Now these anticipations are to a considerable extent justified.
Remoteness on the earth's surface is usually an indication of diversity
in the fauna and flora, while strongly contrasted climates are always
accompanied by a considerable contrast in the forms of life. But this
correspondence is by no means exact or proportionate, and the converse
propositions are often quite untrue. Countries which are near to each
other often differ radically in their animal and vegetable productions;
while similarity of climate, together with moderate geographical
proximity, are often accompanied by marked diversities in the prevailing
forms of life. Again, while many groups of animals--genera, families,
and sometimes even orders--are confined to limited regions, most of the
families, many genera, and even some species are found in every part of
the earth. An enumeration of a few of these anomalies will better
illustrate the nature of the problem we have to solve.
As examples of extreme diversity, notwithstanding geographical
proximity, we may adduce Madagascar and Africa, whose animal and
vegetable productions are far less alike than are those of Great Britain
and Japan at the remotest extremities of the great northern continent;
while an equal, or perhaps even a still greater, diversity exists
between Australia and New Zealand.
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