Seite - 154 - in The Origin of Species

154 ORIGIN OF SPECIES than any other rodent; for they live under the cold climate of Faroe in the north and of the Falklands in the south, and on many an island in the torrid zones. Hence adap- tation 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 pecu- liar climate is due to mere habit, and how much to the natural selection of varieties having different innate consti- tutions, and how much to both means combined, is an ob- scure question. That habit or custom has some influence, I must believe, both from analogy and from the incessant ad- vice given in agricultural works, even in the ancient Ency- clopaedias of China, to be very cautious in transporting ani- mals 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 consti- tutions 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 pub- lished 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 ad- vanced, as proving that acclimatisation cannot be effected, for it is now as tender as ever it was ! The case, also, of the