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. 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 nomads acquire their Near Easten 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.

Now, if Eastern Europe was indeed a bifurcation hotspot for R1, then a large proportion, or in fact the majority of R1a and R1b in Eurasia, might well be of Eastern European origin. This might mean, for instance, that the Yamnaya males belonging to R1b-Z2103 are close relatives of steppe nomads who moved to the Near East and perhaps introduced Hittite, Armenian and other Indo-European languages to the region.

If so, there should be some support for this in genome-wide DNA of present-day Asians, and indeed I think there is.

Below are a couple of principal component analyses (PCA). The first is from Haak et al. and the second from my own West Eurasia K8 analysis (see here). Unfortunately, I don't yet have access to the Yamnaya genomes, but I think it's petty easy to guesstimate where they will land on my plot when I run them in the K8. I marked this spot with an X.

Note that most of the Near Eastern and Caucasian populations are clearly shifted east towards ANE, and also up towards Europe. Moreover, I'd say many of these groups are specifically pushing up towards the Volga-Ural samples and thus the Yamnaya nomads.

There's really no other way to explain this outcome. Quite simply, the vast majority of West Asians have relatively recent (post-Neolithic?) ancestry from the Ural or Kazakh steppe, which manifests itself as a west to east cline on PCA, running from the southern Levant to the north Caucasus. This result is easily reproduced on any decent PCA with West Eurasian populations, and can be seen on the Haak et al. plot.

I'm yet to find solid evidence that Indo-European speakers from the Near East, like Armenians, Kurds and Iranians, don't harbor fairly significant ancestry from this northeastern source.

For instance, unlike many people, I don't find unsupervised ADMIXTURE analyses very convincing when they show these groups to be entirely of Near Eastern ancestry. That's because when ADMIXTURE creates a modern Near Eastern/West Asian cluster, it usually lumps within it all of the ancient ancestral components that are today ubiquitous in the Near East. In other words, the steppe admixture which shows up amongst most West Asians on the PCA above is classified as native to the Near East, even though this is unlikely to be true.

Ancient DNA from the Near East will either verify or debunk my claims here. I know there's some on the way later this year, courtesy of the ancient DNA lab at Copenhagen University.



(Source: eurogenes.blogspot.com.au)