The results were quite striking, so striking that they attracted global media attention. “Indigenous Australians most ancient civilisation on Earth, extensive DNA study confirms” read one UK headline.
Some care must in fact be exercised in interpreting the results, for the statistical techniques used give you date ranges, a central date and then a confidence interval, a range within which the actual date might fall. These can be large, 20,000+ years, something that can be quite frustrating when you are trying to match dates to understand a pattern. That said, the results were remarkable.
They suggest that Aboriginal Australians and Papuans are more closely related to each other than to anyone else on earth. They also suggest that the Aboriginal-Papuan population diverged from Eurasians following a single out-of-Africa migration 51,000 to 72,000 years ago. See what I mean about date ranges.
In their long travels, that small band or bands of Australo-Papuans appear to have mixed with two related archaic human species. The first were the Neanderthal, something shared with Eurasians. Between one and six per cent of modern Eurasian’s genes derive from the Neanderthal, a percentage higher in some individuals depending on their exact family lineage.
Much later, the travelers mixed with the Denisovans, with about four per cent of the Aboriginal genome traceable to that admixture. We did not discover the existence of the Denisovans, a group named after Denisova Cave in the Altai Mountains in Siberia, until excavations that began in 2008. Subsequent work suggests that the cave had also been inhabited by Neanderthals and modern humans over 125,000 years of intermittent occupation.
Speaking of the meeting with the Denisovans, study leader Professor Eske Willerslev is reported as saying: "We don't know who these people were, but they were a distant relative of Denisovans, and the Papuan/Australian ancestors probably encountered them close to Sahul."
Extinct Denisovans from Siberia made stunning jewellery - but did they also discover Australia?, 14 September 2017). The UK Daily Mail carried a rather more sensationalised verson.(Will Stewart and Tim Collins, Were ancient Denisovans the first to discover Australia? Scientist believes traces of their DNA found in Aboriginal people suggest they beat homo-sapiens to the continent, 15 September 2017). Hat tip to regular commenter JohnB for pointing me to the Siberia Times story.
While the stories have a beat-up tone, the recent discoveries do raise the question of just when and where the ancestors of the modern Australians did meet the Denosovans. If, as the present consensus seems to suggest, they met them near Sahul, the extended continent that became Australia as the sea levels fell, the Denosovans must have been wide spread.
In an earlier 2013 paper in Science, Alan Cooper and Chris Stringer posed the question Did the Denisovans Cross Wallace's Line?. The summary of the paper reads:
The recent discovery of Denisovans (1, 2) and genetic evidence of their hybridization with modern human populations now found in Island Southeast Asia, Australia, and the Pacific (3) are intriguing and unexpected. The reference specimen for the Denisovan genome (4), a distal phalanx from a young girl, was recovered from the geographically distant Denisova Cave in the Russian Altai mountains. Three Denisovan mitochondrial genomes have been generated from material in the cave, dated by poorly associated fauna (5) at more than 50,000 years old. The diversity of these genomes indicates that the Denisovan population had a larger long-term average size than that of the Neandertals (6, 7), suggesting that the Denisovans were formerly widespread across mainland East Asia. However, interbreeding with modern humans only appears to have occurred in remote Island Southeast Asia, requiring marine crossings and raising questions about the distribution and fossil record of Denisovans in Island Southeast Asia.So far we still have only one known Denisovan site, the original at one at Altai. Based on the material remains there, they have appear to have been an advanced hunter-gatherer group. It seems unlikely that the Altai Denisovans "discovered" Australia. It is more likely that there were a number of Denisovan migration paths with possible northern and southern migration routes. But we just don't know. As Professor Richard 'Bert' Roberts, Director of the Centre for Archaeological Science at the University of Wollongong suggested in the Siberia Times piece, We need deep study of ancient migration routes to understand how the Denisovan DNA exists to this day in the native people of Australia. More broadly, we just need more information about them!
We also need, I think, to consider the latest results from the Madjedbebe rockshelter in the Northern Territory, something I wrote about in The lessons and questions from Madjedbebe, which showed occupancy as well as a sophisticated tool kit from around 65,000 years ago. Recognising my own lack of professional expertise, there is an apparent tension now between some of the date ranges generated by genomic analysis and archaeological analysis.
I have no idea how these conundrums will be resolved, nor what picture we will find at the end of the process. I suspect that it will be as different from current knowledge as current knowledge is from the world view holding even thirty years ago. . . .