Major study of Central Asian populations (Martinez-Cruz et al. 2010)

I have often commented on the fact that Central Asians were mainly formed by the pendulum of Western Eurasians (Caucasoids) moving east with Indo-Iranian languages during prehistory and the later historical westward movement of Turkic speakers. There were other movements besides these, e.g., the Tocharians represent a non-Indo-Iranian eastward Caucasoid movement, while the Mongols represent a non-Turkic westward Mongoloid movement.

Central Asians are therefore today a variable mix of Caucasoids and Mongoloids, formed over the last few millennia, although the constituent elements are still present and recognizable. The Turkicization of the region was, to a large extent, the result of language shift among Iranian populations (Sakas-Scythians), but not without some genetic contribution from the original Turks who were a Mongoloid people akin to their linguistic Altaic cousins, the Mongols. This Mongoloid component is attenuated westward, reaching its minimum among Anatolian and Balkan Turkish speakers.

With respect to the admixture proportions (figure top left) presented in the paper, I have a couple of quick comments:

• Using modern south Asians as representatives of a source population of Central Asia is problematic, as modern south Asians are admixed, comprised of Caucasoids and indigenous South Asians. While South Asia may have been a population source during remote periods of the Paleolithic, in the more recent post-Neolithic times when Central Asian populations were formed, South Asia was a population sink.
• The use of only a few autosomal markers does give a broad overview of the east-west components in these populations, but it should be noted that the use of few markers tends to overestimate minority ancestral components.

Even with such a small number of markers, it is evident that the separation of groups at the population level is possible, as the correspondence analysis indicates: green/European, red/East Asian, blue/Indo-Iranian from Central Asia, orange/Turkic from Central Asia.

UPDATE

The paper includes STRUCTURE results for K=2 to K=6. Below is the STRUCTURE run for K=6:



While less distinct than what we would get with more markers, the emergence of several clusters of individuals is apparent (from left to right: East Asian, Turkic, Central Asian Iranian, South Asian, West Eurasian, Sub-Saharan). Notice how Hazaras and Uyghurs are islands of the Turkic component in the Central/South Asian cluster, and how some Uzbeks are Iranian-like while others are Turkic-like. I am reminded of an older study which found how mythology was used among some Uzbek groups to create a common ancestry for groups of unrelated origin.

European Journal of Human Genetics , (8 September 2010) | doi:10.1038/ejhg.2010.153

In the heartland of Eurasia: the multilocus genetic landscape of Central Asian populations

Begoña Martínez-Cruz

Located in the Eurasian heartland, Central Asia has played a major role in both the early spread of modern humans out of Africa and the more recent settlements of differentiated populations across Eurasia. A detailed knowledge of the peopling in this vast region would therefore greatly improve our understanding of range expansions, colonizations and recurrent migrations, including the impact of the historical expansion of eastern nomadic groups that occurred in Central Asia. However, despite its presumable importance, little is known about the level and the distribution of genetic variation in this region. We genotyped 26 Indo-Iranian- and Turkic-speaking populations, belonging to six different ethnic groups, at 27 autosomal microsatellite loci. The analysis of genetic variation reveals that Central Asian diversity is mainly shaped by linguistic affiliation, with Turkic-speaking populations forming a cluster more closely related to East-Asian populations and Indo-Iranian speakers forming a cluster closer to Western Eurasians. The scattered position of Uzbeks across Turkic- and Indo-Iranian-speaking populations may reflect their origins from the union of different tribes. We propose that the complex genetic landscape of Central Asian populations results from the movements of eastern, Turkic-speaking groups during historical times, into a long-lasting group of settled populations, which may be represented nowadays by Tajiks and Turkmen. Contrary to what is generally thought, our results suggest that the recurrent expansions of eastern nomadic groups did not result in the complete replacement of local populations, but rather into partial admixture.

Link