strictly adapted to their native climate, but in all ordinary cases we
assume such to be the case; nor do we know that they have subsequently
become acclimatised to their new homes.
As I believe that our domestic animals were originally chosen by
uncivilised man because they were useful and bred readily under
confinement, and not because they were subsequently found capable of
far-extended transportation, I think the common and extraordinary
capacity in our domestic animals of not only withstanding the most
different climates but of being perfectly
fertile (a far severer test) under them, may be used as an argument
that a large proportion of other animals, now in a state of nature,
could easily be brought to bear widely different climates. We must not,
however, push the foregoing argument too far, on account of the
probable origin of some of our domestic animals from several wild
stocks: the blood, for instance, of a tropical and arctic wolf or wild
dog may perhaps be mingled in our domestic breeds. The rat and mouse
cannot be considered as domestic animals, but they have been
transported by man to many parts of the world, and now have a far wider
range than any other rodent, living free under the cold climate of
Faroe in the north and of the Falklands in the south, and on many
islands in the torrid zones. Hence I am inclined to look at adaptation
to any special climate as a quality readily grafted on an innate wide
flexibility of constitution, which is common to most animals. On this
view, the capacity of enduring the most different climates by man
himself and by his domestic animals, and such facts as that former
species of the elephant and rhinoceros were capable of enduring a
glacial climate, whereas the living species are now all tropical or
sub-tropical in their habits, ought not to be looked at as anomalies,
but merely as examples of a very common flexibility of constitution,
brought, under peculiar circumstances, into play.
How much of the acclimatisation of species to any peculiar climate is
due to mere habit, and how much to the natural selection of varieties
having different innate constitutions, and how much to both means
combined, is a very obscure question. That habit or custom has some
influence I must believe, both from analogy, and from the incessant
advice given in agricultural works, even in the ancient Encyclop dias
of China, to be very cautious
in transposing animals from one district to another; for it is not
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