The domestication history of pigs (Sus scrofa) is a bit of an archaeological puzzle, in part because of the nature of the wild boar that our modern pigs are descended from. Many species of wild hog exist in the world today, such as the warthog (Phacochoreus africanus), the pygmy hog (Porcula salvania), and the pig-deer (Babyrousa babyrussa); but of all the suid forms, only Sus scrofa (wild boar) has been domesticated.
That process took place independently about 9,000-10,000 years ago in two locations: eastern Anatolia and central China. After that initial domestication, pigs accompanied early farmers as they spread out of Anatolia to Europe, and out of central China to the hinterlands.
All of the modern swine breeds today - there are hundreds of breeds around the globe - are considered forms of Sus scrofa domestica, and there is evidence that the genetic diversity is decreasing as cross-breeding of commercial lines threatens indigenous breeds. Some countries have recognized the issue and are beginning to support the continued maintenance of the non-commercial breeds as a genetic resource for the future.
Distinguishing Domestic and Wild Pigs
It must be said that it is not easy to distinguish between wild and domestic animals in the archaeological record. Since the early 20th century, researchers have segregated pigs based on the size of their tusks (lower third molar): wild boars typically have broader and longer tusks than domestic pigs. Overall body size (in particular, measures of knucklebones astralagi, front leg bones humeri and shoulder bones scapulae) has been commonly used to differentiate between domestic and wild pigs since the mid-twentieth century. But wild boar body size alters with climate: hotter, drier climates mean smaller pigs, not necessarily less wild ones. And there are notable variations in body size and tusk size, among both wild and domestic pig populations even today.
Other methods used by researchers to identify domesticated pigs include population demography - the theory is that pigs kept in captivity would have been slaughtered at younger ages as a management strategy, and that can be reflected in the ages of the pigs in an archaeological assemblage. The study of Linear Enamel Hypoplasia (LEH) measures the growth rings in tooth enamel: domestic animals are more likely to experience stress episodes in diet and those stresses are reflected in those growth rings. Stable isotope analysis and tooth wear can also give clues to the diet of a particular set of animals because domestic animals are more likely to have had grain in their diets. The most conclusive evidence is genetic data, which can give indications of ancient lineages.
See Rowley-Conwy and colleagues (2012) for a detailed description of the benefits and pitfalls of each of these methods. In the end, all a researcher can do is look at all of these available characteristics and make her best judgment.
Independent Domestication Events
Despite the difficulties, most scholars are agreed that there were two separate domestication events from geographically separated versions of the wild boar (Sus scrofa). Evidence for both locations suggest that the process began with local hunter-gatherers hunting wild boars, then over a period of time began managing them, and then purposefully or unconsciously keeping those animals with smaller brains and bodies and sweeter dispositions.
In southwest Asia, pigs were part of a suite of plants and animals that were developed in the upper reaches of the Euphrates river about 10,000 years ago. The earliest domestic pigs in Anatolia are found in the same sites as domestic cattle, in what is today southwestern Turkey, about 7500 calendar years BC (cal BC), during the late Early Pre-Pottery Neolithic B period.
Sus Scrofa in China
In China, the earliest domesticated pigs date to 6600 cal BC, at the Neolithic Jiahu site. Jiahu is in east-central China between the Yellow and Yangtze Rivers; domestic pigs were found associated with the Cishan/Peiligang culture (6600-6200 cal BC): in Jiahu's earlier layers, only wild boars are in evidence.
Beginning with the first domestication, pigs became the main domestic animal in China. Pig sacrifice and pig-human interments are in evidence by the mid-6th millennium BC. The modern Mandarin character for "home" or "family" consists of a pig in a house; the earliest representation of this character was found inscribed on a bronze pot dated to the Shang period (1600-1100 BC).
Pig domestication in China was a steady progress of animal refinement lasting a period of some 5,000 years. The earliest domesticated pigs were primarily herded and fed millet and protein; by the Han dynasty, most pigs were raised in small pens by households and fed millet and household scraps. Genetic studies of Chinese pigs suggest an interruption of this long progress occurred during the Longshan period (3000-1900 BC) when pig burials and sacrifices ceased, and previously more or less uniform pig herds became infused with small, idiosyncratic (wild) pigs. Cucchi and colleagues (2016) suggest this may have been the result of a social-political change during the Longshan, although they recommended additional studies.
The early enclosures used by Chinese farmers made the process of pig domestication much faster in China compared to the process used on western Asian pigs, which were allowed to roam freely in European forests up through the late Middle Ages.
Pigs Into Europe
Beginning about 7,000 years ago, central Asian people moved into Europe, bringing their suite of domestic animals and plants with them, following at least two main paths. The people who brought the animals and plants into Europe are known collectively as the Linearbandkeramik (or LBK) culture.
For decades, scholars researched and debated whether Mesolithic hunters in Europe had developed domestic pigs prior to the LBK migration. Today, scholars mostly agree that European pig domestication was a mixed and complex process, with Mesolithic hunter-gatherers and LBK farmers interacting at different levels.
Soon after the arrival of LBK pigs in Europe, they interbred with the local wild boar. This process, known as retrogression (meaning successful interbreeding of domesticated and wild animals), produced the European domestic pig, which then spread out from Europe, and, in many places replaced the domesticated Near Eastern swine.
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