A thorough analysis of the site of Australia鈥檚 oldest human remains may settle the long and acrimonious debate over how long ago humans first colonised the continent.
Experts have been arguing for decades about the age of the skeleton, dubbed Mungo Man. Now its discoverer says he has confirmed that it is 40,000 years old.
That date will reassure many palaeontologists, because if it were 60,000 years as suggested, Mungo Man would have challenged the popular 鈥淥ut of Africa鈥� hypothesis.
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This states that Homo sapiens evolved in the Rift Valley 100,000 years ago and then migrated around the world, displacing its hominid relatives. Many palaeontologists believe early humans could not have moved quickly enough to arrive in Australia before 50,000 years ago.
鈥淎ustralia鈥檚 colonisation is one of the keys to our understanding of how Homo sapiens evolved and spread around the world. It is critical we get the story correct,鈥� says Jim Bowler at the University of Melbourne, who discovered the remains at Lake Mungo in southeastern Australia in 1974.
DNA evidence
In 1976, Bowler and his colleague Alan Thorne estimated the remains to be 30,000 years old. But in 1999, Thorne and his team at Australian National University in Canberra published a sensational new paper claiming Mungo Man was 62,000 years old.
That early date, along with mitochondrial DNA evidence from remains gathered in 2001 by another team led by Thorne, suggested that modern humans had evolved independently in Australia, as well as in Africa. Thorne鈥檚 team estimated Mungo Man鈥檚 age by analysing how much uranium had decayed in a sample from the skeleton. But this is considered to be an unreliable technique, as porous bone can take up uranium-rich minerals at uneven rates.
However, they also confirmed that the sand strata in which the skeleton was buried was of a similar age, using a more dependable technique called thermoluminescence, which measures how long it has been since quartz crystals were exposed to sunlight.
Burial site
Now researchers at four separate laboratories, including Bowler and a member of Thorne鈥檚 original team, claim that the burial of Mungo Man took place 40,000 years ago.
The new dates were derived using optically stimulated luminescence (OSL), similar but more reliable than thermoluminescence. Crucially, the researchers sampled sand from the exact burial sites, whereas it has emerged that Thorne鈥檚 team had sampled sand 400 metres away. They have also dated stone tools 鈥� the earliest evidence of human occupation at the site 鈥� to 50,000 years ago.
The revised dates are consistent with archaeological evidence that humans occupied sites in northern and western Australia around 50,000 years ago, the team says.
鈥淎nd they could have an impact on another contentious area of archaeology 鈥� the disappearance of the Australian megafauna,鈥� says Don Colgan, head of evolutionary biology at the Australian Museum in Sydney.
Evidence that people spread rapidly across Australia around 50,000 years ago would support the 鈥渂litzkrieg鈥� theory of the extinction of the continent鈥檚 exotic megafauna soon after humans arrived. Other researchers have suggested that climate change could be to blame.
Journal reference Nature: (vol 421, p 837)