140 DOCTRINE OF EVOLUTION 



many of the latter, there will be more cats, fewer field- 

 mice, more bees, richer clover fields, and finer cattle ! 

 Each link is real and the whole chain is a characteristic 

 example of the countless ways that the natural destinies 

 of living things are interrelated and intertwined. 



The reality of such organic interrelationships is 

 revealed with wonderful clearness in the numerous 

 instances where some disturbing factor has altered one 

 or another element of the balanced system. The 

 invasion of the new world by Europeans has directly 

 led to the partial or complete extinction of the tribes 

 of Indians to whom the land formerly belonged; they 

 have disappeared almost entirely from our state of 

 New York, together with the bear and wolf and many 

 other species of animals that formerly existed here. 

 Wild horses and bison have also vanished before the 

 advances of civilization and the alteration of their 

 homes. Sometimes the extermination of one pest 

 has resulted in an increase in the number of another 

 through human interference with nature's equilibrium. 

 In some of our Western states, a bounty was offered for 

 the scalps of wolves, so as to lessen the number of these 

 predatory foes of sheep. But when the wolves were 

 diminished in number, their wild food-animals, the 

 prairie dogs, found their lot much bettered, and they 

 have multiplied so rapidly that in some places they 

 have become even more destructive than the wolves. 



One of the most remarkable illustrations is that of 

 the rabbits introduced into Australia. This island 

 continent was cut off from the surrounding lands long 

 before the higher mammals evolved in far distant re- 

 gions, so that the balance of nature was worked out 



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