I 



Extinction of Species. 75 



upon the failure of a food supply. " Did those 

 plains fail of pasture, which have since been overrun 

 by thousands and hundreds of thousands of the 

 descendants of the stock introduced by the Span- 

 iards? Have the subsequently introduced species 

 consumed the food of the great antecedent races? 

 Can we believe that the Capybara has taken the food 

 of the Toxodon, the Guanaco of the Macrauchenia, 

 the existing small Edentata of their numerous gigan- 

 tic prototypes ? Certainly no fact in the long history 

 of the world is so startling as the wide and repeated 

 exterminations of its inhabitants." 



In these thoughts and conclusions of the young 

 naturalist we see the germs of the genius that re- 

 sulted long after his trip in the greatest of his works, 

 the " Origin of Species." He did not assign any 

 direct cause for their disappearance, but concluded 

 that the laws of nature regulated the increase and 

 decrease of forms. For some the conditions were 

 favourable for perpetuation ; for others they were 

 not, so that in one direction we might find rapid 

 multiplication, and in another a tendency to extinc- 

 tion or running out. 



The reasoning of Darwin at this time is so pro- 

 phetic of his later work that it will add to the inter- 

 est to quote his words as given in his note-book : " In 

 the cases where we can trace the extinction of a 

 species through man, either wholly or in one limited 

 district, we know that it becomes rarer and rarer, 

 and is then lost ; it would be difficult to point out 

 any just distinction between a species destroyed by 

 man or by the increase of its natural enemies. The 



