LAWS OF VARIATION US 



been made by Mr. H. C. Watson on European species of plants 

 brought from the Azores to England ; and I could give other cases. 

 In regard to animals, several authentic instances could be ad- 

 duced of species having largely extended, within historical times, 

 their range from warmer to colder latitudes, and conversely; but 

 we do not positively know that these animals were strictly adapted 

 to their native climate, though in all ordinary cases we assume 

 such to be the case ; nor do we know that they have subsequently 

 become specially acclimated to their new homes, so as to be better 

 fitted for them than they were at first. 



As we may infer that our domestic animals were originally 

 chosen by uncivilized man because they were useful, and because 

 they bred readily under confinement, and not because they were 

 subsequently found capable of far-extended transportation, 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 may perhaps be mingled in our domestic 

 breeds. The rat and mouse cannot be considered as domestic ani- 

 mals, 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 of the 

 Falklands in the south, and on many an island in the torrid zones. 

 Hence adaptation to any special climate may be looked at as 

 quality readily grafted on an innate wide flexibility of constitu- 

 tion, 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 rhi- 

 noceros 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 circum- 

 stances, into action. 



How much of the acclimatization of species to any peculiar 

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

 tion 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 



