The Variation of Animals and Plants under Domestication — Volume 1. Darwin Charles
Nathusius' work, with its excellent figures, should be studied. The whole of the exterior in all its parts has been altered: the hinder surface, instead of sloping backwards, is directed forwards, entailing many changes in other parts; the front of the head is deeply concave; the orbits have a different shape; the auditory meatus has a different direction and shape; the incisors of the upper and lower jaws do not touch each other, and they stand in both jaws beyond the plane of the molars; the canines of the upper jaw stand in front of those of the lower jaw, and this is a remarkable anomaly: the articular surfaces of the occipital condyles are so greatly changed in shape, that, as Nathusius remarks (s. 133), no naturalist, seeing this important part of the skull by itself, would suppose that it belonged to the genus Sus. These and various other modifications, as Nathusius observes, can hardly be considered as monstrosities, for they are not injurious, and are strictly inherited. The whole head is much shortened; thus, whilst in common breeds its length to that of the body is as 1 to 6, in the "cultur-racen" the proportion is as 1 to 9, and even recently as 1 to 11. (3/15. 'Die Racen des Schweines' s. 70.) Figure 3 (3/16. These woodcuts are copied from engravings given in Mr. S. Sidney's excellent edition of 'The Pig' by Youatt 1860. See pages 1, 16, 19.) of the head of a wild boar and of a sow from a photograph of the Yorkshire Large Breed, may aid in showing how greatly the head in a highly cultivated race has been modified and shortened.
Nathusius has well discussed the causes of the remarkable changes in the skull and shape of the body which the highly cultivated races have undergone. These modifications occur chiefly in the pure and crossed races of the S. indicus type; but their commencement may be clearly detected in the slightly improved breeds of the S. scrofa type. (3/17. 'Schweineschadel' s. 74, 135.) Nathusius 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 muzzles, have, whilst young, to exert the powerful muscles 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. There can hardly be a doubt that so great a change in habits would 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 has shown, this seems caused by an abnormal state of the primordial 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. (3/18. Nathusius 'Die Racen des Schweines' s. 71.) We shall in a future chapter see also that the skull and limbs are apparently in some manner correlated, so that any change in the one tends to affect the other.
Nathusius 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. (3/19. 'Die Racen des Schweines' s. 47. 'Schweineschadel' s. 104. Compare also the figures of the old Irish and the improved Irish breeds in Richardson on 'The Pig' 1847.)
The nature of the food supplied during many generations has apparently affected the length of the intestines; for, according to Cuvier (3/20. Quoted by Isid. Geoffroy 'Hist. Nat. Gen.' tome 3 page 441.), 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 length may be due either to descent from a distinct species or to more ancient domestication. The number of mammae vary, as does the period of gestation. The latest authority says (3/21. S. Sidney 'The Pig' page 61.) that "the period averages from 17 to 20 weeks," but I think there must be some error in this statement: in M. Tessier's observations on 25 sows it varied from 109 to 123 days. The Rev. W.D. Fox has given me ten carefully recorded cases with well-bred pigs, in which the period varied from 101 to 116 days. According to Nathusius the period is shortest in the races which come early to maturity; but the course of their development does not appear to be actually shortened, for the young animal is born, judging from the state of the skull, less fully developed, or in a more embryonic condition (3/22. 'Schweineschadel' s. 2, 20.) than in the case of common swine. In the highly cultivated and early matured races the teeth, also, are developed earlier.
The difference in the number of the vertebrae and ribs in different kinds of pigs, as observed by Mr. Eyton (3/23. 'Proc. Zoolog. Soc.' 1837 page 23. I have not given the caudal vertebrae, as Mr. Eyton says some might possibly have been lost. I have added together the dorsal and lumbar vertebrae, owing to Prof. Owen's remarks ('Journal Linn. Soc.' volume 2 page 28) on the difference between dorsal and lumbar vertebrae depending only on the development of the ribs. Nevertheless the difference in the number of the ribs in pigs deserves notice. M. Sanson gives the number of lumbar vertebrae in various pigs; 'Comptes Rendus' 93 page 843.), and as given in the following table, has often been quoted. The African sow probably belongs to the S. scrofa type; and Mr. Eyton informs me that, since the publication of this paper, cross-bred animals from the African and English races were found by Lord Hill to be perfectly fertile.
TABLE 2: NUMBER OF VERTEBRAE IN VARIOUS PIGS:
ENGLISH LONG-LEGGED MALE.
Dorsal 15. Lumbar 6. Dorsal plus Lumbar 21. Sacral 5. Total 26.
AFRICAN FEMALE.
Dorsal 13. Lumbar 6. Dorsal plus Lumbar 19. Sacral 5. Total 24.
CHINESE MALE.
Dorsal 15. Lumbar 4. Dorsal plus Lumbar 19. Sacral 4. Total 23.
WILD BOAR FROM CUVIER.
Dorsal 14. Lumbar 5. Dorsal plus Lumbar 19. Sacral 4. Total 23.
FRENCH DOMESTIC BOAR, FROM CUVIER.
Dorsal 14. Lumbar 5. Dorsal plus Lumbar 19. Sacral 4. Total 23.
Some semi-monstrous breeds deserve notice. From the time of Aristotle to the present time solid-hoofed swine have occasionally been observed in various parts of the world. Although this peculiarity is strongly inherited, it is hardly probable that all the animals with solid hoofs have descended from the same parents; it is more probable that the same peculiarity has reappeared at various times and places. Dr. Struthers has lately described and figured (3/24. 'Edinburgh New Philosoph. Journal' April 1863. See also De Blainville 'Osteographie' page 128 for various authorities on this subject.) the structure of the feet; in both front and hind feet the distal phalanges of the two greater toes are represented by a single, great, hoof-bearing phalanx; and in the front feet, the middle phalanges are represented by a bone which is single towards the lower end, but bears two separate articulations towards the upper end. From other accounts it appears that an intermediate toe is likewise sometimes superadded.
(FIGURE 4. OLD IRISH PIG, with jaw appendages. (Copied from H.D. Richardson on Pigs.))
Another curious anomaly is offered by the appendages, described by M. Eudes-Deslongchamps as often characterizing the Normandy pigs. These appendages are always attached to the same spot, to the corners of the jaw; they are cylindrical, about three inches in length, covered with bristles, and with a pencil of bristles rising out