DNA study sheds light on aboriginal Australians' heritage
Researchers turn up evidence of interbreeding between native Australians and people who came from India.January 14, 2013
By Rosie Mestel, Los Angeles Times
When modern humans left Africa as far back as 70,000 years ago, they dispersed across the world, reaching Australia 50,000 to 40,000 years ago. From then until the 18th-century arrival of European colonists, aboriginal Australians did not mix their DNA with anyone else in the world —
or so many scientists believed.
Now a study has turned up evidence of much more recent interbreeding between native Australians and people who came from India. The findings, based on a detailed examination of the DNA of aboriginal Australians and hundreds of people of other pedigrees, found that mixing occurred as recently as 4,200 years ago.
.....They found, for example, that aboriginal Australians, Papua New Guinea highlanders and the Mamanwa people from the Philippines were genetically closest to each other and diverged about 36,000 years ago. This fit well with earlier genetic studies.
But the team was surprised to find — using four separate statistical methods — that a much more recent genetic mixing with people from India had occurred. They estimated that about 11% of the DNA of aboriginal Australians is derived from this event.
.....Using the size and number of DNA stretches in people alive today, the team ran computer simulations to calculate that 141 generations have passed since the initial interbreeding. With each generation assumed to be 30 years, that adds up to 4,230 years.
It isn't clear how the mixing took place.
Though it might make sense that the gene flow occurred in Indonesia, no traces of Indian DNA could be found among the Indonesians in the sample and no Indonesian DNA could be found in the Australians, the authors said — perhaps suggesting the migrants came directly to Australia by water. Still, a more detailed analysis of Indonesian genomes would be needed to rule out that connection, Stoneking said.