Chap. XI. 
SINGLE CENTEES OF CREATION. 
355 
most of its inhabitants are closely related to, or belong 
to the same genera with the species of a second region, 
has probably received at some former period immigrants 
from this other region, my theory will be strengthened; 
for we can clearly understand, on the principle of 
modification, why the inhabitants of a region should be 
related to those of another region, w^hence it has been 
stocked. A volcanic island, for instance, upheaved and 
formed at the distance of a few hundreds of miles from a 
continent, would probably receive from it in the course 
of time a few" colonists, and their descendants, though 
modified, would still be plainly related by inheritance to 
the inhabitants of the continent. Cases of this nature 
are common, and are, as we shall hereafter more fully 
see, inexplicable on the theory of independent creation. 
This view of the relation of species in one region to 
those in another, does not differ much (by substituting 
the word variety for species) from that lately advanced 
in an ingenious paper by Mr. Wallace, in which he con¬ 
cludes, that every species has come into existence 
coincident both in space and time wfith a pre-existing 
closely allied species.” And I now know from corre¬ 
spondence, that this coincidence he attributes to gene¬ 
ration with modification. 
The previous remarks on single and multiple centres 
of creation” do not directly bear on another allied 
question,—namely w"hether all the individuals of the 
same species have descended from a single pair, or 
single hermaphrodite, or whether, as some authors 
suppose, from many individuals simultaneously created. 
With those organic beings w"hich never intercross (if 
such exist), the species, on my theory, must have de¬ 
scended from a succession of improved varieties, which 
will never have blended with other individuals or varie¬ 
ties, but will have supplanted each other; so that, at each 
