320 THE PRINCIPLES OF SEXUAL SELECTION. Part II. 
.some variation in their constitution produced fewer eggs 
or young, would produce them of greater size or vigour ; 
and the adults reared from such eggs or young would 
manifestly have the best chance of surviving, and 
would inherit a tendency towards lessened fertility. 
The parents, moreover, which had to nourish or provide 
for fewer offspring would themselves be exposed to a 
less severe strain in the struggle for existence, and 
would have a better chance of surviving. By thes 
steps, and by no others as far as I can see, natural 
selection under the above conditions of severe com- 
petition for food, would lead to the formation of a new 
race less fertile, but better adapted for survival, than 
the parent-race. 
