292 THE DESCENT 



races which havo already become somewhat infertile. 

 Besides the several causes previously alluded to, the greater 

 facility of parturition among savages, and the less conse- 

 quent injury to their male infants, would tend to increase 

 the proportion of live-born males to females. There does 

 not, however, seem to be any necessary connection between 

 savage life and a marked excess of males; that is if we may 

 judge by the character of the scanty offspring of the lately 

 existing Tasmanians and of the crossed offspring of the 

 Tahitians now inhabiting Norfolk Island. 



As the males and females of many animals differ some- 

 what in habits, and are exposed in different degrees to 

 danger, it is probable that in many cases more of one sex 

 than of the other are habitually destroyed. But as far as I 

 can trace out the complication of causes an indiscriminate 

 though large destruction of either sex would not tend to 

 modify the sex-producing power of the species. With 

 strictly social animals, such as bees or ants, which produce 

 a vast number of sterile and fertile females in comparison 

 with the males, and to whom this preponderance is of para- 

 mount importance, we can see that those communities 

 would flourish best which contained females having a 

 strong inherited tendency to produce more and more 

 females; and in such cases an unequal sex-producing ten- 

 dency would be ultimately gained through natural selection. 

 With animals living in herds or troops^in which the males 

 come to the front and defend the herd, as with the bisons 

 of North America and certain baboons, it is conceivable 

 that a male-producing tendency might be gained by natural 

 selection; for the individuals of the better defended herds 

 would leave more numerous descendants. In the case of 

 mankind the advantage arising from having a preponderance 

 of men in the tribe is supposed to be one chief cause of 

 the practice of female infanticide. 



In no case, as far as we can see, would an inherited ten- 

 dency to produce both sexes in equal numbers or to produce 

 one sex in excess, be a direct advantage or disadvantage to 

 certain individuals more than to others; for instance, an 

 individual with a tendency to produce more males than 

 females would not succeed better in the battle for life than 

 an individual with an opposite tendency; and therefore a 

 tendency of this kind could not be gained through natural 

 selection. Nevertheless, there are certain animals (for 



