ADAPTATION FOR THE INDIVIDUAL gI 
study of adaptation, the more likely we are to find 
changes which have but little bearing on the safety of 
the individual. They work for the good of the entire 
species, sometimes to the distinct disadvantage of the 
individual. The King Salmon may make its long run 
to the headwaters of our western rivers, deposit its 
eggs, have them fertilized, and then float down to 
death. But it does not die before abundant prepara- 
tion has been made for the continuance of the race. 
Such adaptation for the good of the species will be 
considered in the next chapter. 
The first and most important struggle any animal 
has to enter is the never-ending battle for its food. 
Occasionally there is a similar straining after the air 
it breathes. But ordinarily air is sufficiently abundant, 
except to animals living in the water, where the sup- 
ply is always more or less restricted and easily be- 
comes exhausted. But food is the constant need of 
every organism, and most creatures die for lack of it. 
In this struggle the animal is pitted against those of 
his own kind, rather than against those of other spe- 
cies. Even his brother is his enemy, for he desires 
the same food. In many a nest of birdlings one of 
them fails to reach its development simply because the 
parent either is unable to find or it cannot carry 
enough food to satisfy all the hungry mouths in the 
same nest. Before the nestlings are ready to take 
