The taming of pigs: DNA sheds light on farming

Today’s pigs in China have a pedigree dating back at least 8,000 years to some of the first domesticated swine, scientists say. The finding provides a more detailed picture about the history of animal husbandry and shows that pigs may have been tamed in places archaeologists had never before guessed.

The study, published online Monday in Proceedings of the National Academy of Sciences, is part of an effort to chart the movement of domesticated pigs by comparing DNA samples from the animals across the globe. Tracking the swine could shed light on human migration over the last several millenniums, researchers said.

Researchers from Britain, Sweden, China and the United States compared 18 samples of DNA extracted from ancient swine bones collected along China’s Yellow River to more than 1,500 modern pig specimens culled from museums, hunters’ private collections and farms. The scientists analyzed a specific kind of DNA called mitochondrial DNA, which is passed down maternally.

They found that the stock of modern-day pigs in Asia matched that of ancient pigs in the same region, demonstrating that the modern animals had ancient roots in the region, rather than having being imported from elsewhere more recently.

The researchers also found that the Asian pigs came from only a few species among today’s many existing species of wild boar.

What this means for agriculture is that many traits that exist among wild species — resistance against diseases, for example — have not yet been exploited through breeding, said UCLA evolutionary biologist Robert Wayne, who was not involved in the study. Therefore it’s important that the remaining populations of these wild animals are preserved, Wayne said.

“There’s a lot of untapped natural diversity.… They’re a genetic reservoir for variation not present that we might some day need,” he said.

The researchers also found evidence that pigs had been independently domesticated in isolated pockets of Asia — India, Southeast Asia and Taiwan — that archaeologists had never before noted as part of the pig-taming storyline.

The fact that the same pigs have stuck around for a while meant their humans probably did too, Wayne said.

“Continuity [in the pig population] implies some kind of cultural continuity as well — that the original people bred specific pigs instead of being overwhelmed by trade or foreigners that supplanted them and brought their own breeds,” he said.

Tracing the roots of pig domestication may help in tracking past human migrations and cultural development, said study lead author Greger Larson, an evolutionary biologist at the University of Durham in England.

Though they are not the earliest known domesticated species — dogs beat them out for that title — pigs were bred in large enough numbers as a food source to leave plenty of bone remnants to study. Domesticated dogs, in contrast, were so limited in number that it’s harder to cull information from the few remains they leave behind, Larson said.

Using animal DNA to study human history is easier for several reasons, Larson said. For one thing, the animals outnumbered their human owners and thus left more bones behind to be analyzed. For another, digging up and testing ancient human DNA is ethically problematic.

“Local cultural groups are not super keen for us grind up the bones [from burial sites] to see what their signatures are,” Larson said.

amina.khan@latimes.com