will have been less severe, and there will
have been less modification and less extermination. 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. While the area existed as a continent the
inhabitants will have been numerous in individuals and kinds, and will
have been subjected to severe competition. When converted by subsidence
into large separate islands there will still have existed many
individuals of the same species on each island: intercrossing on the
confines of the range of each new species will have been checked: after
physical changes of any kind immigration will have been prevented, so
that new places in the polity of each island will have had to be filled
up by the modification of the old inhabitants; and time will have been
allowed for the varieties in each to become well modified and perfected.
When, by renewed elevation, the islands were reconverted into a
continental area, there will again have been very severe competition;
the most favoured or improved varieties will have been enabled to
spread; there will have been much extinction of the