128 ON THE ORIGIN OF SPECIES 



extended transportation, I think 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 pro- 

 portion of other animals, now in a state of nature, 

 could easily be brought to bear widely different 

 climates. We must not, however, push the fore- 

 going 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 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, 

 living free under the cold climate of Faroe in the 

 north and of the Falklands in the south, and on many 

 islands in the torrid zones. Hence I am inclined to 

 look at adaptation to any special climate as a quality 

 readily grafted on an innate wide flexibility of consti- 

 tution, which is common to most animals. On this 

 view, the capacity of enduring the most different 

 climates by man himself and by his domestic animals, 

 and such facts as that former species of the elephant 

 and rhinoceros were capable of enduring 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 merely as examples of a very 

 common flexibility of constitution, brought, under 

 peculiar circumstances, into play. 



How much of the acclimatisation of species to any 

 peculiar climate is due to mere habit, and how much to 

 the natural selection of varieties having different innate 

 constitutions, and how much to both means combined, 

 is a very obscure question. That habit or custom has 

 some influence I must believe, both from analogy, and 

 from the incessant advice given in agricultural works, 

 even in the ancient Encyclopaedias of China, to be very 

 cautious in transposing animals from one district to 



