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Ancient Australia 'deliberately' settled

First Australians Prehistoric Australia was settled by thousands, not just a handful, of humans, suggesting deliberate rather than accidental colonisation of the continent, according to new research.

Archaeologist Alan Williams, of the Fenner School of Environment and Society at the Australian National University, reports his new model of population growth and decline today in the Proceedings of the Royal Society B.

"This paper presents a new reconstruction of prehistoric population of Australia," says Williams, whose publication is part of a PhD he is completing.

He says previous regional models of Australia's prehistoric population have suggested a small founding population of around 50 people.

"Typically, the founding population has always been thought to be quite low -- literally a family group or a small band of people accidentally getting here, for example on a raft," says Williams.

"But what this paper suggests is it probably would have taken 1000 to 3000 people to reach the numbers of Aboriginal people observed at time of [European] contact."

He says the findings suggest Aboriginal colonisation of Australia could have been deliberate rather than accidental.

"A thousand plus [people] is not just a couple of guys falling off a raft -- it's something more than that."

Comprehensive population curve

Williams' new population curve spans around 50,000 years, leading up to the time of European contact.

"I've accumulated radiocarbon data from every archaeological site I can get my hands on in Australia," he says.

"We've got about 5500 dates, which is the most comprehensive data base of that sort in Australia."

The findings support previous suggestions that the Aboriginal population peaked 500 years ago at around 1.2 million. The data also shows the population suffered an 8 per cent decline following contact with Macassans and Europeans after 1700.

Also supported are previous findings that population levels were low during the Pleistocene, but rose substantially in the Holocene.

Importantly, says Williams, his study was able to control for what is known as "taphonomic bias", which is where more recent data is more plentiful because it hasn't had a chance to degrade.

Williams calculated the latest founding population size by extrapolating the new population curve backwards.

"I've used an equation developed in America that converts the radiocarbon data into a percentage growth and decline of population value. I've then applied that data to founding population numbers," he says.

Climate change

Williams says previous research found the rise in population in the Holocene happened in the second half of this epoch, following an intensification of the El Niño-Southern Oscillation pattern.

He says this suggests the trials of climate variability led to innovation and thus population growth.

But the latest research has found the rise in population started earlier in the Holocene -- 11 to 12,000 years ago, which calls for other factors to explain the population rise, says Williams.

The study shows during the glacial maximum 18,000 to 21,000 years ago, the population of around 3500 people fell dramatically.

"Australia was incredibly arid and cool during that period and it would have been an incredibly hard place to live," says Williams. "The data suggests we lost 60 per cent of the population then."

He says it took 9000 years for the population to recover to the same levels.

Biases

Archaeologist Associate Professor Joe Dortch from the University of Western Australia welcomes the research, but says a 2009 study, not cited by Williams, found that in the Pilbara region, the increase in population in the Holocene could be explained by taphonomic bias.

He says radiocarbon dating is also subject to many other biases.

"For example, Williams says, the majority of human activity was on the eastern seaboard of Australia. To me the concentration of dating in the east reflects the concentration of European populations, and hence archaeologists' field projects," says Dortch.

"The distribution of Aboriginal language groups suggests the greatest concentrations of people were in fact in the Top End and the Kimberley. These areas are relatively difficult to access from centres of European-Australian population, and archaeological preservation in the tropics is quite mixed."

Dortch is currently working with geneticists to investigate the prehistoric population of Australia. He hopes that this method will provide more robust answers to questions such as the size of the founding population.