May 8, 2007
Aboriginal Australians are descended from the same modern human ancestors who left Africa to populate other parts of the world, says a new genetic study.
The study supports the Out of Africa theory about the dispersal of modern humans, but scientists disagree over how many entry points people used to reach Australia.
Georgi Hudjashov, of Tartu University (http://www.ut.ee/index.aw/set_lang_id=2) in Estonia, and colleagues report their study online today in the Proceedings of the National Academy of Sciences (http://www.pnas.org).
The team analysed samples of Y chromosome and mitochondrial DNA, previously collected from Aboriginal Australian and Melanesian people.
"All these lineages trace back to the same Out of Africa migration," says co-author Dr Toomas Kivisild, an evolutionary geneticist at the UK's University of Cambridge (http://www.cam.ac.uk/).
The researchers say modern humans dispersed from Africa somewhere between 50,000 and 70,000 years ago, travelled along the coast of India and down through Southeast Asia before splitting off into Papua New Guinea and Australia.
"Australia would have been settled by only one migration," says Kivisild. "This is the hypothesis that we see is most consistent with the data."
The study provides further support for the Out of Africa model, in which a single wave of modern humans fanned out from Africa, replacing early humans as they went.
And 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.
One entry point?
Dr Sheila van Holst Pellekaan, an Australian molecular anthropologist from the University of New South Wales (http://www.unsw.edu.au/), 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 she disagrees with the conclusion that modern humans only entered Australia at one point.
"They've been a bit selective in their conclusion," says van Holst Pellekaan. "Their data does not exclude the possibility of people having come down from a more northern route and across different island crossings."
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 says.
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," says van Holst Pellekaan.