LAWS OF VARIATION 201 



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 extraor- 

 dinary 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 anin als 

 from several wild stocks; the blood, for iustaace, of a 

 tropical and arctic wolf may perhaps be mingled in our 

 domestic breeds. The rat and mouse cannot be consid- 

 !ered 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 Falk- 

 lands 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, 

 jjand the fact of the extinct elephant and rhinoceros hav- 

 ing formerly endured a glacial climate, whereas the living 

 jpecies are now all tropical or sub-tropical in their habits, 

 3ught not to be looked at as anomalies, but as examples of 



