Chap. IV.] SEXUAL SELECTION. 89 



undergo modification and improvement at the same time in the 



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 different habits 

 of life, as is sometimes the case ; or for one sex to be mod : 5ed in 

 relation to the other sex, as commonly occurs. This lead* 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 com- 

 petitor, 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 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 cockfighter by the care- 

 ful 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 insects 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 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, 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* 



