According to an international team of anthropologists, an ancient skull collected from a cave in the Annamite Mountains in northern Laos is the oldest modern human fossil found in Southeast Asia.

The skull pushes back the clock on modern human migration through the region by as much as 20,000 years and indicates that ancient humans out of Africa left the coast and inhabited diverse habitats much earlier than previously appreciated.

The scientists, who found the skull in 2009, were likely the first to dig for ancient bones in Laos since the early 1900s, when a team found 16,000-year-old skulls and skeletons of several modern humans in another cave in the Annamite Mountains.

“It’s a particularly old modern human fossil and it’s also a particularly old modern human for that region,” said Dr Laura Shackelford, anthropologist at the University of Illinois and co-author of the study published in the Proceedings of the National Academy of Sciences.

“There are other modern human fossils in China or in Island Southeast Asia that may be around the same age but they either are not well dated or they do not show definitively modern human features. This skull is very well dated and shows very conclusive modern human features,” she added.

“No other artifacts have yet been found with the skull, suggesting that the cave was not a dwelling or burial site, Shackelford said. It is more likely that the person died outside and the body washed into the cave sometime later,” Dr Shackelford explained. “The find reveals that early modern human migrants did not simply follow the coast and go south to the islands of Southeast Asia and Australia, as some researchers have suggested, but that they also traveled north into very different types of terrain.”

“This find supports an ‘Out-of-Africa’ theory of modern human origins rather than a multi-regionalism model,” she said. “Given its age, fossils in this vicinity could be direct ancestors of the first migrants to Australia. But it is also likely that mainland Southeast Asia was a crossroads leading to multiple migratory paths.”

The discovery also bolsters genetic studies that indicate that modern humans occupied that part of the world at least 60,000 years ago, she said.

“This is the first fossil evidence that supports the genetic data.”

The scientists used uranium/thorium dating to determine the age of the skull, which they determined was about 63,000 years old.

They also found that the layer of soil surrounding the fossil had washed into the cave between 46,000 and 51,000 years ago.

“Those dates are a bit younger than the direct date on the fossil, which we would expect because we don’t know how long the body sat outside the cave before it washed in,” Dr Shackelford said.

“This fossil find indicates that the migration out of Africa and into East and Southeast Asia occurred at a relatively rapid rate, and that, once there, modern humans weren’t limited to environments that they had previously experienced,” she said. “We now have the fossil evidence to prove that they were there long before we thought they were there.”

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Bibliographic information: Demeter et al. 2012. Anatomically modern human in Southeast Asia (Laos) by 46 ka. PNAS, published online before print August 20, 2012; doi: 10.1073/pnas.1208104109