Thursday, January 27, 2011

Archeologists find humans left Africa earlier, along different route

Our human ancestors’ first steps out of Africa were taken some 50,000 years earlier than previously thought – and in a completely unexpected direction.

Stone tools found buried in the baking Arabian Desert show that our early forebears may well have left the natal continent 125,000 years ago and in an eastward direction, before turning north and moving up into Europe and Asia, a groundbreaking new study says.

“The discovery of the site in southeast Arabia, which was occupied by early, anatomically modern humans . . . solves a deep gap in our knowledge about the appearance of our own species outside Africa,” says German archaeologist Hans-Peter Uerpmann, the study’s senior author.

The research, released Thursday by the journal Science, twists theories about human migratory routes in new directions and has already sparked controversy amongst archaeologists.

When and how our human ancestors left Africa, and where they sprung up about 200,000 years ago, have consumed that scientific discipline for decades.

Previously, it was generally held that early humans travelled up the Nile Valley and around the Mediterranean Sea before spreading into more northern latitudes some 60,000 years ago.

But the discovery of distinctly human tools — dated between 135,000 and 100,000 years in age — on the southeast shank of the Arabian Peninsula point to a very different and much earlier migration.

The tools, first unearthed in 2006, were the only evidence the international team of archaeologists found to indicate there were humans at the site, a rock overhang known as Jebel Faya in the modern United Arab Emirates.

The desert conditions that subsequent climate changes created – with summer temperatures that frequently hit 40C – were far too harsh to preserve skeletal remains.

But the tools, says Southern Methodist University archeologist Tony Marks, could only have been made by the same culture of early humans who populated East Africa at the time.

“An origin in East Africa for the (people who made them) was most plausible based on the stone tools and how they were made,” says Marks, a study co-author.

In particular, the tools, which included axes and two-sided blades, were beyond the technological prowess of other, non-human ‘hominids”, like the Neanderthals, who existed at the same time.

Claims that the tools were made by humans of east African heritage have already drawn howls of scorn.

In an accompanying Science article, University of Cambridge archaeologist Paul Mellars says the attribution of the tools to east African humans is unjustified.

“I’m totally unpersuaded,” Mellars says. “There’s not a scrap of evidence here that these were made by modern humans, nor that they came from Africa.”

Still, Oxford University archeologist Michael Petraglia was sold by the findings.

“This is really quite spectacular,” Petraglia says in the companion article. “It breaks the back of the current consensus view.”

Uerpmann, of the Eberhard Karls University in Tubingen, Germany, says descendants of the Jebel Faya humans may have moved up the peninsula and into Mesopotamia or the Indian subcontinent, a completely alternate route to the one posited with a Mediterranean exit.

As interesting as the migratory story told by the tools may be, however, is the ingenious way they were dated.

Employing a technique known as stimulated luminescence, scientists used the infinitesimally small flashes of radiation that were stored in sand grains stuck to the stone artifacts to show when they were buried.

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