CHAPTER VI. 
GEOGRAPHICAL DISTRIBUTION. 
THE argument from geology is the argument from 
the distribution of species in time. I will next take 
the argument from the distribution of species in space— 
that is, the present geographical distribution of plants 
and animals. 
Seeing that the theory of descent with adaptive 
modification implies slow and gradual change of one 
species into another, and progressively still more slow 
and gradual changes of one genus, family, or order 
into another genus, family, or order, we should expect 
on this theory that the organic types living on any 
given geographical area would be found to resemble 
or to differ from organic types living elsewhere, ac- 
cording as the area is connected with or disconnected 
from other geographical areas. For instance, the 
large continental islands of Australia and New Zealand 
are widely disconnected from all other lands of the 
world, and deep sea soundings show that they have 
probably been thus disconnected, either since the time 
of their origin, or, at the least, through immense 
geological epochs. The theory of evolution, there- 
fore, would expect to find two general facts with 
regard to the inhabitants of these islands. First, that 
