6 EVOLUTION OF TO-DAY. 



living to-day could be traced backward, they would 

 all be found to converge, until finally they met at a 

 common point of union, which would represent a 

 common ancestor living in the remote past. In 

 short, evolution, as the term is commonly under- 

 stood to-day, is chiefly a denial of the former belief 

 that species were independently created, and the 

 replacement of this belief with its opposite. It as- 

 sumes that no species is an independent creation, 

 but that all are derived from past forms now mostly 

 extinct. This is evolution as Danvin understood it ; 

 this is the common understanding of the term to- 

 day in scientific literature ; and this is the question 

 which has been so thoronghly investigated in the 

 last twenty-five years. 



As thus defined, it is easy to see that the theory 

 is not complete, since nothing is said as to the 

 origin of life. The essential idea which underlies 

 the whole theory is that species have had a natural 

 rather than a supernatural origin ; and it is evident 

 that unless we give a natural explanation of the 

 origin of life, the idea is lacking at its very founda- 

 tion. Nor is this all ; for the same logical necessity 

 will compel us to explain, in a similar way, the ori- 

 gin of the world and the solar system, and thus to 

 reach a theory something like that of Spencer. But 

 even this theory does not reach any bottom, for it 

 assumes the existence of the nebula, and Spencer 

 found it necessary to put behind and beneath his 

 system an " unknowable," which he considered the 

 same as the God of theology. It is therefore im- 

 possible to make evolution a complete theory. 



