808 THE PRINCIPLES OF [Part II. 



Let us now take the case of a species producing, from 

 the unknown causes just alluded to, an excess of one sex 

 — we- will say of males — these being superfluous and use- 

 less, or nearly useless. Could the sexes he equalized 

 through natural selection ? We may feel sure, from all 

 characters being variable, that certain pairs would pro- 

 duce a somewhat less excess of males over females than 

 other pairs. The former, supposing the actual number of 

 the offspring to remain constant, would necessarily pro- 

 duce more females, and would therefore be more pro- 

 ductive. On the doctrine of chances a greater number of 

 the offspring of the more productive pairs would survive ; 

 and these would inherit a tendency to procreate fewer 

 males and more females. Thus a tendency toward equali- 

 zation of the sexes would be brought about. But our 

 supposed species would by this process be rendered, as 

 just remarked, more productive ; and this would in many 

 cases be far from an advantage ; for, whenever the limit to 

 the numbers which exist depends, not on destruction by 

 enemies, but on the amount of food, increased fertility 

 will lead to severer competition and to most of the sur- 

 vivors being badly fed. In this case, if the sexes were 

 equalized by an increase in the number of the females, a 

 simultaneous decrease in the total number of the offspring 

 would be beneficial, or even necessary, for the existence 

 of the species ; and this, I believe, could be effected through 

 natural selection in the manner hereafter to be described. 

 The same train of reasoning is applicable in the above, as 

 well as in the following case, if we assume that females 

 instead of males are produced in excess, for such females 

 from not uniting with males would be superfluous and 

 useless. So it would be with polygamous species, if we 

 assume the excess of females to be inordinately great. 



An excess of either sex, we will again say of the males, 

 could, however, apparently be eliminated through natural 



