Gene Expression

A few months ago I read Empires of the Silk Road, where the author makes the argument that contrary to the common perception of Inner Asians as uncouth barbarians who were inimical to civilization as we understand it, in fact these populations were critical to the emergence of particular civilized values, as well as their role as facilitators of the spread of particular ideas and technologies. The latter is addressed in a somewhat overly enthusiastic fashion in Genghis Khan and the Making of the Modern World, but the point seems to be robust. The transmission of chariots and horse culture to China and the civilizations of the ancient Near East seems to have been a function of mobile populations expanding out of the western margins of the Inner Asian plain. Religions such as Buddhism, Christianity and Islam were spread by the cultural networks of Inner Asians. This explains how a substantial number of Mongol tribesmen in Genghis Khan’s armies were Nestorian Christians, while Buddhism’s arrival in China nearly 2,000 years ago almost certainly was facilitated by Inner Asian traders and warriors.

But in the historical era there is a peculiar bias in our perceptions. The Huns, and later the Avars, Magyars and Bulgars are all instances of populations which emigrated from the zone between the lower Volga and Mongola into the heart of Europe. The Turks made an impact on a huge swath of the Ecumene, from India through the world of Islam, to southeastern Europe, and all the way into the heart of what is now European Russia! The Mongols exploded out from their heartlands and came near to conquering all of Eurasia, while only the farthest reaches of western Europe and southern India escaping their threats.

Notice a pattern? These are east-to-west movements. Until the expansion of the Russians into Siberia there was no historical record of an intrusion of west Eurasian populations analogous to what occurred in Hungary, Bulgaria or Anatolia. The Arabs and the Persians never made it beyond Transoxiana. In contrast there were multiple leap-frogs from east to west. One explanation is that over the past 2,000 years China has been a robust political entity. The rise of barbarian confederacies led by populations with roots in eastern Inner Asia, the Huns and Avars, in central Europe, date to the period of the decline of Roman hegemony.

But this is not the only story. There is the other half of the swing of the historical pendulum, when western barbarians pushed to the east. That movement is obscured because it occurred on the margins of, and prior to, history. In The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World much of the argument rests on archaeology, in contrast to Empires of the Silk Road, which utilizes philology and conventional historical records. The former book focuses on the west-to-east swing, which the author asserts is correlated with the expansion of Indo-European speaking populations.

That there needs something to be explained is evident when one glances at a map of the distribution of Indo-European langauges. We don’t have a historical record of what was going on here; unlike in the case of the spread of Turkic or Arabic. But that’s unfortunate because the expansion had a bigger linguistic impact. Something big happened, but we don’t really know much about it. And we don’t think about it. This is why the fact that the Tarim mummies seem to be of west Eurasian provenance is always of interest, it goes against our expectations. But those expectations sample only the historical record, one half of the swing of the pendulum.

Genetics tells us something about the first half of the arc. The modern Uyghurs, who speak a Turkic language, live in a region which was once Indo-European speaking. Their genetics seems to show that they are a recent admixture, on the order of 2,000 years, between western and eastern Eurasian populations. Specifically, when two populations with very different genomes admix the population is naturally genetically going to be equidistant to both. But, that may also be the case where you have clinal variation, that is, gene frequencies shifting gradually with distance. In the case of the Uyghurs it is unlikely to be just clinal variation, the archaeological record suggests that much of Inner Asia was very lightly populated until recently (and still is), while the patterns of linkage disequilibrium decay in their genomes are those of a population which was the outcome of a recent hybridization event.

Of course it is not simply the DNA of modern populations which we can draw upon. Over the past 10 years many individuals who were resident in East Asia have been sequenced whose genetics implies that their parental population was related to those of western, not eastern, Eurasia. But these are simply individuals. How about populations? DNA extraction and analysis has told us that European looking populations were extant in southern Siberia in the Bronze and Iron Ages.

Now a new study highlights the mtDNA and Y chromosomal lineages, that is, female and male lines respectively, of a bit more than a dozen individuals from a cemetery in the northeast Tarim basin dated to 4,000 years before the present. Evidence that a West-East admixed population lived in the Tarim Basin as early as the early Bronze Age:

Background
The Tarim Basin, located on the ancient Silk Road, played a very important role in the history of human migration and cultural communications between the West and the East. However, both the exact period at which the relevant events occurred and the origins of the people in the area remain very obscure. In this paper, we present data from the analyses of both Y chromosomal and mitochondrial DNA (mtDNA) derived from human remains excavated from the Xiaohe cemetery, the oldest archeological site with human remains discovered in the Tarim Basin thus far.

Results
Mitochondrial DNA analysis showed that the Xiaohe people carried both the East Eurasian haplogroup (C) and the West Eurasian haplogroups (H and K), whereas Y chromosomal DNA analysis revealed only the West Eurasian haplogroup R1a1a in the male individuals.

Conclusion
Our results demonstrated that the Xiaohe people were an admixture from populations originating from both the West and the East, implying that the Tarim Basin had been occupied by an admixed population since the early Bronze Age. To our knowledge, this is the earliest genetic evidence of an admixed population settled in the Tarim Basin.

The results are straightforward. It looks as if the population here is in eastern Xinjiang, approaching the borders of China proper. They were characterized by a mix between eastern and western lineages which was strongly sex-biased. In particular, seven out of seven male lineages were R1a1. Since both sexes have mtDNA, there were 20 successful extraction and analyses of these, and there seemed to be an eastern bias in them. Here are the haplogroup assignments for genealogy nerds….

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The R1a1 haplogroup should be familiar to you. There’s a lot of controversy about the phylogeny and origins of the sub-clades within this Y lineage. In particular, there is the position that the South Asian and non-South Asian lineages have a deep common ancestry, not a recent one. Though some scholars note that even if this is true that does not preclude the intrusion of European R1a1 lineages amongst South Asian ones. Additionally, in Europe the lineage seems to have undergone a demographic expansion recently, in particular in eastern Europe. Finally, there seems to be a trend of ancient putatively Indo-European lineages in Inner Asia (e.g., the Andronovo) being of this lineage.

An admixture between very different populations with there being a sex-bias is not unknown. This is common in Latin America, and something of the sort seems to also characterize South Asia. We don’t know what happened in the latter case, but in the former the details have been well documented. Elite men of European origin tended to enter into polygynous relationships with many indigenous women. By the time European women arrived in any numbers the demographic momentum was such that the pairings between the first male settlers and indigenous women was to have long term impact

Going back to Inner Asia, the model that seems to be plausible to me is one of men on the move. The Indo-European mythos is heavily biased toward patriarchal values and concerns.* These war-bands shared a common ethos and technological toolkit, but it was likely not in their power to be very mobile if they moved with their women. So it seems plausible that young male bands would operate under the assumption that they could “live off the land” so to speak when it came to securing mothers for their sons.

All of this points to the reality that culture and genes can be transmitted very differently. The populations of western Europe and central India have much less in common genetically than they do linguistically, and that is likely because of the cultural power of Indo-European war-bands in imposing their values, including their language, upon the sons born to them by the conquered. The mestizos of Latin America worship the god of their forefathers, and speak the language of their forefathers. During the early years of the Arab Caliphates the importance of the father’s identity was clear, as sons of Persian and Berber women were Arab-identified (though notably they initially had inferior status to those of pure lineage).

This is probably just one dynamic which characterizes world history. But it is striking to me that there is now genetic evidence for admixture sex-biases among the peoples of the Tarim basin which mimic what we seem among the descendants of conquistadors and indigenous women, as some scholars have suggested that western Europeans during the Age of Discovery were more like Inner Asians in their cultural ethos than other civilized populations.

Citation: BMC Biology 2010, 8:15doi:10.1186/1741-7007-8-15

H/T Dienekes

* Though I think that one should note that Indo-European patriarchy was of a different quality than that of civilized settled societies (or, at least what it became when Indo-Europeans became civilized and settled). The later eastern nomads, such as the Mongols ,were patriarchal, but women also were strong independent actors. Similarly, the Arabs during the time of Muhammad were patriarchal, but women such as Khadija had some power.

Comments

  1. #1 John Emerson
    February 24, 2010

    My understanding from “The Horse, the Wheel, and Language” is that the two Indo-European incursions on the steppe were widely separated and different in significance. The Tokharians were the earliest group to separate from the other Indo-Europeans (before 2000 BC), brought a lot of new technology East (wheeled vehicles, maybe metalworking), and had a formative influence on Chinese civilization (they may have been responsible for a break (ca. 1500 BC) in the Shang dynasty between the early period and the Yin era. The Iranian steppe people came considerable later, 1500-1000 BC, and were the northern part of the same peoples who settled India and Iran. Nomadism and cavalry warfare were developed by the latter group; this way of life was later taken over by Turks and Mongols when the Iranians became entangled with Greek, Roman, Persian, and Northern Indian states.

    Of the great civilizations, the Persians had the nearest relation to the steppe. The present Turkish Republics (Uzbekistan, etc.) once were ruled by Iranians (Sogdians, Sakas, etc.) and the present culture of the area is described as Turko-Persian. (The Tajiks still live there and are essentially Persians). When Persia was strong it ruled Central Asia, and when Central Asia was strong it ruled Persia. One common pattern was for nomadic Turks to control the military and the sedentary Persians to control the economy and do the work; the rulers were usually Turks but adopted Persian ways and intermarried.

    The more I’ve studied these things the more I’ve found that assigning ethnicities is a risky enterprise. There have been a lot of bicultural peoples, most of which ended going one way or another, but the Persian-Turk symbiosis is at least 1500 years old and is still a factor in Uzbekistan. (For political reasons, estimates of the Persian / Tajik population of Uzbekistan range from 5% to 20%. The median might be a good bet.)

    Last “men on the move” dynamic is often associated with the segmentary clan, which essentially kicks some its younger sons out in the world to sink or swim, often at the expense of neighboring peoples. Ethnic aggression is often explained by “overpopulation”, but densely populated nations like Bengal, Bali, or Egypt tend toward stagnation and an impoverished equilibrium. The excess population of Norsemen or Turks or Normans is made up of elite, well-fed men (and their commoner followers) who feel that they deserve more respect and power than their society is willing to give them, not of men who are having trouble surviving. Often they’ve been exiled so they don’t cause trouble at home. (“Younger sons” founded the British Empire.)

  2. #2 onur
    February 24, 2010

    Nomadic Indo-European groups such as Scythians and Sarmatians also had powerful women in their societies, as indicated by archaeology and ancient records.

  3. #3 razib
    February 24, 2010

    Nomadic Indo-European groups such as Scythians and Sarmatians also had powerful women in their societies, as indicated by archaeology and ancient records.

    yes. see my note.

    The Iranian steppe people came considerable later, 1500-1000 BC, and were the northern part of the same peoples who settled India and Iran.

    minor elaboration: indo-iranians. the iranian aryans and indo-aryans seem to be distinct. the “indo” group probably includes populations which never made it to india, such as the mitanni.

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