NEW YORK – An ancient genome analysis by investigators in Germany, Australia, Switzerland, and France is providing a closer look at the population changes that took place in southcentral Europe towards the end of the Neolithic and start of the Bronze Age.
"Our analyses suggest that this genetic turnover was a complex process lasting more than 1,000 years and involved highly genetically structured populations in this region," co-senior and corresponding author Johannes Krause, an archeological sciences and archaeogenetics researcher affiliated with the University of Tubingen, the Max Planck Institute for the Science of Human History, and the Canton of Bern's Archeological Service, and his colleagues wrote in a study published in Nature Communications on Monday.
The researchers assessed almost 100 European samples dated to the Neolithic and Bronze Age, alongside available sequence data from other ancient and modern individuals in Europe. Their results were consistent with complex human migrations into an area that now includes parts of France, Germany, and Switzerland, including a rise in representation by pastoralists with Pontic-Caspian steppe ancestry in Switzerland during the Late Neolithic period.
"We find the expected large genetic turnover at the beginning of the third millennium [before the common era (BCE)] and a highly genetically structured population in the region of present-day Switzerland at that time period," the authors reported.
Past research suggests individuals with European hunter-gatherer and Western Anatolian farmer ancestry were found in Central Europe in the Neolithic, or Stone Age, the team explained, though new populations with genetic ties to Yamnaya individuals from the Pontic-Caspian steppe region appeared to move into the region near the Neolithic-to-Bronze Age transition at around the time that Corded Ware Complex cultures appeared in the area.
Even so, the dynamics and details of these population interactions are yet to be determined, the authors explained, noting that only a handful of ancient genomes have been described so far from Switzerland — an area with a wealth of archeological data that "makes the region relevant for studies of population history in Central Europe."
"Our study is the first to report a substantial number of ancient genomes from Switzerland, following a trend of population-scale archaeogenetic sequencing studies in Europe, made possible by capture technology," they noted.
For the latest study, the researchers screened for DNA in more than 250 ancient samples from Switzerland, southern Germany, and France's Alsace region, focusing in on 96 samples for targeted capture enrichment, shotgun sequencing, and genotyping at roughly 1.2 million SNPs across the genome.
The team's analyses, which included available modern sequence data and sequence data for hundreds more ancient genomes from Central Europe and Western Europe, pointed to two main genetic clusters.
The first of these clusters included individuals with Anatolian farmer-related ancestry and Western hunter-gatherer ancestry, with the latter ancestry component becoming more prominent in samples assessed towards the middle Neolithic time points.
On the other hand, individuals sampled from the late Neolithic and early Bronze Age shifted towards a second genetic cluster marked by a rise in ancestry related to the Yamnaya complex, the researchers reported. They noted there appear to have been still other population shifts in the region, since ancient individuals from the late Neolithic and early Bronze Age do not cluster genetically with present-day populations in Switzerland, but do share ancestry with other modern-day Europeans.
"In accordance with previous studies," they wrote, "the middle and late Neolithic Swiss individuals are descendants of late European Hunter-Gatherers and early farmers, whilst the individual after 2700 BCE also carry steppe-related ancestry."
The team also took a closer look at the timing of these transitions, admixture patterns, and ancestry shifts in the newly profiled individuals, along with some of the potential functional consequences of these population interactions, including changes in allele frequencies related to traits such as skin or eye color and lactose tolerance.
Moreover, based on the ancestry identified at different burial sites, the investigators suggested that the ancient societies profiled tended to be "patrilocal," meaning men typically stayed close to the places they were born, while women moved into new communities.
"[W]e identified several female individuals without any detectable steppe-related ancestry up to 1000 years after this ancestry arrives in the region," the authors noted, adding that these and other results are consistent with "a high level of genetic structure in this region at the beginning of the Bronze Age with potential parallel societies living in close proximity to each other."