Early chariot riders of Transcaucasia came from...

I'm finding it increasingly difficult nowadays to fully appreciate all of the ancient DNA samples that are accumulating in my dataset. But it's not entirely my fault.

Among the hundreds of ancient samples published last year there was a couple of Middle Bronze Age (MBA) individuals from what is now Armenia labeled "Lchashen Metsamor" (see here). I wasn't planning to do much with these samples because, even after reading the Nature paper that they came with a couple times over, I didn't have a clue what they were about. But after some digging around, I now know that their people, those associated with the Lchashen Metsamor archeological culture, were among the earliest in Transcaucasia, and indeed the Near East, to use the revolutionary spoked-wheel horse chariot. How awesome is that?

The invention of the spoked-wheel chariot is generally credited to the Middle Bronze Age Sintashta culture of the Trans-Ural steppe in Central Asia, and its rapid spread is often associated with the early expansions of Indo-European languages deep into Asia. On the other hand, some have argued that this type of chariot was first developed in the Near East, and directly derived from solid-wheeled wagons pulled by donkeys.

It's now obvious, thanks to ancient DNA, that the Sintashta people were by and large migrants to Central Asia from somewhere in Eastern Europe, and that they didn't harbor any recent ancestry from the Near East. So if chariot technology spread into the steppes from the Near East, then it did so without any accompanying gene flow, which is possible but not entirely convincing. This begs the question of whether the Lchashen Metsamor population was of Sintashta-related origin, because if it was, then this would corroborate the consensus that spoked-wheel chariots were introduced into Transcaucasia from the steppes to the north.

Below is a Principal Component Analysis (PCA) of West Eurasian genetic variation. It does suggest that the Lchashen Metsamor pair (labeled Armenia_MBA_Lchashen), as well as most of the other currently available samples from what is now Armenia dating to the Middle to Late Bronze Age (MLBA), harbor some steppe ancestry. That's because they appear to form a cline between samples associated with the Sintashta and Kura-Araxes cultures. Of course, the Kura-Araxes culture was a major Early Bronze Age (EBA) archeological phenomenon centered on Transcaucasia and surrounds, so its population can be reasonably assumed to have formed the genetic base of most subsequent populations in the region. The relevant PCA datasheet is available here.

To investigate the possibility of Sintashta-related admixture in Lchashen Metsamor with formal methods, I ran a series of mixture models with the qpAdm software. Here are the three statistically most sound outcomes that I was able to come up with for Lchashen Metsamor:

Armenia_MBA_Lchashen
CWC_Kuyavia 0.183±0.036
Kura-Araxes_Kaps 0.817±0.036
chisq 13.941
tail prob 0.378021
Full output

Armenia_MBA_Lchashen
Balkans_BA_I2163 0.193±0.045
Kura-Araxes_Kaps 0.807±0.045
chisq 14.780
tail prob 0.321267
Full output

Armenia_MBA_Lchashen
Kura-Araxes_Kaps 0.788±0.043
Sintashta_MLBA 0.212±0.043
chisq 14.871
tail prob 0.315451
Full output

I sorted the output by "tail prob", but the fact that Sintashta_MLBA is in third place isn't a problem because the stats in all of these models are basically identical. Indeed, CWC_Kuyavia (Corded Ware culture samples from present-day Kuyavia, North-Central Poland) and Balkans_BA_I2163 (a Bronze Age singleton from what is now Bulgaria) are both very similar and probably closely related to each other and to the Sintashta samples.

Interestingly, and, I'd say, importantly, ancients from the steppe that are closest to Lchashen Metsamor in both space and time, but not particularly closely related to the Sintashta people, don't work too well as a mixture source in such models.

Armenia_MBA_Lchashen
Kubano-Tersk 0.184±0.046
Kura-Araxes_Kaps 0.816±0.046
chisq 22.179
tail prob 0.0526526
Full output

A couple of months ago I suggested that populations associated with the Early to Middle Bronze Age (EMBA) Catacomb culture were the vector for the spread of steppe ancestry into what is now Armenia during the MLBA (see here). After taking a closer look at the Lchashen Metsamor samples, I now think that the peoples of the Sintashta and related cultures were also important in this process. If so, they may have moved from the steppe into Transcaucasia both from the west via the Balkans and the east via Central Asia, and brought with them spoked-wheel chariots. I don't have a clue what language they spoke, but I'm guessing that it may have been something Indo-European.

See also...

The mystery of the Sintashta people

A potentially violent end to the Kura-Araxes Culture (Alizadeh et al. 2018)

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...

Armenians vs Georgians

Armenians and Georgians are ethnic groups that live side by side in the south Caucasus, or Transcaucasia. By all accounts, they've both been there since prehistoric times and they're very similar in terms of overall genetic structure.

However, they speak languages from totally unrelated families: Indo-European and Kartvelian, respectively. How did this happen and might the answer lie in the small genetic differences that do exist between them?

To investigate this issue, I ran a series of qpAdm formal mixture models of present-day Armenians and Georgians using tens of ancient reference populations. To come up with as straightforward and meaningful results as possible, I constrained myself to two-way models. I then discarded the runs that produced "tail probs" under 0.1 and retained less than 400K SNPs. Only a handful of models passed muster, including these two:

Armenian
Mycenaeans_&_Empuries2 0.233±0.041
Kura-Araxes_Kaps 0.767±0.041
chisq 18.422
tail prob 0.142151
Full output

Georgian
Globular_Amphora 0.071±0.025
Kura-Araxes_Kaps 0.929±0.025
chisq 18.419
tail prob 0.142266
Full output

At the most basic level, the results suggest that both Armenians and Georgians are overwhelmingly derived from populations of Bronze Age Transcaucasia associated with the Kura-Araxes archeological culture, albeit with minor ancestries from somewhat different sources from the west. As far as I can see, when using more than 400K SNPs and a wide range and large number of outgroups (or right pops), neither Armenians nor Georgians can pass perfectly for any one ancient population in my dataset.

The best proxies for the minor but significant western ancestry in Armenians are Mycenaeans of the Bronze Age Aegean region and Greek colonists from Iron Age Iberia (Empuries2). Obviously, and perhaps importantly, these are both attested Indo-European-speaking groups. On the other hand, the very minor western ancestry in Georgians is best characterized as gene flow from Middle to Late Neolithic European farmers rich in indigenous European forager ancestry. It's practically impossible to say what language or languages these farmers spoke. How about something Kartvelian?

In any case, for me, the perplexing thing about present-day Armenians is that they harbor very little steppe ancestry. By and large, no more than a few per cent. Compare that to the currently available samples from what is now Armenia dating to the Middle to Late Bronze Age, which show ratios of steppe ancestry of up to 25%. For now, I'm guessing that what we're dealing with here is the classic bounce back of older ancestry layers that has been documented for different parts and periods of prehistoric Europe.

See also...

Early chariot drivers of Transcaucasia came from...

Catacomb > Armenia_MLBA

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...

Catacomb > Armenia_MLBA

It's now clear, thanks to ancient DNA, that Transcaucasia and surrounds were affected by multiple, and at times significant, population movements from Eastern Europe during the Chalcolithic and Bronze Age periods. Based on the ancient samples from what is now Armenia, I'd say that this process peaked during the Middle Bronze Age. But who exactly were the people who perhaps swarmed south of the Caucasus at this time?

The most likely suspects are the various groups that occupied the southernmost parts of the Pontic-Caspian steppe throughout the Bronze Age. They were associated with the so called Catacomb, Kubano-Tersk and Yamnaya archeological cultures. Below is a Principal Component Analysis (PCA) that compares samples from these cultures with those from Middle to Late Bronze Age Armenia (labeled Armenia_MLBA). The relevant datasheet is available here.

Note that Armenia_MLBA forms a cline that appears to be stretching out towards the Catacomb, Kubano-Tersk, Yamnaya and other Bronze Age steppe groups, and this suggests that it harbors significant and probably recent steppe-related ancestry. But PCA plots based on just two dimensions of genetic variation can be misleading at times, so let's check this out with some formal mixture models using qpAdm.

Armenia_MLBA
Catacomb 0.234±0.028
Kura-Araxes_Kaps 0.766±0.028
chisq 10.723
tail prob 0.826248
Full output

Armenia_MLBA
Kubano-Tersk 0.254±0.030
Kura-Araxes_Kaps 0.746±0.030
chisq 13.535
tail prob 0.633284
Full output

Armenia_MLBA
Kura-Araxes_Kaps 0.768±0.028
Yamnaya_Kalmykia 0.232±0.028
chisq 14.454
tail prob 0.564954
Full output

Armenia_MLBA
Kura-Araxes_Kaps 0.762±0.029
Yamnaya_Caucasus 0.238±0.029
chisq 15.916
tail prob 0.458816
Full output

All of these models are statistically very sound, and even though I ranked the results by "tail prob", there's nothing in the output that clearly points to any one of the southern steppe groups as the obvious source of the steppe-related ancestry in Armenia_MLBA. But, interestingly, Catacomb tops the ranking, and it probably also makes the most sense based simply on Carbon-14 chronology. So, for now, I'm going with Catacomb.

I didn't get a chance yet to investigate this issue in detail with the Global25. Does it contradict the results from my PCA and qpAdm analyses? If anyone reading this would like to take a close look that'd be great. Feel free to post your findings in the comments below. And if the answer is indeed Catacomb, then what language did these Catacomb-derived migrants, or perhaps invaders, speak? If not proto-Armenian then what?

By the way, please be aware that the Kubano-Tersk samples in my analyses are the same individuals as those featured in Wang et al. 2019 under the label "North Caucasus".

See also...

Early chariot drivers of Transcaucasia came from...

Likely Yamnaya incursion(s) into Northwestern Iran

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...

Steppe admixture in Mycenaeans, lots of Caucasus admixture already in Minoans (Lazaridis et al. 2017)

Over at Nature at this LINK. Why is the presence of steppe admixture in Mycenaeans important? And why does it matter if the Minoans already had a lot of ancestry from the Caucasus or surrounds? Because Mycenaeans were Indo-Europeans and Minoans weren't. I'm still reading the paper and will update this entry regularly over the next few days. Below is the abstract and, in my opinion, a key quote. Emphasis is mine.

The origins of the Bronze Age Minoan and Mycenaean cultures have puzzled archaeologists for more than a century. We have assembled genome-wide data from 19 ancient individuals, including Minoans from Crete, Mycenaeans from mainland Greece, and their eastern neighbours from southwestern Anatolia. Here we show that Minoans and Mycenaeans were genetically similar, having at least three-quarters of their ancestry from the first Neolithic farmers of western Anatolia and the Aegean [1, 2], and most of the remainder from ancient populations related to those of the Caucasus [3] and Iran [4, 5]. However, the Mycenaeans differed from Minoans in deriving additional ancestry from an ultimate source related to the hunter–gatherers of eastern Europe and Siberia [6, 7, 8], introduced via a proximal source related to the inhabitants of either the Eurasian steppe [1, 6, 9] or Armenia [4, 9]. Modern Greeks resemble the Mycenaeans, but with some additional dilution of the Early Neolithic ancestry. Our results support the idea of continuity but not isolation in the history of populations of the Aegean, before and after the time of its earliest civilizations.

...

The simulation framework also allows us to compare different models directly. Suppose that there are two models (Simulated1, Simulated2) and we wish to examine whether either of them is a better description of a population of interest (in this case, Mycenaeans). We test f4(Simulated1, Simulated2; Mycenaean, Chimp), which directly determines whether the observed Mycenaeans shares more alleles with one or the other of the two models. When we apply this intuition to the best models for the Mycenaeans (Extended Data Fig. 6), we observe that none of them clearly outperforms the others as there are no statistics with |Z|>3 (Table S2.28). However, we do notice that the model 79%Minoan_Lasithi+21%Europe_LNBA tends to share more drift with Mycenaeans (at the |Z|>2 level). Europe_LNBA is a diverse group of steppe-admixed Late Neolithic/Bronze Age individuals from mainland Europe, and we think that the further study of areas to the north of Greece might identify a surrogate for this admixture event – if, indeed, the Minoan_Lasithi+Europe_LNBA model represents the true history.

Lazaridis, Mittnik et al., Genetic origins of the Minoans and Mycenaeans, Nature, Published online 02 August 2017, doi:10.1038/nature23310

Update 03/08/2017: This is my own Principal Component Analysis (PCA) of the Minoan and Mycenaean samples, which are freely available at the Reich Lab website here. The Armenian angle for the eastern admixture in Mycenaeans looks forced. The trajectory of this admixture obviously runs from Northern or Eastern Europe to the Minoans. If it did arrive from Armenia, then realistically only via a heavily steppe-admixed population. Right click and open in a new tab to enlarge:

Update 05/08/2017: Much like Lazaridis et al., I ran a series to qpAdm analyses to find the best mixture model for the Mycenaeans. However, just to see what would happen, unlike Lazaridis et al., I didn't group any of the archaeological populations into larger clusters based on their genetic affinities. The three models below stood out from the rest in terms of their statistical fits.

Mycenaean
Minoan_Lasithi 0.786±0.049
Sintashta 0.214±0.049
taildiff: 0.96574059
chisq: 6.030
Full output

Mycenaean
Corded_Ware_Germany 0.210±0.043
Minoan_Lasithi 0.790±0.043
taildiff: 0.961238695
chisq: 6.198
Full output

Mycenaean
Minoan_Lasithi 0.791±0.043
Srubnaya 0.209±0.043
taildiff: 0.950419642
chisq: 6.558
Full output

So it's essentially the same outcome as the one obtained by Lazaridis et al., because Sintashta and Srubnaya are part of their Steppe_MLBA cluster, while Corded Ware is part of their Europe_LNBA cluster, and it's these clusters that, along with Minoan_Lasithi, provided their most successful mixture models for the Mycenaeans. But it's nice to see Sintashta at the top of my results, because it fits so well with the long postulated archaeological links between Sintashta and the Mycenaeans (for instance, see here).

By the way, here's what I said back in May when the Mathieson et al. 2017 preprint came out (see here). So things are falling into place rather nicely.

The same paper also includes the following individual from present-day Bulgaria dated to the start of the Late Bronze Age (LBA), which is roughly when the Mycenaeans appeared nearby in what is now Greece:

Bulgaria_MLBA I2163: Y-hg R1a1a1b2 mt-hg U5a2 1750-1625 calBCE

This guy is the most Yamnaya-like of all of the Balkan samples in Mathieson et al. 2017, and, as far as I can see based on his overall genome-wide results, probably indistinguishable from the contemporaneous Srubnaya people of the Pontic-Caspian steppe. He also belongs to Y-haplogroup R1a-Z93, which is a marker typical of Srubnaya and other closely related steppe groups such as Andronovo, Potapovka and Sintashta. So there's very little doubt that he's either a migrant or a recent descendant of migrants to the Balkans from the Pontic-Caspian steppe.

See also...

A Mycenaean and an Iron Age Iranian walk into a bar...

Main candidates for the precursors of the proto-Greeks in the ancient DNA record to date

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...