Early Baltic Corded Ware form a genetic clade with Yamnaya, but…

This is what Mittnik et al. 2018 say about a couple of their Corded Ware, or Baltic Late Neolithic (Baltic_LN), samples from what is now Lithuania:

Computing D-statistics for each individual of the form D(Baltic LN, Yamnaya; X, Mbuti), we find that the two individuals from the early phase of the LN (Plinkaigalis242 and Gyvakarai1, dating to ca. 3200–2600 calBCE) form a clade with Yamnaya (Supplementary Table 7), consistent with the absence of the farmer-associated component in ADMIXTURE (Fig. 2b). Younger individuals share more alleles with Anatolian and European farmers (Supplementary Table 7) as also observed in contemporaneous Central European CWC individuals [2].

We can add a third early Baltic Corded Ware sample, Latvia_LN1, to this list, because this individual was also shown to lack the above mentioned farmer-associated component in ADMIXTURE by Jones et al. 2017.
However, in my Principal Component Analysis (PCA) of ancient West Eurasia, all three samples fall just “northwest” of Yamnaya, along with one German Corded Ware outlier, and form a separate cluster that is shifted slightly closer to European hunter-gatherers and farmers. Hence, Plinkaigalis242 and Gyvakarai1 only form a clade with Yamnaya to the limit of the resolution in the analysis by Mittnik et al., but aren’t exactly identical to Yamnaya. The relevant datasheet is available here.

So what might this mean? Possibly that the ancestors of this Corded Ware trio “absorbed” trace forager and/or farmer admixture as they migrated from the Pontic-Caspian steppe to the East Baltic. Or it could mean that they came from a more westerly part of the Pontic-Caspian steppe where people harbored slightly elevated forager and/or farmer ancestry relative to Yamnaya.
More sampling of Eneolithic and Early Bronze Age (EBA) burial sites on the Pontic-Caspian steppe, particularly north of the Black Sea, will probably solve this mystery. Please note, however, that we already have an Eneolithic sample from the Pontic-Caspian steppe that not only packs extra farmer admixture over Yamnaya, but also belongs to Y-haplogroup R1a-M417, which is a marker intimately associated with the Corded Ware expansion (see here).
By the way, this is how the Corded Ware set from Mittnik et al. behaves in another of my PCA, which is designed to focus on entho-linguistic-specific genetic drift in Northern Europe. I don’t usually run samples older than the Bronze Age in this analysis, the reason being that they often don’t share enough genetic drift with modern-day Europeans to produce meaningful output. And to be honest, I’m not quite sure what to make of these results. But it’s probably not a coincidence that the Scandinavian Corded Ware (CWC_Battle_Axe) individual clusters so strongly with the Nordic Iron Age and modern-day Scandinavian samples. The relevant datasheet is here.

See also…
Late PIE ground zero now obvious; location of PIE homeland still uncertain, but…
Modern-day Poles vs Bronze Age peoples of the East Baltic
The genetic history of Northern Europe (or rather the South Baltic)

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