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Show 72 DOMESTIC PIGS. CHAP. III. of the head of a wild boar and of a sow from a photograph of tho Yorkshire Large Breed, may aid in showing ho¥~ greatly the head in a highly cultivated race has been modified and shortened. N atlmsius has well discussed the causes of the remarkable changes in the skull and shape of the body which the highly cultivated races have undergone. 'rhese modifications occur chiefly in the pure . and crossed races of the S. Indica type ; but their commencement may be clearly detected in the slightly improved breeds of the S. scroja typeY N athusius states positively (s. 99, 103), as the result of common experience and of his experiments, that rich and abundant food, given during youth, tends by some direct action to make the head broader and shorter; and that poor food works a contrary result. He lays much stress on the fact that all wild and semi-domesticated pigs, in ploughing up the ground with their muz- Fig. 3.-lleud of Wild lloar, and of" Golden Days," zles, ha VC, whilst young, to a pig of tho Yorkshire Large Brc'Cd; the latter from a photograph. (Copied from Sidney's edit. exert the powerful muscles of' The Pig,' by Youatt.) fixed to the hinder part of the head. In highly cultivated races this habit is no longer followed, and consequently the back of the skull becomes modified in shape, entailing other changes in other parts. 'rhere can hardly be a doubt that so great a change in habits would 1i 'Schwei.ucschadel,' s. 74., 1.:35. CHAP. III. THEIR VARIATION. 73 affect the skull ; but it seems rather doubtful how far this will account for the greatly reduced length of the skull and for its concave front. It• is well known (Nathusius himself advancing many cases, s. 104) that there is a strong tendency in many domestic animals-in bull- and pug- dogs, in the niata cattle, in sheep, in Polish fowls, short-faced tumbler pigeons, and in one variety of the carp-for the bones of the face to become greatly shortened. In the case of the dog, as H. Muller bas shown, this seems caused by an abnormal state of the primordiaJ cartilage. We may, however, readily admit that abundant and rich food supplied during many generations would give an inherited tendency to increased size of body, and that, from disuse, the limbs would become :finer and shorter. 18 We shall in a future chapter also see that the skull and limbs are apparently in some manner correlated, so that any change in the one tends to affect the other. N athusius has remarked, and the observation is an interesting one, that the peculiar form of the skull and body in the most highly cultivated races is not characteristic of any one race, but is common to all when improved up to the same standard. Thus the large-bodied, long-eared, English breeds with a convex back, and the small-bodied, short-eared, Chinese breeds with a concave back, when bred to the same state of perfection, nearly resemble each other in the form of the head and body. This result, it appears, is partly due to similar causes of change acting on the several races, and partly to man breeding the pig for one sole purpose, namely, for the greatest amount of flesh and fat; so that selection has always tended towards one and the same end. ·with most domestic animals the result of selection has been divergence of character, here it has been convergence.19 The nature of the food supplied during many generations has apparently affected the length of the intestines; for, according to Cuvier,20 their length to that of the body in the wild boar is as 9 to 1,-in the common domestic boar as 13·5 to 1,-and in the Siam breed as 16 to 1. In this latter breed the greater 18 Nathusius, ' Die Raccn des Schweines,' s. 71. 19 'Dio Hacen des Schweincs,' s. 47. 'Schweiucscbadol,' s. 104. Compare, also, the figurea of tho old Irish and tho improved Irish breeds in Richardson on ''!'he Pig,' 1847. 20 Quoted by Isid. Gcofli·oy, • Hi~;t. Nat. Gen.,' tom. iii. p. 441. |