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The search for Eden and the pursuit of humanity’s origins

Our species, Homo sapiens, evolved in Africa over hundreds of thousands of years and now we are beginning to understand how

By Robin McKie  /  The Observer

Illustration: Lance Liu

Underneath our skins, we are all Africans. That is the recent, simple conclusion of scientists studying the origins of our species.

Genes, ancient stone tools and fossil bones — analyzed over the past few decades — make it clear that men and women today are the direct descendants of hunter-gatherers who evolved somewhere in Africa and took over the continent before one group departed to conquer the rest of the world tens of thousands of years ago.

However, the location in Africa where we first appeared has never been established. Some researchers have argued that the cradle of humankind lay in the east, in Ethiopia or Kenya. Others have put their money on South Africa.

Most are sure that it is only a matter of time before our species’ birthplace is pinpointed — perhaps on land covering a huge estuary that once groaned with fish, or near a vast slice of savannah rich with game.

It was here, in some Stone Age paradise, that our more primitive predecessors honed their intellectual and cultural skills, and were transformed into Homo sapiens, a primate species notable for its rounded skull, small face, prominent chin, advanced tools, high intelligence and sophisticated culture.

It is a neat picture — but in recent years, cracks have begun to appear in this simple image of our distant past, mainly because plausible candidates for our birthplace have proved difficult to find.

As a result, a growing number of researchers are turning away from the idea that such an Arcadia existed. As Harvard geneticist David Reich has put it: “When it comes to human ancestry, there was no Garden of Eden.”

‘A BRAIDED STREAM’

Archeologists, fossil experts and geneticists are instead backing a dramatic new idea to explain the evolution of Homo sapiens, saying that a multitude of places in Africa acted as the cradle of modern humankind. We did not appear in one place and then spread, but instead constantly evolved for almost half-a-million years across the continent’s sprawling vastness.

“The immediate predecessors of modern humans probably arose in Africa about 500,000 years ago and evolved into separate populations,” said Chris Stringer, a research leader at the Natural History Museum, London. “When times were bad — for example, when the Sahara was arid, as it is now — you would get little isolated pockets of humans clinging on to existence. Some of these people would have gone extinct. Others managed to hang on.”

Later, when conditions improved — for example, when the Sahara became green again and lakes and rivers formed — surviving populations expanded and came into contact with each other. When they did, they would have exchanged ideas — and genes. Then the climate would have turned grim again and they would have separated.

“This happened over and over again in different places for different reasons for the next 400,000 years,” Stringer said. “The end product was Homo sapiens, the species that is more or less the version of modern humanity that now inhabits every continent on Earth.”

“Homo sapiens probably descended from a set of interlinked groups of people, who were separated and connected at different times. Each one had different combinations of physical features, with their own mix of ancestral and modern traits,” Eleanor Scerri of the University of Oxford said.

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