Discussions on the history and historiography of Australia's New England

Sunday, February 03, 2019

New evidence on the Neanderthal/Denisovan overlap

Summary timeline for the archaeology, hominin fossils and hominin DNA retrieved from the sediments at Denisova Cave. All age ranges are shown at the 95.4% confidence interval. Bert Roberts,
Interesting paper by Zenobia Jacobs, Bo Li, Kieran O'Gorman and Richard Roberts all from the University of Wollongong in The Conversation:  Fresh clues to the life and times of the Denisovans, a little-known ancient group of humans (31 January 2018) .

The Denisova site is interesting because it is the only known site so far for the Denisovan species of hominin, the only site where Denisovans and Neanderthals overlapped. The latest dating results are summarised this way.
 The new studies show that hominins have occupied the site almost continuously through relatively warm and cold periods over the past 300,000 years, leaving behind stone tools and other artefacts in the cave deposits. 
Fossils and DNA traces of Denisovans are found from at least 200,000 to 50,000 years ago, and those of Neanderthals from between 200,000 and 100,000 years ago. The girl with mixed ancestry reveals that the two groups of hominins met and interbred around 100,000 years ago.
Both the Aborigines and Papuans have significant traces of Denisovan DNA suggesting that their ancestors met and mixed with the Denisovans on their journey to Sahul. An alternative but still less likely explanation is that the Denisovans had already reached Sahul at least in small numbers and the admixture occurred here.

I say this only because there is now an apparent tension that I do not understand between the archaeological dates and those generated by DNA analysis. The first presently suggests earliest occupation of perhaps 62,000 years ago based on archaeological dating, while the second suggests an out of Africa date for the Aborigines and Papuans of perhaps 51-72,000 years based on DNA modelling. There is still an overlap, but it has become too small for my comfort. .

I think that what is clear is that the new evidence is progressively changing our understanding of the human pattern of settlement in Eurasia and that this will necessarily change our understanding of Sahul's history.


Johnb said...

I believe that there is considerable archeological effort being undertaken in China as well as East of the Urals Jim of which the Denisovan Cave excavations are but a part. We are also confident that Homo erectus was the first modern hominid to leave Africa successfully and eventually colonise the entire Eurasian landmass, they even successfully crossed the Wallace line in Indonesia as we have the evidence found in Flores dated to some 840,000 years ago. No evidence has yet been found for them continuing their journey into Sahel but that could well be a case of living long enough. H.denisova , H. Neanderthal and H. Floriensis have no evidence that they evolved in Africa. My own conclusion is that they evolved independently outside Africa from H erectus populations in classic Darwinian fashion. H.erectus was around out of Africa for 1.5 million years before extinction, that is plenty of time for evolution to take place. I can well imagine that evidence for other hominid populations will be found over time via hybridisation between hominid populations with H.erectus as the base archaic population. Most classifications focus on the skull and brain capacity, I think there is a case to put a deal more focus on the birth canal and the evolving placenta as evolution can’t change skull size and brain capacity without adaption for birthing the new. The particular H.sapiens journey through the birth canal is quite complex relative to earlier hominid spp. and also brought social change with it as a degree of cooperation is required, midwifery is a very old profession with profound consequences for our social development.

Jim Belshaw said...

Interesting comments John that I lack the expertise to critique. Your analysis strikes me as plausible in the absence of evidence to the contrary.

Johnb said...

Just come across a more populist report of the findings in the NYT Jim.


I tend to hold ideas as personal hypotheses to test against new knowledge as it is found and validated Jim, at times I get it right, other times not so but mostly nearly so. As Poirot would say it keeps the little grey cells active.

Johnb said...

Ha e just read the following Jim and whilst it might be about penguins, evolution works just the same for Hominids in isolated breeding populations.


Jim Belshaw said...

That was interesting, John. It's what you would expect, I think, and it does suggest that there would be more differentiation in the hominid population if only we had the evidence

Johnb said...

To my mind the virtually unsurmountable difficulty we have in reference to hominid differentiation is the historical legacy associated with it.
Colonialism, eugenics, the rascism of difference, how is that conversation to be conducted. My Haplogroup Ydna tells me it originated on the steppes of Central Asia before moving West into Central Europe and ultimately the UK. My Haplogroup mtdna had a different journey from North Africa via the Atlantic conveyor into UK. I share those Haplogroups with a large population and Within historical times this backbone dna has been added to by a Scandinavian and Irish contribution. My wife has a much greater Scandinavian contribution. That genetic inheritance is expressed in my physical form.