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Thursday, September 24, 2009

More on mtDNA discontinuity in Europe

Apparently, modern Swedes don't have as much in common with their Scandinavian hunter-gatherer predecessors as do Lithuanians and Latvians from across the Baltic Sea, at least according to a new study on ancient mtDNA from Gotland....

The driving force behind the transition from a foraging to a farming lifestyle in prehistoric Europe (Neolithization) has been debated for more than a century [1,2,3]. Of particular interest is whether population replacement or cultural exchange was responsible [3,4,5]. Scandinavia holds a unique place in this debate, for it maintained one of the last major hunter-gatherer complexes in Neolithic Europe, the Pitted Ware culture [6]. Intriguingly, these late hunter-gatherers existed in parallel to early farmers for more than a millennium before they vanished some 4,000 years ago [7,8]. The prolonged coexistence of the two cultures in Scandinavia has been cited as an argument against population replacement between the Mesolithic and the present [7,8]. Through analysis of DNA extracted from ancient Scandinavian human remains, we show that people of the Pitted Ware culture were not the direct ancestors of modern Scandinavians (including the Saami people of northern Scandinavia) but are more closely related to contemporary populations of the eastern Baltic region. Our findings support hypotheses arising from archaeological analyses that propose a Neolithic or post-Neolithic population replacement in Scandinavia [7]. Furthermore, our data are consistent with the view that the eastern Baltic represents a genetic refugia for some of the European hunter-gatherer populations.

Helena Malmström et al., Ancient DNA Reveals Lack of Continuity between Neolithic Hunter-Gatherers and Contemporary Scandinavians, Current Biology, 24 September 2009, doi:10.1016/j.cub.2009.09.017

FYI, the Pitted Ware hunter-gatherer samples mostly belonged to mtDNA haplogroups U4, U5 and U5a, while the Funnel Beaker or TRB farmers carried H, J and T (only three samples). For a related story on mtDNA discontinuity in Central and Eastern Europe see
here. By the way, the comments above about the eastern Baltic as a refugia for hunter-gatherers are interesting. But the argument isn't particularly strong yet, considering the small samples and lack of Y-DNA haplogroup and genome-wide SNP data.

Friday, September 18, 2009

Central Europe's first farmers apparently did not descend from local hunter-gatherers

This paper has been all over the press and various blogs this week, so I won't spend too much time on it. But I will say that conclusions based on mtDNA need to be made very carefully, especially if there's no other genetic data available to corroborate them. The vast majority of the hunter-gatherers sampled here carried mtDNA U lineages (mostly U4 and U5), while the farmers from earlier studies showed a much greater variety of haplogroups, including quite a bit of N1a. So far, neither population seems particularly close to modern Europeans.

We compare new mitochondrial DNA (mtDNA) sequences from late European hunter-gatherer skeletons with those from early farmers, and from modern Europeans. We find large genetic differences between all three groups that cannot be explained by population continuity alone. Most (82%) of the ancient hunter-gatherers share mtDNA types that are relatively rare in Central Europeans today. Together, these analyses provide persuasive evidence that the first farmers were not the descendants of local hunter-gatherers but immigrated into Central Europe at the onset of the Neolithic.

B. Bramanti et al., Genetic Discontinuity Between Local Hunter-Gatherers and Central Europe’s First Farmers, Published Online September 3, 2009, Science DOI: 10.1126/science.1176869