Among
These Are Seven Quadrumana (Apes, Monkeys, And Lemurs), Animals
Who Pass Their Whole Existence In Forests, Who Never Swim,
And
who would be quite unable to traverse a single mile of sea;
nineteen Carnivora, some of which no doubt
Might cross by
swimming, but we cannot suppose so large a number to have passed
in this way across a strait which, except at one point, is from
thirty to fifty miles wide; and five hoofed animals, including
the Tapir, two species of rhinoceros, and an elephant. 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. But
no such uniformity exists, and the bats of each island are
almost, if not quite, as distinct as the other mammals. For
example, sixteen species are known in Borneo, and of these ten
are found in Java and five in Sumatra, a proportion about the
same as that of the Rodents, which have no direct means of
migration. We learn from this fact, that the seas which separate
the islands from each other are wide enough to prevent the
passage even of flying animals, and that we must look to the same
causes as having led to the present distribution of both groups.
The only sufficient cause we can imagine is the former connection
of all the islands with the continent, and such a change is in
perfect harmony with what we know of the earth's past history,
and is rendered probable by the remarkable fact that a rise of
only three hundred feet would convert the wide seas that separate
them into an immense winding valley or plain about three hundred
miles wide and twelve hundred long. It may, perhaps, be thought
that birds which possess the power of flight in so pre-eminent a
degree, would not be limited in their range by arms of the sea,
and would thus afford few indications of the former union or
separation of the islands they inhabit. This, however, is not the
case. A very large number of birds appear to be as strictly
limited by watery barriers as are quadrupeds; and as they have
been so much more attentively collected, we have more complete
materials to work upon, and are able to deduce from them still
more definite and satisfactory results. Some groups, however,
such as the aquatic birds, the waders, and the birds of prey, are
great wanderers; other groups are little known except to
ornithologists. I shall therefore refer chiefly to a few of the
best known and most remarkable families of birds as a sample of
the conclusions furnished by the entire class.
The birds of the Indo-Malay region have a close resemblance to
those of India; for though a very large proportion of the species
are quite distinct, there are only about fifteen peculiar genera,
and not a single family group confined to the former district.
If, however, we compare the islands with the Burmese, Siamese,
and Malayan countries, we shall find still less difference, and
shall be convinced that all are closely united by the bond of a
former union. In such well-known families as the woodpeckers,
parrots, trogons, barbets, kingfishers, pigeons, and pheasants,
we find some identical species spreading over all India, and as
far as Java and Borneo, while a very large proportion are common
to Sumatra and the Malay peninsula.
The force of these facts can only be appreciated when we come to
treat the islands of the Austro-Malay region, and show how
similar barriers have entirely prevented the passage of birds
from one island to another, so that out of at least three hundred
and fifty land birds inhabiting Java and Borneo, not more than
ten have passed eastward into Celebes. Yet the Straits of
Macassar are not nearly so wide as the Java sea, and at least a
hundred species are common to Borneo and Java.
I will now give two examples to show how a knowledge of the
distribution of animals may reveal unsuspected facts in the past
history of the earth. At the eastern extremity of Sumatra, and
separated from it by a strait about fifteen miles wide, is the
small rocky island of Banca, celebrated for its tin mines. One of
the Dutch residents there sent some collections of birds and
animals to Leyden, and among them were found several species
distinct from those of the adjacent coast of Sumatra.
Enter page number
PreviousNext
Page 53 of 112
Words from 53020 to 54026
of 114260
