CiiAP. V. ACCLIMATIZATION. Ii5 



chosen by uncivilized nuin because they ■were useful^ and be- 

 cause they bred readily inider confinement, and not because 

 they were subsequently found cai)ablc of far-extended trans- 

 portation, the common and extraordinary capacity in our do- 

 mestic animals of not only withstandinf^ the most dillcrent 

 climates, but of beiii<T perfectly fertile (a far severer test) under 

 tliem, 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 prob- 

 able 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 ; 

 for they, live under the cold climate of Faroe in the north and 

 of the Falklands in the south, and on many islands in the tor- 

 rid zones. Hence adaptation to an}' special climate may be 

 looked at as a quality readily grafted on an innate wide ilexi- 

 bility of constitution, common to most animals. On this view, 

 the ca]iacity of enduring the most different climates by man 

 himself and by his domestic animals, and the fact of the extinct 

 elephant and rhinoceros ha\nng formerly endured a glacial cli- 

 mate, whereas the living species are now all trojiical 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 acclimatization of species to any peculiar 

 climate is due to mere habit, and how much to the natural se- 

 lection of varieties having diilerent innate constitutions, and 

 how much to both means combined, is an obscure question. 

 Tliat habit or custom has some influence I nuist believe, both 

 from analogy and from the incessant advice given in agricul- 

 tural works, even in the ancient Encyclopicdias of China, to be 

 very cautious in trans])orting animals from one district to 

 another; for 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 nuist, I think-, 

 be due to habit. On the other hand, natural si^lection would 

 inevitably tend to preserve those individuals wliich were born 

 with constitutions l)est adapted io any country which they in- 

 li ibih'd. In treatises on many kinds of cultivated plants, ccr- 

 7 



