which already have been victorious over many competitors, will be those
that will spread most 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 Europ o-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 of the range
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