Masterpieces of Science 



prehensile organs for holding her. These various 

 structures for charming or securing the female 

 are often developed in the male during only 

 part of the year; namely, the breeding season. 

 They have in many cases been transferred in a 

 greater or less degree to the females; and in 

 the latter case they often appear in her as mere 

 rudiments. They are lost or never gained by 

 the males after emasculation. Generally they 

 are not developed in the male during early 

 youth, but appear a short time before the age 

 for reproduction. Hence, in most cases the 

 young of both sexes resemble each other; and 

 the female somewhat resembles her young off- 

 spring throughout life. In almost every great 

 class a few anomalous cases occur, where there 

 has been an almost complete transposition of 

 the characters proper to the two sexes; the fe- 

 males assuming characters which properly be- 

 long to the males. This surprising uniformity 

 in the laws regulating the differences between 

 the sexes in so many and such widely separated 

 classes is intelligible if we admit the action 

 throughout all the higher divisions of the animal 

 kingdom of one common cause; namely, sexual 

 selection. 



Sexual selection depends on the success of 

 certain individuals over others of the same sex, 

 in relation to the propagation of the species; 

 while natural selection depends on the success 

 of both sexes, at all ages, in relation to the 

 general conditions of life. The sexual struggle 

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