Chap. VIII. Proportion of the Sexes. 259 



alluded to, the greater facility of parturition amongst savages, 

 and the less consequent injury to their male infants, would 

 tend to increase the proportion of live-born males to females. 

 Taere 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 somewhat 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 com- 

 plication 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 paramount 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 tendency would be ulti- 

 mately 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 pre- 

 ponderance 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 tendency 

 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 instance, fishes and cirripedes) in which two 

 or more males appear to be necessary for the fertilisation of the 

 female; and the males accordingly largely preponderate, but it 

 is by no means obvious how this male-producing tendency could 

 have been acquired. I formerly thought that when a tendency 

 to produce the two sexes in equal numbers was advantageous to 

 the species, it would follow from natural selection, but I now 



