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Show 26 DARWINIAN .A. ing conditions in Nature. We separate and protect a favorite race against its foes or its competitors, and thus learn what it might become if Nature ever afforded it equal opportunities. Even when, to subserve human uses, we modify a domesticated race to the detriment of its native vigor, or to the extent of practical monstrosity, although we secure forms which would not be originated and could not be perpetuated in free Nature, yet we attain wider and juster views of the possible degree of variation. We perceive that some species are more variable than others, but that no species subjected to the experiment persistently refuses to vary; and that, when it has once begun to vary, its varieties are not the less but the more subject to variation. "No case is on record of a variable being ceasing to be variable under cultivation." It is fair to conclude, from the observation of plants and animals in a wild as well as domesticated state, that the tendency to vary is general, and even universal. Mr. Darwin does "not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought." No one supposes variation could occur under all circumstances ; but the facts on the whole imply a universal tendency, ready to be manifested under favorable circumstances. In reply to the assumption that man has chosen for domestication animals and plants having an extraordinary !nherent tendency to vary, and likewise to withstand diverse climates, it is asked: "How could a savage possibly know, when he first tamed an animal, whether it ·would vary in succeeding generations, THE ORIGIN OF SPECIES. 27 and whether it would endure other climates? lias the little variability of the ass or Guinea-fowl, or the small power of endurance of warmth by tho reindeer, or of cold by the common camel, prevented their domestication? I cannot doubt that if other animals and plants, equal in number to our domesticated productions, and belonging to equally diverse classes and countries, were taken from a state of nature, and could be made to breed for an equal number of generations under domestication, they would vary on an average as largely as· tho parent species of our existing domesticated productions hnvo varied." As to amount of variation, there is the common remark of nat~ralists that the varieties of domesti~ cated plants or animals often differ more widely than do the individuals of distinct species in a wild state : and even in Nature the individuals of some species are known to vary to a degree sensibly wider than that which separates related species. In his instructive section on the breeds of the domestic pigeon, our author remarks that " at least a score of pigeons might be chosen which if shown to an ornithologist, and he were told that they were w~ld birds, would certainly be ranked by him as well-defined species. Moreover, I do not believe that any ornithologist would place the English carrier, the short-faced tumbler, the runt, the barb, pouter, and fantail, in the same genus ; more especially as in each of these breeds several trulyinherited sub-breeds, or species, as he might have called them, could be shown him." That this is not a case like that of dogs, in which probably the blood of more than one species is mingled, :Mr. Darwin proceeds to show; adducing cogent reasons for the common opinion that all have descended from the wild rockpigeon. Then follow some suggestive remarks: |
