Hints of earlier human exit from Africa

Stone tools suggest a surprisingly ancient move eastward

Stone Age people apparently took a surprisingly fast track out of Africa via an unexpected route — Arabia. Modern humans reached Arabia’s eastern edge, not far from the shores of southwestern Asia, as early as 125,000 years ago, according to a report in the Jan. 28 Science. That’s a good 65,000 years earlier than the generally accepted date for the first substantial human migrations beyond Africa.

HEADED EAST Stone tools found at Jebel Faya in Arabia suggest that modern humans, starting from East African sites, might have journeyed across the Bab al-Mandab Strait and the Arabian Peninsula much earlier than previously thought. These ancient travelers may have moved on to India’s Jwalapuram Valley, some researchers suspect. Science/AAAS
ARABIAN FLIGHTS Stone tools unearthed near the Persian Gulf, such as this hand axe shown from different angles, suggest to their discoverers that modern humans left Africa and trekked across Arabia as early as 125,000 years ago, possibly setting up early migrations to Asia. Science/AAAS

Stone tools unearthed at an Arabian Peninsula rock shelter called Jebel Faya resemble sharpened points and cutting implements from East African sites of about the same age, says a scientific team led by physical geographer Simon Armitage of the University of London and archaeologist Hans-Peter Uerpmann of the University of Tübingen in Germany. Jebel Faya is located in what’s now the United Arab Emirates.

“New dates at Jebel Faya reveal that modern humans migrated out of Africa much earlier than previously thought, helped by global fluctuations in sea-level and climate change in the Arabian Peninsula,” Armitage says.

Modern humans originated in East Africa around 200,000 years ago, according to fossil and genetic evidence (SN: 2/26/05, p. 141).

DNA analyses of people living in different regions of the world today suggest that modern humans rapidly migrated from Africa to Asia around 60,000 years ago. Most researchers suspect that those ancient travelers moved through the Middle East or along Arabia’s south coast to reach Asia.

Many advocates of this later African departure suspect that a massive eruption of Indonesia’s Mount Toba around 74,000 years ago created a global “volcanic winter” that decimated modern human populations in Africa and rendered the Indian subcontinent uninhabitable for thousands of years.

Finds at Jebel Faya call that scenario into question, Armitage says. By about 130,000 years ago, decreased sea levels narrowed the Bab al-Mandab Strait separating East Africa from southwest Arabia to about 4 kilometers, allowing safe passage, the researchers estimate. Travelers could have then moved through a network of Arabian lakes and rivers created by warm, wet conditions at that time.

Jebel Faya sits just across the Persian Gulf from Iran, at another narrow water crossing where low sea levels would again have eased passage, Armitage says.

Excavations began at Jebel Faya in 2003. Initial finds came from settlements dating to between about 3,000 and 10,000 years ago. Stone tools from roughly 38,000 years ago then turned up. In March 2006, investigators began to unearth tools from the ancient rock shelter, which was occupied between 100,000 and 125,000 years ago.

Estimated ages are based on a widely accepted method that measures accumulated natural radiation in sand grains to determine the amount of time elapsed since the grains were exposed to sunlight.

Another cache of stone tools encased in sediment just above the rock shelter has not been dated.

Finds at Jebel Faya consist of stone points, a few teardrop-shaped cutting implements known as hand axes and a variety of other sharpened rocks. These tools, in particular the points and hand axes, closely resemble African Stone Age artifacts from around the same time, the scientists assert.

So far, the site has yielded no modern human fossils.

Still, archaeologists familiar with the new report say that Jebel Faya provides an important glimpse of an early push by modern humans into Arabia. That’s where agreement ends.

Ravi Korisettar of Karnatak University in Dharwad, India, agrees with Armitage’s team that Arabia possibly served as hub between Africa and Asia for early modern human migrations. Since 2003, Korisettar has codirected excavations of Stone Age sites in southern India’s Jwalapuram Valley. Modern humans’ stone tools found there come from sediment just below and above an ash layer deposited by the Toba eruption, suggesting that people arrived before the blast and endured its devastation, he says.

Jebel Faya and Jwalapuram tools display some similarities, but the oldest Indian finds date to shortly before Toba’s detonation 74,000 years ago and look more like African implements from that time, Korisettar holds.

Tough, adaptable modern humans could have forged into Asia at least 100,000 years ago and withstood Toba’s insults, agrees John Shea of Stony Brook University in New York. But stone points from Jebel Faya are shorter, thicker and less pointy than those found throughout Africa beginning 100,000 years ago, he says.

Similarities of Jebel Faya points to Indian finds suggest that the Arabian site could as easily reflect an ancient westward movement of Asians — possibly Homo sapiens from the Persian Gulf region — to Arabia, Shea proposes. So humans could have been migrating away from Asia, not toward it as argued in the new report. It’s more likely that warm, wet conditions around 100,000 years ago prompted dead-end migrations of modern humans into Arabia and the Middle East, argues Stanley Ambrose of the University of Illinois at Urbana-Champaign. Previously unearthed fossils from several Israeli caves indicate that modern humans moved from Africa to the Middle East approximately 100,000 years ago but — either because they died out or returned to Africa — gave way to Neandertals by 70,000 years ago.

Pollen evidence indicates that the Toba explosion set off 10,000 years of extreme cold and environmental devastation that nearly wiped out African Homo sapiens, Ambrose contends. Modern human survivors of the blast’s aftermath then colonized Asia, in his opinion.

Paul Mellars of the University of Cambridge agrees with that scenario. But like Shea, he sees critical size and shape differences between Jebel Faya and African stone tools, casting doubt on the African origins of the Arabian tool-makers. “These Arabian finds are too ambiguous to say what was happening with human movements out of Africa,” Mellars remarks.

If the Arabian discoveries indeed signal an early human migration to Asia, then excavations of Stone Age sites in Iran should produce similar tools, Shea predicts. Iran’s current political climate, however, makes such work difficult, he says.


View larger image Credit: Altaileopard/Wikimedia commons

Though paleoanthropologists differ over when modern humans first expanded beyond Africa, there is little dispute about what happened once people did leave the continent. Genetic, linguistic and fossil evidence shows that waves of migration (see map) rapidly carried Homo sapiens to virtually every habitable region of the globe. By 1,500 years ago, people had reached even the high Arctic and the remotest Pacific islands.
Bruce Bower

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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