The male genetic landscape of the European continent has been shown to be clinal and influenced primarily by geography rather than by language. 1 One of the most outstanding phenomena in the Y-chromosomal diversity in Europe concerns the population of Poland, which reveals geographic homogeneity of Y-chromosomal lineages in spite of a relatively large geographic area seized by the Polish state. 2 Moreover, a sharp genetic border has been identified between paternal lineages of neighbouring Poland and Germany, which strictly follows a political border between the two countries. 3 Massive human resettlements during and shortly after the World War II (WWII), involving millions of Poles and Germans, have been proposed as an explanation for the observed phenomena. 2, 3 Thus, it was possible that the local Polish populations formed after the early Slavic migrations displayed genetic heterogeneity before the war owing to genetic drift and/or gene flow with neighbouring populations.