In the second place, the vital struggle includes the battles of every
species with other kinds of living things whose interests are in
opposition. The relations of protozoa and bacteria, conger-eels and other
fish, English sparrows and hawks, plants and herbivorous animals, are
typical examples of the universal conflict in which all organisms are
involved in some way. Again it is only too evident that human beings must
participate every day in some form of warfare with other species. In order
that food may be provided for mankind the lives of countless wild
organisms must be sacrificed in addition to the great numbers of
domesticated animals reared by man only that they may be destroyed. The
wolf and the wildcat and the panther have disappeared from many of our
Eastern states where they formerly lived, while no longer do vast herds of
bison and wild horses roam the Western prairies. Because one or another
human interest was incompatible with the welfare of these animals they
have been driven out by the stronger invaders.
That the victory does not always fall to the human contestant is
tragically demonstrated by the effects of the incessant assaults upon man
made by just one kind of living enemy,--the bacillus of tuberculosis.
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