Into, out of, and across the Eurasian steppe

A new paper in Nature adds to the earlier study in the same journal by presenting data from 101 ancient Eurasians. The year is not yet halfway over, but it seems that the ancient DNA field is moving towards a new norm of studying dozens of individuals at a time and comprehensively tackling the "big problems" that have vexed archaeologists, linguists, and historians for decades if not centuries.

The first conclusion of the new study is the detection of the migration from the steppe to Europe that was the title piece of the earlier study. The authors do not present quantitative estimates of the amount of demographic replacement effected by the Yamnaya-to-Corded Ware migration, so it will be interesting to see if there are any minor significant differences in these. But, the two papers have different Yamnaya and Corded Ware samples, and yet arrive at qualitatively similar conclusions, so at least this part of the story should be considered firmly "settled".

The second conclusion is the migration from the European steppe to the Afanasievo culture of the Altai. This has been long-hypothesized based on the physical type of the Afanasievo people and their possession of a similar pastoralist/wheeled vehicle toolkit that would have allowed them to cover the huge difference between Europe and the Altai. This confirms movement #2 of the Anthony/Ringe model, although I doubt that this migration had anything to do with Tocharians as detailed below. But, it did happen.

The third conclusion is that the later steppe cultures of the Sintashta and Andronovo (putative Indo-Iranians according to some), were not a continuation of the Yamnaya-Afanasievo people, but had extra Neolithic farmer ancestry. So, it seems that Neolithic farmers entered the steppe, and the development of steppe cultures did not happen in isolation. Whether this involved migration of Corded Ware people (as the authors prefer), who were already a mixture of Yamnaya and Neolithic farmers, or some other mixture of Neolithic farmers with steppe populations (e.g., Tripolye plus Yamnaya) remains to be seen.

The fourth conclusion of the paper is that these steppe cultures were also later replaced by people of at least partial East Asian or "Native American"-like ancestry.  So, it seems that movements into the steppe happened both on the western end (as the incursion of Neolithic farmer ancestry into the Sintashta proves), but also on the eastern end, with the Europeoid populations of western origin receiving admixture from the eastern periphery of the Eurasian steppe.

As for the Yamnaya, the authors do not find a very strong signal of admixture (as did the earlier study), which they attribute quite plausibly to the lack of eastern hunter-gatherers in their dataset. On the other hand, they claim that the "Caucasus" genetic component in the steppe populations was of steppe ancestry rather than Near Eastern/Caucasian origin as was claimed in the earlier paper. This is based on the statistic D(Yoruba, Armenia BA; Yamnaya, Corded Ware) that is not significantly different from zero. However, Corded Ware is a mixture of Yamnaya and European Neolithic, so the sign of this statistic is determined by the sign of the statistic D(Yoruba, Armenia BA; Yamnaya, European Neolithic). If Yamnaya was simply a steppe population, descendants of local people without ancestry from the Middle East/Caucasus, then this statistic would be positive because of the shared Middle Eastern ancestry of Armenia BA and European Neolithic. Whereas, if Yamnaya is a mixture of a steppe population and a Middle Eastern/Caucasian one, then the statistic would be positive/negative for the respective parts, which would be consistent with an average not different from zero. I am sure that when the new data is re-analyzed together with the eastern hunter-gatherers it will be clear that the Yamnaya are not a pure steppe population.

Nonetheless, I am quite glad to read a sentence such as this:

Populations in northern and central Europe were composed of a mixture of the earlier hunter-gatherer and Neolithic farmer10 groups, but received ‘Caucasian’ genetic input at the onset of the Bronze Age (Fig. 2).

It seems that my prediction the the West_Asian component would appear in post-5ka Europeans and was related to Indo-Europeans has been adequately confirmed by the last two papers.

Speaking of the Caucasus/Middle East, it seems clear as a first approximation that the Bronze Age Armenians are quite similar to modern Armenians. Whether the genetic continuity of Armenians extends beyond the Bronze Age, or Armenians were formed by mixture in the Bronze Age remains to be seen. The question of Armenian linguistic origins is of course separate as it is commonly understood that the Armenian language is unrelated to Anatolian languages and may have arrived in Armenia from the Balkans at around the Bronze Age-Iron Age transition.

The authors also study some phenotypic traits such as lactase peristence (Yamnaya had some, but overall prevalence was much lower than modern Europeans, hence lots of selection to the present), and skin eye pigmentation. Like Wilde et al., and Mathieson et al., the steppe populations seem to have had brown eyes. Given that so did Neolithic Europeans, and (presumably) ancient Middle Easterners/Caucasians, I think it's a good bet that Proto-Indo-Europeans (whatever solution to the PIE urheimat one accepts) were a brown-eyed people, or in the very least far from the blue-eyed "Aryans" of racial mythology. Even the Bronze Age and Iron Age Asians seem to have been a predominantly brown-eyed people, although the derived HERC2 allele seems to be at a higher frequency in them than in the steppe Europeans.

The story of the Y-chromosomes seems very interesting, although these are not resolved to fine detail. The most interesting aspect of this part of the work is the appearance of haplogroup J in Iron Age samples from Russia, Armenia, and the Altai. This may tie in to the question of the Tocharian origins, which I have claimed were associated with R1b, rather than R1a (as the Indo-Iranians were). The modern Uygurs (who are partially of Tocharian origin) have both J2 and R1b, so were the recipients of West Eurasian elements other than the R1a that so seem to have dominated the eastern steppe, including the Afanasievo. I continue to think there's no evidence that the Afanasievo is Proto-Tocharian, as it's in the wrong place and 3,000 years before the attestation of Tocharian. 

Overall this is an amazing study which adds a lot to what we know about Bronze Age Eurasia. Hopefully there is more to come in the second half of 2015, but for the time being there is plenty to chew on.

Nature 522, 167–172 (11 June 2015) doi:10.1038/nature14507

Population genomics of Bronze Age Eurasia

Morten E. Allentoft, Martin Sikora, Karl-Göran Sjögren, Simon Rasmussen, Morten Rasmussen, Jesper Stenderup, Peter B. Damgaard, Hannes Schroeder, Torbjörn Ahlström, Lasse Vinner, Anna-Sapfo Malaspinas, Ashot Margaryan, Tom Higham, David Chivall, Niels Lynnerup, Lise Harvig, Justyna Baron, Philippe Della Casa, Paweł Dąbrowski, Paul R. Duffy, Alexander V. Ebel, Andrey Epimakhov, Karin Frei, Mirosław Furmanek, Tomasz Gralak, Andrey Gromov, Stanisław Gronkiewicz, Gisela Grupe, Tamás Hajdu, Radosław Jarysz, Valeri Khartanovich, Alexandr Khokhlov, Viktória Kiss, Jan Kolář, Aivar Kriiska, Irena Lasak, Cristina Longhi, George McGlynn, Algimantas Merkevicius, Inga Merkyte, Mait Metspalu, Ruzan Mkrtchyan, Vyacheslav Moiseyev, László Paja, György Pálfi, Dalia Pokutta, Łukasz Pospieszny, T. Douglas Price, Lehti Saag, Mikhail Sablin, Natalia Shishlina, Václav Smrčka, Vasilii I. Soenov, Vajk Szeverényi, Gusztáv Tóth, Synaru V. Trifanova, Liivi Varul, Magdolna Vicze, Levon Yepiskoposyan, Vladislav Zhitenev, Ludovic Orlando, Thomas Sicheritz-Pontén, Søren Brunak, Rasmus Nielsen, Kristian Kristiansen & Eske Willerslev

The Bronze Age of Eurasia (around 3000–1000 BC) was a period of major cultural changes. However, there is debate about whether these changes resulted from the circulation of ideas or from human migrations, potentially also facilitating the spread of languages and certain phenotypic traits. We investigated this by using new, improved methods to sequence low-coverage genomes from 101 ancient humans from across Eurasia. We show that the Bronze Age was a highly dynamic period involving large-scale population migrations and replacements, responsible for shaping major parts of present-day demographic structure in both Europe and Asia. Our findings are consistent with the hypothesized spread of Indo-European languages during the Early Bronze Age. We also demonstrate that light skin pigmentation in Europeans was already present at high frequency in the Bronze Age, but not lactose tolerance, indicating a more recent onset of positive selection on lactose tolerance than previously thought.

Link

Dolgopolsky on the two homelands of PIE

A classic study of the problem, which makes the two most important linguistic points:

1. Lexical borrowing between PIE and Kartvelian/Semitic languages places the early PIE homeland in the Near East
2. The maximum dialectal diversity within IE in the Balkans places the secondary PIE homeland in Southeastern Europe

My only point of disagreement with Dolgopolsky's model is that the secondary Balkan homeland was responsible only for the European IE languages (and Armenian) but not for the eastern migration of the Tocharians and Indo-Iranians.

I have argued elsewhere in my blog about the West Asian origin of these Asian IE branches; a Balkan origin for them seems unlikely at the moment, due to the lack of Y-haplogroup I and of the "Southern European" component among the eastern Indo-Europeans. Of course, we must wait to see what surprises archaeogenetics may have in store for us.

Mediterranean Language Review 1987 3:7-31

The Indo-European Homeland and Lexical Contacts of Proto-Indo-European with Other Languages

A. Dolgopolsky

Link (doc)

On Tocharian origins

Where did the Tocharians originate from? J.P. Mallory's recent talk has been somewhat of an eye-opener for me, as Prof. Mallory brought to my attention two important issues:

1. The lack of a clear connection between Afanasyevo and the Tarim Basin.
2. The existence (in Tocharian) of a rich agricultural IE terminology related to cereals, as well as the domesticated pig, which cannot be easily explained if Tocharians arrived in Xinjiang from the steppes to the north, and, ultimately from eastern Europe.

To begin with, I want to point out an important issue: we cannot assume that the earliest Caucasoids of Xinjiang, including some of the famous early Tarim mummies were Tocharian speaking. There are several arguments why this is so:

1. Tocharian is first attested in the 8th c. AD, that is, about 3 thousand years after the earliest detected Caucasoids in the region
2. There has been a shift in the region from Tocharian and eastern Iranian languages to Turkic over the last thousand years or so. Why assume linguistic continuity in the preceding three thousand?
3. Indeed, there has been linguistic shift throughout other regions of Eurasia in shorter timespans, such as the spread of Slavic across most of eastern Europe, the virtual extinction of Celtic in most of western Europe, the replacement of multiple languages by Arabic in the Near East, and so on. Linguistic continuity does not seem to be an appropriate default position in the absence of direct evidence.
4. The earliest Caucasoids of the Tarim were already substantially mixed with Mongoloids at least in their mtDNA. This reduces our confidence that they spoke an Indo-European language, as there is a pattern of Caucasoid patrilineages combined with Mongoloid mtDNA in present-day non-IE South Siberians
5. Indeed, the current Turkic Uyghurs, who are closer (temporally) to the Tocharians than the early Bronze Age Caucasoids have a rich assortment of Caucasoid Y-chromosome haplogroups, whereas the early Bronze Age ones seem to have belonged uniformly to R1a1. What languages were spoken by the non-R1a1 Caucasoids who arrived in the Tarim prior to the Turkification of the region?

To summarize the first part of the argument: the early population of the Tarim does not have clear steppe connections, it may not have been Indo-European speaking, and even if it were, it did not necessarily speak the same language as the later Tocharians. Moreover, the Tocharian language has a vocabulary without clear steppe associations, but with rich agricultural ones.

In search of the Tocharians

We may discover the origin of the Tocharians by a careful sorting of Y-chromosome lineages in the present-day Uyghur population of Xinjiang that is assumed to have absorbed the pre-Turkic inhabitants of the region:

1. Remove all east Eurasian lineages that are likely to be associated with the Xiongnu, Mongols, or Uyghur
2. Remove all west Eurasian lineages that can be explained from a non-Tocharian source (such as Iranians, or various Silk Road outliers)
3. See if anything is left

A recent paper by Zhong et al. provides rich data on Uyghurs that can be used to carry out this program.

The phylogeographic analysis of these lineages does leave some candidates:

1. Haplogroup D can be excluded as Mongolian/Tibetan
2. Haplogroup E can be excluded as Mediterranean/African
3. Haplogroup C can be excluded as Altaic/South Asian (C5)
4. Haplogroup G2a* (West Asian) does not seem to have an important presence (3 samples)
5. Haplogroup H can be excluded as South Asian
6. Haplogroup I can be excluded as a European outlier (1 sample)
7. Haplogroup J*(xJ2) can be excluded as NE Caucasian/Semitic with small presence (2 samples)
8. Haplogroup NO; haplogroup N has been founded in a Xiongnu context, so it is likely intrusive; O is East Eurasian
9. Haplogroup Q is also associated with Xiongnu nomads from Pengyang

This analysis leaves four candidates: J2-M172, R1a1a-M17, R1b-M343, and L-M20.

We can exclude L-M20 because its overall low frequency in most populations makes it difficult, at present, to make a definitive pronouncement on its origin, except perhaps for its Indian L1 clade which is absent here.

J2, present in both its J2a and J2b subclades here at substantial frequencies has an origin in West Asia, as well as a substantial presence among Indo-Iranian speakers. While it is possible (indeed likely, in my opinion) to have been present among the Tocharians, we cannot exclude the possibility that it represents either a specifically Iranian influence, or even something earlier than both.

R1a1a is present in both the steppe, as well as South Asia and West Asia. Its high frequency among some Indo-Iranian populations also makes it difficult to ascribe a specifically Tocharian origin to it.

This leaves only R1b-M343 as a candidate. Have we found a genuine Tocharian genetic signature?

The West Asian roots of R-M343 (?)

R-M343 and its main R-M269 clade are in a sense exasperating: the combination of their widespread distribution from Africa, the Atlantic, to the depths of Inner Asia, combined with their apparent Y-STR-estimated youth make it nearly impossible to associate them with a specific archaeological or historical phenomenon.

Where could R-M269 have come from? It was not present, as far as we can tell, in early Bronze Age Xinjiang, and neither has it been detected in south Siberians. The steppe/"northern" route seems out.

A southern route, from the Indian subcontinent also seems out, as despite its ubiquity elsewhere in Eurasia, it seems to have (mostly) skipped both India and (to an extent) Pakistan.

An indigenous origin seems highly unparsimonious, as it would require that it trek all the way to the Atlantic, but make hardly an impact in either East Asia or South Asia.

As far as I can tell, the only explanation for the presence of R-M343 in Xinjiang is West Asia, or at least Central Asia west of the Tarim. There it can be found at a high frequency in Armenians, Turks, north Iranians, and Lezgins among others. And, unlike both J2 and R1a1a, R-M343 does not seem to be Indo-Iranian (due to its absence in India).

Gamkrelidze and Ivanov cited W. N. Henning to the effect that the ancestors of the Tocharians could be identified with the Gutians from the Zagros, a people that attacked the Sumerians and founded a dynasty. As usual, I don't presume to know the linguistic evidence for this, but this hypothesis would place the ancestors of the Tocharians in the "right spot": virtually all of their Caucasoid Y-chromosome gene pool could be explained with an origin in north Iran.

A model of Tocharian origins

The model of Tocharian origins I present is simplicity itself:

First, Tocharians are descended from a group of farmers that moved east of the PIE homeland and settled on the Zagros and beyond, south of the Caspian sea.

Second, their trek to the Tarim was a simple west-to-east movement along what would later become the Silk Road, beyond the Taklamakan desert and into the Tarim basin. There they must've mixed with the early pre-IE mixed Caucasoid/Mongoloid population of the early Bronze Age. The desert probably sheltered them, to an extent, from encroachments by the Iranians.

An open question remains: were the Tocharians late fugitives who were pushed out of their ancestral homelands by the emergence of the Iranians and entered the Tarim late? Or were they established there fairly early and were the historical Tocharians are the eastern relics of a once great people that was not Iranized unlike most of the people of Central Asia?

Autosomal evidence

The fine-scale analysis of the Dodecad project on a sample of 10 Uyghurs provides some additional evidence:

The Uyghurs seem to lack the Southwest Asian component that is ubuiquitous in most of West Asia today, and may have, in large part, expanded with the more recent spread of Semitic languages. They are similar, in that respect with South Asians, suggesting that neither the spread of Islam to the east nor the cosmopolitanism of the Silk Road were enough to bring this component to the region. Hence, the plethora of Caucasoid Y-haplogroups in the region cannot be attributed to recent arrivals.

The absence of specific South European components in them also suggests that the opinion of some linguists and archaeologists that would see the Tocharians related to Celts and moving from deep within Europe, or even Western Europe to the Tarim, are unlikely; the south European component is ubuiquitous in Europe, and the Uyghurs, like South Asians, seem to lack it entirely.

Their Caucasoid components are primarily West Asian and North European. Projecting them on the East Eurasian/West Asian/North European PCA plot (left), it is clear that they are more West Asian than North European, a result that is in agreement with their ADMIXTURE results.

Notice also how the North European/West Asian ratio is reversed for the more northern-latitude Uralic/Altaic speakers (Selkups, Dolgans, etc.).

Of course, the results should be interpreted with caution, but they seem perfectly in agreement with the model presented here:

• the Uyghurs are partly Mongoloid both because they may carry the legacy of the ancient mixed population of the Tarim, and also because of their more recent Turkic/Xiongnu associations.
• with respect to their Caucasoid components, they are mainly West Asian (with the West Asian component also being primary in South Asia), but somewhat shifted to the north due to their absorption of mixed Northern Caucasoid/Mongoloid peoples from the steppelands.

Conclusion

The mystery of the Tocharians may be that there is no mystery. The Tocharians are revealed to have been just another West Asian branch of the Indo-European family that, unlike most of its cousins, went east, absorbed Northern Caucasoid, Mongoloid, and South Asian population elements, emerged long enough in history to leave us a written record of their presence, before succumbing to the Xiongnu and the Mongols.

Thankfully, by combining the remnants of their language, and fragments of their DNA in their descendants, we are able to reconstruct the history of this, once forgotten people