NATURAL SELECTION 69 



many species ever undergo modification and improvement at the 

 same time in the same area. 



SEXUAL SELECTION 



Inasmuch as peculiarities often appear under domestication in 

 one sex and become hereditarily attached to that sex, so no doubt 

 it will be under nature. Thus it is rendered possible for the two 

 sexes to be modified through natural selection in relation to dif- 

 ferent habits of life, as is sometimes the case; or for one sex to be 

 modified in relation to the other sex, as commonly occurs. This 

 leads me to say a few words on what I have called sexual selection. 

 This form of selection depends, not on a struggle for existence in 

 relation to other organic beings or to external conditions, but on a 

 struggle between the individuals of one sex, generally the males, 

 for the possession of the other sex. 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 de- 

 pends not so much on general vigor, 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 in- 

 domitable 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. 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 huge 

 mandibles of other males ; the males of certain hymenopterous in- 

 sects have been frequently seen by that inimitable observer M. 

 Fabre, 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 

 polygamous animals, and these seem oftenest provided with spe- 

 cial 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 of 

 the lion, and the hooked jaw to the male salmon; for the shield 

 may be as important for victory as the sword or spear. 



Among birds, the contest is often of a more peaceful character. 



