The effect of climate on the stature of the body is shewn by the smallness of the horses in Scotland and North Wales; and by the remarkable differences in this respect in the different provinces of Sweden. Must we not also explain on the same principle the constant and re markable degeneracy of the horse in France ? According to Bunn, the Spa nish or Barbary horses, where the breed is not crossed, degenerate into French horses in the second, or at latest in the third generation.
The effect of food on the body is very obvious in the well known fact of several singing birds, chiefly of the lark and finch kinds, becoming gradually black, if they are fed on hemp-seed only. The texture of the hair has been changed, in an African sheep brought into Eng land, from the coarse nature of that of the camel, to considerable softness and fineness, by one year's feeding in the pastures of this country. The influence of the same cause on the stature and pro portions of the body is shewn in the horse, which grows to a large size in the marshy grounds of Friesland, while on stony soils or dry heaths they remain dwarfish. Oxen become very large and fat in rich soils, but are distinguished by shortness of the leg ; while in drier situa tions their whole bulk is much less, and the limbs are stronger and more fleshy. I do not advert to the well-known differ ences of flavour and weight produced by different food.
Manner of life. Under this head we include all those causes which can act on the animal economy besides climate and food; and which, by their longtontinued influence on the body, effect considera ble changes in it. Culture and the pow er of habit are the most efficacious of these, and exert a very powerful and in disputable action on our domestic ani mals. Observe the striking difference of form and proportion between the horse trained in the manege, and the wild, untaught, and unbroken animal. The latter bites rather than kicks ; while the former, reined, and armed with iron shoes, uses these as his means of offence. The ass in its wild state is remarkably swift and lively, and still remains so in his native countries in the east. The argali, or wild original of the sheep, is covered with hair instead of wool; and the bison, or wild ox, has a long flowing mane, hanging almost to the ground. Most of the mainmalia, which have been tamed by man, betray their subjugated state, by having the ears and tail pendulous. In many, the very functions of the body, as the secretions, generation, &c. are great ly changed. The domestic sow produces young twice a year, and the wild animal only once.
The domestic pig acquires a vast accu mulation of fat under the skin, which is never seen in the wild animal, which on the contrary possesses a soft downy hair among its bristles, speedily lost in the timed individuals. The domesticated animals become liable to produce mon strous fetuses, and are exposed to new and numerous diseases : their bodies are even invaded by new kinds of worms, of which the hydatids in swine, forming what is commonly called the measles, are an indubitable instance.
The three causes now mentioned pro duce their effect in changing the original character of the animal, and giving origin to a variety, only after a great length of time, and a continued action through se veral generations. But these changes are communicated much more quickly by the process of generation. When two varieties copulate together, the offspring resembles neither parent wholly, but par takes of the form and other peculiarities of both. This cannot with propriety be
termed hybrid generation; as authors apply that expression to the produce of the copulation of different species, as of the horse and ass, &c. In this sense hy brids are never produced in the human species : for although we read various in stances of men and women having com merce with animals, there is not a shadow of reason for supposing that such copu lations ever produced an offspring. Breed ing from different has a great effect in changing the colour and form of the animal produced; and hence this method of improving and ennobling the race is practised with great effect in the domestic animals, particularly the horse and sheep.
it seems even possible that a disposi tion originally morbid may be transmitted by generation, and acquire a permanent character. The peculiar whiteness of the skin, with red colour of the eye, oc curring in the rabbit and ferret, and va rious other animals, as well as in the Al bino of the human race, appears in ..the first instance to be a morbid affection of the body ; and when it occurs in one or two instances only, in the human subject, has the appearance of a leprous cachexy. But, in the animals just mentioned, all the unnatural characters have been lost, and it is established as a permanent va riety. We have, moreover, many facts, spewing that, in some cases, casual muti lations are transmitted to the offspring : as want of tail in a cat or dog. (Philoso phical Magazine, vol. iv. p. 2. Ander son's Recreations, vol. i. p. 69.) The Jews are frequently born with so little foreskin, that it is hardly possible to cir cumcise them : this they call being born circumcised. (Philosophical Magazine, vol. iv. p. 5.) In applying the reasonings derived from the causes just mentioned, it may not be amiss to advert to the following rules :— 1. The greater the number of causes of degeneration, and the longer they con tinue to act on the same species, the more obviously will that species deviate from its original formation. Man, there fore, must be expected to vary more than any animal, since he has been subjected from his very origin to the united agen cies of climate, food, and way of life. 2. A cause, possessing in itself sufficient effi cacy, may be weakened by the concur rence of other conditions, tending to diminish its operations. Thus, countries placed under the same parallel of latitude have very different temperatures ; and the effects of situation on the human subject are varied, according as it is more or less elevated, or as it may be influenced by the neighbourhood of the sea, marshes, mountains, or woods, &c. 3. The source of degeneration is often to be sought for, not in any immediate cause, but in the mediate influence of some more latent agency. Thus, the dark colour of the skin may not arise from the direct action of the sun, but from its more remote, but very signal, influence on the hepatic sys tem. 4. These indirect and mediate causes may be so very obscure, that we cannot form even any probable conjecture as to their nature ; yet we seem to be warranted in referring those phenomena of degeneration, which hitherto appear enigmatical, to the operation of such un known powers. Thus we must explain the constant national forms of crania, colours of the eye, &c.