SEXUAL SELECTION. 81 



those which do survive, the best adapted individuals, sup- 

 posing that there is any variability in a favorable direction, 

 will tend to propagate their kind in larger numbers than 

 the less well adapted. If the numbers be wholly kept 

 down by the causes just indicated, as will often have been 

 the case, natural selection will be powerless in certain ben- 

 eficial directions; but this is no valid objection to its effi- 

 ciency at other times and in other ways; for we are far 

 from having any reason to suppose that many species ever 

 undergo modification and improvement at the same time 

 in the same area. 



SEXUAL. SELECTIOlf. 



Inasmuch as peculiarities often appear under domestica- 

 tion in one sex and become hereditarily attached to that 

 sex, so no doubt it will be under nature. Thus it is ren- 

 dered 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 rela- 

 tion 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 exist- 

 tence 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 competi- 

 tor, but few or no offspring. Sexual selection is, there- 

 fore, 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 vigor, a son 

 having special weapons, confined to the male sex. A horn- 

 less 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. 

 How low in the scale of nature the law of battle descends 

 I know not; male alligators have been described as fight- 

 ing, bellowing and whirling round, like Indians in a war- 

 dance, for the possession of the females; male salmons have 



