Assyrians and Finns in a Worldwide Genetic Context

8/23/2013 11:57:14 PM
Assyrians and Finns Admixture

Dienekes is now allowing people to “out” themselves in terms of their ancestry on a comment thread over at the Dodecad Ancestry Project. One of the major purposes of the project has been to survey variation in under-sampled groups which could give us insights into human genetic history. Yesterday I pointed to an analysis of Europeans from the British Isles to Russia. Basically Northern Europeans. There wasn’t anything too revolutionary about the nature of the results; rather, it confirmed some patterns we’d seen. Additionally it obviously didn’t resolve issues of timing, though it clarified hypotheses on the margin.

The main benefit of the ADMIXTURE bar plots is that it gives you a gestaltsense of relationships in a quantitative fashion. This is especially important for groups in the Eurasian Heartland, who are in some ways at the center of both genetic and cultural exchange. In the comments above some information was divulged as the provenance of two clusters of samples, Finns and Assyrians. The Assyrians here presumably represents the remnants of Mesopotamia’s Christian majority at the time of the Arab conquests in the 7th century. Prior to the Arab conquests Mesopotamia had been under the rule of the Sassanid Persian dynasty for nearly four centuries, but by early 7th century the Syriac speaking majority by and large adhered to a range of Christian sects (the balance seem to have been heterodox non-Christian Gnostics and Jews), with the ancient Church of the East dominant. Because of the social constraints which Christians were placed under within the Muslim Middle East prior to the modern era these communities may be particular informative as to the demographic impact of the Arab conquests, and the cosmopolitan and international nature of the Muslim polities and how they reshaped the genetics of the Middle East. A good approximation is that the Christian minorities are the dominant parent population of the Muslim majority, but that because of their tendency to withdraw into more isolated regions and their enforced economic marginality they would have not intermixed so much with the influx of slaves, both northern (Turk and Slav), Indian, and African, which characterized much of Mesopotamia over the past 1,400 years.

First things first: the different ancestral components are popping out of ADMIXTURE and are suggestive inferences base on the data input. They do not necessarily represent real concrete ancestral populations! As I keep pointing out, the purple South Asian element is probably a compound of at least two very genetically distinct ancient groups in about equal measures, one with strong West Eurasian/European affinities, and another a long resident indigenous South Asian group with distant, but definite, affinities to East Eurasians (it may be that the latter South Asian element gave rise to the various branches of East Eurasians and Amerindians further back in prehistory).

The “Northeast Asian” element in the ancestry of the four Finns is not that surprising (though I believe some of these are related). In 23andMe Finns often seem to show trace “Asian” ancestry, on the order of ~1%. Uniparental markers, especially Y chromosomal lineages, have long indicated ancient affinities between the Finnic peoples of Europe and various groups in Siberia. The major question has been whether the migration has been from the west to the east, or the east to the west. And yet perhaps this is the wrong way of looking at it, perhaps both these groups derive from an expansion south of the margins of the glaciers in the wake of the last Ice Age? The Finns clearly physically resemble their fellow Nordics more than the Yakuts. But perhaps this is not to be unexpected when you have mobile low density populations on the margins of more numerous conventional agriculturalists? I believe that the Mercator projection has also caused problems in assessing the plausibilities of connections between circumpolar peoples.

Next let’s move to the Assyrians. As with other such surveys the lack of African ancestry in relation to similar Muslim populations is striking. The Syrian set is probably the best point of comparison. Note the small slices from other populations in the Syrians. I would normally ignore that, but their absence in the Assyrians may be informative. This may be a function of close relatedness of the Assyrians, but I’d give it even odds that a low fraction of exogenous post-Islamic ancestry which is associated with travel within the Muslim lands explains some of the difference between the majority and minority populations (above and beyond the clear African element).

Finally, I’m going make up stories on the fly to generate some discussion (I think the stories correspond to reality more than expectation, but I have very weak confidence in them myself).

  • The “Southern European” element which is maximal in Sardinia indicates the very first wave of agriculturalists. The Sardinians may not be purely descended from agriculturalists, but like the composite “South Asian” quantum this represents possibly the very first hybridization due to a rapid demographic pulse driven by agriculture which synthesized with the hunter-gatherers of Western Europe. Like the “Ancient South Indians” I doubt that the Ice Age Europeans of Western Europe are present in “pure” form anymore. The influence of this component can be found far to the east among the Assyrians, but it almost disappears in Afghanistan and Pakistan. I think this may have something to do with R1b1b2.
  • The “Northern European” element which is maximal in the Lithuanians is found among the Pashtuns and non-Arab Middle Easterners, but not Arab speakers. It drops off in India very quickly. I don’t think the Lithuanians are the “purest” Indo-Europeans, and I don’t think that this element was necessarily exclusive to Indo-Europeans. But there has to have been some leap-frogging going on, because on average Semitic Middle Eastern groups are more like Europeans than Gujaratis are in total genetic distance, but Gujaratis seem to have a higher fraction of this quantum. And suggestively Punjabis seem to carry the Central Eurasian lactase persistence alleles (I know this from the literature and genome sharing on 23andMe). Again, because these ancestral quanta don’t represent real populations, but are proportions popping out of ADMIXTURE, we shouldn’t take the orange fraction as the “Aryan” ancestry in South Asia. But that seems the most plausible explanation for why it seems at far higher frequency in Indo-European speaking northwest India than it does in the Semitic speaking Fertile Crescent.
  • The light-blue “West Asian” fraction gets around. It’s found at the same proportions in Tuscans as Uyghurs, and, you can find it pretty far south and east in South Asia (I have a fair amount of it, as does a Reddy from South India, and the Kannada speakers in the global Dodecad set have some of it too, though less). I assume that it is present at high frequency among the Uyghurs because of the Indo-European speakers. But it clearly doesn’t have an Indo-European origin as such. It has a high frequency among the Cypriots, but not the Sardinians, with modal proportions among various Caucasian groups. I assume it has something to do with agriculture, but seems to have less of an influence in Western Europe than further to the east. The Finns and Lithuanians have a little bit, about the same as South Indians. So again, something which probably hitch-hiked with population movements in the center of Eurasia, but I assume pre-dating the Indo-Europeans.