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Lock of hair pins down early migration of Aborigines

From: http://www.bbc.co.uk/news/science-environment-15020799

Sep 23, 2011

A lock of hair has helped scientists to piece together the genome of Australian Aborigines and rewrite the history of human dispersal around the world.

DNA from the hair demonstrates that indigenous Aboriginal Australians were the first to separate from other modern humans, around 70,000 years ago.

This challenges current theories of a single phase of dispersal from Africa.

An international team of researchers published their findings in the journal Science.

While the Aboriginal populations were trailblazing across Asia and into Australia, the remaining humans stayed around North Africa and the Middle East until 24,000 years ago.

Only then did they spread out and colonise Europe and Asia, but the indigenous Aborigines had been established in Australia for 25,000 years.

Australian Aborigines therefore have a longer claim to the land in which they now live than any other population known.

The research also highlights the exciting future possibilities of comparing the genomes of multiple individuals to track migration of small indigenous groups.

Archaeological remains are known from Australia from around 50,000 years ago, putting a maximum age of the Aborigines' settlement there.

But the history of their journey and their relationship with the indigenous people of Asia and Europe had not been solved.

It was previously thought that modern humans dispersed in one pulse out of Africa and the Middle East, and because of the distances involved, the modern Europeans would have separated from the Asians and Australians first.

Genetic information from a lock of Aboriginal hair has been used to show that the Australians set off a lot earlier.

By looking at the tiny (fraction of one percent) differences between the DNA of Aborigines and other ancient humans, the scientists show that the indigenous Australians were first isolated 70,000 years ago.

Dr Francois Balloux, of Imperial College London described how a "population expanded along the coastline because of the rich resources available there. They could walk almost the entire way because the sea level was much lower". Just one small sea crossing would be required to reach Australia.

Any potential archaeological remains of this journey, which lasted 25,000 years, would be lost to the deep sea under rising sea levels.

The remaining populations in the Middle East moved out to colonise Europe and Asia 24,000 years ago, and the aboriginal genome records some interbreeding between Asian populations and aboriginal ancestors at this time.

Discovering the history of human migration with DNA has been made possible by improvements in the techniques used to study the genome.

Traditionally, genetic divergence dates were arrived at by combining the number of unique mutations in the DNA with an assumed rate of acquiring those mutations.

Now, computationally powerful models can simulate lots of different scenarios for migration timings and directions, and researchers can compare and choose the situation that most closely matches what is seen in the genome.

By comparing the Aboriginal genome with the DNA of African, European and Han Chinese individuals it was possible to highlight the later interbreeding after initial colonisation.