t Essay, the author does not make a
separate section for such cases as the occurrence of fossil
Marsupials in Europe (_Origin_, Ed. i. p. 340, vi. p. 486) as he
does in the present Essay; see the section on _Changes in
geographical distribution_, p. 177.

We find some evidence of the same general fact in a relation between the
recent and the Tertiary sea-shells, in the different main divisions of
the marine world.

This general and most remarkable relation between the lately past and
present mammiferous inhabitants of the three main divisions of the world
is precisely the same kind of fact as the relation between the different
species of the several sub-regions of any one of the main divisions. As
we usually associate great physical changes with the total extinction of
one series of beings, and its succession by another series, this
identity of relation between the past and the present races of beings in
the same quarters of the globe is more striking than the same relation
between existing beings in different sub-regions: but in truth we have
no reason for supposing that a change in the conditions has in any of
these cases supervened, greater than that now existing between the
temperate and tropical, or between the highlands and lowlands of the
same main divisions, now tenanted by related beings. Finally, then, we
clearly see that in each main division of the world the same relation
holds good between its inhabitants in time as over space{391}.

{391} "We can understand how it is that all the forms of life,
ancient and recent, make together one grand system; for all are
connected by generation." _Origin_, Ed. i. p. 344, vi. p. 491.

_Changes in geographical distribution._

If, however, we look closer, we shall find that even Australia, in
possessing a terrestrial Pachyderm, was so far less distinct from the
rest of the world than it now is; so was S. America in possessing the
Mastodon, horse, [hyaena,]{392} and antelope. N. America, as I have
remarked, is now, in its mammifers, in some respects neutral ground
between S. America and the great Africo-Asiatic division; formerly, in
possessing the horse, Mastodon and three Megatheroid animals, it was
more nearly related to S. America; but in the horse and Mastodon, and
likewise in having the elephant, oxen, sheep, and pigs, it was as much,
if not more, related to the Africo-Asiatic division. Again, northern
India was much more clos