A CCLIMA riZA TION. I35 



the fact of the extinct elephant and rhinoceros liavin^ for- 

 merly 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 vtrv 

 common flexibility of constitution^ brought, under pecuhur 

 circumstances, into action. 



How much of the acclimatization of species to any 

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

 natural selection of varieties having different innate con- 

 stitutions, and how much to both means combined, is an 

 obscure question. That habit or custom has some influ- 

 ence, I must believe, both from analogy and from tlie in- 

 cessant advice given in agricultural works, even in the 

 ancient Encyclopedias of China, to be very cautious in 

 transporting animals from one district to another. And 

 as it is not likely that man should have succeeded in select- 

 ing 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 selec- 

 tion would inevitably tend to preserve those individuals 

 which were born with constitutions best adapted to any 

 country whicli they inhabited. In treatises on many kinds 

 of cultivated plants, certain varieties are said to with- 

 stand certain climates better than others; this is strik- 

 ingly shown in works on fruit-trees published in the United 

 States, in which certain varieties are habitually recom- 

 mended for the northern and others for the southern states; 

 and as most of these varieties are of recent origin, they can 

 not owe their constitutional differences to habit. The case 

 of the Jerusalem artichoke, which is never propagated in 

 England by seed, and of which, consequently, new varieties 

 have not been produced, has even been advanced, as prov- 

 ing that acclimatization cannot be effected, for it is now as 

 tender as ever it was! The case, also, of the kidney-bean 

 has been often cited for a similar purpose, and with much 

 greater weight; but until some one will sow, during a score 

 of generations, his kidney-beans so |early tliat a very large 

 proportion are destroyed by frost, and then collect seed 

 from the few survivors, with care to prevent accidental 

 crosses, and then again get seed from these seedlings, with 

 the same precautions, the experiment cannot be said to 

 have been tried. Nor let it be supposed that differences ia 



