Archaeologists have known for a long time that many of the earliest domesticated plants (wheat, barley) and animals (goats, sheep, maybe even cats) were domesticated in one place and time--central Asia, southern Turkey and Iran, about 10,000 years ago, more or less. Beginning about 7,000 years ago, the animals and plants moved into Europe as a package, along at least two paths. The people who moved the animals and plants and themselves are known collectively as the Linearbandkeramik culture.
Pigs into Europe
But one question that remains more or less unsolved is that of pigs (Sus scrofa). Unlike wild forms of wheat, sheep, goats and barley, wild pigs are indigenous to Europe. So, researchers were always of two minds: were pigs domesticated only in central Asia, or were they independently domesticated in Europe?
A research team reporting in the Proceedings of the National Academy of Sciences in 2007, suggested that, even though the wild boar was indigenous to the Paris basin, until the LBK culture came along, there were no domesticated swine in Europe. Genetics indicate that although many of today's pigs are related to the European wild boar, they are also related to the Sus scrofa of the Near East.
Replacement Pigs
There is, however, evidence that European wild boars were introduced into the Near Eastern domesticates soon after their arrival in Europe. This process, known as retrogression (meaning successful breeding of domesticated and wild animals), produced the European domestic pig, which was spread out from Europe in many places replacing the domesticated Near Eastern swine.
So, based on this research, pigs, like sheep and goats, originally derive from central Asia, where they were domesticated perhaps as early as 11,000 BC, and definitely present at sites such as Hallam Çemi, Çayönü Tepesi, and Neval Çori in eastern Turkey as early as 7000 BC.
Coat Color Variation
A paper on Sus scrofa genetics published in 2009 in PLoS Genetics points out that, although wild Asian and European boars are mainly camouflage-colored, the coats of domestic pigs are extremely variegated. The mutations in the genes affecting coat colors occurred only within the past 10,000 years-after domestication. The researchers argue that therefore, coat color variation was selected for by humans, which makes perfectly reasonable piggy sense. A wild pig would likely survive better on its own if it were to stay hidden; while a human might very well choose to be able to find and identify her own pigs.
Distinguishing Domestic and Wild Pigs
It continues to be difficult to distinguish 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 M3): wild boars typically have broader and longer tusks then domestic ones. Overall body size (particularly measures of astralagi, humeri and scapulae) has been commonly used since the mid-twentieth century. But wild boar body size alters with climate: hotter, drier climates mean smaller pigs, not necessary less wild ones. And there are notable variabilities of body size, and tusk size, within both wild and domestic pigs even today.
Other methods used by researchers include population demography (the theory is that pigs kept in captivity are slaughtered at younger ages as a management strategy) and the appearance of pigs outside their natural habitats. The study of Linear Enamel Hypoplasia (LEH) measures the growth rings in tooth enamel: domestic animals are more likely to experience stress episodes. Isotope analysis and toothwear can give clues to diet of a particular set of animals (domestic animals are more likely to have grain in their diets); and of course genetics can give indications of lineages.
In a 2012 article in the Journal of World Prehistory, Rowley-Conwy and colleagues describe the benefits and pitfalls of each of these methods, and suggest that an approach combining the metrical and non-metrical methods has the clearest potential for understanding pig domestication.
Sources
This article is part of the About.com Guide to the History of Animal Domestication.
Cucchi T, Fujita M, and Dobney K. 2009. New insights into pig taxonomy, domestication and human dispersal in Island South East Asia: molar shape analysis of Sus remains from Niah Caves, Sarawak. International Journal of Osteoarchaeology 19(4):508-530.
Fang, Meiying, et al. 2009 Contrasting Mode of Evolution at a Coat Color Locus in Wild and Domestic Pigs. PLoS Genetics 5(1):e1000341. Open Access
Larson, Greger et al. 2007. Ancient DNA, pig domestication, and the spread of the Neolithic into Europe. Proceedings of the National Academy of Sciences Open Access.
Larson G, et al. 2005. Worldwide Phylogeography of Wild Boar Reveals Multiple Centers of Pig Domestication. Science 307(5715):1618-1621.
Rowley-Conwy P, Albarella U, and Dobney K. 2012. Distinguishing Wild Boar from Domestic Pigs in Prehistory: A Review of Approaches and Recent Results. Journal of World Prehistory 25:1-44.
