328 EX'flNCTlOtf. 



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 weaking 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 natural- 

 ized quadrupeds in several parts of South America. 



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

 tions, 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 forerunner of death — to 

 feel no surprise at sickness, but, when the sick man dies, 

 to wonder, and to suspect that he died by some deed of 

 violence. 



The theory of natural selection is grounded on the belief 

 that each new variety, and ultimately each new species, is 

 produced and maintained by having some advantage over 

 those with which it comes into competition ; and the con- 

 sequent extinction of the less-favored forms almost inevita- 

 bly follows. It is the same with our domestic productions ; 

 when a new and slightly improved variety has been raised, 

 it at first supplants the less improved varieties in the same 

 neighborhood ; when much improved it is transported far 

 and near, like our short-horn cattle, and takes the place of 

 other breeds in other countries. Thus the appearance of 

 new forms and the disappearance of old forms, both those 

 naturally and those artificially produced, are bound together. 

 In flourishing groups, the number of new specific forms 

 which have been produced within a given time has at some 

 periods probably been greater than the number of the old 

 specific forms which have been exterminated ; but we know 

 that species have not gone on indefinitely increasing, at 

 least during the later geological epochs, so that, looking to 

 later times, we may believe that the production of new 

 forms has caused the extinction of about the same number 

 of old forms. 



The competition will generally be most severe, as for- 



