On the Mechanical Conception of Nature. 65 1 



the majority of individuals, but this species buries 

 itself by day in the loose soil (Acherontta Atropos). 



To this it may be objected that there are also 

 compulsory changes in the conditions of life from 

 which the species cannot withdraw itself, but in 

 which adaptation must necessarily follow, or ex- 

 termination would take place. 



Such compulsory conditions of life do most 

 assuredly occur, and there is indeed no doubt that 

 many living forms have perished through not 

 becoming transformed. I believe, however, that 

 such conditions occur much more rarely than one 

 is inclined to admit at first sight. As a rule the 

 alternative of immediate change or of extermina- 

 tion is offered only by such changes in the con- 

 ditions of life as occur very rapidly. The sudden 

 appearance of a new and dominant enemy, such 

 as man, has already caused the extinction of 

 the Dodo (Didus ineptus), and of Steller's Sea 

 Cow (Rhytina Stclleri), and of other vertebrate 

 animals, and constantly leads to the extermination 

 of many other species of different classes. When 

 in America hundreds of thousands of acres of 

 primeval forest are annually destroyed, the con- 

 ditions of life of a numerous fauna and flora must 

 be thereby suddenly changed, leaving no choice 

 but extermination. 



Such abrupt changes in the conditions of life 

 occur, however, but seldom in nature unless 

 caused by man, and must therefore have very 



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