widely, will give rise to most new varieties and species,
and will thus play an important part in the changing history of the
organic world.

We can, perhaps, on these views, understand some facts which will
be again alluded to in our chapter on geographical distribution; for
instance, that the productions of the smaller continent of Australia
have formerly yielded, and apparently are now yielding, before those
of the larger Europaeo-Asiatic area. Thus, also, it is that continental
productions have everywhere become so largely naturalised on islands. On
a small island, the race for life will have been less severe, and there
will have been less modification and less extermination. Hence, perhaps,
it comes that the flora of Madeira, according to Oswald Heer, resembles
the extinct tertiary flora of Europe. All fresh-water basins, taken
together, make a small area compared with that of the sea or of the
land; and, consequently, the competition between fresh-water productions
will have been less severe than elsewhere; new forms will have been
more slowly formed, and old forms more slowly exterminated. And it is
in fresh water that we find seven genera of Ganoid fishes, remnants of
a once preponderant order: and in fresh water we find some of the most
anomalous forms now known in the world, as the Ornithorhynchus and
Lepidosiren, which, like fossils, connect to a certain extent orders now
widely separated in the natural scale. These anomalous forms may almost
be called living fossils; they have endured to the present day, from
having inhabited a confined area, and from having thus been exposed to
less severe competition.

To sum up the circumstances favourable and unfavourable to natural
selection, as far as the extreme intricacy of the subject permits. I
conclude, looking to the future, that for terrestrial productions a
large continental area, which will probably undergo many oscillations
of level, and which consequently will exist for long periods in a broken
condition, will be the most favourable for the production of many new
forms of life, likely to endure long and to spread widely. For the area
will first have existed as a continent, and the inhabitants, at this
period numerous in individuals and kinds, will have been subjected
to very severe competition. When converted by subsidence into large
separate islands, there will still exist many individuals of the same
species on each island: intercrossing on the confines