In Fact, The 100-Fathom
Line Round New Guinea Marks Out Accurately The Range Of The True
Paradise Birds.
It is further to be noted - and this is a very interesting point
in connection with theories of the
Dependence of special forms of
life on external conditions - that this division of the
Archipelago into two regions characterised by a striking
diversity in their natural productions does not in any way
correspond to the main physical or climatal divisions of the
surface. The great volcanic chain runs through both parts, and
appears to produce no effect in assimilating their productions.
Borneo closely resembles New Guinea not only in its vast size and
its freedom from volcanoes, but in its variety of geological
structure, its uniformity of climate, and the general aspect of
the forest vegetation that clothes its surface. The Moluccas are
the counterpart of the Philippines in their volcanic structure,
their extreme fertility, their luxuriant forests, and their
frequent earthquakes; and Bali with the east end of Java has a
climate almost as dry and a soil almost as arid as that of Timor.
Yet between these corresponding groups of islands, constructed as
it were after the same pattern, subjected to the same climate,
and bathed by the same oceans, there exists the greatest possible
contrast when we compare their animal productions. Nowhere does
the ancient doctrine - that differences or similarities in the
various forms of life that inhabit different countries are due to
corresponding physical differences or similarities in the
countries themselves - meet with so direct and palpable a
contradiction. Borneo and New Guinea, as alike physically as two
distinct countries can be, are zoologically wide as the poles
asunder; while Australia, with its dry winds, its open plains,
its stony deserts, and its temperate climate, yet produces birds
and quadrupeds which are closely related to those inhabiting the
hot damp luxuriant forests, which everywhere clothe the plains
and mountains of New Guinea.
In order to illustrate more clearly the means by which I suppose
this great contrast has been brought about, let us consider what
would occur if two strongly contrasted divisions of the earth
were, by natural means, brought into proximity. No two parts of
the world differ so radically in their productions as Asia and
Australia, but the difference between Africa and South America is
also very great, and these two regions will well serve to
illustrate the question we are considering. On the one side we
have baboons, lions, elephants, buffaloes, and giraffes; on the
other spider-monkeys, pumas, tapirs, anteaters, and sloths; while
among birds, the hornbills, turacos, orioles, and honeysuckers of
Africa contrast strongly with the toucans, macaws, chatterers,
and hummingbirds of America.
Now let us endeavour to imagine (what it is very probable may
occur in future ages) that a slow upheaval of the bed of the
Atlantic should take place, while at the same time earthquake-
shocks and volcanic action on the land should cause increased
volumes of sediment to be poured down by the rivers, so that the
two continents should gradually spread out by the addition of
newly-formed lands, and thus reduce the Atlantic which now
separates them, to an arm of the sea a few hundred miles wide.
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