80 ON THE ORIGIN OF SPECIES 



hereditarily attached to that sex, the same fact prob- 

 ably occurs under nature, and if so, natural selection 

 will be able to modify one sex in its functional rela- 

 tions to the other sex, or in relation to wholly different 

 habits of life in the two sexes, as is sometimes the case 

 with insects. And this leads me to say a few words on 

 what I call Sexual Selection. This depends, not on a 

 struggle for existence, but on a struggle between the 

 males for possession of the females ; the result is not 

 death to the unsuccessful competitor, but few or no 

 offspring. Sexual selection is, therefore, less rigorous 

 than natural selection. Generally, the most vigorous 

 males, those which are best fitted for their places in 

 nature, will leave most progeny. But in many cases, 

 victory depends not 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 offspring. Sexual selection by always allow- 

 ing the victor to breed might surely give indomitable 

 courage, length to the spur, and strength to the wing 

 to strike in the spurred leg, as well as the brutal cock- 

 fighter, who knows well that he can improve his breed 

 by careful selection of the 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 seen fighting all day long ; male stag-beetles 

 often bear wounds from the huge mandibles of other 

 males. The war is, perhaps, severest between the males 

 of polygamous animals, and these seem oftenest pro- 

 vided with special weapons. The males of carnivorous 

 animals are already well armed ; though to them and to 

 others, special means of defence may be given through 

 means of sexual selection, as the mane to the lion, the 

 shoulder-pad to the boar, and the hooked jaw to the 

 male salmon ; for 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, 



