The most recent literature demonstrated significant impact of Caucasus-related ancestry in the Central European Late-Neolithic and Bronze-Age through the migrations of Yamnaya/Pontic-Steppe herders. Accordingly, our results confirm that Caucasus-related admixture via Yamnaya is present in Eastern and Central-Western European clusters (i.e. Continental Europe; Supplementary Table S8, Supplementary Information). However, among our Mediterranean groups, evidence of Yamnaya (and EHG) introgression seems to be present at a lesser extent and was detected mainly in Balkan-related groups (Supplementary Table S8, Supplementary Information), which in turn display traces of admixture with Eastern Europe (Fig. 4, Supplementary Fig. S2). In addition, outgroup-f3 values for Late Neolithic/Bronze Age samples (especially Yamnaya) appear lower in all our newly analysed Mediterranean populations (Supplementary Fig. S9). These results suggest that the genetic history of Southern Italian and Balkan populations may have been, at least in part, independent from that of Eastern and Central Europe, involving specific migratory events that carried Caucasian and Levantine genetic contributes along the Mediterranean shores (see Supplementary Information). This picture may bring important implications for our understanding of the cultural history of Europe, and in particular for the diffusion of Indo-European languages. The Steppe in the Early Bronze Age has been supported as a source of at least some Indo-European languages entering North-Central Europe at that time. In southern Mediterranean Europe, however, our results suggest lower impacts. Any significant Steppe/northern component may have arrived in the south Balkan mainland and southern Italy only later, by which time Indo-European languages of the Italic, Greek and various Balkan branches had already established themselves there. This would suggest that a Bronze Age Steppe source may be not highly consistent with all branches of the Indo-European family (see also Broushaki et al.).
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Summing it up, our analyses show that a Caucasus-related ancestry is observed in both Southern Italian and Southern Balkan populations. Nevertheless, these populations do not seem to reveal such significant evidence of Bronze-Age Yamanya-like introgressions, which have been interpreted as the most probable vectors of CHG-like ancestry in Central-Eastern and Northern Europe and were also linked with the demographic diffusion of some Indo-European languages. These results may suggest that Caucasus-related ancestry reached our Mediterranean populations through migratory events at least partly independent from those postulated for Central Europe, most likely through Anatolia. If so, the spread of Indo-European languages in Europe may be envisaged as a more complex multi-way phenomenon, rather than the one-way result of a single diffusion process.
Sarno et al. "Ancient and recent admixture layers in Sicily and Southern Italy trace multiple migration routes along the Mediterranean". Scientific Reports, 2017.
