But in many cases victory depends not so much on general vigour, but 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 of spur, and strength to the wing to strike in the spurred leg, in nearly the same manner as does the brutal cockfighter by the careful selection of his best cocks.