Modern humans may have left Africa thousands of years earlier than previously thought, turning right and heading across the Red Sea into Arabia rather than following the Nile to a northern exit, an international team of researchers says.
Stone tools discovered in the United Arab Emirates indicate the presence of modern humans between 100,000 and 125,000 years ago, the researchers report in Friday's edition of the journal Science.
While science has generally accepted an African origin for humans, anthropologists have long sought to understand the route taken as these populations spread into Asia, the Far East and Europe. Previously, most evidence has suggested humans spread along the Nile River valley and into the Middle East about 60,000 years ago.
"There are not many exits from Africa. You can either exit" through Sinai north of the Red Sea or across the straits at the south end of the Red Sea, explained Hans-Peter Uerpmann of the Center for Scientific Archaeology of Eberhard-Karls University in Tuebingen, Germany.
"Our findings open a second way which, in my opinion, is more plausible for a massive movement than the northern route," he said in a telephone briefing.
Because of the different climate at the time, Arabia was moister and would have been a grassland with plenty of animals for prey, he added.
And the lower sea levels at that time meant that the narrow point at the southern end of the Red Sea would have separated Africa and Arabia by between one-half and 2 1/2 miles( 1 and 3 kilometers), said Adrian G. Parker of Oxford Brookes University in England.
That should not have been a difficult crossing for people used to dealing with east African lakes and rivers where they used rafts or boats, Uerpmann said.
The techniques used to make the hand axes, scrapers and other tools found at Jebel Faya in Sharjah Emirate suggest they were produced by people coming from somewhere else, said Anthony E. Marks of Southern Methodist University, adding that there are similar tools made about that time in East Africa.
"If these tools were not made by modern man, who might have made them?," Marks asked. "Could Neanderthals have made them?"
Neanderthals were mainly in Europe and migrated into Russia but "there is no evidence for any Neanderthals south of that" zone at that time, he said. "To suggest one group of Neanderthals took a turn south and went several thousand kilometers ... seems to me a very difficult explanation and one that doesn't follow any reasonable logic."
The tools were dated using optically stimulated luminescence, which is able to date the sand grains on top of the tools and determine when they were last exposed to light, explained Simon J. Armitage of the University of London.
The discovery "points convincingly to an early dispersal of (anatomically modern humans) along a southern route, from eastern Africa into South Arabia," said G. Philip Rightmire of Harvard University, who was not part of the research team.
Rightmire said "it is reasonable to hypothesize that Arabia represents a separate center for population expansion, in addition to the northern Levantine corridor. This hypothesis remains to be tested, as new evidence is compiled."
The research was supported by the government of Sharjah, Heidelberg Academy of Sciences, Humboldt Foundation, Oxford Brookes University and the German Science Foundation.