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We are all out of Africa – new genetic research finds

14 October 20160 comments

One single migration out of Africa 60,000 years ago produced nearly all the modern Eurasian populations, new research has found.

Some researchers had theorised that the ancestors of Australia’s Aborigines were the first modern humans to surge out of Africa, spreading swiftly eastward along the coasts of southern Asia thousands of years before a second wave of migrants populated Eurasia.

Australian Aborigines have long been thought of as a people apart with unique languages and cultural adaptations.

But a raft of new genomic studies, the first to analyse many full genomes from Australia and New Guinea, have found that like most other living Eurasians, Aborigines descend from a single group of modern humans who swept out of Africa 50,000 to 60,000 years ago.

The group then spread in different directions meaning that most people outside of Africa today trace their ancestry back to a single great expansion.

The study also reaffirms Aborigines’ deep roots and long isolation in Australia, underpinning Aboriginal myths and legends of their prehistory.

The three human genome studies published in the journal Nature provided the first new clues as to when Homo sapiens, our earliest anatomically modern human ancestors, first left Africa.

After analysing the DNA of 800 people from more than 270 populations, including a large number of aboriginal people in Australia and Papua New Guinea, the researchers found genetic evidence for a migration of humans out of Africa about 100,000 years ago – long before the migration that most modern Europeans, Asians, and Australians are descended from, which came about 60,000 years ago.

But that earlier migration largely failed. The populations died out within a few generations, ultimately contributing no more than a few per cent of the genome to anyone alive today, the researchers say.

The studies all found that in Eurasians and also Papua New Guineans, the majority of their genomes come from the same major migration.

University of Cambridge biologist and author of one of the studies Dr Luca Pagani said that by testing hundreds of samples of DNA from various populations, researchers in each study traced genetic markers across the globe to gain insight into the flow of early humans.

“All the other Eurasians we had were very homogenous in their split times from Africans,” Dr Pagani said.

“This suggests most Eurasians diverged from Africans in a single event … about 75,000 years ago, while the Papua New Guinea split was more ancient – about 90,000 years ago. So we thought there must be something going on,” he said.

Another of the study said that after leaving Africa in a mass migration, anatomically modern humans reproduced with Neanderthals already living in Europe and Asia until 58,000 years ago, when ancestors of the aboriginal group made their way to Australia via a land bridge that then connected the Papua New Guinea with Australia.

The third study, by the Department of Genetics at Harvard Medical School, also found evidence for a significant mass migration by 100,000 years ago, but said that those early humans were not the ancestors of any particular modern group.

“Indigenous Australians, New Guineans, and Andamanese do not derive substantial ancestry from an early dispersal of modern humans; instead, their modern human ancestry is consistent with coming from the same source as that of other non-Africans,” the Harvard researchers said.

Teeth from Homo sapiens found in China last year were dated to 80,000 and 120,000 years ago, placing humans in Asia tens of thousands of years earlier than previously thought – further complicating the story of early human movement across the globe.

Laurie Nowell
AMES Australia Senior Journalist