The paradigm that all people arose from a single mass exit from Africa by Homo sapiens 60,000 years ago isnt accurate, says a team of archaeologists summing up the most recent archaeological and genetic research.
Modern humans began to exit Africa in small hunter-gatherer groups some 120,000 years ago, wandering and mating with various other species of hominin as they went along – and they may have left traces in the DNA of some groups existing today.
We collected all the fossil, genetic archaeology and environmental data available and dispute the mantra, says Prof. Michael Petraglia, co-author of the study published in Science on Sunday by archaeologists from the Max Planck Institute for the Science of Human History and the University of Hawaii at Manoa.
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Archaeologists have long suspected that Homo sapiens was running around Eurasia before the purported great exit 60,000 years ago. But they had assumed that earlier waves of humans who left Africa before that went extinct. Many evidently did, but did they all?
At this point, we cannot even say how long Homo sapiens has been around. The paradigm that man evolved in eastern Africa, starting around 200,000 years ago, is also looking rocky, following the discovery of a primitive Homo sapiens skull in Morocco dating to 300,000 years ago. Holy paradigm shift!
Petraglia and the team do not dispute that Homo sapiens evolved in Africa sometime in late-middle Pleistocene (the time period that spanned from 2.6 million to 11,700 years ago). The question is when dispersal happened to Eurasia, ultimately reaching northern Europe, Australia and, later, the rest of the continents.
Dispersal certainly began by 120,000 years ago, Petraglia tells Haaretz. Our species made it out of Africa many times in the past.
Where did that 60,000-year paradigm come from, anyway? From genetic analysis – which is controversial even among geneticists, let alone in archaeological circles.
To the archaeologists, the evidence doesnt compute. Fossils of modern-type man found in southern and central China have been dated to between 70,000 and 120,000 years ago.
Israel has Homo sapiens fossils as old as 80,000 to 120,000 years, Petraglia points out: In two caves, Qafzeh (aka Kedumim) and Es Skhul on Mount Carmel, archaeologists found skulls that are among the earliest found outside of Africa.
When those skulls were found in the 1930s, they were classified as Palaeoanthropus palestinensis. The consensus now is that they were human with archaic traits: the brain case size is Homo sapiens, but they possessed beetling brow ridges and a projecting profile like Neanderthals.
Moreover, Petraglia himself has worked in Arabia and Southern Asia, critical zones in terms of out of Africa ideas, and says the Mount Carmel evidence is not isolated.
We find archaeological sites in Saudi Arabia and India that are coincident with that early migration. The sites in Israel were part of much greater dispersal, he postulates.
Some argue that, geographically, Israel is part of Africa and therefore the Mount Carmel people prove little. Be that as it may, according to the old paradigm, there were early dispersals out of Africa, but they were isolated migration events that failed.
Or not. The initial dispersals out of Africa prior to 60,000 years ago were likely by small groups of foragers, and at least some of these early dispersals left low-level genetic traces in modern human populations, Petraglia explains.
Wait, is he saying we all have bits in us from these archaic humans who meandered out of Africa well over 60,000 years ago, in small hunting-gathering groups that roamed over the land? Well, in some of us.
And then there were none?
Petraglia does not dispute there was a huge exodus of Homo sapiens from Africa around 60,000 years ago. His point is that there had been people leaving Africa for twice as long.
There are also signs of early humans in India: Excavation in Jwalapuram, southern India, in 2007 found evidence of people there 78,000 years ago.
I argue that Homo sapiens made it to India before the Mount Toba eruption 74,000 years ago, Petraglia says. (Toba, a volcano in Indonesia, produced a catastrophic eruption back then that spread ash worldwide; Petraglia, however, doesnt fully buy the theory that Toba also produced a global volcanic winter that lasted years and killed off all of Asias humans.) Also, teeth previously found in Sumatra turned out to belong to anatomically modern humans who lived 63,000 to 73,000 years ago.
Then there are the Australian Aborigines, who may have reached the continent as much as 70,000 years ago. Geneticists estimate their arrival at around 60,000 years ago (and would argue that any earlier humans before genetic coalescence in Australia went extinct). But frankly, either puts quite the damper on the Out of Africa 60,000 years ago theory. They werent beamed over by a simian Scotty.
There was no exit event from Africa, there was a constant leak. Dispersal was early onset and, also, multiple, Petraglia sums up.
The latest genetic studies indicate that most of us do arise from that great exit 60,000 years ago. But older humans left genetic traces in certain population groups, notably isolated Papua New Guineans. Some 2 percent of their DNA arises from that earliest movement out of Africa over 100,000 years ago, says Petraglia. Evidently, the later people mated with earlier people who had survived.
To be clear, not even geneticists agree about archaic genes in modern genomes. Theyre still wrangling over the base mutation rate.
But the evidence is leaning toward pre-60,000-year-old waves of human migration out of Africa. Most probably died out, or were simply diluted out by later generations. But first our frisky forefathers had sex with other humans and hominins. At the very least, they bred with Denisovans, Neanderthals and at least one unknown one that left ghost signals in some groups DNA.
When? We dont know, but we do know the other hominin types were living across Eurasia when Homo sapiens got there between 125,000 and 60,000 years ago, Petraglia says. Opportunities for interbreeding were certainly there for people in an early exodus, he adds.
What about Homo floresiensis – the midget human species also known as the hobbit, discovered on the island of Flores? Does it support incredibly early dispersal of humans? The consensus nowadays is that it was an isolated population of Neanderthals that descended from Homo erectus. Or it might have been some Neanderthal hybrid with another hominin species. But modern man it was not, explains Petraglia.
He also points out theres very little human archaeological and genetic work from Asia. There are vast gaps in our knowledge of early human development there.
We think of Homo sapiens as such a successful species, but I think extinction happened to many of these groups, he concludes. We might be able to see early exodus in archaeology and in fossils, but what happened to all these people? In most Eurasians today, geneticists are not finding them.
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