s in the south, and on many an
island in the torrid zones. Hence adaptation to any special climate may
be looked at as a quality readily grafted on an innate wide flexibility
of constitution, common to most animals. On this view, the capacity of
enduring the most different climates by man himself and by his domestic
animals, and the fact of the extinct elephant and rhinoceros having
formerly endured 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 as examples of a very common flexibility of
constitution, brought, under peculiar circumstances, into action.

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 an 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 Encyclopaedias
of China, to be very cautious in transporting animals from one district
to another. And as it is not likely that man should have succeeded in
selecting so many breeds and sub-breeds with constitutions specially
fitted for their own districts, the result must, I think, be due to
habit. On the other hand, natural selection would inevitably tend to
preserve those individuals which were born with constitutions best
adapted to any country which they inhabited. In treatises on many kinds
of cultivated plants, certain varieties are said to withstand certain
climates better than others; this is strikingly shown in works on
fruit-trees published in the United States, in which certain varieties
are habitually recommended for the northern and others for the southern
states; and as most of these varieties are of recent origin, they cannot
owe their constitutional differences to habit. The case of the Jerusalem
artichoke, which is never propagated in England by seed, and of which,
consequently, new varieties have not been produced, has even been
advanced, as proving that acclimatisation cannot be effected, for it
is now as tender as ever it was! The case, also, of the kidney-bean has
been often cited for a similar purpose, and with much greater weight;
but until some one will sow, during a score of generations, his
kidney-beans so early that a very large proportion are destroyed by
fros