SUMMARY. 201 



with large families of genetically related species. It 

 has appeared that, as a rule, anatomical relationship 

 is parallel with geographical relationship: allied 

 species inhabit contiguous areas, allied genera 

 usually follow the same rule ; while families and 

 orders from their extreme antiquity have almost 

 always lost all traces of this relation ; that species, 

 genera, families, and orders have had each a central 

 point of origin ; and that each has spread from this 

 central point over a greater or less territory, depend- 

 ing on the length of time since the common union, 

 and upon the powers of migration which the animals 

 in question possess. All of this, it is hardly neces- 

 sary to say, is in harmony with evolution. It is cer- 

 tainly not out of harmony with the idea of special 

 creation, which might also assume that each species 

 has arisen from a single pair. But it is difficult to 

 see how any theory but that of descent would ex- 

 plain the unitary origin of genera, families, and or- 

 ders, all of which are with about equal force traced 

 back to a common point of origin. Geographical 

 distribution is in harmony with evolution, and the 

 fauna of oceanic islands very strongly indicate the 

 derivative origin of species. But this is all that this 

 source of evidence proves, for it could not possibly 

 be out of harmony with the idea of special creation. 

 It remains to be pointed out, that although at pres- 

 ent the subject of geographical distribution is capable 

 of being made into a science, with definite laws, this 

 possibility is disappearing. The influence of man 

 constantly tends to destroy all of the relations above 

 deduced. Man is transporting inhabitants from one 



