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Australian evidence for Out of Africa theory

09 May 2007

Scientists have produced DNA evidence confirming that Australia and New Guinea's earliest settlers came from one small group of people, the same group all modern humans came from.

Genetic data suggest that this group of modern humans, or Homo sapiens , evolved in Africa and migrated out about 50-70,000 years ago. As well as remaining in Africa, they spread throughout the world to become the human race we know today. This is known as the Out of Africa theory , a theory that was originally developed from fossil evidence, but is now supported by both genetic and archaeological data.

Some scientists disagree with this theory and have suggested that modern humans descended from, or interbred with, more ancient human relatives outside of Africa such as Homo erectus (in Asia) and the Neanderthals (in Europe).

Comparing genetic information

Claimed inconsistencies in the fossil and archaeological record of early modern humans in Australia and New Guinea led some people to question the Out of Africa theory.

However, an international team of scientists has compared genetic information from native populations in Australia and New Guinea with those from other modern people. They found no evidence of a genetic inheritance from non-African ancestors, indicating that they share the same African origins as the rest of us.

'For the first time,' says Dr Peter Forster, one of the leaders of the research, 'this evidence gives us a genetic link showing that the Australian Aboriginal and New Guinean populations are descended directly from the same specific group of people who emerged from the African migration.'

Support for Out of Africa

Chris Stringer, human origins expert at the Natural History Museum says, 'This new study clearly supports a strong Out of Africa model i.e. one without archaic hybridisation.'

'It provides the first large and detailed comparison of Australian female-inherited (mitochondrial) and male-inherited (Y chromosome) DNA, and indicates there was apparently one colonisation of Australia and New Guinea about 50,000 years ago by modern humans who had recently dispersed from Africa.'

'The important native population of Tasmania was not included in this work, but it provides an excellent comparative base for such studies in the future.'

Australian inconsistencies

Scientists have debated the origins of native Australians and New Guineans because some believe that there are inconsistencies in the fossil and archaeological records.

Early modern human skeletons dating from about 40,000 years ago have been uncovered showing a slender or gracile form, while some later material shows a much more robust form .

Some scientists suggested that this robusticity could indicate interbreeding with, or descent from, more ancient human relatives like H. erectus .

Tools and dingos

An increase in the abundance and complexity of Australian tools after 10,000 years ago, and the arrival of the first domesticated dogs (dingos), also suggested extensive migrations into the continent at that time.

However, this new research helps to clarify the situation. The populations of Australia and New Guinea diverged quite early, and evolved in relative isolation , and there is scant evidence of gene flow into Australia after the original migration.

Chris adds, 'The results certainly fit with my view of human evolution in Australia. There is considerable variation in size and robusticity in ancient Australian populations, but it looks like this variation developed within the continent between 50,000 and 10,000 years ago, without the influence of interbreeding or descent from archaic populations.'

The study was carried out by an international team of scientists, including the  Cambridge and Anglia Ruskin Universities. The work is reported in the new issue of Proceedings of the National Academy of Sciences .