478 EECAPITULATION. Chap. XIV. 



as the presence of peculiar species of bats, and the ab- 

 sence of all other mammals, on oceanic islands, are 

 utterly inexplicable on the theory of independent acts 

 of creation. 



The existence of closely allied or representative spe- 

 cies in any two areas, implies, on the theory of descent 

 with modification, that the same parents formerly in- 

 habited both areas ; and we almost invariably find 

 that wherever many closely allied species inhabit two 

 areas, some identical species common to both still exist. 

 Wherever many closely allied yet distinct species occur, 

 many doubtful forms and varieties of the same species 

 likewise occur. It is a rule of high generality that the 

 inhabitants of each area are related to the inhabitants 

 of the nearest source whence immigrants might have 

 been derived. We see this in nearly all the plants and 

 animals of the Galapagos archipelago, of Juan Fernandez, 

 and of the other American islands being related in the 

 most striking manner to the plants and animals of the 

 neighbouring American mainland ; and those of the 

 Cape de Verde archipelago and other African islands to 

 the African mainland. It must be admitted that these 

 facts receive no explanation on the theory of creation. 



The fact, as we have seen, that all past and present 

 organic beings constitute one grand natural system, with 

 group subordinate to group, and with extinct groups 

 often falling in between recent groups, is intelligible 

 on the theory of natural selection with its contingencies 

 of extinction and divergence of character. On these 

 same principles we see how it is, that the mutual 

 affinities of the species and genera within each class 

 are so complex and circuitous. We see why certain 

 characters are far more serviceable than others for 

 classification ; — why adaptive characters, though of 

 paramount importance to the being, are of hardly any 



