The genetic history of Northern Europe (or rather the South Baltic)

A second preprint in only a few days on the Neolithic transition in the Baltic region has just appeared at bioRxiv: Mittnik et al. 2017. You can read about the first one here. Keep in mind also that we recently saw a paper on the same topic at Current Biology.

Can't these labs coordinate things a little better and perhaps focus on different parts of Europe? Wouldn't that be the sensible thing to do considering the limited funding for ancient DNA research?

Nevertheless, Mittnik et al. is an important addition to what we've already seen, for me mainly because it shows that largely unadmixed Western Hunter-Gatherers (WHG) lived in the South Baltic region at least as late as ~4,450 calBCE, which is the date assigned to the four Narva samples in the preprint. So now we have a plausible explanation for the inflated WHG-related ancestry in modern-day Balts and Northern Slavs.

Despite its geographically vicinity to EHG [Eastern Hunter-Gatherers], the eastern Baltic individual associated with the Mesolithic Kunda culture shows a very close affinity to WHG in all our analyses, with a small but significant contribution from EHG or SHG [Scandinavian Hunter-Gatherer], as revealed by significant D-statistics of the form D(Kunda, WHG; EHG/SHG, Mbuti) (Z>3; Supplementary Information Table S2).

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The results for the Kunda individual are mirrored in the four later eastern Baltic Neolithic hunter-gatherers of the Narva culture (Fig. 2) and further supported by the lack of significantly positive results for the D-statistic D(Narva, Kunda; X, Mbuti) (Supplementary Information Table S2) demonstrating population continuity at the transition from Mesolithic to Neolithic, which in the eastern Baltic region is signified by a change in networks of contacts and the use of pottery rather than a stark shift in economy as seen in Central and Southern Europe [15].

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Furthermore, the individual Spiginas2, which is dated to the very end of the Late Neolithic, has a higher proportion of the hunter-gatherer ancestry, as seen in ADMIXTURE (darker blue component in Fig. 2b), and is estimated to be admixed between 78±4% Central European CWC and 22±4% Narva (Supplementary Information Table S6). A reliance on marine resources persisted especially in the north-eastern Baltic region until the end of the Late Neolithic [29] and in combination with the proposed large population size for Baltic hunter-gatherers a ‘resurgence’ of hunter-gatherer ancestry in the local population through admixture between foraging and farming groups is likely, and has been described for the European Middle Neolithic [2,30].

The only gripe I have with this manuscript are the Principal Component Analyses (PCA). They just look messy and appear to suffer from projection bias, so they're hard to read and probably confusing for a lot of people.

Projection bias is also known as shrinkage. Basically it's when the PCA space shrinks for the projected samples compared to the reference samples. It happens a lot in ancient DNA papers. I find it irritating. But whenever I bring up this issue with authors of these papers, I'm basically told that their PCA look like other PCA from similar papers, so there's no problem. So, essentially, since everybody's doing it wrong, then it's the right way to do it. Awesome logic there.

Citation...

Mittnik et al., The Genetic History of Northern Europe, bioRxiv, Posted March 3, 2017, doi: https://doi.org/10.1101/113241

Update 08/01/2018: the paper was published at Nature Communications today under the title The genetic prehistory of the Baltic Sea region (see here).

See also...

Modern-day Poles vs Bronze Age peoples of the East Baltic