victory depends not so much
on general vigour as on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor chance of
leaving numerous offspring. Sexual selection, by always allowing the
victor to breed, might surely give indomitable courage, length to the
spur, and strength to the wing to strike in the spurred leg, in nearly
the same manner as does the brutal cock-fighter by the careful selection
of his best cocks.

How low in the scale of Nature the law of battle descends I know not.
Male alligators have been described as fighting, bellowing, and whirling
round, like Indians in a war-dance, for the possession of the females;
male salmons have been observed fighting all day long; male stag-beetles
sometimes bear wounds from the mandibles of other males; the males of
certain other insects have been frequently seen fighting for a
particular female who sits by, an apparently unconcerned beholder of the
struggle, and then retires with the conqueror. The war is, perhaps,
severest between the males of the polygamous animals, and these seem
oftenest provided with special weapons. The males of carnivorous animals
are already well armed, though to them special means of defence may be
given through means of sexual selection, as the mane of the lion and the
hooked jaw of the salmon. The shield may be as important for victory as
the sword or spear.

Amongst birds, the contest is often of a more peaceful character. All
those who have attended to the subject believe that there is the
severest rivalry between the males of many species to attract, by
singing, the females. The rock-thrush of Guiana, birds of paradise, and
some others, congregate; and successive males display with the most
elaborate care, and show off in the best manner, their gorgeous plumage;
they likewise perform strange antics before the females, which, standing
by as spectators, at last choose the most attractive partner.

If man can in a short time give beauty and an elegant carriage to his
bantams, according to his standard of beauty, I can see no good reason
to doubt that female birds, by selecting, during thousands of
generations, the most melodious or beautiful males, according to their
standard of beauty, might produce a marked effect.

_VI.--The Struggle for Existence_

Under domestication we see much variability, caused, or at least
excited, by changed conditions of life; but often in so obscure a manner