Chap. V.] ACCLIMATISATION. 175 



instances could be adduced of species having largely 

 extended, within historical times, 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, though in all ordinary 

 cases we assume such to be the case; nor do we know 

 that they have subsequently become specially acclima- 

 tised to their new homes, so as to be better fitted for 

 them than they were at first. f 



As we may infer that our domestic animals were 

 originally chosen by uncivilised 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 ex- 

 traordinary 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, how- 

 ever, 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 con- 

 sidered as domestic animals, but they have been trans- 

 ported 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 an island in 

 the torrid zones. Hence adaptation to any special cli- 

 mate may be looked at as a quality readily grafted on 

 an innate wide flexibility of constitution, common to 



