DNA yields surprises about taming of pigs

Mean-tempered, big-tusked wild boars were transformed thousands of years ago into floppy-eared domestic pigs not once or twice, but repeatedly in many parts of the world as humans abandoned foraging and hunting for a settled farming life.

In a report published Friday in the journal Science, scientists used DNA from wild boars and pigs to conclude that pig domestication occurred in at least seven places through the millenniums.

"The question is no longer where pigs were domesticated but where pigs were not domesticated," said Greger Larson, a University of Oxford graduate student and the paper's first author.

The surprisingly widespread origin of domestic pigs about 9,000 years ago is unusual in the history of animal domestication. Sheep, cows, horses and goats traditionally were believed to have been domesticated a handful of times during human-farming history, mostly in the Fertile Crescent of the Near East.

Charles Darwin, among others, proposed that pigs were domesticated twice — in Asia and the Near East — then transported by Neolithic migrants who carried their farming culture with them.

Larson and co-authors in Sweden, England and New Zealand extracted DNA from bones of wild boars and domestic pigs and scrutinized previously gathered genetic samples of pigs.

Comparing the structure of a tiny segment of DNA from 362 wild boars and 324 domestic pigs from 40 countries, they found that wild boars had distinct genetic sequences depending on where they originated.

The scientists then matched the DNA of the pigs to the boars. They concluded that pigs were domesticated in central Italy, India, Burma/Thailand, western Indonesia/New Guinea, in addition to the previously identified locations of the Near East and China.

The pig data add to emerging theories that the domestication of animals occurred multiple times in different places, said Jared Diamond, a professor of geography and physiology at the University of California, Los Angeles, and a scholar of human civilizations.

"There's now evidence not only for pigs but that cows were domesticated at last three times — around the Fertile Crescent ... in India ... and North Africa," Diamond said.

The first steps in pig domestication likely were initiated by the boar. Boars that were less cautious and more friendly would venture close to human villages to root through trash.

Boars that exhibited this juvenile behavior were better fed and were able to breed more. Over time, juvenile traits — tameness, along with shorter snouts, smaller tusks and squealing — became bred into early domesticated pigs.

Only later would pigs have been deliberately bred by human beings for traits such as extreme size and hairlessness, said Keith Dobney, a co-author of the study and an archaeologist at Britain's University of Durham.

The work provides a new tool for tracking movements of prehistoric humans, the authors said. By assessing the genes of local domestic pigs, researchers could learn where the animals' wild-boar ancestors hailed from — and thus uncover ancient trade routes and human-migration paths.