The distributional area of the pig genus, before curtailed by human agency, was extensive, comprising the greater part of Europe, Southern, and a portion of Central Asai, Japan, the islands of the Malayan region, and Africa. Domesticated pigs have been turned loose in many parts of the world, such as America, the West Indies, and New Zealand, where they have formed feral races tending to revert more or less completely to the wild type, some even producing striped young.
Although some of the species are markedly distinct, the pigs (exclusive of those form South Africa) are an exceedingly puzzling group, scarcely any two zoologists being in accord as to the number of existing species. Some of the most important distinctive features are afforded by the cheek-teeth; but as such differences, after all, are but slight, and difficult to recognize, we shall in the main, confine out attention to some of the better known species, such as those in Europe and India.
The type of the genus is the European wild pig, or wild boar, ranging over Europe, Northern Africa, and part of western and Central Asia. It was formerly abundant throughout the British Islands, as is attested not only by historical evidence, but also by the abundance of its remains in the peat-mosses and fens. The Indian wild boor is so closely allied to its European cousin that it is frequently regarded as specifically inseperable. The habits of all swine are very similar. Pigs generally frequent moist or marshy situation, where there is plenty of cover, and their great characteristic is their habit of turning up the ground with their snouts in search of food, leaving marks by which their presence can be instantly recognized. During the day the Indian wild boar makes his lair in any convenient cover, sometimes in tall grass, at others in reeds or sugar-cane, and at others in bushes or forest, while not infrequently standing crops other than sugar-cane afford the necessary shelter. In the mornings and evenings he wanders forth in search of food, in cultivated districts devastating the crops, but away from human haunts he depends chiefly upon roots, those of a kind of sedge being special favorites. Wild pigs will, however, readily feed on the carcasses of animals and other carrion. Pigs are less nocturnal in their habits in remote districts than in those where they are much disturbed. While he females and young associate in droves or "sounders", usually comprising from ten to a dozen head, and rarely exceeding twenty, the old boars are solitary. The number of young produced at a birth by the European species varies from six to ten, after a gestation of four months; and frequently at least two litters are produced a year.
There are many different species of pigs including; Andaman pig, Pigmy hogs, Malayan pigs, and domestic swine. Much discussion has taken place as to the origin of the numerous domesticated breeds of swine, and very different views on the subject have been expressed by different writers; some urging that certain of the earlier races found in Europe had an Eastern origin, while others regard the whole of them as descended directly from the European wild boar. the earliest evidence of the existence of domesticated swine in Europe is afforded by the remains found on the sites of the prehistorical lake-dwellings of Switzerland. these were regarded as indicating two distinct breeds- one nearly allied to the European wild boar, and the other more resembling some of the Asiatic kinds. There was failure in detecting evidence of Asiatic affinity ion any prehistoric swine of Europe, and accordingly came to the conclusion that they were all probably derived from the European wild species, although these might possibly have some crossing with an Asiatic stock. In modern times, there has certainly been a great amount of intercrossing between the various breeds of domestic swine; and many of the races now most esteemed in Europe have a large proportion of Asiatic blood in their veins. The effects of domestication have been very marked on the swine, although the degree of variation from the wild type depends largely upon the amount of care that has been bestowed upon the breed. It has already been mentioned that the European breed differs from all wild species by the concave profile of the face; while as a rule domesticated races have uniformly-colored young. Whenever the young of domestic swine are striped, a recent crossing with a wild race may not be unreasonable suspected. When domesticated pigs revert to a wild condition, the striping of the young is, however, frequently resumed. Domestication invariably greatly reduces the size of the tusks of the boars, which in some breeds are very small indeed; and in this respect we have a reversion to extinct species of swine, in the earlier forms of which the tusks were but slightly developed. There are also modifications in the form of the hinder part of the skull, in the number of joints in the backbone, and in the length of the intestines.
Domesticated pigs are now found over the greater part of the habitable world; but while those kept in more northern regions are generally confined more or less closely to the homestead, the races of the warmer parts of the world are allowed to run more or less at liberty. Those kept in confinement are generally larger and fatter, although often more delicate animals, than the breeds which are allowed to roam almost at will; the latter being longer-limbed and thinner than the former, but at the same time bolder and more independent in disposition. In Southern Hungary, Croatia, Bosnia, Servia, Turkey, and Spain, the herds of swine are allowed to run in the woods throughout the year, but in less warm districts they have to be taken in and fed during the winter. in the Sierra Nevada of Spain, these herds ascend to an elevation of some nine thousand feet above the sea, and thus become expert climbers.
