SEXUAL SELECTION 291 



Too little is known of tte habits of reptiles and fishes 

 to enable us to speak of their marriage arrangements. The 

 stickleback (Gasterosteus), however, is said to be a polyga- 

 mist;" and the male during the breeding season differs 

 conspicuously from the female. 



To sum up on the means through which, as far as we 

 can jxidge, sexual selection has led ,to the development of 

 secondary sexual characters. It has been shown that the 

 largest number of vigorous offspring will be reared from the 

 pairing of the strongest and best- armed males, victorious 

 in contests over other males, with the most vigorous and 

 best-nourished females, which are the first to breed in the 

 spring. If such females select the more attractive, and at 

 the same time vigorous males, they will rear a larger num- 

 ber of offspring than the retarded females, which must pair 

 with the less vigorous and less attractive males. So it will 

 be if the more vigorous males select the more attractive and 

 at the same time healthy and vigorous females; and this 

 will especially hold good if the male defends the female, 

 and aids in providing food for the young. The advantage 

 thus gained by the more vigorous pairs in rearing a larger 

 number of offspring has apparently sufficed to render sexual 

 selection efficient. But a large numerical preponderance of 

 males over females will be still more efficient; whether the 

 preponderance is only occasional and local, or permanent; 

 whether it occurs at birth, or afterward from the greater 

 destruction of the females; or whether it indirectly follows 

 from the practice of polygamy. 



The Male Generally more Modified than the Female. — 

 Throughout the animal kingdom, when the sexes differ in 

 external appearance, it is, with rare exceptions, the male 

 which has been the more modified; for, generally, the fe- 

 male retains a closer resemblance to the young of her own 

 species, and to other adult members of the same group. 

 The cause of this seems to lie in the males of almost all 



" 'Ndel Humphreys, "River Gardens." 1857. 



