The physical differences in the appearance of Australia’s Aboriginal people across the continent led many observers to conclude that human settlement came in several waves, separated by long time periods.
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The latest DNA studies released in Nature suggest this view is incorrect, that our Aboriginal peoples came primarily from a group or groups who reached the old continent of Sahul between 47,000 and 55,000 years ago.
The studies reveal genetic diversity across the continent. "The genetic diversity among Aboriginal Australians is amazing,” co-author Dr Anna-Sapfo Malaspinas, from the Universities of Copenhagen and Bern said.
"Because the continent has been populated for such a long time, we find groups from south-western Australia are genetically more different from north-eastern Australia, than, for example, Native Americans are from Siberians."
The study also suggested genetic adaptation to meet local conditions, with Western Desert Aboriginal people developing mutations that would make it easier for them to survive in temperature extremes. These genetic variations are a marker not just of antiquity or of local adaptation, but of the impact of climate variation.
The Pleistocene was the age of the glaciers, of recurrent ice ages during which the sea level fell and the climate became cooler and drier. That first, probably small, group of Aboriginal ancestors arrived on Sahul during a benign period that allowed them to spread quickly across the continent.
From around 25,000 years ago, the climate began to deteriorate. The climate became very dry, marked by intense conditions. Sea levels fell to around 130 metres below current levels.
On Sahul, there was an almost constant 9000-year dust storm. Rivers and waterholes dried up. The deserts spread, with sand dunes occupying a large part of the content.
The effects on the Aboriginal populations must have been devastating. It was during this long period that genetic variation emerged.
Accepting problems with the dating, I don’t think that it’s a coincidence that we have a burst of Aboriginal occupation dates from the Hunter and Liverpool Plains during the first part of this period, for these are relatively well-watered areas.
In northern NSW, the continental shelf is narrow. The fall in sea levels probably destroyed previous riverine and estuary environments. Inland, the Tablelands and slopes were cold and windy. People were forced to retreat. Yet, despite the problems, the Aboriginal people had survived and would now re-occupy the continent.
Jim Belshaw’s email is ndarala@optusnet.com.au. He blogs at newenglandaustralia.blogspot.com.au and newenglandhistory.blogspot.com.au
