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Show CHAPTER III. . . tl t tl t of an individual-Species which arc V . b'l'ty of' a specu:~s compare o la ana II . . b ltereJ. greatly in o. short time, o.ml in a susceptible of motllficatlOn may e u . . . 1 . h th maiu stationary-The ammals now subJect few ,.,.enerabons ; after w liC ey re . . .. o . . t't d to domcsticity-Acqmred pecuhanbes to man had ongmally an ap I u e . . . f . h 1 connexion with the hab1ts or mshncts o which become hereditary ave o. c ose . . . . . 1 b . . 'ld t t -Some quahhes m certam ammals lave . een the spec1es m a WI 8 a e d t' t d conferred w1. th n. . f tl . r relation to man-Wild elephant omes tea e v1ew o 1e1 in a few years, but its faculties incapable of fUl'ther development. W d d l·n the last chapter to show, that a belief in E en eavoure the reality of species is not inconsistent with ~he idea of a considerable degree of variability in the specific .character. rrhis opinion, indeed' is little more t~an ~n extens~on. ~f the idea which we must entertain of the Identity of an mdividual, throughout the chanO"eS which it is capable of undergoing. If a quadruped, inhabiting a cold northern latitude, and covered with a warm coat of hair or wool, be transported to a southern climate, it will often, in the course of a few years, shed a considerable portion of its coat, which it gradually recovers on being aO"ain reHtored to its native country. Even there the 0 same chanO"eS are, perhaps, superinduced to a certam• ex ten t by the re~n·ns of winter and summer. We know_ that the Alpine hare* and the ermine t become white during wmter, and again obtain their full colour during the warmer season ; th~t the plumage of the ptarmigan undergoes a like metamorphosiS in colour and quantity, and that the change is equally temporary. We are aware that, if we reclaim so~e ~ild ~nimal, and modify lts habits and instincts by domesticatiOn, It may, if it escapes, become in a few years nearly as wild and untra~table as ever; and if the same individual be again retaken, lt may be reduced to its former tame state. A plant is placed in a prepared soil in order that the petals of its flowers may multiply, and their colour be heightened or changed; if we * Lepus variabilis.-Pullas. t Mustela ermineo..-Linu. Ch. III.] EXTENT 01<" CIIANGE IN SPECIES, 37 then withhold our care, the flowers of this same individual become again single. In these, and innumerable other instances, we must suppose that the individual was produced with a certain number of qualities; and, in the case of animals, with a variety of instincts, some of which may or may not be developed according to circumstances, or which, after having been called forth, may again become latent when the exciting causes are removed. Now the formation of races seems the necessary consequence of such a capability in individuals to vary, if it be a general law that the offspring should very closely resemble the parent. But, before we can infer that there are no limits to the deviation from an original type which may be brought about in the course of an indefinite number of generations, we ought to have some proof that, in each successive generation, individuals may go on acquiring an equal amount of new peculiarities, under the influence of equal changes of circumstances. The balance of evidence, however, inclines most decidedly on the opposite side, for in all cases we find that the quantity of divergence diminishes from the first in a very rapid ratio. It cannot be objected, that it is out of our power to go on varying the circumstances in the same manner as might happen in the natural course of events during some great geological cycle. For in the first place, where a capacity is given to individuals to adapt themselves to new circumstances, it does not generally require a very long period for its development; if, indeed, such were the case, it is not easy to see how the modification would answer the ends proposed, for all the individuals would die before new qualities, habits, or instincts, were conferred. When we have succeeded in naturalizing some tropical plant in a temperate climate, nothing prevents us from attempting gradually to extend its distribution to higher latitudes, or to greater elevations above the level of the sea, allowing equal quantities of time, or an equal number of generations for habitu- |