CHAPTER VI. 



GEOGRAPHICAL DISTRIBUTION. 



THE argument from geology is the argument from 

 the distribution of species in time. I will next take 

 the argument from the distribution of species in space 

 that is, the present geographical distribution of plants 

 and animals. 



Seeing that the theory of descent with adaptive 

 modification implies slow and gradual change of one 

 species into another, and progressively still more slow 

 and gradual changes of one genus, family, or order 

 into another genus, family, or order, we should expect 

 on this theory that the organic types living on any 

 given geographical area would be found to resemble 

 or to differ from organic types living elsewhere, ac- 

 cording as the area is connected with or disconnected 

 from other geographical areas. For instance, the 

 large continental islands of Australia and New Zealand 

 are widely disconnected from all other lands of the 

 world, and deep sea soundings show that they have 

 probably been thus disconnected, either since the time 

 of their origin, or, at the least, through immense 

 geological epochs. The theory of evolution, there- 

 fore, would expect to find two general facts with 

 regard to the inhabitants of these islands. First, that 



