CiiAP. VIII.] SEXUAL SELECTION. 287 



the laws of inheritance extremely complex, but so are the 

 causes which induce and govern variability. The varia- 

 tions thus caused are preserved and accumulated by sexual 

 selection, which is in itself an extremely complex affair, 

 depending, as it does, on ardor in love, courage, and the 

 rivalry of the males, and on the pov/ers of perception, 

 taste, and will, of the female. Sexual selection will also 

 be dominated by natural selection for the general welfare 

 of the species. Hence the manner in which the individu- 

 als of either sex or of both sexes are affected through 

 sexual selection cannot fail to be complex in the highest 

 degi'ce. 



When variations occur late in life in one sex, and are 

 transmitted to the same'^sex at the same age, the other sex 

 and the young are necessarily left unmodified. When 

 they occur late in life, but are transmitted to both sexes 

 at the same age, the young alone are left unmodified. 

 Variations, however, may occur at any period of life in 

 one sex or in both, and be transmitted to both sexes at 

 all ages, and then all the individuals of the species will 

 be similarly modified. In the following chapters it will 

 be seen that all these cases frequently occur under nature. 



Sexual selection can never act on any animal while 

 young, before the age for reproduction has arrived. From 

 the great eagerness of the male it has generally acted on 

 this sex and not on the females. The males have thus be- 

 come provided with weapons for fighting with their rivals, 

 or with organs for discovering and securely holding the 

 female, or for exciting and charming her. When the sexes 

 differ in these respects, it is also, as we have seen, an ex- 

 tremely general law that the adult male diflers more or 

 less from the young male ; and we may conclude from this 

 fact that the successive variations, by which the adult 

 male became modified, cannot have occurred much before 

 the age for reproduction. How, then, are we to account 



