478 
EECAPITULATION. 
Chap. XIV. 
as the presence of peculiar species of bats, and the ah' 
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 V erde 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 
classificationwhy adaptive characters, though of 
paramount importance to the being, are of hardly any 
