David of the Eurogenes Genetic Ancestry Project has a cautionary post up, When is a genetic map also a geographic map? Always and never. In it, he uses a specific peculiar pattern as a launching point into a broader exploration of the relationship between visualizations of genetic variation, and geography. That pattern is that Russians, the most geographically furthest east of European peoples, are closer to the Slavs of Central Europe than the Balts when plotted on the two largest dimensions of variation. I’ve highlighted this pattern from a PCA David extracted from a paper on northeast European genetics. This disjunction between geography and genetics has a pretty straightforward possible explanation: the current distribution of Russian-speaking peoples is a function of a massive demographic expansion to the east by Slavic farmers within the last 2,000 years. We already know that the borderlands between the steppe and the forest were long dominated by North Iranian people, from the Scythians to the Sarmatians, while further north the Great Russians absorbed a Finnic substrate (clear because some of the absorption is attested down to the early modern period).
With that duly …