Seite - 153 - in The Origin of Species

ACCLIMATISATION 153 limited in their ranges by the competition of other organic beings quite as much as, or more than, by adaptation to par- ticular cHmates. But whether or not this adaptation is in most cases very close, we have evidence with some few plants, of their becoming, to a certain extent, naturally habituated to different temperatures; that is, they become acclimatised: thus the pines and rhododendrons, raised from seed collected by Dr. Hooker from the same species grow- ing at dififerent heights on the Himalaya, were found to pos- sess in this country different constitutional powers of re- sisting cold. Mr. Thwaites informs me that he has observed similar facts in Ceylon ; analogous observations have been made by Mr. H. C. Watson on European species of plants brought from the Azores to England ; and I could give other cases. In regard to animals, several authentic instances could be adduced of species having largely extended, within historical times, their range from warmer to cooler lati- tudes, and conversely ; but we do not positively know that these animals were strictly adapted to their native climate, though in all ordinary cases we assume such to be the case ; nor do we know that they have subsequently become specially acclimatised to their 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 uncivilised man because they were useful and be- cause they bred readily under confinement, and not because they were subsequently found capable of far-extended trans- portation, 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 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 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