2 Descent 



bringing the theory of common descent to its 

 present high rank in scientific and social phi- 

 losophy. 



Two main features in his work have contrib- 

 uted to this early and unexpected victory. One 

 of them is the almost unlimited amount of com- 

 parative evidence, the other is his demonstration 

 of the possibility of a physiological explanation 

 of the process of descent itself. 



The universal belief in the independent crea- 

 tion of living organisms was revised by 

 Linnaeus and was put upon a new foundation. 

 Before him the genera were supposed to be 

 created, the species and minor forms having 

 arisen from them through the agency of ex- 

 ternal conditions. In his first book Linnaeus 

 adhered to this belief, but later changed his 

 mind and maintained the principle of the sep- 

 arate creation of species. The weight of his 

 authority soon brought this conception to uni- 

 versal acceptance, and up to the present time 

 the prevailing conception of a species has been 

 chiefly based on the definition given by Linnaeus. 

 His species comprised subspecies and varieties, 

 which were in their turn, supposed to have 

 evolved from species by the common method. 



Darwin tried to show that the links which 

 bind species to genera are of the same nature 

 as those which determine the relationship of 



