CAUSES OF EXTINCTION. [CHAI-. vm. 



What shall we say of the extinction of the horse? Did those 

 plains fail of pasture, which have since been overrun by thousands 

 and hundreds of thousands of the descendants of the stock intro- 

 duced by the Spaniards? 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 gigantic prototypes? Certainly, no fact in the long 

 history of the world is so startling as the wide and repeated 

 exterminations of its inhabitants. 



Nevertheless, if we consider the subject under another point of 

 view, it will appear less perplexing. We do not steadily bear in 

 mind, how profoundly ignorant we are of the conditions of existence 

 of every animal ; nor do we always remember, 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 average, 

 remains constant ; yet the tendency in every animal to increase by 

 propagation is geometrical ; and its surprising effects have nowhere 

 been more astonishingly shown, than in the case of the European 

 animals run wild during the last few centuries in America. Every 

 animal in a state of nature regularly breeds; yet in a species long 

 established, any great increase in numbers is obviously impossible, 

 and must be checked by some means. We are, nevertheless, seldom 

 able with certainty to tell in any given species, at what period of 

 life, or at what period of the year, or whether only at long intervals, 

 the check falls ; or, again, what is the precise nature of the check. 

 Hence probably it is, that we feel so little surprise at one, of two 

 species closely allied in habits, being rare and the other abundant 

 in the same district; or, again, that one should be abundant in one 

 district, and another, filling the same place in the economy of 

 nature, should be abundant in a neighbouring district, differing 

 very little in its conditions. If asked how this is, one immediately 

 replies that it is determined by some slight difference in climate, 

 food, or the number of enemies : yet how rarely, if ever, we can 

 point out the precise cause and manner of action of the check ! 

 We are, therefore, driven to the conclusion, that causes generally 

 quite inappreciable by us, determine whether a given species shall 

 be abundant or scanty in numbers. 



In the cases where we can trace the extinction of a species 

 through man, either wholly or in one limited district, we know 



