Lost Lake May Have Helped Humans Leave Africa

Long-lost lake may have helped humans out of Africa - 22 January 2014 - New Scientist

Another piece has probably just fallen into place in the jigsaw puzzle of human evolution and our diversification out of Africa into the Middle East and Euro-Asia.

Migrating populations rarely up sticks and go on a long journey to distant lands. Instead the movement can be slow, spread over many generations and involve long stops and stable populations on the way. One problem, for example, is taking enough food for the journey because fruit and vegetables go bad after a while and livestock needs food and water. Sure you can hunt and gather on the way but that presupposes there will be something to hunt and gather. For this reason, deserts and barren mountain ranges are impassable barriers to human migration, especially early, low tech people like our early human ancestors.

It had long been assumed that modern Homo sapiens didn't come out of Africa until we had developed to a certain threshold level of intelligence and technology about 70,000 years ago to enable us to adapt to new environments on the way, but this was thrown into question when remains of very early humans from about 100,000 years ago were found in Israel. The mystery was how these people managed to cross the Sahara and the expanses of desert between East Africa and the Eastern Mediterranean.

But Martin Williams of the University of Adelaide in Australia and Tim Barrows of the University of Exeter, UK, have analysed samples collected from former lake-shore deposits, and dated them to about 109,000 years ago. This lake would have been one of the largest lakes in the world if it existed today at about 450,000 square kilometers and would have been in just the right place at the right time to support a large human population north of Ethiopia and with connections to the Nile which forms a narrow fertile strip across the Sahara to the Mediterranean coast. Although the size of the lake would have varied with the seasons it would have been large enough to still be a sizeable lake even in dry periods.

A big lake like this would have been a great place to live. It would have supported a large population, probably fishing and hunting game.

Stephen Oppenheimer, University of Oxford

Then, due to climate change and loss of monsoon rains the lake began to shrink, disappearing sometime between 70,000 and 100,000 years ago. The population would have been forced to migrate, and the obvious route is via the Nile to the Mediterranean and then east to modern Israel. A lake-side people could have easily adapted to living along a river.

So, we now have an explanation of how humans reached the Eastern Mediterranean before we had reached the assumed intelligence/technological threshold. However, DNA analysis shows that the modern Euro-Asian population only came out of Africa about 71,000 years ago, presumably absorbing or exterminating any earlier migration, assuming anyone had survived.

The question is whether the newly-discovered lake played any part in this second wave. This depends on precisely when it finally disappeared and there is not enough evidence to determine that precisely. It's disappearance could have triggered the second wave but it seems more likely that by then sea levels had dropped as the last Ice-Age reached its height, so making it possible to walk across what is now the Red Sea basin into Arabia.

'via Blog this'

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