384 BIOLOGY AND ITS MAKERS 
number of any one kind remains practically constant. 
Although the face of nature seems undisturbed, there is 
nevertheless a struggle for existence among all animals. 
This is easily illustrated when we take into account the 
breeding of fishes. The trout, for illustration, lays from 60,000 
to 100,000 eggs. If the majority of these arrived at maturity 
and gave rise to progeny, the next generation would represent 
a prodigious number, and the numbers in the succeeding 
generations would increase so rapidly that soon there would 
not be room in the fresh waters of the earth to contain their 
descendants. What becomes of the immense number of 
fishes that die? They fall a prey to others, or they are not 
able to get food in competition with other more hardy rela- 
tives, so that it is not a matter of chance that determines 
which ones shall survive; those which are the strongest, the 
better fitted to their surroundings, are the ones which will 
be perpetuated. 
The recognition of this struggle for existence in nature, 
and the consequent survival of the fittest, shows us more 
clearly what is meant by natural selection. Instead of man 
making the selection of those particular forms that are to 
survive, it is accomplished in the course of nature. This is 
natural selection. 
Various Aspects of Natural Selection.—Further illustra- 
tions are needed to give some idea of the various phases of 
natural selection. Speed in such animals as antelopes may 
be the particular thing which leads to their protection. It 
stands to reason that those with the greatest speed would 
escape more readily from their enemies, and would be the 
particular ones to survive, while the weaker and slower ones 
would fall victims to their prey. In all kinds of strain due to 
scarcity of food, inclemency of weather, and other untoward 
circumstances, the forms which are the strongest, physio- 
logically speaking, will have the best chance to weather the 
