Jan. 1834. causes of extinction'. 211 



the same grounds which, before knowing more than the size 

 of the remains, perplexed me, by not allowing any great 

 change of climate, now that we can guess the habits of the 

 animal, are strangely confirmed. What shall we say of the 

 death of the fossil horse ? Did those plains fail in pasture, 

 which afterwards were overrun by thousands and tens of 

 thousands of the successors of the fresh stock introduced 

 with the Spanish colonist? In some countries, we may 

 believe, that a number of species subsequently introduced, 

 by consuming the food of the antecedent races, may have 

 caused their extermination ; but we can scarcely credit that 

 the armadillo has devoured the food of the immense Mega- 

 therium, the capybara of the Toxodon, or the guanaco of 

 the camel-like kind. But granting that all such changes 

 have been small, yet we are so profoundly ignorant concern- 

 ing the physiological relations, on which the life, and even 

 health (as shown by epidemics) of any existing species 

 depends, that we argue with still less safety about either the 

 life or death of any extinct kind. 



One is tempted to believe in such simple relations, as 

 variation of climate and food, or introduction of enemies, or 

 the increased numbers of other species, as the cause of the 

 succession of races. But it may be asked whether it is pro- 

 bable than any such cause should have been in action during 

 the same epoch over the whole northern hemisphere, so as 

 to destroy the Elephas primigenus, on the shores of Spain, 

 on the plains of Siberia, and in Northern America ; and in 

 a like manner, the Bos urus, over a range of scarcely less 

 extent ? Did such changes put a period to the life of 

 Mastodon angustidens, and of the fossil horse, both in 

 Europe and on the Eastern slope of the Cordillera in 

 Southern America? If they did, they must have been 

 changes common to the whole world; such as gradual 

 refrigeration, whether from modifications of physical geo- 

 graphy, or from central cooling. But on this assumption, 

 we have to struggle with the difficulty that these supposed 

 changes, although scarcely sufficient to affect molluscous 



p 2 



