CHAPTER VII 
THE CROWD OF ANIMALS AND THE STRUGGLE FOR 
EXISTENCE 
68. The crowd of animals,—Al]] animals feed upon living 
organisms, or on their dead bodies. Hence each animal 
throughout its life is busy with the destruction of other 
organisms, or with their removal after death. If those 
creatures upon which others feed are to hold their own, there 
must be enough born or developed to make good the drain 
upon their numbers. If the plants did not fill up their 
ranks and make good their losses, the animals that feed 
on them would perish. If the plant-eating animals were 
destroyed, the flesh-eating animals would in turn disappear. 
But, fortunately, there is a vast excess in the process of 
reproduction. More plants sprout than can find room to 
grow. More animals are born than can possibly survive. 
The process of increase among animals is correctly spoken 
of as multiplication. Each species tends to increase in 
geometric ratio, but as it multiplies its members it finds 
the world already crowded with other species doing the 
same thing. A single pair of any species whatsoever, if not 
restrained by adverse conditions, would soon increase to 
such an extent as to fill the whole world with its progeny. 
An annual plant producing two seeds only would have 
1,048,576 descendants at the end of twenty-one years, if 
each seed sprouted and matured. The ratio of increase is 
therefore a matter of minor importance. It is the ratio of 
net increase above loss which determines the fate of a spe- 
cies. Those species increase in numbers whose gain exceeds 
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