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."
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. . . .
7 comments:
If sea levels are relevant to this migration story Jim then http://onlinelibrary.wiley.com/enhanced/figures/doi/10.1002/2015RG000482#figure-viewer-rog20091-fig-0002
would be a useful dating reference. Whatever the sea level some form of raft/boat technology was essential and sufficient to transport more than the odd individual as whole families would have been involved. There is a history of adoption into hunter gatherer groups evident into the 19thC in Australia, there is no reason to suppose that such behaviour is recent. If present that early it may part explain the incorporation of differing DNA for our science to find.
I found the Wiley material difficult to interpret, John, not helped because it didn't load properly onto my old box.
You are right on the sea technology, I think. The adoption one is interesting. It comes back to timing question.
Just to record a conversation elsewhere for later discussion.
On my my public Facebook page, Winton Bates asked: "So the First People might have been second." I responded:
One: I think the evidence so far supports the first peoples argument. Recognising my own lack of expertise in DNA, the Aborigines and Papuans come from common stock. At this point, both seem (I think) to have common proportions of Denosovan DNA. The DNA suggests that Papuans and Aborigines diverged a considerable time ago. I can't remember the suggested date range, So their common ancestor met and matched with the Denosovans. millenia before the split between Aborigines and Papuans. Hitting enter.
Two: We don't know the early migration patterns onto Sahul. If there was one Aboriginal group that arrived on the continent and then moved north and south as common ancestor for both the modern Aborigines and Papuans, then it would be possible that they met and mated with Denisovans already here to give a common trace. although there may be time issues. If as I think quite likely, there was several migration paths, then that pushes the Denisovan contact point back into South East Asia. Hitting enter
Three: It all gets quite complicated! I think the one thing that is becoming increasingly clear is that the old linear model of human evolution is getting increasingly suspect.
Winton replied: Ok! However, I hope there is someone looking for Denisovan bones in Tasmanian caves in the hope of putting a cat among the pigeons.
I responded: Yes. However, we really need more skeletal discoveries more broadly. Tasmania was linked to the mainland until the the sea level rises at the end of the Late Glacial Maximum. That's quite recent. I think final separation of the two occurred about 6-7,000 years ago. It's highly unlikely that the Tasmanian Aborigines were in any way remnant populations.
Quote ' if, as I think quite likely, there was several migration paths, then that pushes the Denisovan contact point back into South East Asia."
I think you have hit a nail on its head there Jim. We need to remember that the numbers involved are small by today's standards and for hunter gatherers the range would be large per extended family group. Meeting 'others' would be the exception, not the rule. What social rituals would be involved when such meetings occurred Ethnographers have yet to give us guidance. Entering and moving through South East Asia could only have increased the Probability of social intercourse between 'others'. Whilst the Denisovan DNA quotient is a current focus it only amounts to ~6% of the Aboriginal genome, what other information lies within it that might give insight. My own DNA tells of a journey from East to West across Northern Europe to the British Isels, my wife's of a journey North from Iberia along the Atlantic Conveyor. Much more recent journeys but now identifiable.
One of the difficulties, John, is that we don't actually know the numbers involved. If you think of the leading edge, the people entering new territory, then they would likely be small in numbers. But why did they move in the first place? People like staying in their places, in the familiar. That suggests to me that in the absence of some form of shock, movement was incremental. But with multiple migrations, the question of what happens when you meet someone else who is either resident already or in movement at the same time is an interesting one. What, as you imply, do you do?
Based on what we know, the Aborigines must at some point have entered territory already occupied by the Denisovans. We don't know what happened then. There may have been conflict or coexistence or some combination of the two. Denisovan women may have been acquired. The small Denisovan proportion in the DNA suggests limited interbreeding.
DNA may help us as in the example you give at the end
The younger sons may have been the driver Jim or disaster striking a home range sufficiently hard to force a move. We must also remember that constant movement was the norm, something we can easily forget with our settled existence. Movement is especially the norm across Savannah environments. I do recall reading recently that there is some evidence that the Denisovan DNA was principally a male contribution, if so that gives further pause for thought and a look towards our Ethnographer friends. We find ourselves at times constrained in our thinking by our own cultural norms.
I totally agree with your last point, John: "We find ourselves at times constrained in our thinking by our own cultural norms." It's a constant problem! It's also an issue in interpreting ethnographic evidence. This is always at a point in time. What does it actually tell us about interpreting the past?
I need to think more about your comment before responding!
Following up on this one now, John. I think that we need to distinguish between movement within a range as compared to movement out of a range. My view on the early pattern of Aboriginal settlement was that movement occurred into related areas beyond the range as a consequence of population increase - your younger son point.
Out of curiosity, I looked at the Wikipedia entry on Hunter-Gatherers. https://en.wikipedia.org/wiki/Hunter-gatherer. I think that people may underestimate the capacities of early societies, especially when long time horizons are involved with plenty of time to learn adaptation skills. If the Madjedbebe date is correct, there appears to be quite a sophisticated life style c65,000 years ago. More DNA stuff that you may not have seen yet - http://www.cell.com/cell/pdf/S0092-8674(17)31008-5.pdf https://www.nytimes.com/2017/09/21/science/africa-dna-migration.html?smid=tw-nytimesscience&smtyp=cur
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