief preliminary postulates of sexual selection is the
unequal number of individuals in the two sexes, for if every male
immediately finds his mate there can be no competition for the
possession of the female. Darwin has shown that, for the most part, the
inequality between the sexes is due simply to the fact that there are
more males than females, and therefore the males must take some pains
to secure a mate. But the inequality does not always depend on the
numerical preponderance of the males, it is often due to polygamy; for,
if one male claims several females, the number of females in proportion
to the rest of the males will be reduced. Since it is almost always
the males that are the wooers, we must expect to f