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Pig DNA Study Suggests New Path of Pacific Human Migration

John Roach
for National Geographic News
March 20, 2007
 
Like following a trail of genetic breadcrumbs, researchers have used pig DNA to reconstruct the migration route of humans out of Asia and into the Pacific.

The porcine clues have revealed that the story is more complex than long-held theories suggest.

Based on their evidence, the scientists say that various pig-toting cultures from Vietnam traveled south through the Malaysian Peninsula into the Indonesian islands of Sumatra and Java and into the Lesser Sunda Islands (Indonesia map).

From there the travelers reached New Guinea and then moved into Hawaii and French Polynesia (Oceania map).

This route is in stark contrast to the conventional theory that the first Pacific settlers originated in Taiwan and traveled as a single cultural unit through the Philippines to New Guinea and then further east.

"We know for certain that the pigs that are in the Pacific did not follow what's traditionally called the 'out of Taiwan' route," said Greger Larson, lead study author and a geneticist currently at Uppsala University in Sweden.

Larson's team looked in vain along the Taiwan-Philippines route for pigs with the same genetic signature as those that dominate in the Pacific, he added.

The pigs they found along that path are East Asian domestics, which Larson says were introduced to the region more recently.

Writing in last week's issue of the Proceedings of the National Academy of Sciences, the team suggests that if earlier travelers took that route, they did so without pigs.

"What it forces people immediately to say is, OK, the 'out of Taiwan' model, though it may be true for humans, is certainly not true for pigs," Larson said.

Where's the Pork?

Pig genes contain a signature that tells exactly where the animals came from, said Larson, who performed the research while at the University of Oxford in conjunction with Keith Dobney, an archaeologist at England's Durham University.

Since pigs were domesticated and carried with at least some of the first people to settle the Pacific, the swine are an easy and accessible way to track human migration (explore an interactive atlas of human migration).

"The irony here is the best way to study humans is by studying what the humans took with them rather than the humans themselves," Larson said.

(Related news: "Rat DNA Offers Clues to Pacific Colonization, Study Says" [June 9, 2004].)

His team therefore sampled DNA from 781 modern and ancient pig specimens to trace which types of pigs wound up where.

The results suggest that one type of pig did disperse from southern China through Taiwan and the Philippines and into the islands of the western Pacific.

But other, earlier dispersals of a different kind of pig took the southern route out of Vietnam. This pig became the dominant species in the eastern Pacific.

According to Larson, the findings support the theory that, instead of an entire language and culture migrating en masse from Taiwan, each component first came together in eastern Indonesia about 3,500 years ago.

The resulting cultural complex, known as Lapita, then spread as a unit to Fiji and Tonga. The Lapita were ancestors to the Polynesians, who spread the culture to Hawaii, Tahiti, and other remote islands, Larson said.

"What's nice about the pigs is that there is a very strong argument for exactly that: that each one of these items is moving along a different trajectory" until they reach New Guinea, Larson said.

"If everything is [considered] one unit but actually it's not," Larson said, "then the oversimplification can lead to a misinterpretation of what really happened."

Pigs vs. Linguistics

Peter Bellwood, an archaeologist at Australia National University in Canberra, is a proponent of the 'out of Taiwan' model.

In an email, he said that the archaeological and linguistic evidence "make it clear that Pacific Island languages … and the ancestral cultures associated with them" originated in Taiwan.

"They were not transmitted from Vietnam," he added.

He also thinks it odd that the two pig dispersals noted in the paper did not have much overlap, since the various human populations transporting the pigs would have been in constant contact.

"And this in itself warrants caution before we reject the conclusions from the past century of careful multidisciplinary research."

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