Geographical Distribution. 215 
natural affinity among inhabitants of the same areas ; 
second, another of a more detailed character between 
degrees of geographical restriction and degrees of 
natural affnity, The more distant the affinity, the 
more general is the extension. This, of course, is 
what we should expect on the theory of descent 
with modification, because the more distant the 
affinity, and therefore, ex hypothesi, the larger and 
the older the original group of organisms, the greater 
must be the chance of dispersal. The 400 species 
of humming-birds may well be unable to migrate 
from their native continent; but it would indced 
have been an unaccountable fact if no other species 
of all the class of birds had ever been able to have 
crossed the Atlantic Occan. Thus, on the theory of 
evolution, we can well understand the second corre- 
lation now before us—-namely, between remoteness 
of affinity and generality of dispersal,—so that 
there is no considerable portion of the habitable 
globe without representatives of all the classes of 
animals, few portions without representatives of all 
the orders, but many portions without many of the 
families, innumerable portions without innumerable 
genera, and, of course, all portions without the great 
majority of species. Now, while this general correla- 
tion thus obviously supports the theory of natural 
descent with progressive modification, it makes di- 
rectly against the opposite theory of special creation. 
For we have recently seen that when we restrict our 
view to the case of species and genera, the theory of 
special creation is obliged to suppose that for some 
inscrutable reason the Deity had regard to systematic 
affinity while determining on what laige areas to 
