VI. CONCLUSIOX. 



1. The student of morphological and historical evo- 

 lution is concerned with the origin of the Linnean or col- 

 lective species, genera, families and larger groups. The 

 student of experimental evolution is concerned with the 

 origin of elementary species, or rather with the origin 

 of specific characters. 



2. ''The real difficulty of Darwin's theory is the 

 transition from artificial to natural selection" (Paul 

 Janet). This difficulty can only be surmounted by ad- 

 mitting that the improvement of races and the origin of 

 new forms are really entirely different, and only ap- 

 ])arently similar, processes. 



In Darwin's time no distinction was drawn between 

 these tw^o processes. 



3. "No two individuals in a generation are abso- 

 lutely alike." This well-known saying refers to fluctu- 

 ating variability and has nothing to do with the theory 

 of descent. 



4. ''Species have arisen by natural selection resulting 

 from the struggle for existence." This statement also 

 needs some explanation. The struggle for existence, that 

 is to say the competition for the means of subsistence, 

 may refer to two entirely different things. On the one 

 liand the struggle takes place between the individuals of 

 one and the same elementary species, on the other be- 



• tween the various species themselves. The former is a 



