176 ACCLIMATISATION. [Chap. V. 



most animals. On this view, the capacity of enduring 

 the most difEerent climates hy man himself and by his 

 domestic animals, and the fact of the extinot elephant 

 and rhinoceros having formerly endured a glacial cli- 

 mate, whereas the living species are now all tropical 

 or suh-tropical in their habits, ought not to be looked 

 at as anomahes, but as examples of a very common 

 flexibility of constitution, brought, under peculiar cir- 

 •cumstances, into action. 



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 an 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 Encyclopagdias of China, to be very cau- 

 tious in transporting animals from one district to an- 

 other. And 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 must, I think, be due to habit. On the other 

 hand, natural selection would inevitably tend to pre- 

 serve those individuals which were born with consti- 

 tutions best adapted to any country which they in- 

 habited. In treatises on many kinds of cultivated 

 plants, certain varieties are said to withstand certain 

 climates better than others; this is strikingly shown in 

 works on fruit-trees published in the United States, in 

 which certain varieties are habitually recommended for 

 the northern and others for the southern States; and as 

 most of these varieties are of recent origin, they cannot 

 owe their constitutional differences to habit. The case 



