Thursday, May 12, 2005

News: Out of Africa and straight to the beach

This news article is of interest because it confirms earlier studies suggesting humans coming out of Africa hugged the seacoast and acquired much of their food from the sea.

Paul Kekai Manansala

Out of Africa and straight to the beach

Modern humans emerged just once out of Africa - and headed straight for the beach - new genetic research suggests.

Most scientists agree that modern humans left Africa relatively recently, and it was traditionally thought that the route taken was northwards, overland into the Middle East and beyond.

But by measuring genetic variation in an isolated population in southeast Asia, Vincent Macaulay at the University of Glasgow, UK, and a team of international colleagues, conclude that the dispersal actually took a southern coastal route.

“It looks likely that a founder population crossed the Red Sea, and spread to Australia via India and southeast Asia, taking a southern route along the coast,” says Macaulay.
Original inhabitants

Mitochondrial DNA (mtDNA) accumulates mutations over generations, so measuring differences between different human populations can estimate the time since they diverged from one another. The team analysed the mtDNA of 260 members of an isolated population living in Malaysia, called the Orang Asil. The ancestors of these people were the original inhabitants of the Malay Peninsula.

Comparisons of mtDNA between the Orang Asil and other sources from Eurasia and Australasia allowed Macaulay’s team to calculate that the first humans arrived in Malaysia around 65,000 years ago. At this time, the northern route out of Africa from the Sinai Peninsula across northern Arabia to the Indian Ocean was blocked by a desert, which early humans would have found almost impossible to cross.

“The southern route has been seen as just another route taken by anatomically modern humans out of Africa,” says Macaulay. “But we are proposing that it is the only route required to explain the mtDNA evidence.”

After reaching Malaysia, a group that would eventually settle Europe branched away, but the main dispersal group made a speedy onward journey to Australia, reaching it only a few thousand years later.
Ancient Australians

The work clears up a question that has long troubled anthropologists: how did modern humans from Africa populate distant Australia long before nearby Europe? The oldest human remains in Australia date from 46,000 to 50,000 years ago, fitting neatly with the new genetics data.

The oldest European human remains, however, consist of an adult male’s jawbone, discovered in Romania and dated to between 34,000 and 36,000 years old.

“If the migrants had taken the northern route by looping northwards to Turkey to avoid the desert, then the question arises why they did not continue to Europe as well and leave ancient finds there,” says Peter Forster of the McDonald Institute for Archaeological Research at the University of Cambridge, UK. “By default, the southern route makes more ecological sense.”

The southern coastal route might have made more culinary sense, too. “The change to the incorporation of shellfish in the human diet [suggested by earlier research] may have made the coastal route attractive,” says Macaulay. “It’s even possible that the motivation for expanding eastwards was declining fish stocks in the Red Sea at the time of the glacial maximum, around 70,000 years ago.”

Journal source: Science (vol 308, p 1034)