The enigma of the Kalash

Last year Garrett Hellenthal et al. claimed that the Kalash people of the Hindu Kush received a large pulse of admixture from somewhere in the west, possibly Europe, as late as 327–326 BCE. They even suggested that Alexander's soldiers may have been the culprits. But this was naive and wrong.

Now, Qasim Ayub et al. are claiming that the Kalash are an Ancient North Eurasian (ANE) population that has remained genetically isolated for the past 11,800 years. This is also naive and wrong.

One day, perhaps in the not too distant future, someone will study the population history of the Hindu Kush using ancient DNA and methods that actually work. What I think they will find is that the Kalash, just like most of their neighbors, are largely the result of an admixture event during the Bronze Age between Indo-Iranian migrants from the steppe and Central Asian agriculturists. They will confirm that the Kalash are an extreme isolate, but only since the Bronze Age, not the early Neolithic.

These results will correlate very nicely with mainstream linguistics and archeology, latest expansion dates for uniparental markers, and even common sense.

Citation...

Ayub et al., The Kalash Genetic Isolate: Ancient Divergence, Drift, and Selection, The American Journal of Human Genetics (2015), http://dx.doi.org/10.1016/j.ajhg.2015.03.012

See also...

The teal people: did they actually exist, and if so, who were they?

The teal people: did they actually exist, and if so, who were they?

The ADMIXTURE analysis in Haak et al. 2015 includes a series of intriguing teal colored components from K=16 to K=20 (see image here). The main reason I'm so intrigued by these components is because they generally make up over 40% of the genetic structure of the potentially Proto-Indo-European-speaking Yamnaya people.

But there's only so much one can learn by starring at a bar graph, so I thought I'd have a go at isolating the same signal with ADMIXTURE to study it in more detail. You can view the results of my experiment in the spreadsheet here.

I wasn't able to completely nail any one of the teal components from Haak et al., because I don't have access to all of the samples used in the paper (I'd have to sign a waiver to get them). Nevertheless, the signal looks basically the same.

Below is a bar graph based on the output featuring selected populations and ancient genomes from Europe and Asia. The Fst genetic distances between the nine components are available here.

Note that the teal component peaks in the Caucasus and the Hindu Kush, and generally shows a strong correlation with regions of relatively high MA1-related or Ancient North Eurasian (ANE) admixture. On the other hand, the orange component peaks among Early European Farmers (EEF), who basically lack ANE.

To learn about the structure of the three main West Eurasian components - blue, orange and teal - I made synthetic individuals from the P output to represent each of the components, and tested them with my K8 model. As expected, the teal component harbors a high level of ANE, while the orange component lacks it altogether. Refer to the spreadsheet here.

It's very likely that the teal and orange components from Haak et al. share these traits. I think this is more than obvious by looking at their frequencies across space and time in Eurasia.

I also analyzed the synthetic individuals with PCA based on their K8 ancestry proportions. The samples representing the orange component fall just south of the Stuttgart genome from Neolithic Germany, and this is basically where I expect Neolithic genomes from the Near East to cluster when they become available.

Interestingly, the samples representing the blue component are dead ringers for Scandinavian hunter-gatherers (SHG). However, I suspect this is something of a coincidence caused by the small number of Western European hunter-gatherer (WHG) and Eastern hunter-gatherer (EHG) genomes in the dataset. The algorithm probably doesn't have enough variation to latch onto to create both WHG and EHG components, and in the end settles for something in between, which just happens to resemble SHG.

But the fact that the orange and blue samples more or less pass for ancient populations leaves open the possibility that the same might be said for the teal samples.

So did the teal people actually exist, and if so, who were they?

My view at the moment is that a population very similar to the teal samples formed in Central Asia or the North Caucasus during the Neolithic as result of admixture between MA1-like and Near Eastern groups. This population, I believe, then expanded into the Pontic-Caspian steppe by the onset of the Eneolithic.

Were they perhaps the Proto-Indo-Europeans? Probably not. I'd say they were Neolithic farmers who eventually played a role in the formation of the Proto-Indo-Europeans. In any case, someone had to bring the Caucasian or Central Asian admixture to the steppe, and I have it on good authority that it was already present among the Khvalynsk population of the Eneolithic, albeit at a lower level than among the Yamnaya of the early Bronze Age.

Citation...

Haak et al., Massive migration from the steppe was a source for Indo-European languages in Europe, Nature, Advance online publication, doi:10.1038/nature14317

Update 16/11/2015: 'Fourth strand' of European ancestry originated with (Caucasus) hunter-gatherers isolated by Ice Age

Modeling the ancestry of Yamnaya with qpAdm

I've been playing around with the new qpAdm program and the Haak et al. dataset over the past few days and managed to come up with what I think are some very promising results. For instance, the Yamnaya genomes from the Samara Valley and surrounds fit rather well as 0.514 Samara hunter-gatherer + 0.486 Georgian (std. errors 0.032, chisq 3.890).

This is an interesting outcome, mainly because Georgian is a Kartvelian language, and linguistics data suggest that the early Indo-Europeans - presumably the Yamnaya nomads or their ancestors - were in close contact with Proto-Kartvelian speakers. Moreover, even though the Yamnaya males tested to date all belong to Y-chromosome haplogroup R1b, which they probably inherited from their hunter-gatherer ancestors, because the Samara forager also belonged to this haplogroup, some of their mtDNA lineages appear to be derived from the Caucasus and/or nearby areas of the Near East.

However, the main problem with this analysis is that it's attempting to model an ancient population as a mixture of a modern one. Indeed, my estimate is that present-day Georgians harbor around 20% of the so called Ancient North Eurasian (ANE) component, which probably arrived in the Caucasus from the Eurasian steppe (see here). If so, then the qpAdm run might be overestimating the non-steppe admixture in the Yamnaya genomes by at least 10%. Nevertheless, I'm quite happy with this result as I await ancient DNA from the Caucasus and Near East.

By the way, I also pretty much nailed the Corded Ware sample: 0.73 Yamnaya + 0.27 Esperstedt_MN (std. errors 0.060, chisq 2.621). Admittedly, an identical result for the same genomes was reported months ago at the ASHG 2014 conference (see here), but that's OK, because it means I'm on the right track.

qpAdm is easy to run, but the quality of its output heavily reliant on the outgroup or "right set" of populations picked by the user. As far as I can see, the following ten populations (a subset of the "magic set" of 15 from Haak et al.) produce the most robust outcomes when analyses are limited to West Eurasian groups.

Biaka
Bougainville
Chukchi
Eskimo
Han
Ju_hoan_North
Karitiana
Mbuti
Ulchi
Yoruba

Why do they work so well? I really have no idea, but through simple trial and error I found that some of the others from the "magic set", in particular the Ami, produced much poorer results.

I'll probably end up posting a whole catalog of qpAdm output in the comments section below over the next couple of weeks. I'm open to suggestions about the models to test and how to improve my runs.

Citation...

Haak et al., Massive migration from the steppe was a source for Indo-European languages in Europe, Nature, Advance online publication, doi:10.1038/nature14317

Yamnaya-related ancestry proportions in Europe and west Asia

Here's a quick and dirty attempt to flush out a Yamnaya-specific ancestral component with the ADMIXTURE software and a few Yamnaya genomes from the recent Haak et al. paper: K6 spreadsheet.

Obviously, we'll need many more ancient samples from the vast Yamnaya horizon to be able to estimate direct Yamnaya ancestry in modern populations with any great confidence. But I'd say this looks like a very reasonable attempt, with more or less comparable results to those published by Haak et al. (see here).

Please note that this wasn't a supervised run. In other words, I didn't mark the Yamnaya genomes as reference samples with the aim of creating a cluster from them.

However, I initially excluded all individuals from northeastern Europe, the north Caucasus and South Asia from the analysis. The reason I did this was because samples from these regions have a peculiar habit of creating very robust clusters in ADMIXTURE, which is useful when looking at recent variation and wanting low cross validation errors, but not so great when trying to resurrect genetic components from the depths of prehistory.

Once I had a dataset that was forcing the algorithm to focus its attention on the ancient genomes and producing consistent results, I tested the problem samples in batches of 5-10, thus making sure they didn't skew the analysis.

Interestingly, the Yamnaya-specific component peaks in Udmurts, who live close to where the Yamnaya samples were collected. This can hardly be a coincidence.

In any case, I'm hoping to look at this issue in more detail soon with the help of qpAdm, a new program released recently with the updated ADMIXTOOLS package (see here). Based on f4 statistics, qpAdm is specifically designed for analyzing ancient admixture events.

Citation...

Haak et al., Massive migration from the steppe was a source for Indo-European languages in Europe, Nature, Advance online publication, doi:10.1038/nature14317

New release of ADMIXTOOLS with two additional programs

ADMIXTOOLS 3.0 is now available at github via the Reich Lab site. The updated package includes minor bugfixes and improvements and two new programs: qpWave and qpAdm for studying migration and admixture. Scroll down the page at the link below.

Reich Lab software

Documentation is minimal, but I'm told that users of the old ADMIXTOOLS should be able to get things running. I haven't had a chance to check it out yet, but I'm looking forward to trying qpWave and qpAdm, hopefully this weekend.

Update 28/06/2020: Major updates to ADMIXTOOLS

The Near East ain't what it used to be

Up for public comment at bioRxiv this week is this paper on the population history of the Near East, with a special focus on Armenians. Here's the abstract:

The Armenians are a culturally isolated population who historically inhabited a region in the Near East bounded by the Mediterranean and Black seas and the Caucasus, but remain underrepresented in genetic studies and have a complex history including a major geographic displacement during World War One. Here, we analyse genome-wide variation in 173 Armenians and compare them to 78 other worldwide populations. We find that Armenians form a distinctive cluster linking the Near East, Europe, and the Caucasus. We show that Armenian diversity can be explained by several mixtures of Eurasian populations that occurred between ~3,000 and ~2,000 BCE, a period characterized by major population migrations after the domestication of the horse, appearance of chariots, and the rise of advanced civilizations in the Near East. However, genetic signals of population mixture cease after ~1,200 BCE when Bronze Age civilizations in the Eastern Mediterranean world suddenly and violently collapsed. Armenians have since remained isolated and genetic structure within the population developed ~500 years ago when Armenia was divided between the Ottomans and the Safavid Empire in Iran. Finally, we show that Armenians have higher genetic affinity to Neolithic Europeans than other present-day Near Easterners, and that 29% of the Armenian ancestry may originate from an ancestral population best represented by Neolithic Europeans.

Unfortunately, the authors failed to even mention the main cause of what they're seeing; the massive influx of Ancient North Eurasian (ANE) admixture into the Near East. They included ancient genomes Oetzi the Iceman and La Brana-1 in their analysis, but not MA-1 or Mal'ta boy, the main ANE proxy.

MA-1 is a low coverage genome, and not easy to work with, but until better ANE reference genomes are sequenced, it simply can't be ignored in studies on the population history of West Eurasia. Here's why:

Above is my Fateful Triangle PCA. Note the eastern shift of the Islamic Near Eastern groups relative to their non-Islamic neighbors. Here are the relevant ANE ancestry proportions:

Anatolian Turks ~16.54%
Armenians ~15.48%

Iranians ~19.61%
Iranian Jews ~14.01%

Lebanese Muslims ~9.82%
Lebanese Christians ~7.14%

The differences aren't very dramatic, but they're consistent and, as per the PCA, hard to overlook. Indeed, the contrast would be even more obvious if we were to add to the list other exotic admixtures, such as East Asian, South Asian and/or Sub-Saharan.

If you're wondering why it is that Muslims generally carry more ANE than their non-Muslim neighbors, it's probably because the Islamic expansion had a homogenizing effect on the Near East, and it didn't have as much of an impact on the religious minorities in the region.

How and when ANE arrived in the Near East is still a mystery which can only be solved with ancient DNA. However, my bet is that most of it came after the Neolithic from the Eurasian steppe, the northeast Caucasus and the Altai, with the Indo-Europeans, Kura-Araxes people and Turks, respectively.

Citation...

Marc Haber et al., Genetic evidence for an origin of the Armenians from Bronze Age mixing of multiple populations, bioRxiv, Posted February 18, 2015. doi: https://dx.doi.org/10.1101/015396

See also...

First look at an ancient genome from Neolithic Anatolia

Eastern Europe as a bifurcation hotspot for Y-hg R1

The main angle of the recently released epic manuscript Haak et al. 2015 is that ancient DNA supports the steppe origin of at least some of Europe's Indo-European languages. That's certainly a move in the right direction, so that we can eventually do away with the Anatolian hypothesis, which was always a failed proposition.

But it's clear that the authors are holding back. They've obviously decided to be very cautious until they've looked at more ancient DNA, particularly from the Near East, Central Asia and India, before backing fully any one Proto-Indo-European (PIE) urheimat model.

That's understandable, considering how much opposition there is still to the steppe hypothesis, even though it does by and large have the support of historical linguists, which is what really counts. Nevertheless, my feeling is that Haak et al. are underselling their data, particularly the stuff from Eastern Europe.

I'm of the opinion that the steppe or Kurgan PIE model works just fine, and also not surprised by the ancient DNA evidence pointing to a massive expansion of people from the western steppe during the Late Neolithic/Early Bronze Age. So for me, the really big news in this paper is that the only two Eastern European forager samples belong to basal lineages of Y-chromosome haplogroups R1a and R1b. What this suggests, Id' say, is that ancient Eastern Europe was a key bifurcation region for R1.

Remarkably, it's possible to basically lay out the history and phylogeny of R1a in Europe using just three R1a samples from the paper. This can't be a coincidence.

- Mesolithic Hunter-Gatherer from Karelia: R1a (xM198)

- Late Neolithic Corded Ware pastoralist from Germany: R1a (M198, M417, xZ282)

- Late Bronze Age Urnfielder from Germany: R1a (M198, M417, Z282, Z280)

What we can see there is the progression from a basal R1a in pre-Neolithic Northeastern Europe to a derived R1a in late prehistoric Central Europe. The derived R1a is actually R1a1a1b1a2, which is by far the most common subclade of R1a in Europe today, and closely related to the Asian and Indo-Iranian-specific R1a1a1b2.

Interestingly, all seven of the Yamnaya males sampled by Haak et al., mostly from the Samara Valley, belong to R1b-M269, the most common subclade of R1b today. However, five belong to the West Asian-specific R1b-Z1203, but none to the West European-specific R1b-M412. Also, all nine Yamnaya samples show Near Eastern admixture, described in the paper as Armenian-like.

Does this perhaps mean that the Proto-Indo-Europeans (and thus Yamnaya) originated in the Near East, as per the Armenian Plateau hypothesis?

I doubt it. The aforementioned Eastern European R1b forager is also from the Samara Valley, and he clearly lacks Near Eastern admixture. So what are the chances that a Near Eastern population with a frequency of R1b-M269 of around 100% moved into an area of Eastern Europe where a more basal R1b was already present, and in fact in a population with no Near Eastern ancestry? Very slim, I'd say.

So how did the Yamnaya herders acquire their Near Eastern admixture? The answer is obvious if we look at their mtDNA haplogroups. These include H, T and W, all of which might have come to Eastern Europe from the Near East.

Of course this doesn't mean that the Eastern European steppe was overrun by Near Eastern Amazons. It's generally accepted that during the Neolithic the steppe was settled by farmers from the Near East, just like much of the rest of Europe, and I'd say that it was mostly the women from these groups who were incorporated into the later pastoralist societies of the steppe. The men, who probably belonged to Near Eastern haplogroups like G or T, might have been killed or marginalized in some way, so that their reproductive success was seriously hampered.

This is not a far fetched scenario. Typical hunter-gatherer Y-haplogroups like I2 and C6 have already been recorded alongside Near Eastern-specific mtDNA lineages at several Neolithic sites in Western and Central Europe. The social mechanisms for this might have been different there than on the steppe, but in any case, it seems that European hunter-gatherer males shacking up with farm girls of largely Near Eastern ancestry was not an unusual occurrence back in the day.

See also...

Ust'-Ishim belongs to K-M526

Massive migration from the steppe is a source for Indo-European languages in Europe (Haak et al. 2015 preprint)

I'll probably end up writing a whole series of posts on this paper. But for now, here's the abstract and a PCA.

We generated genome-wide data from 69 Europeans who lived between 8,000-3,000 years ago by enriching ancient DNA libraries for a target set of almost four hundred thousand polymorphisms. Enrichment of these positions decreases the sequencing required for genome-wide ancient DNA analysis by a median of around 250-fold, allowing us to study an order of magnitude more individuals than previous studies and to obtain new insights about the past. We show that the populations of western and far eastern Europe followed opposite trajectories between 8,000-5,000 years ago. At the beginning of the Neolithic period in Europe, ~8,000-7,000 years ago, closely related groups of early farmers appeared in Germany, Hungary, and Spain, different from indigenous hunter-gatherers, whereas Russia was inhabited by a distinctive population of hunter-gatherers with high affinity to a ~24,000 year old Siberian6. By ~6,000-5,000 years ago, a resurgence of hunter-gatherer ancestry had occurred throughout much of Europe, but in Russia, the Yamnaya steppe herders of this time were descended not only from the preceding eastern European hunter-gatherers, but from a population of Near Eastern ancestry. Western and Eastern Europe came into contact ~4,500 years ago, as the Late Neolithic Corded Ware people from Germany traced ~3/4 of their ancestry to the Yamnaya, documenting a massive migration into the heartland of Europe from its eastern periphery. This steppe ancestry persisted in all sampled central Europeans until at least ~3,000 years ago, and is ubiquitous in present-day Europeans. These results provide support for the theory of a steppe origin of at least some of the Indo-European languages of Europe.

Haak et al., Massive migration from the steppe is a source for Indo-European languages in Europe, bioRxiv, Posted February 10, 2015, doi: https://dx.doi.org/10.1101/013433

Half of our ancestry comes from the Pontic-Caspian steppe

Here's the latest teaser for the new David Reich et al. paper on the ethnogenesis of present-day Europeans. It's part of an abstract for a seminar to be held by Professor Reich at Jesus College, Oxford, on February 9. Interestingly, it argues that migrations from the steppe resulted in a ~50% population turnover across northern Europe from the late Neolithic onwards, which is very much in agreement with recent discussions on the topic at Eurogenes (for instance, see here).

By ~6,000-5,000 years ago, a resurgence of hunter-gatherer ancestry had occurred throughout much of Europe, but in Russia, the Yamnaya steppe herders of this time were descended not only from the preceding eastern European hunter-gatherers, but also from a population of Near Eastern ancestry. Western and Eastern Europe came into contact ~4,500 years ago, as the Late Neolithic Corded Ware people from Germany traced ~3/4 of their ancestry to the Yamnaya, documenting a massive migration into the heartland of Europe from its eastern periphery. This steppe ancestry persisted in all sampled central Europeans until at least ~3,000 years ago, and comprises about half the ancestry of today’s northern Europeans. These results support the theory of a steppe origin of at least some of the Indo-European languages of Europe, and show the power of genome-wide ancient DNA studies to document human migrations.

Source: Ancient DNA documents three ancestral populations for present-­day Europeans


Update 11/02/2015: Massive migration from the steppe is a source for Indo-European languages in Europe (Haak et al. 2015 preprint).

Haak et al., Massive migration from the steppe is a source for Indo-European languages in Europe, bioRxiv, Posted February 10, 2015, doi: https://dx.doi.org/10.1101/013433

Yamnaya genomes are a 50/50 mix of eastern Euro foragers and something else ANE-rich

I'm posting a new entry about the upcoming Corded Ware/Yamnaya paper because the last entry (see here) now has over 400 comments which aren't easy to load for many people.

One of the authors of this eagerly awaited paper, Nick Patterson of the Broad Institute, briefly joined our discussion. Nick's contribution is much appreciated. He wasn't able to reveal a great deal, because the manuscript is in submission, but he did make a couple of interesting points:

- the paper will feature Y-haplogroup results from the Yamnaya culture, represented by nine samples in all, including seven males

- the population with Near Eastern ancestry that mixed with the Eastern Hunter-Gatherers (EHG) on the Russian steppe to form the Yamnaya pastoralists by 5,000 YBP was also "rich" in ANE

- ancient DNA from the Caucasus, Iran and India is probably necessary to work out how the Indo-Europeans got to India, but the paper won't feature such data

It's nice to hear that Y-haplogroups aren't being ignored. My opinion is that they're at least as important as genome-wide data when tracking the movements across vast space and time of highly patriarchal and patrilineal groups like the ancient Indo-Europeans.

Indeed, we already know that the Slavic, Baltic and Norse-specific R1a1a1b1, defined by the Z282 mutation, is the sister clade of the Indo-Iranian-specific R1a1a1b2, defined by Z93. Thus, if the Yamnaya males were found to belong to these or upstream markers, this would suggest that they were the paternal ancestors of many Balts, Scandinavians, Slavs and Indo-Iranians, and correlate very nicely with the linguistic and archeological "steppe hypothesis" of Indo-European origins.

In fact, even if analyses based on high density genome-wide data suggest that Indians don't harbor any genome-wide European ancestry, we'd still have to accept the likelihood of gene flow - albeit perhaps very indirect gene flow - from the European steppe to India because many Indians belong to R1a1a1b2.

The second point made by Nick is perhaps surprising, but at least for me not totally unexpected. That's because we've already known for a while that the Yamnaya genomes can be successfully modeled as half Karelian EHG and half present-day Armenian (see here), and according to my own estimates Armenians carry an average of 15.5% ANE.

The fact that these Armenian-like, ANE-rich newcomers dampened the genome-wide affinity to ANE-proxy MA-1 on the Russian steppe might look like a contradiction, but not if we remember that the higher the Near Eastern ancestry the lower the genome-wide affinity to MA-1, and also consider that the steppe foragers probably carried a lot more ANE than the newcomers.

Actually, as far as I know, all of the Yamnaya samples in this study come from the Samara Valley, which is some distance north of the Caspian Sea near the southern Urals. So it makes senses that the pseudo Armenians who turned up there more than 5,000 years ago were not like the Neolithic farmers of Western and Central Europe, who lacked ANE.

I'd say that this as yet unidentified group (wild guess: immediate ancestors of the Repin culture people?) was the result of an admixture event, or perhaps a series of admixture events, with ANE-rich foragers somewhere on the steppe south of the Samara. If so, I won't be surprised if it turns out that R1a only appeared in the Samara Valley after their arrival.

In any case, it looks like even after this paper comes out, we'll still need a lot more ancient DNA from across Eurasia to help map out the early Indo-European dispersals with any confidence.

Update 11/02/2015: Massive migration from the steppe is a source for Indo-European languages in Europe (Haak et al. 2015 preprint) .