5l4 The Descent of Man. Tart III, 



and are endowed with the requisite quahties of courage and 

 pugnacity. They are provided, either exclusively or in a much 

 liigher degree than the females, with organs for vocal or instru- 

 mental music, and with odoriferous glands. They are ornamented 

 with infinitely diversified appendages, and with the most 

 brilliant or conspicuous colours, often arranged in elegant 

 patterns, whilst the females are unadorned. When the sexes 

 differ in more important structures, it is the male which is 

 provided with special sense-organs for discovering the female 

 with locomotive organs for reaching her, and often with 

 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 more or less transferred 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, hut appear a short time before the age for reproduction. 

 Hence in most cases the young of both sexes resemhle each other ; 

 and the female somewhat resembles her young offspring through- 

 out 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 females assuming 

 characters which properly belong 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 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 ; whilst natural selection depends on the success of both 

 sexes, at all ages, in relation to the general conditions of life. 

 The sexual struggle is of two kinds ; in the one it is between the 

 individuals of the same sex, generally the males, in order to drive 

 away or kQI their rivals, the females remaining passive ; whilst in 

 the other, the struggle is hkewise between the individuals of the 

 same sex, in order to excite or charm those of the opposite 

 sex, generally the females, which no longer remain passive, but 

 select the more agreeable partners. This latter kind of selection 

 is closely analogous to that which man unintentionally, yet 

 effectually, brings to bear on his domesticated productions, 

 when he preserves during a long period the most pleasing or 

 useful individuals, without any wish to modify the breed. 



'J'he laws of inheritance determine whether characters gained 

 through sexual selection by either sex sliall be transmitted to the 



