284 ANIMAL STUDIES 



every species. In some regions the one phase may be more 

 destructive, in others another. Where the conditions of 

 life are most easy, as in the tropics, the struggle of species 

 with species, of individual with individual, is the most 

 severe. 



No living being can escape from any of these three 

 phases of the struggle for existence. For reasons which we 

 shall see later, it is not well that any should escape, f or ' the 

 sheltered life," the life withdrawn from the stress of effort, 

 brings the tendency to degeneration. 



Because of the destruction resulting from the struggle 

 for existence, more of every species are born than can 

 possibly find space or food to mature. The majority fail 

 to reach their full growth because, for one reason or an- 

 other, they can not do so. All live who can. Each strives 

 to feed itself, to save its own life, to protect its young. 

 But with all their efforts only a portion of each species 

 succeed. 



24=9. Selection by Nature. But the destruction in Nature 

 is not indiscriminate. In the long run those least fitted to 

 resist attack are the first to perish. It is the slowest ani- 

 mal which is soonest overtaken by those which feed upon 

 it. It is the weakest which is crowded away from the feed- 

 ing-place by its associates. It is the least adapted which is 

 first destroyed by extremes of heat and cold. Just as a 

 farmer improves his herd of cattle by destroying his weak- 

 est or roughest calves, reserving the strong and fit for par- 

 entage, so, on an inconceivably large scale, the forces of 

 Nature are at work purifying, strengthening, and fitting to 

 their surroundings the various species of animals. This 

 process has been called natural selection, or the survival of 

 the fittest. But by fittest in this sense we mean only best 

 adapted to the surroundings, for this process, like others in 

 Nature, has itself no necessarily moral element. The song- 

 bird becomes through this process more fit for the song-bird 

 life, the hawk becomes more capable of killing and tear- 



