224 CAUSES OF EXTINCTION. 



first inroad into South America, destroy, as has 

 been suggested, the unwieldy Megatherium and 

 the other Edentata 1 We must at least look to 

 some other cause for the destruction of the little 

 tucutuco at Bahia Blanca, and of the many fossil 

 mice and other small quadrupeds in Brazil. No 

 one will imagine that a drought, even far severer 

 than those which cause such losses in the provinces 

 of La Plata, could destroy every individual of 

 every species from Southern Patagonia to Behring's 

 Straits. What shall we say of the extinction of the 

 horse 1 Did those plains fail of pasture, which 

 have since been overrun by thousands and hun- 

 dreds of thousands of the descendants of the stock 

 introduced by the Spaniards 1 Have the subse- 

 quently 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 gigantic proto- 

 tyj^es 1 Certainly no fact in the long history of the 

 world is so startling as the wide and repeated ex- 

 terminations of its inhabitants. 



Nevertheless, if we consider the subject under 

 another point of view, it will appear less pei-plex- 

 ing. We do not steadily bear in inind how pro- 

 foundly ignorant we are of the conditions of exist- 

 ence of every animal ; nor do we always remem- 

 ber that some check is constantly preventing the 

 too rapid increase of every organized being left in 

 a state of nature. The supply of food, on an av- 

 erage, remains constant, yet the tendency in every 

 animal to increase by propagation is geometrical ; 

 and its surprising eft'ects have nowhere been more 

 astonishingly showi'i than in the case of the Euro- 

 pean animals run wild during the last few centu- 

 ries in America. Every animal in a state of na- 



