Hence, we can understand how it is that the flora of
Madeira, according to Oswald Heer, resembles to a certain extent 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.
Consequently, the competition between fresh water productions will have
been less severe than elsewhere; new forms will have been more slowly
produced, and old forms more slowly exterminated. And it is in fresh water
basins 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 at present widely
separated in the natural scale. These anomalous forms may be called living
fossils; they have endured to the present day, from having inhabited a
confined area, and from having been exposed to less varied, and therefore
less severe, competition.
To sum up, as far as the extreme intricacy of the subject permits, the
circumstances favourable and unfavourable for the production of new species
through natural selection. I conclude that for terrestrial productions a
large continental area, which has undergone many oscillations of level,
will have been the most favourable for the production of many new forms of
life, fitted to endure for a long time and to spread widely.
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