THE WAY OF THE WILD 69 



Significance of numbers. In so far as natural selection is a 

 contest between different species the question of relative numbers 

 is an important one, because the hazard of a good " fit " is greatly 

 reduced with increasing numbers. Rare and slow-multiplying 

 species not only run the chance of few good fits with the environ- 

 ment, but they recover slowly after disastrous experiences. 



The stronghold of insect life is their rapid reproduction. A 

 succession of adverse seasons may seem to have almost, if not 

 quite, exterminated some troublesome species, but a few espe- 

 cially hardy and resistant individuals manage to live over, and, 

 with their rapid breeding powers, soon produce a new stock even 

 more vigorous than before. This is improvement by natural 

 selection. In this way adversity is good for the species, — 

 though fatal to most individuals, — and, providing only enough 

 can live through to restock the region, the species will be rapidly 

 modified by the selective process. 



When it is a troublesome insect or weed that is involved, we 

 are not interested in its prosperity, but the same principle applies 

 to valuable species even in domestication. For example, it is 

 the pigs that produce large litters whose descendants finally 

 constitute the herd, while some favorite may, from sheer lack of 

 breeding powers, 1 leave nothing behind. 



The perfectly wholesale production of seed by plants in gen- 

 eral is, to a considerable extent, an offset against their natural 

 disadvantage in being fixed as to habitat and unable to move 

 away from undesirable conditions to find better ones. 



Significance of vigor and length of life. This is of even more 

 importance to the race than is rapid reproduction. The experi- 

 ences of life make the mature individual of higher usefulness 

 than the younger, especially with races in which the young are 

 cared for and to some extent trained by the parents. 



1 Farmers often fail to notice the operation of this principle, and keep many 

 breeding animals because they are favorites in form or have fine pedigrees, 

 when they are doing practically nothing as breeders. The herd will of course 

 consist of the descendants of prolific breeders, which alone can produce 

 numbers sufficient to afford material for good selection. 



