How did humans come to populate the rest of the Earth after supposedly evolving in Africa about 200,000 years ago?

Did ancient humans move out of Africa in a single dispersion, or did the migration come in waves spread out throughout the course of thousands of years?

These questions about human evolution have remained unanswered for decades, but a new study suggests that there may now be an explanation.

A Single Migration

Thanks to a series of genome sequences, three separate groups of scientists conclude that all modern non-Africans trace their ancestry to a single population that emerged from Africa about 50,000 to 80,000 years ago.

Although there were "multiple dispersals" out of Africa, the ancestry can definitely be traced back to a single migration, said Joshua Akey from the University of Washington, who made a commentary on the study.

"I think all three studies are basically saying the same thing," said Akey.

The three reports involved scientists who analyzed the genomes of 787 indigenous people, including African pygmies, Basques, Bedouins, Cree Indians, Sherpas and Mayans.

The genome data were used to tackle different questions such as how populations spread across Africa and how people populated Australia.

African Exodus

One of these three separate studies was conducted in collaboration with elders of various indigenous communities.

In the report, international scientists sequenced the DNA of 83 Aboriginal Australians from the Pama-Nyungan-speaking group, which encompasses more than 90 percent of the continent, as well as the genome of 25 Highland Papuans.

In the end, the research revealed evidence for a single colonization event in Australia and a continuity of occupation from that genome signature for about 40,000 years.

The study suggests that Aboriginal and Papuan ancestors moved out of Africa about 72,000 years ago and were then separated from the main group approximately 58,000 years ago.

These ancestors likely reached the supercontinent of "Sahul," which originally united New Guinea, Tasmania and Australia 50,000 years ago. Along the way, the ancestors likely picked up the DNA of Denisovans, Neanderthals and other extinct ancient humans.

Then, about 37,000 years ago, Aboriginals and Papuans split, long before these continents were separated from each other 8,000 years ago, researchers said.

Michael Westaway of Griffith University, a co-author of the Aboriginal Australian study, said that although New Guinea and Australia were linked until the early Holocene, the Carpentaria basin flooding event and the increasing salinity of the water may have contributed to population isolation.

Details of the Aboriginal Australian study were published [PDF] in the journal Nature.

Watch the video below for more details.

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