126 CAUSES OF EXTINCTION. [CHAP. vin. 



Australia, and in North and South America, that those conditions which 

 favour the life of the larger quadrupeds were lately co-extensive with 

 the world : what those conditions were, no one has yet even conjectured. 

 It could hardly have been a change of temperature, which at about the 

 same time destroyed the inhabitants of tropical, temperate, and arctic 

 latitudes on both sides of the globe. In North America we positively 

 know from Mr. Lyell, that the large quadrupeds lived subsequently to 

 that period, when boulders were brought into latitudes at which ice- 

 bergs now never arrive : from conclusive but indirect reasons we may 

 feel sure, that in the southern hemisphere the Macrauchenia, also, lived 

 long subsequently to the ice-transporting boulder-period. Did man, 

 after his first inroad into South America, destroy, as has been suggested, 

 the unwieldy Megatherium and the other Edentata? 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 ? 

 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 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 ol their 

 numerous gigantic prototypes ? Certainly, no fact in the long history 

 of the world is so startling as the wide and repeated exterminations ot 

 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 geome- 

 trical ; 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 i\s conditions. If asked how this is, one 



