Geographic patterns of mtDNA diversity in Europe

Genetic diversity in Europe has been interpreted as a reflection of phenome na occurring during the Paleolithic (similar to 45,000 years before the pre sent [BP]), Mesolithic (similar to 18,000 years BP), and Neolithic (similar to 10,000 years BP) periods. A crucial role of the Neolithic demographic t ransition is supported by the analysis of most nuclear loci, but the interp retation of mtDNA evidence is controversial. More than 2,600 sequences of t he first hypervariable mitochondrial control region were analyzed for geogr aphic patterns in samples from Europe, the Near East, and the Caucasus. Two autocorrelation statistics were used, one based on allele-frequency differ ences between samples and the other based on both sequence and frequency di fferences between alleles. In the global analysis, limited geographic patte rning was observed, which could largely be attributed to a marked differenc e between the Saami and all other populations. The distribution of the zone s of highest mitochondrial variation (genetic boundaries) confirmed that th e Saami are sharply differentiated from an otherwise rather homogeneous set of European samples. However, an area of significant clinal variation was identified around the Mediterranean Sea (and not in the north), even though the differences between northern and southern populations were insignifica nt. Both a Paleolithic expansion and the Neolithic demic diffusion of farme rs could have determined a longitudinal dine of mtDNA diversity. However, a dditional phenomena must be considered in both models, to account both for the north-south differences and for the greater geographic scope of clinal patterns at nuclear loci. Conversely, two predicted consequences of models of Mesolithic reexpansion from glacial refugia were not observed in the pre sent study.