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,! 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. 
