350 THE DESCENT OF MAN. 



gained by the more vigorous pairs in rearing a larger 

 number of offspring has apparently sufficed to render sex- 

 ual selection efficient. But a large numerical preponder- 

 ance 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 in- 

 directly 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 

 female 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 

 animals having stronger passions than the females. Hence 

 it is the males that fight together and sedulously display 

 their charms before the females; and the victors transmit 

 their superiority to their male offspring. Why both sexes 

 do not thus acquire the characters of their fathers will be 

 considered hereafter. That the males of all mammals 

 eagerly pursue the females is notorious to every one. So it 

 is with birds; but many cock birds do not so much pursue 

 the hen, as display their plumage, perform strange antics, 

 and pour forth their song in her presence. The male in the 

 few fish observed seems much more eager than the female; 

 and the same is true of alligators, and apparently of 

 Batrachians. Throughout the enormous class of insects, 

 as Kirby remarks,* " the law is that the male shall seek the 

 female," Two good authorities, Mr. Blackwall and Mr. C. 

 Spence Bate, tell me that the males of spiders and crusta- 

 ceans are more active and more erratic in their habits than 

 the females. When the organs of sense or locomotion are 

 present in the one sex of insects and crustaceans and absent 

 in the other, or when, as is frequently the case, they are 

 more highly developed in the one than in the other, it Is, as 

 far as I can discover, almost invariably the male which 

 retains such organs, or has them most developed; and this 



* Kirby and Spence, " Introduction to Entomology," vol. iii, 1826, 

 p. 342. 



