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) .