found in this country to possess different
constitutional powers of resisting cold. Mr. Thwaites informs me that he
has observed similar facts in Ceylon, and analogous observations have been
made by Mr. H. C. Watson on European species of plants brought from the
Azores to England. In regard to animals, several authentic cases could be
given of species within historical times having largely extended their
range from warmer to cooler latitudes, and conversely; but we do not
positively know that these animals were 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 {141} 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