31 January 2011
Tools suggest earlier human migration from Africa
Stone Age people apparently took a surprisingly fast track out of Africa via an unexpected route - Arabia. Modern humans reached Arabia's eastern edge as early as 125,000 years ago, according to a report in the Science magazine. That's a good 65,000 years earlier than the generally accepted date for the first substantial human migrations beyond Africa.
A cache of 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.
The timing and dispersal of modern humans out of Africa has been the source of long-standing debate, though most evidence has pointed to an exodus along the Mediterranean Sea or along the Arabian coast approximately 60,000 years ago. 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. "These 'anatomically modern' humans - like you and me - had evolved in Africa about 200,000 years ago and subsequently populated the rest of the world," said Armitage. "Our findings should stimulate a re-evaluation of the means by which we modern humans became a global species." 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.
Initial finds at Jebel Faya 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. Finds at Jebel Faya consist of stone points, a few hand axes and a variety of other sharpened rocks. The researchers analysed these Palaeolithic stone tools using a technique called luminescence dating and discovered that they were technologically similar to tools produced by early modern humans in east Africa, but very different from those produced to the north, in the Levant and the mountains of Iran. Dr Armitage calculated the stone tools at Jebel Faya are 125,000 years old, and they were made immediately after the period in which the Bab al-Mandab seaway and Nejd Plateau were passable. This suggests that early modern humans migrated into Arabia directly from Africa and not via the Nile Valley and the Near East.
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. Korisettar has codirected excavations of Stone Age sites in southern India's Jwalapuram Valley; tools found there display some similarities with the onews discovered at Jebel Faya, 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.
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. Paul Mellars of the University of Cambridge 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.
"This is a huge milestone, but unfortunately it raises more questions than it answers," said Jeffrey Rose, an archaeologist at the University of Birmingham in England. Richard Klein, a paleoanthropologist at Stanford University, said that the Uerpmann team's case for an earlier out-of-Africa expansion was "provocative, but in the absence of human remains, it's not compelling." Christopher Stringer, a paleoanthropologist at the Natural History Museum in London, said that Arabia had long been a black hole in terms of early human migrations and that the new discovery was an impressive first start. He, like Dr. Klein, said it was hard to say who made the tools without having any fossil bones from the same site. But the tools are 'suggestive' of having been made by people who came out of Africa, Dr. Stringer said.
Edited from EurekAlert!, ScienceNews, The New York Times (27 January 2011), Past Horizons (30 January 2011)