430 ON THE ORIGIN OF SPECIES 



species of bats, which can traverse the ocean, should 

 so often be found on islands far distant from any 

 continent. Such facts as the presence of peculiar 

 species of bats, and the absence 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 

 species in any two areas, implies, on the theory of 

 descent with modification, that the same parents for- 

 merly inhabited 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 immi- 

 grants 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 in- 

 telligible on the theory of natural selection with its 

 contingencies of extinction and divergence of char- 

 acter. 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 char- 

 acters, though of paramount importance to the being, 

 are of hardly any importance in classification ; why 

 characters derived from rudimentary parts, though of 



