POINTING TO OLDER ORIGINS: A collection of Paleolithic tools unearthed from a rock shelter in the U.A.E. suggest that humans might have left Africa some 125,000 years ago--rather than 60,000 years ago as genetic data suggests Image: AAAS/SCIENCE
Just beyond a shallow, narrow sea lay an open topography of grassy savanna, populated by plentiful game and few predators. This watery barrier—likely not more than five kilometers wide—would have been but a small obstacle for a group of modern humans accustomed to navigating African lakes with boats and rafts. But this short crossing, enabled by coincidental climate change, might have led the species—possibly for the first time—out of Africa and into Arabia, and eventually deeper into Asia, Europe and the rest of the globe.
After finding a trove of Paleolithic stone tools in what is today the United Arab Emirates (U.A.E.), a team of researchers now proposes that just such a pivotal journey across what is now the Red Sea occurred at least 125,000 years ago—about 75,000 years after Homo sapiens are thought to have evolved and tens of thousands of years earlier than they were thought to have left the African continent. And although small watercraft certainly helped, it was a trick of climatic shifts—a window of plentiful rains on the heels of a glacial period—that made the trip possible.
Direct human fossil evidence for such an early—and southeastward—migration is still lacking, however, the sand deposits around the stone tools suggest they have been buried 100,000 to 120,000 years. A middle Stone Age residence in this area would suggest that humans reached the Arabian Peninsula not from the more-northern Nile Valley 119,000 to 81,000 years ago or from the Mediterranean Sea's shores 65,000 to 40,000 years ago—as previous evidence has suggested—but rather directly from the Horn of Africa, and much earlier.
Even with "the confounding lack of diagnostic fossil evidence," says Chris Stringer, a professor of paleontology at the Natural History Museum in London and who was not involved in the research, the new archaeological work "provides important clues that early modern humans might have dispersed from Africa across Arabia, as far as the Strait of Hormuz, by 120,000 years ago." The new findings will be published in the January 28 issue of Science, and researchers think that the results could have broad implications for thinking not just about when and where humans first decamped from Africa, but also why and how.
"The mechanisms of getting out of Africa should be understood in a different way," Hans-Peter Uerpmann of the University of Tübingen in Germany and a co-author of the new study said in a telephone conference call with reporters on Wednesday. "Up until now we thought of cultural developments leading to the opportunity of people to move out of Africa. Now we see, I think, that it was the environment that was the key."
Flakes of Jebel Faya
The site where the tools were found, Jebel Faya, is about 65 kilometers from the coast of both the Persian Gulf and the Indian Ocean. Some 125,000 years ago, it would have been a grassy home to gazelles, ibex and wild asses. But before March 2006, when the first piece of a hand ax was identified, the site was known to local research teams as simply "a nice shady picnic place for a weekend without archaeology," Uerpmann said. But once striking stone tools started turning up, researchers realized they were on to something.
At the site, which is a collapsed rock shelter, excavators found three distinct layers of ancient tools (labeled A, B and C, with C being the oldest). "Assemblages A and B were similar, but assemblage C, the lowest, was radically different," said Anthony Marks, of Southern Methodist University in Dallas and research team member. The tools from the C group, which were dated to approximately 120,000 years ago, included denticulates, end-scrapers, foliates, hand axes and side-scrapers.
"We looked at what was in southeastern Arabia at that time, there was literally nothing,", Marks said during the Wednesday call. And, as Stringer points out, "the fact that artifacts in assemblage C at Jebel Faya do not resemble those associated with contemporaneous Homo sapiens [east of Egypt] signals yet more complexity in the exodus of modern humans from Africa."