Did modern humans go global twice as early as thought?
来源：未知 作者：邹到圉 时间：2019-03-07 08:08:01
By Bob Holmes Homo sapiens might have spread across the world much earlier than previously thought – and it was a favourable climate, not a sophisticated culture, that allowed them to go. Anatomically modern humans evolved in Africa about 200,000 years ago. Most palaeoanthropologists believe they stayed there for 140,000 years before migrating around the world, except for an abortive colonisation of what is now Israel about 120,000 years ago. Genetic evidence suggests that modern humans finally moved out of Africa and into the Middle East about 60,000 years ago. From there, they quickly spread throughout Asia and Europe, outcompeting the indigenous populations of Homo erectus and Neanderthals. It had been assumed that it was the development of more sophisticated tools and culture that led to this exodus. But that assumption has been challenged thanks to an archaeological find at Jebel Faya in the United Arab Emirates. In the desert near the Straits of Hormuz, Hans-Peter Uerpmann of the University of Tubingen, Germany, and his colleagues have excavated stone tools that date from about 125,000 years ago. The pattern of flaking on the stone tools, which is determined by how they are made, is distinct from that seen on tools made by the Neanderthals who were living further north at the time, and nothing like the tools made by Homo erectus. They are also distinct from the 120,000-year-old Israeli tools found 2000 kilometres to the north-west, suggesting they are not more evidence of that aborted migration event. But they do look like the primitive tools made around the same time by early modern humans in eastern Africa, and so likely represent a previously unrecognised “out of Africa” migration, says team member Anthony Marks, an archaeologist now retired from Southern Methodist University in Dallas, Texas. As such, the new tools suggest that Homo sapiens managed to travel across the forbidding Arabian peninsula about 60,000 years earlier than had been thought. That’s the “first big step” towards global dominance, says Marks. Moreover, this move to Arabia happened long before the development of the sophisticated stone tools that are typically associated with the first Homo sapiens outside Africa. This suggests that it wasn’t cultural deficiencies that confined our ancestors to the African continent. Instead, Uerpmann suggests the physical environment – in particular the Red Sea and the deserts of Arabia – may have been the obstacle to migration out of Africa. That obstacle may have been less insurmountable 125,000 years ago, however. Around 130,000 years ago, sea levels were still low at the end of a glacial period, making the Red Sea smaller and easier to cross. Soon after, interglacial warming brought monsoon rains to Arabia, transforming the deserts into eminently crossable savannahs. Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, notes that it is still unclear whether the new finds record the activity of the Homo sapiens that ultimately spread across the rest of the Old World, or just another aborted migration attempt. It is possible that the globally successful migration didn’t happen until 60,000 years ago, he says. If the stone tools were made by the Homo sapiens that went on to conquer the world, it suggests that the global migration may have happened slower than thought. “Our work essentially doubles the length of time that Homo sapiens had to get to these various places,” says Marks. “I’m much more comfortable with that.” Journal reference: Science, DOI: 10.1126/science.1199113. More on these topics: