48 THE SCIENTIFIC EVIDENCES OF 



IV. 



THE ARGUMENT FROM GEOGRAPHICAL 

 DISTRIBUTION. 



THE argument from geology is the argument 

 from the distribution of species in time. I will, 

 therefore, next take the argument from the 

 distribution of species in space — that is, the 

 present geographical distribution of plants and 

 animals. It is easy to see that this must be a 

 most important argument, if we reflect that as 

 the theory of descent with adaptive modifica- 

 tion implies slow and gradual change of one 

 species into another, and a still more slow and 

 gradual change of one genus, family, or order 



