EVOLUTION AS A NATURAL PROCESS 127 



and bacteria, conger-eels and other fish, English spar- 

 rows 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 addi- 

 tion 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. Every 

 year more than one hundred and twenty-five thousand 

 people of the United States die because they are unable 

 to withstand its persistent attacks ; five million 

 Americans now living are doomed to death at the hands 

 of these executioners, and the figures must be more 

 than doubled to cover the casualties on the human 

 side in the battles with the regiments of all the species 

 of bacteria causing disease. 



The competition between and among the individuals 

 of one and the same species is the third part of the 

 struggle for existence, and it is often unsurpassed in 



