234 CLASSICS OF MODERN SCIENCE 



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 different habits of 

 life, as is sometimes the case; or for one sex to be modified in re- 

 lation 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 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 sometimes bear wounds from the huge mandibles 

 of other males ; the males of certain h}TTienopterous insects have been 

 frequently seen by that inin^itable observer, M. Fabre, fighting for a 

 particular female who sits by, an apparently unconcerned beholder 

 of the struggle, and then retires with the conquerer. 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 



