|
see it also in the birds of the caves of Brazil. Mr. Woodward has shown that the same law holds good with
from the wide distribution of most
molluscs, it is not well displayed by them. Other cases could be added, as the relation between the extinct and living land-shells of Madeira; and between the extinct and living
of the Aralo-Caspian Sea. |
|
| Now what does this remarkable law of the succession of the same types within the same areas mean? He would be a bold
after comparing the present climate of Australia and of parts of South
under the same latitude, would attempt to account, on the one
dissimilar physical
for the dissimilarity of the inhabitants of these two
and, on the other
similarity of conditions, for the uniformity of the same types in each
the later tertiary periods. Nor can it be pretended that it is an immutable law that marsupials should have been chiefly or solely produced in Australia; or that Edentata and other American types should have been solely produced in South America. For we know that Europe in ancient times was peopled by
marsupials; and I have shown in the publications above alluded to, that in America the law of distribution of terrestrial mammals was formerly different from what it now is. North America formerly partook strongly of the present character of the southern half of the continent; and the southern half was formerly more closely allied, than it is at present, to the northern half. In a similar manner we
from Falconer and
discoveries, that
India was formerly more closely related in its mammals to Africa than it is at the present
→time. Analogous facts could be given in relation to the distribution of marine animals. |
|
| On the theory of descent with modification, the great law of the long enduring, but not immutable, succession of the same types within the same areas, is at once explained; for the inhabitants of each quarter of the world will obviously tend to leave in that quarter, during the next succeeding period of time, closely allied though in some degree modified descendants. If the inhabitants of one continent formerly differed greatly from those of another continent, so will their modified descendants still differ in nearly the same manner and degree. But after very long intervals of
and after great geographical changes, permitting much
the feebler will yield to the more dominant forms, and there will be nothing immutable in the
of
→organic beings.
|
|
| It may be asked in ridicule, whether I suppose that the megatherium and other allied huge
→which formerly lived
|
