SEXUAL SELECTION 343 



in such cases an unequal sex-producing tendency would 

 be ultimately gained through natural selection. With ani- 

 mals 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 le^ve 

 more numerous descendants. In the case of mankind the 

 advantage arising from having a preponderance of r:'^n in 

 the tribe is supposed to be one chief cause of t!:9 practice 

 of female infanticide. 



In no case, as far as we can see, would za inherited 

 tendency to produce both sexes in equal numbers, or to 

 produce one sex in excess, be a direct advantage or dis- 

 advantage to certain individuals more than 1o others; for 

 instance, an individual with a tendency to ;3roduce 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 cirripeds) in which two 

 or more males appear to be necessary for the fertilization 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 see that the whole prob- 

 lem is so intricate that it is safer to leave its solution 

 for the future. 



