The composite map in Fig. 1a shows the coverage of the 13 most frequent clusters in Europe and neighboring regions. We found a clear differentiation among historical geopolitical regions coincident with previous studies [3], [5], [9], [16] and [21]:
Western Europe: cluster
6,
Eastern Europe: cluster
17,
Northwestern Africa: cluster
3,
Western Fenno-Scandinavia: cluster
4, and
Finland and the Baltic: cluster
9. In Southeastern Central Europe and the Balkans several clusters were alternatively predominant. Two circumscribed and densely sampled areas stood out from the surroundings:
central Anatolia (cluster
5) and
central Hungary (cluster
14). It is worth mentioning that while a genetic differentiation of central Anatolia is in accordance with previous studies [17] and [18], a reliable characterization of the not sampled surrounding areas may require further evaluation. Two clusters were assigned to large areas of the Balkan Peninsula: (1)
Croatia, Bosnia and Herzegovina, Serbia, Romania, Western and Eastern Hungary, and Central Ukraine: cluster
18; (2) continental
Greece, Bulgaria, and Macedonia: cluster
2. Cluster
13 was assigned to
Albania and to the
western area of the Balkans and cluster
11 to the
Caucasus. The regionalization of Iceland in two concentric areas may indicate that a second group (cluster 4) is present in high frequency along with the most frequent Western European group (cluster 6). How these two groups spatially distribute in this area requires further examination.