The first migration of Homo sapiens, when they left the East African landscapes where they evolved and began a long trek across the Sahara, may have followed a different route than previously believed. A new study shows that prehistoric river channels fed by monsoons once traced a path north through the desert and argues that the modern humans may have followed those channels, going from oasis to oasis until they reached the sea. The Sahara has had several periods of increased rainfall that made it a wetter and greener place, including one interlude between 130,000 to 170,000 years ago when the researchers believe these river channels flowed with water.
Now only visible with satellite radar, the channels flowed intermittently from present-day Libya and Chad to the Mediterranean Sea, says [lead researcher] Anne Osborne.... Up to five kilometres wide, the channels would have provided a lush route from East Africa – where modern humans first evolved – to the Middle East, a likely second stop on Homo sapiens' world tour [New Scientist].
While it is widely accepted modern humans originated in sub-Saharan Africa 150,000 to 200,000 years ago, their exit route across the arid Sahara remains controversial.... The Nile Valley is widely believed to be the most likely route out of sub-Saharan Africa for early modern humans 120,000 years ago [Press Association].
But the study, published in the Proceedings of the National Academy of Sciences [subscription required], challenges this view. After discovering the remnants of the riverbeds with satellite radar, the researchers collected fossilized snail shells that were buried in the sand in Libya and showed that they were chemically identical to shells excavated from a volcano hundreds of miles away. The shells found in Libya must have been carried there by the river, researchers say. If water was that plentiful, the river channels would have offered an inviting habitat for Homo sapiens on the move, the researchers say.
"We now need to focus archaeological fieldwork around the large drainage channels an palaeo-lakes to test these ideas," said co-author Dr Nick Barton [BBC News].
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