THE STRUGGLE FOR EXISTENCE 117 
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, for “ 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sheltered life,” the life withdrawn from the stress of effort, 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. 
70. Selection by Nature—But the destruction in Nature 
is not indiscriminate. In the long run those least fitted tc 
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- 
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