If, when most of the species inhabiting one region are different
from those of another region, though closely allied to them, it can be
shown that migration from the one region to the other has probably occurred
at some former period, our general view will be much strengthened; for the
explanation is obvious on the principle of descent with modification. 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 related by inheritance to the inhabitants of that continent.
Cases of this nature are common, and are, as we shall hereafter see,
inexplicable on the theory of independent creation. This view of the
relation of the species of one region to those of another, does not differ
much from that advanced by Mr. Wallace, who concludes that "every species
has come into existence coincident both in space and time with a
pre-existing closely allied species." And it is now well known that he
attributes this coincidence to descent with modification.
The question of single or multiple centres of creation differs from another
though allied question, namely, whether all the individuals of the same
species are descended from a single pair, or single hermaphrodite, or
whether, as some authors suppose, from many individuals simultaneously
created.
Pages:
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602