s growing at different heights on the
Himalaya, were 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 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 flexi