1834.] CAUSES OF EXTINCTION. 179 



hundreds of thousands of the descendants of the stock 

 introduce<f 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 extermina- 

 tions 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, 01 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 some place in the economy 

 of nature, should be abundant in the neighbouring district, 

 differing very little in its conditions. If asked how this 

 is, one immediately replies that it is determined by some 

 slight difference m 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 



i'cies through man, either wholly or in one limited 



Ml lii( 1, \v( Ictiow that it becomes rarer and i-urT, .md is 



