Chap. YIII.J SEXUAL SELECTION. 311 



escape of at least some individuals from various dangers) 

 is quite beyond our power of judgment. 



When an organism has once been rendered extremely 

 fertile, how its fertility can be reduced through natural 

 selection is not so clear as how this capacity was first ac- 

 quired. Yet it is obvious that if individuals of a species, 

 from a decrease of their natural enemies, were habitually 

 reared in larger numbers than could be supported, all the 

 members would suffer. Nevertheless the offspring from 

 the less fertile parents would have no direct advantage 

 over the offspring from the more fertile parents, when all 

 were mingled together in the same district. All the in- 

 dividuals would mutually tend to starve each other. The 

 offspring indeed of the less fertile parents would lie under 

 one great disadvantage, for, from the simple fact of being 

 produced in smaller numbers, they would be the most lia- 

 ble to extermination. Indirectly, however, they would 

 partake of one great advantage ; for, under the supposed 

 condition of severe competition, when all were pressed for 

 food, it is extremely probable that those individuals which 

 from some variation in their constitution produced fewer 

 eggs or young, would produce them of greater size or 

 vigor; and the adults reared from such eggs or young 

 would manifestly have the best chance of surviving, and 

 would inherit a tendency toward lessened fertility. The 

 parents, moreover, which had to nourish or provide for 

 fewer offspring would themselves be exposed to a less se- 

 vere strain in the struggle for existence, and would have 

 a better chance of surviving. By these steps, and by no 

 others as far as I can see, natural selection, under the 

 above conditions of severe competition for food, would 

 lead to the formation of a new race less fertile, but better 

 adapted for survival, than the parent-race. 



