If we were to try to guess--without knowing the facts--what means the male
animals make use of to overcome their rivals in the struggle for the
possession of the female, we might name many kinds of means, but it would
be difficult to suggest any which is not actually employed in some animal
group or other. I begin with the mere difference in strength, through
which the male of many animals is so sharply distinguished from the female,
as, for instance, the lion, walrus, "sea-elephant," and others. Among
these the males fight violently for the possession of the female, who falls
to the victor in the combat. In this simple case no one can doubt the
operation of selection, and there is just as little room for doubt as to
the selection-value of the initial stages of the variation. Differences in
bodily strength are apparent even among human beings, although in their
case the struggle for the possession of the female is no longer decided by
bodily strength alone.

Combats between male animals are often violent and obstinate, and the
employment of the natural weapons of the species in this way has led to
perfecting of these, e.g. the tusks of the boar, the antlers of the stag,
and the enormous, antler-like jaws of the stag-beetle. Here again it is
impossible to doubt that variations in these organs presented themselves,
and that these were considerable enough to be decisive in combat, and so to
lead to the improvement of the weapon.

Among many animals, however, the females at first withdraw from the males;
they are coy, and have to be sought out, and sometimes held by force. This
tracking and grasping of the females by the males has given rise to many
different characters in the latter, as, for instance, the larger eyes of
the male bee, and especially of the males of the Ephemerids (May-flies),
some species of which show, in addition to the usual compound eyes, large,