34 SEXUAL SELECTION. [CHAP. IV. 



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 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 con- 

 ditions, 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 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 

 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 some- 

 times 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 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. 



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 dis- 



