Preliminary attempt to distinguish the domesticated pigs from wild boars by the methods of carbon and nitrogen stable isotope analysis

Abstract

Despite great achievements in the origins of domestic pigs made by the methods of zooarchaeology and molecular biology, how to scientifically distinguish the domesticated pigs from wild boars during the early stage of pig domestication is still poorly understood. Compared to wild boar’s diets which come from the natural environment, the diets of domestic pigs are more easily influenced by human feeding activities. Therefore, in principle, exploration of the dietary differences among pigs and under-standing the impact on pig diets fed by humans can have great potential to differentiate between wild boars and domesticated pigs. To reveal dietary differences among pigs and distinguish the domesticated pigs from wild boars based on comparison with the diets of humans and other animals, we analyzed the carbon and nitrogen stable isotopes of human bones from Xiaojingshan Site and animal bones from Yuezhuang Site, both of which belong to Houli Culture in Shandong Province and date to about 8500-7500 years ago. The mean δ13C value ((−17.8 ± 0.3)‰) and δ15N value ((9.0±0.6)‰) in human collagen indicate that although millet agriculture began it was not the main subsistence strategy as millets are typical of C4 plants and that humans made a living mainly by gathering, hunting or raising some domesticated animals. The δ13C value (−16.1‰) and δ15N value (6.9‰) in the bovine suggest that C3 plants were dominant in its diet with some C4 plants complemented. The fish has lower δ13C value (−24.9‰) and higher δ15N value (8.8‰) than the bovine, which is the characteristic of the isotopic values from Eurasian freshwater fish. Based on the differences in carbon and nitrogen isotope values, the pigs can be divided into three groups. A group, composed of two pigs, has low δ13C values (−18.1‰, −20.0‰) and low δ15N values (4.7‰, 6.0‰). B group, only one pig, has the highest δ13C value (−10.6‰) and mediate δ15N value (6.4‰). As for the C group, also only one pig, low δ13C value (−19.0‰) and the highest δ15N value (9.1‰) are observed. Previous studies on the stable isotopes from modern or ancient wild boars’ bones have suggested that C3 plants are predominated in their diets and that their δ15N values are close to those in herbivores and far from those in carnivores. Based on the comparison with the isotope values from humans, the wild boars and the domestic pigs from Xipo Site in Henan 6000-5500 years ago and Kangjia Site in Shaanxi 4500-4000 years ago, we conclude that A pig group belongs to wild boars while B and C groups can be attributed to domesticated pigs.