Saturday, September 24, 2011

Lots of interesting new prehistoric DNA data points

It is becoming more and more clear that there are been multiple episodes of profound population genetic shifts driven by migration in human prehistory. Ancient DNA analysis and more sophisticated techniques for analyzing the entire genomes of large populations have made it possible to get some sense of the broad outline of these migrations, although the data is fragmentary, so it is a big, incomplete puzzle to fit together in time and space, according to rules that we are only beginning to grasp.

* A comparison of the Denisovian ancient genome from Siberia to various world populations confirms the hypothesis that Papuans have the highest proportion of Denisovian ancestry (probably about 7% before admixture with outsiders), that Australian aboriginal populations have the same amount of Denisovian ancestry as Papuans, and that the proportion of Denisovian admixture in other populations is quite tightly aligned with their proportion of Papuan and Australian admixture.

Some Philippine Negrito populations also have elevated proportions of Denisovian admixture (60% of that found in Papuans) relative to their proportion of Papuan and Australian admixture, and some other Philippinos show elevated Denisovian admixture probably attributable to admixture with those Philippine Negrito populations.

Other Asian Negrito, Asian Aboriginal and Indonesian populations have slightly elevated levels of Denisovian admixture, but in these populations the proportion of Denisovian admixture doesn't exceed 0.8% and averages something on the order of half of that percentage of less.

There is little or no Denisovian admixture in other Asian populations, which suggests that there was a wave of modern humans in or around Southeast Asia ththat acquired Denisovian admixture, and then a much larger and later population wave that did not from which most modern mainland Asian populations overwhelmingly descend.

* An Australian aboriginal whole genome has been published. "We show that Aboriginal Australians are descendants of an early human dispersal into eastern Asia, possibly 62,000 to 75,000 years ago. This dispersal is separate from the one that gave rise to modern Asians 25,000 to 38,000 years ago. We also find evidence of gene flow between populations of the two dispersal waves prior to the divergence of Native Americans from modern Asian ancestors. Our findings support the hypothesis that present-day Aboriginal Australians descend from the earliest humans to occupy Australia, likely representing one of the oldest continuous populations outside Africa."

The age estimates are a tad old compared to estimates from non-genetic means, who put the first modern humans in Australia and Papua New Guinea ca. 45,000-50,000 years ago, making a 62,000-75,000 years ago wave, if there is one, based on an assumption that it traces back to a predecessor population in South Asia where one sees modern human traces that old. I'm not convinced that there wasn't a thin wave of modern humans into Asia prior to the Australian/Papuan one, although I'm not conviced that there was a prior wave either.

* Ancient DNA from "the Lower Xiajiadian culture (LXC) population, a main bronze culture branch in northern China dated 4500–3500 years ago, . . . from northern Asia who had lived in this region since the Neolithic period, as well as genetic evidence of immigration from the Central Plain.

Later in the Bronze Age, part of the population migrated to the south away from a cooler climate, which ultimately influenced the gene pool in the Central Plain. Thus, climate change is an important factor, which drove the population migration during the Bronze Age in northern China. Based on these results, the local genetic continuity did not seem to be affected by outward migration[.]"

Query if this population is better described as "proto-Altaic" than it is as "proto-Chinese." There is circumstancial evience that a lot of Bronze Age technology was added to the indigeneous Northeast Asian Neolithic technological mix via the Silk Road from Indo-Europeans who were basically European genetically. But, this evidence suggests that the technology transfer was largely cultural rather than demic (i.e. technology transfer was not due to population replacement or conquest by an elite minority population).

* Ancient DNA from Neolithic Hungary (i.e. pre-Bronze Age, post-farming and herding), shows a surprising large East Asian influence and surprisingly little continuity with modern Hungary population genetics. As Dienkes comments:

We have genetic discontinuity between Paleolithic and Neolithic, and between Neolithic and present, and, apparently, discontinuity between Neolithic cultures themselves, and wholly unexpected links to East Asia all the way to Central Europe.

When faced with data such as this, one can only say: what the hell happened during European prehistory?

Surprising East Asian genetic links are also found in the Ukraine that Dienekes discussed in a post on Neolithic and Bronze Age Ukraine.

In truth, the Paleolithic/Neolithic genetic discontinuity in much of Europe (although there is great regional variation within Europe on the extent of this discontinuity) has been apparent for some time from early ancient DNA results. But, evidence of major population shift between the Neolithic and the present, and of East Asian genetic influences in the Neolithic as far as Hungary are surprising. The East Asian genetic influence in Europe corroborate physical anthropology of the late Paleolithic and early Neolithic in the area where in the "northwest of Eastern Europe Mongoloid component is detected 10000–8000 years ago; in Dnepr–Donetsk tribes, 7000–6000 years ago, and on the territory of Ivanovo oblast (Sakhtysh), 6000–5000 years ago."

Some Analysis

In my view, the post-Neolithic discontinuity and East Asian influences are both signs of an Indo-European expansion that pushed East Asian influence from Hungary all the way back to the Altai and Mongolia and greatly reshaped the genetic makeup of much of what is now Indo-European Europe, probably mostly in the Bronze Age (perhaps as far back as the Copper Age in core proto-Indo-European areas) and Iron Age, and the discontinuities we see in Europe between different areas reflect Bronze Age communities that had not yet succumbed to this wave of expansion that was beginning around that point in time.

East Asian components to modern European populations are pretty much limited to Uralic language populations in what look like traces of circumpolar population interactions - and all put a very small number of those components are almost entirely absent from European populations. But, this new genetic evidence adds a new twist to the already confusing history of Hungary, which is widely thought to have adopted the Uralic Hungarian language in the Middle Ages as a result of conquering invaders from the East of Hungary (fleeing forces pushing them out of their homes there) whose ancient DNA has little or no surviving remanants in Hungary today.

Siberia, Eastern Europe and Central Europe seem to be a region particularly impacted by the East to West seesaw. In the Upper Paleolithic, one sees European influences to the West and also Paleo-Siberian populations ancestral to Native Americans with stronger East Asian affinities that have left just the slightest Yenesian traces that are probably mostly replaced after the Last Glacial Maximum from both West and East in largely non-overlapping areas. Just before and after the Neolithic revolution arrives in this region, there is a substantial East Asian component in ancient DNA that must have resulted from a population expansion at least 10,000 years ago. The Indo-Europeans seem to push back from the West starting perhaps 6,000 years ago, the Turks push back in the first millenium of the current era, there is a little European pushback with the Slavic expansion, only to be overwhelmed (or at least halted) by the expanding Mongol Empire, and after the Mongol empire collapsed, the Russians expand from West to East again - while the Chinese eventually strengthen their grip over their interior territory, leaving us with the current status quo.

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