| OCR Text |
Show 278 DEFINITE ACTION OF THE CHAP, XXIII. long as plants are grown in certain soils, of which Sageret 27 gives from his own experience some instances. Odart, who insists strongly on tho permanence of the varieties of the grape, admits 28 that some varieties, when grown under a different climate or treated differently, vary in an extremely slight degree, as in the tint of the fruit and in the period of ripening. Some authors have denied that grafting causes even the slightest difference in the scion; but there is sufficient evidence that the fruit is sometimes slightly affected in size and flavour, the leaves in duration, and the flowers in appearance.29 With animals there can be no doubt, from the facts given in the fu·st chapter, that European dogs deteriorate in India, not only in their instincts but in structure; but the changes which they undergo are of such a nature, that they may be partly due to reversion to a primitive form as in the case of feral animals. In parts of India the turkey become~ reduced in size, cc with the pendulous appendage over the beak enormously developed." 30 We have seen how soon the wild duck, when domesticated loses its true character, from the effects of abundant or changed food, 0~ from taking little exercise. From the direct action of a humid climate and poor pasture the horse rapidly decreases in size in the Falkland Islands. From information which I have received, this seems likewise to be the case to a certain extent with sheep in Australia. Climate definitely influences the hairy covering of animals; in the West Indies a great change is produced in the fleece of sheep, in about three generations. Dr. Falconer ~tates 31 that the Thibet mastiff and goat, when brought down from the Hunalaya to Kashmir, lose their fine wool. At Angora no~ only goats, b~t shepherd-d?gs and cats, have fine fleecy hair, a~d Mr. Am~wor.th 32 attnbutes the thickness of the fleece to the severe wmters, and Its silky lustre to the hot summers. Burnes states positivelyss that the ~arakool sheep lose their peculiar black curled fleeces when removed mto any other co.untry. Even within the limits of England, I have been assured that mth two breeds of sheep the wool was slightly changed by the flocks being pastured in different localities.s4 It has been asserted on ?ood autho~ity 35 that horses kept during several years in the deep coal-mmes of Belgium become covered with velvety hair, almost like that on the mole. These cases probably stand in close relation to the natural change of coat in winter and smnmer. Naked varieties of several domestic animals have occasionally appeared; but there is no reason to 27 ' Porn. Phys.,' p. 13G. 28 'Ampelogra.phio,' 1849, p. 19. 29 Gartner, 'Bastarderz.,' s. 606, has collected nearly all recorded facts. AndTew Knight (in ' Transact. Hort. Soc.,' vol. ii. p. 1GO) goes so far as to maintain that few varieties are absolutely permanent in character when propagated by bnds or grafts. 30 Mr. Blyth, in 'Annals and Ma<Y. of Nat. Hist.,' vol. xx., 1847, p. 391. b 31 'Natural Hi:;tory Review' 1862 p. 113. ' ' 02 'Joumal of Roy. Geographical Soc.,' vol. ix., 18'39, p. 275. 33 ' Travels in Bokhara,' vol. iii. p. 151. 34 See also, on the influence of marshy pastUl'eson thowool,Godron, 'L'Espece,' tom. ii. p. 22. 35 Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gen.,' tom. iii. p. 438. CHAP. XXIII. CONDITIONS OF LIFE. 279 believe that this is in any way related to the nature of the climate to which they have been exposed.36 It appears at first sight probable that the increased size, the tendency to fatten, the early maturity and altered forms of our improved cattle, sheep, and pigs, have directly resulted from their abundant supply of food. This is the opinion of many competent judges, and probably is to a great extent true. But as far as form is concerned, we must not overlook the equal or more potent influence of lessened use on the limbs and lungs. We see, moreover, as far as size is concerned, that selection is apparently a more powerful agent than a large supply of food, for we can thus only account for the existence, as remarked to me by Mr. Blyth, of the largest and smallest breeds of sheep in the same country, of Cochin-China fowls and Bantams, of small Tumbler and large Runt pigeons, all kept together and supplied with abundant nourishment. Nevertheless there can be little doubt that our domesticated animals have been modified, independently of the increased or lessened use of parts, by the conditions to which they have been subjected, without the aid of selectipn. For instance, Prof. Rlitimeyer 37 shows that the bones of all domesticated quadrupeds can be distinguished from those of wild animals by the state of their surface and general appearance. It is scarcely possible to read Nathusius's excellent 'Vorstudi~n,' 38 and doubt that, with the highly improved races of the pig, abundant food has produced a conspicuous effect on the general form of the body, on the breadth of the head and face, and even on the teeth. Nathusius rests much on the case of a purely bred Berkshire pig, which when two months old became diseased in its digestive organs, and was preserved for observation until nineteen months old; at this age it had lost several characteristic features of the breed, and had acquired a long, narrow head, of large size relatively to its small body, and elongated legs. But in this case and in some others we ought not to assume that, because certain characters are lost, perhaps through reversion, under one course of treatment, therefore that they had been at first directly produced by an opposite course. In the case of the rabbit, which has become feral on the island of Porto Santo, we are at fu·st strongly tempted to attribute the whole changethe greatly reduced size, the altered tints of the fur, and the loss of certain characteristic marks-to the definite action of the new conditions to which it has been exposed. But in all such cases we have to consider in addition the tendency to reversion to progenitors more or less remote, and the natural selection of the finest shades of difference. The nature of the food sometimes either definitely induces certain peculiarities, or stands in some close relation with them. Pallas long ago asserted that the fat-tailed sheep of Siberia degenerated and lost their enormous tails when removed from certain saline pastures; and recently as Azara has made some good remark:; on this subject, ' QuadrupCdes du Paraguay,' tom. ii. p. 337. See an account of a family of naked mice prouucod in Englund, ' Proc. Zoolog. Soc.,' 1856, p. 38. 3i 'Die Fauna der Pfahlbauten ' 1861 s. 15. ' ' 38 'Schweim;chrodel,' 1864, s. 9D. |
