On the Alps themselves the Pleistocene
population still lingers, their successful adaptation to the cold
now preventing them from descending to the plains.
The animal world in turn was winnowed by the Pleistocene episode.
The hippopotamus, crocodile, turtle, flamingo, and other
warm-loving animals were banished to the warm zone. The mammoth
and the rhinoceros met the cold by developing woolly coats, but
the disappearance of the ice, which had tempted them to this
departure, seems to have ended their fitness. Other animals which
became adapted to the cold--arctic bears, foxes, seals,
etc.--have retreated north with the ice, as the sheet melted. For
hundreds of thousands of years Europe and North America, with
their alternating glacial and interglacial periods, witnessed
extraordinary changes and minglings of their animal population.
At one time the reindeer, the mammoth, and the glutton penetrate
down to the Mediterranean, in the next phase the elephant and
hippopotamus again advance nearly to Central Europe. It is
impossible here to attempt to unravel these successive changes
and migrations. Great numbers of species were destroyed, and at
length, when the climatic condition of the earth reached a state
of comparative stability, the surviving animals settled in the
geographical regions in which we find them to-day.
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