Africa and Aboriginal Tuesdays: Aborigines Descended from Africa, Study Says

A new genetic study says Aboriginal Australians are descended from the same modern human ancestors who left Africa to populate other parts of the world.

The study supports the Out of Africa theory about the origins of modern humans, but scientists disagree over how many entry points people used to reach Australia.

University of Cambridge evolutionary geneticist Dr Toomas Kivisild and colleagues have reported their study online today in the Proceedings of the National Academy of Sciences.

Dr Kivisild says the team analysed samples of Y chromosomes and mitochondrial DNA previously collected from Aboriginal Australian and Melanesian people.

"All these lineages trace back to the same Out of Africa migration," he said.

The researchers say modern humans left Africa somewhere between 50,000 and 70,000 years ago, travelled along the coast of India and down through south-east Asia, before splitting off into Papua New Guinea and Australia.

"Australia would have been settled by only one migration," Dr Kivisild said.

"This is the hypothesis that we see is most consistent with the data."

The Out of Africa model posits that a single wave of modern humans fanned out from Africa, replacing early humans as they went.

It counters the alternative "regional continuity" model that suggests there was more complex interbreeding among humans who had evolved in different parts of the world.

According to this model, there were multiple waves of migration to Australia, which helps explain the diversity in appearance of Aboriginal communities today.

'Selective'

Dr Sheila van Holst Pellekaan, an Australian molecular anthropologist from the University of New South Wales, agrees that genetic evidence supports the Out of Africa theory for modern humans.

Samples of her collection of human DNA were used in the analysis.

But Dr van Holst Pellekaan disagrees with the conclusion that modern humans only entered Australia at one point.

"They've been a bit selective in their conclusion," she said.

"Their data does not exclude the possibility of people having come down from a more northern route and across different island crossings."

Dr Kivisild says there are not enough samples from Australia, New Guinea and Indonesia to be able to identify more than one entry point.

"Given the data that is available now, it seems there was one major migration," he said.

Debate continues on the merits of the regional continuity model, even among geneticists.

"Unless DNA signatures from early humans are discovered in modern humans, this debate is likely to continue," Dr van Holst Pellekaan said.


Note: This article was first published at ABC Online

Tuesday, May 8, 2007

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