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Ancient DNA Sequences Unravel Migrations Into Medieval Bavaria, Prehistoric Iberia

NEW YORK (GenomeWeb) – Two new studies by independent research teams are offering a glimpse back at historical human migrations in different parts of Europe a few hundred to several thousand years ago. 

For one of the two new papers appearing online yesterday in the Proceedings of the National Academy of Sciences, a team from Germany, the US, the UK, and Switzerland did low-coverage, whole-genome sequencing and/or capture array sequencing on remains from 36 individuals at half a dozen burial sites in present-day Bavaria. Those samples from the late 5th century and early 6th century were considered alongside samples from five individuals buried in Munich, Crimea, Serbia, or Russia's Southern Urals in the 2nd century to 6th century.

The researchers used capture sequencing to assess five megabases of neutral sequence and nearly 500 functional SNPs in these 41 individuals, while 11 were subjected to whole-genome sequencing at a mean depth of almost 5.6-fold coverage. 

While the results revealed relatively consistent ancestry from northern and central European in the Bavarian men and some women, the full sample set revealed sex-biased migration by women into the region from southeastern Europe, including some women with East Asian ancestry. Such ancestry was particularly common in women whose remains showed signs of artificial cranial deformation — an intentional elongation of the skull done in early childhood that was believed to have reached Europe through migration into the region from Asia.

"While [artificial cranial deformation] is a worldwide phenomenon that was practiced at least up to the 20th century," the authors noted, "during the Late Roman and Early Medieval period in Europe it is most popularly associated with the Huns, an ambiguously defined nomadic group thought to have migrated into Europe from Asia." Coupled with the genetic diversity in the women with artificial cranial deformation, the team speculated that the women may have arrived in Bavaria as part of a system of female migration and marriage done, in part to "form strategic alliances with entities to the east."

Using the genetic data available, the researchers were also able to piece together phenotypic differences in the women that extended beyond their enlarged crania to include distinct eye and hair coloring.

For the second study published in PNAS yesterday, researchers from the University of Uppsala, the University of Johannesburg, and elsewhere reached back into the even more distant past to explore historical human treks to the Iberian Peninsula — and their consequences for present-day populations in the Mediterranean — using genome-wide data for more than a dozen ancient individuals.

With Illumina HiSeq 2500 or X Ten instruments, the team did genome sequencing on 10 new human samples data from what is now northern and southern Spain, and improved on existing genome sequences for three other ancient individuals in the region. The samples, collected at half a dozen sites in Spain, came from individuals who lived between around 3,500 years and 7,500 years ago.

Based on SNP patterns in these genomes, considered alongside sequences from individuals in dozens of other ancient and contemporary populations profiled previously, the researchers determined that the first Neolithic farming arrivals to Iberia from Anatolia and the Levant had relatively low genetic diversity, perhaps owing to a modest migratory group size. After their arrival, these first Neolithic Iberians seem to have mixed with local hunter-gatherer groups, growing and potentially expanding their population size.

Given the present-day genetic differences, the team put forth a model marked by distinct Neolithic farmers expansions into Iberia compared to those moving into Central Europe, likely along distinct migratory routes. And in contrast to other parts of Europe, results from those analyses suggested the Iberian Peninsula did not experience much in the way of subsequent Bronze Age migration by migrant herds from the Pontic steppe.

"The Neolithization of Europe has been associated with large-scale migrations from Anatolia, which was followed by migrations of herders from the Pontic steppe at the onset of the Bronze Age," senior author Mattias Jakobsson, an organismal biology researcher affiliated with Uppsala University and the University of Johannesburg, and his colleagues explained.

From their results, they argued that the "impact of post-Neolithic migrations on Iberia was much smaller than for the rest of the continent, showing little external influence from the Neolithic to the Bronze Age."