OCR Text |
Show 128 LAWS OF VARIATION. (CHAP. V. that he has observed similar facts in Ceylon, and analogous observations have been made by Mr. H. C. Watson on European species of plants brought from the .Azores to England. In regard to animals, several au~.hentic c~ses could be given of species within historical times havin~ largely extended their range from warmer ~o. cooler latitudes, and conversely ; but 've do not positive~y kn?w that these animals were strictly adapted to their nat1ve climate, but in all ordinary cases we assume such to be the case; nor do we know that they have subsequently become acclimatised to their new homes. As I believe that our domestic animals were ori~inally chosen by uncivilised n1an because they were usetul and bred readily under confinement, and not because they were subsequently found capable of far-extended transportation, I think the cominon 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 proportion of other anilnals, now in a state of nature, could easily be brought to bear widely different climates. We must not, however, 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 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 zone. Hence I am inclined to look ~ at adaptation to any special climate as a quality readily grafted on an innate wide flexibility of constitution, 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 for· mer species of the elephant and rhinoceros were capable of enduring a glacial climate, whereas the living species are now aU tropical or sub-tropical in their habits, ought CHAP. V.] ACCLIMATISATION. 129 not to-be looked at as anomalies, but merely as examples of a very com1non flexibility of constitution brought under peculiar circumstances, into play. ' ' If.ow n~uch o~ the acclimatisati~n of species to any pecuhar chmate IS due to mere habit, and how much to the :z:~tu;al selection of varieties having different innate constitutions, and how rnuch to both means combined is a very obscure question. That habit or custom has so~e ~n:fluence I m?-st b.eliev~; bot~ from analogy, and from the Incessant advwe given In agricultural works even in the ancient ~ncycl?prndias of China! to. be very cautious in transposing animals from one distnct to another · for it is not likely that man should have succeeded in s~lecting 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, I can see ~o reason to doubt that n~tu~a~ selectio~ will continually tend to preserve those Individuals which are born with constitutions best adapted to their native countries. In tr~atises on .many ~inds of cultivated plants, certain varieties are said to Withstand certain climates better than others : this is very strikingly shown in works on fruit trees published in the United States, in which certain varieties are habitually recommended for the northern an~ o~hers for . the south~r~ States ; and as most of thes~ v~ne~Ies are. of recent ongin, they cannot owe their constitutional differences to habit. The case of the Jerusalem art~choke, which is never propagated by seed and of which consequently new varieties have not been produced, has even been advanced-for it is now as tender as ever it was-as proving that acclimatisation cannot be effecte~ ! The c~se: also, of the kidney-bean has been oft~n mted for a ~Imilar purpose, and with much greater weight~ but "?nti~ some one will sow, during a score of generat~ons, his kidney-beans so early that a very large J?roportlon are de~troyed ?Y frost, and then collect seed from the few surviv~rs, 'vith care to prevent accidental crosses, and then again get seed from these seedlino-s with the same precautions, the experiment cannot be 5s~id to have been even tried. Nor let it be supposed that no 6* |