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Humans turned south out of Africa

Which way now?

New research says humans left Africa and turned south, not north, as they populated the world. This may explain why Australia was settled thousands of years before Europe (Image: iStockphoto)

Aboriginal Australians are the descendants of a single, southern migration out of Africa and into Eurasia, according to the latest research on how modern humans colonised the world.

Two studies published in today's issue of the journal Science back the view that humans turned south as they left Africa by travelling across the Red Sea then down along the coast of the Indian Ocean.

Most scientists say that modern humans spread around the world from Africa, the so-called Out of Africa hypothesis.

But exactly what happened next is the subject of controversy, as is the question of whether there was one dispersal or a series.

One debate surrounds whether the dispersal took a northern route up along the Nile and across Egypt's Sinai Peninsula, or a southern route.

So the two sets of international researchers analysed mitochondrial DNA (mtDNA) to reconstruct the possible road that modern humans took.

Mitochondrial DNA does not alter much from generation to generation and scientists can measure the rate of mutations.

This makes it a powerful tool to determine when populations split and allows researchers to track back ancestral lineage over thousands of generations.

The researchers looked at the mtDNA of what they call "relic populations" in the Andaman and Nicobar Islands, in the Bay of Bengal, and the Malaysian Peninsula.

Analysis of these dwindling indigenous populations, including Malaysia's native tribal people the Orang Asli ("original people"), links them back to the first Eurasians, who appear to have reached the coast of the Indian Ocean not long after leaving Africa.

An early southern dispersal

One team, including Dr David Bulbeck of the school of archaeology and anthropology at the Australian National University (ANU) and researchers from Malaysia and Europe, sampled DNA from 260 maternally related Orang Asli.

The researchers concluded that the main dispersal from Africa to Asia and Australasia occurred via a southern route through India about 65,000 years ago, a journey that probably only took a few thousand years.

They say the migration from Africa to Eurasia probably occurred at a rate of 0.7 to 4 kilometres a years.

The team also estimates the number of women who emigrated out of Africa, saying only around 600 of them took the trip.

The researchers say the suggestion of a southern dispersal has recently gained ground.

"Part of its rationale has been the presence of a number of relic populations in southern India and Southeast Asia," the researchers write.

"It has been suggested that these populations might be the descendants of such an earlier dispersal, along with Papuans and Aboriginal Australians."

This southern migration would be several thousands of years earlier than the traditional Out of Africa model suggests, the researchers write.

The other team, which includes researchers from India and Estonia, concentrated on the mtDNA of people from the Andaman and Nicobar Islands.

The researchers found that ancient mtDNA lineages appear to have been isolated since modern humans first penetrated the northern coastal areas of the Indian Ocean 50,000 to 70,000 years ago.

Basically, humans arrived on the island and stayed there.

One cololonisation

Colin Groves, professor of biological anthropology at the ANU, says the two studies argue for essentially one colonisation event.

"Everybody outside Africa is descended from a single stream of people ... and the later events [including European and American colonisation] were just a subset of that," he says.

The studies also show that Aboriginal people are the original immigrants into Australia, he says, and suggest they are originally related to Papuan highlanders, southeast Asians and ultimately Malaysia's Orang Asli.

Groves also backs a commentary published alongside the two papers in Science, which suggests a southern migration, rather than a northern one, could answer why Europe was settled thousands of years after Australia.

But why did modern humans turn south, not north?

Groves says the northern route may have been occupied by Neanderthals.

Tags: indigenous-aboriginal-and-torres-strait-islander, cloning-and-dna, palaeontology