Besides
These There Are Thirteen Rodents And Four Insectivora, Including
A Shrew-Mouse And Six Squirrels, Whose Unaided Passage Over
Twenty Miles Of Sea Is Even More Inconceivable Than That Of The
Larger Animals.
But when we come to the cases of the same species inhabiting two
of the more widely separated islands, the difficulty is much
increased.
Borneo is distant nearly 150 miles from Biliton, which
is about fifty miles from Banca, and this fifteen from Sumatra,
yet there are no less than thirty-six species of mammals common
to Borneo and Sumatra. Java again is more than 250 miles from
Borneo, yet these two islands have twenty-two species in common,
including monkeys, lemurs, wild oxen, squirrels and shrews. These
facts seem to render it absolutely certain that there has been at
some former period a connection between all these islands and the
mainland, and the fact that most of the animals common to two or
more of then, show little or no variation, but are often absolutely
identical, indicates that the separation must have been recent in
a geological sense; that is, not earlier than the Newer Pliocene
epoch, at which time land animals began to assimilate closely with
those now existing.
Even the bats furnish an additional argument, if one were needed,
to show that the islands could not have been peopled from each
other and from the continent without some former connection. For
if such had been the mode of stocking them with animals, it is
quite certain that creatures which can fly long distances would
be the first to spread from island to island, and thus produce an
almost perfect uniformity of species over the whole region.
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