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by step, raised into a continent, and a chain of mountains formed along
the axis of elevation. By the first of these upheavals, the plants and
animals inhabiting Borneo, Sumatra, New Guinea, and the rest, would be
subjected to slightly modified sets of conditions. The climate in
general would be altered in temperature, in humidity, and in its
periodical variations; while the local differences would be multiplied.
These modifications would affect, perhaps inappreciably, the entire
flora and fauna of the region. The change of level would produce
additional modifications: varying in different species, and also in
different members of the same species, according to their distance from
the axis of elevation. Plants, growing only on the sea-shore in special
localities, might become extinct. Others, living only in swamps of a
certain humidity, would, if they survived at all, probably undergo
visible changes of appearance. While still greater alterations would
occur in the plants gradually spreading over the lands newly raised
above the sea. The animals and insects living on these modified plants,
would themselves be in some degree modified by change of food, as well
as by change of climate; and the modification would be more marked
where, from the dwindling or disappearance of one kind of plant, an
allied kind was eaten. In the lapse of the many generations arising
before the next upheaval, the sensible or insensible alterations thus
produced in each species would become organized--there would be a more
or less complete adaptation to the new conditions. The next upheaval
would superinduce further organic changes, implying wider divergences
from the primary forms; and so repeatedly. But now let it be observed
that the revolution thus resulting would not be a substitution of a
thousand more or less modified species for the thousand original
species; but in place of the thousand original species there would arise
several thousand species, or varieties, or changed forms. Each species
being distributed over an area of some extent, and tending continually
to colonize the new area exposed, its different members would be subject
to different sets of changes. Plants and animals spreading towards the
equator would not be affected in the same way as others spreading from
it. Those spreading towards the new shores would undergo changes unlike
the changes undergone by those spreading into the mountains. Thus, each
original race of organis