But this difficulty partially
disappears on the view that New Zealand, South America, and the other
southern lands, have been stocked in part from a nearly intermediate though
distant point, namely, from the antarctic islands, when they were clothed
with vegetation, during a warmer tertiary period, before the commencement
of the last Glacial period. The affinity, which, though feeble, I am
assured by Dr. Hooker is real, between the flora of the south-western
corner of Australia and of the Cape of Good Hope, is a far more remarkable
case; but this affinity is confined to the plants, and will, no doubt, some
day be explained.
The same law which has determined the relationship between the inhabitants
of islands and the nearest mainland, is sometimes displayed on a small
scale, but in a most interesting manner, within the limits of the same
archipelago. Thus each separate island of the Galapagos Archipelago is
tenanted, and the fact is a marvellous one, by many distinct species; but
these species are related to each other in a very much closer manner than
to the inhabitants of the American continent, or of any other quarter of
the world. This is what might have been expected, for islands situated so
near to each other would almost necessarily receive immigrants from the
same original source, and from each other. But how is it that many of the
immigrants have been differently modified, though only in a small degree,
in islands situated within sight of each other, having the same geological
nature, the same height, climate, etc? This long appeared to me a great
difficulty: but it arises in chief part from the deeply-seated error of
considering the physical conditions of a country as the most important;
whereas it cannot be disputed that the nature of the other species with
which each has to compete, is at least as important, and generally a far
more important element of success.
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