198 FROM THE GREEKS TO DARWIN 



Le cours ordinaire de la nature vivante, est en 

 general tou jours constant, tou jours le meme; son 

 mouvement, tou jours regulier, roule sur deux points 

 inebranlables : Tun, la fecondite sans bornes donnee 

 a toutes les especes ; I'autre, les obstacles sans nombre 

 qui reduisent cette fecondite a une mesure determinee 

 et ne laissent en tout temps qu'a peu pres la meme 

 quantite d'individus de chaque espece. 



Again, his idea of the extinction of the least- 

 perfected species is shown in the following pas- 

 sage, also quoted by de Lanessan: 



Les especes les moins parfaites, les plus delicates, 

 les plus pesantes, les moins agissantes, les moins 

 armees, etc., ont deja disparu ou disparaitront. 



Buffon not only observed the negative influ- 

 ences of environment in the reduction of num- 

 bers in certain species and in the disappearance 

 of imperfect types, but also its positive action in 

 the production of new characters. Here we come 

 upon the third and main feature of what may be 

 called Buffon's theory of the factors of Evolu- 

 tion, namely, the direct action of environment in 

 the modification of the structure of animals and 

 plants and the conservation of these modifications 

 through heredity. He especially applied this fac- 

 tor to explain the origin of new species in the 

 New World of America. 



It is amusing to the modern zoologist of Amer- 



