Chap. XI.] EXTINCTION. 97 



and rarer, and finally extinct ; — its place being seized 

 on by some more successful competitor. 



It is most difficult always to remember that the in- 

 crease of every creature is constantly being checked 

 by unperceived hostile agencies ; and that these same 

 unperceived agencies are amply sufficient to cause rarity, 

 and finally extinction. So little is this subject under- 

 stood, that I have heard surprise repeatedly expressed 

 at such great monsters as the Mastodon and the more 

 ancient Dinosaurians having become extinct ; as if mere 

 bodily strength gave victory in the battle of life. Mere 

 size, on the contrary, would in some cases determine, as 

 has been remarked by Owen, quicker extermination from 

 the greater amount of requisite food. Before man in- 

 habited India or Africa, some cause must have checked 

 the continued increase of the existing elephant. A 

 highly capable judge. Dr. Falconer, believes that it is 

 chiefly insects which, from incessantly harassing and 

 weakening the elephant in India, check its increase ; and 

 this was Bruce's conclusion with respect to the African 

 elephant in Abyssinia. It is certain that insects and 

 blood-sucking bats determine the existence of the larger 

 naturalized quadrupeds in several parts of S. America. 



We see in many cases in the more recent tertiary for- 

 mations, that rarity precedes extinction ; and we know 

 that this has been the progress of events with those 

 animals which have been exterminated, either locally or 

 wholly, through man's agency. I may repeat what I 

 published in 1845, namely, that to admit that species 

 generally become rare before they become extinct — to feel 

 no surprise at the rarity of a species, and yet to marvel 

 greatly when the species ceases to exist, is much the same 

 as to admit that sickness in the individual is the fore- 



