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Ancient Genomes Shed Light on Cultural Expansion, Spread of Farming in Europe

NEW YORK (GenomeWeb) – The spread of a distinctive pottery style linked to the "Beaker" culture in prehistoric Europe appears to have occurred through cultural diffusion rather than large-scale human movement in most parts of Europe, new research suggests.

In a pair of papers published online today in Nature, teams led by investigators at Harvard Medical School and other centers analyzed genome-wide array-based SNP profiles and sequencing data for hundreds of ancient European samples to piece together the spread of the Beaker complex in central and western Europe, as well as the spread of farming practices across southeastern Europe.

For one of the studies, Harvard genetics researcher David Reich and evolutionary biologist Carles Lalueza-Fox of Spanish National Research Council (CSIC)-Pompeu Fabra University led an international team that used targeted sequencing to characterize more than 1.2 million SNPs in 400 ancient European samples from the Neolithic Period, Copper Age, and Bronze Age, including 226 individuals with Bell Beaker pottery artifacts from sites in Iberia, southern France, northern Italy, Sicily, central Europe, the Netherlands, and Britain. They combined those data with previously published ancient DNA data for a total of almost 700 ancient samples.

"[B]y 2500 BC the Beaker complex had spread throughout western Europe and northwest Africa and had reached southern and Atlantic France, Italy, and central Europe, where it overlapped geographically with the Corded Ware complex. Within another hundred years, it had expanded to Britain and Ireland," the team explained. "A major debate in archeology has revolved around the question of whether the spread of the Beaker complex was mediated by the movement of people, culture, or a combination of both."

When they compared variant patterns in these individuals with nearly 2,600 individuals genotyped with Thermo Fisher Scientific's Affymetrix Human Origins Array and 300 high-coverage genome sequences, all from present-day populations, the researchers found evidence for distinct genetic patterns in central European and Iberian individuals who received burials that involved Beaker-like pottery.

While steppe population ancestry was relatively prominent in Beaker complex-associated individuals outside of Iberia, for example, the team saw steppe ancestry in only a fraction of the Beaker culture practitioners within Iberia. And similar genetic differences turned up within specific parts of Europe.

"We detected limited genetic affinity between Beaker complex-associated individuals from Iberia and central Europe," the authors wrote, "and thus exclude migration as an important mechanism of spread between these two regions."

"[T]he diffusion of the Beaker culture from Iberia is the first example of a culture being transmitted as an idea," Lalueza-Fox said in a statement.

On the other hand, the researchers' analysis pointed to widespread population replacement between the Neolithic Period and Copper/Bronze Age in Britain, where the Beaker complex introduction coincided with population movement and a dramatic increase in steppe population ancestry.

"[T]he Neolithic people who built Stonehenge (and who had a greater genetic similarity with Neolithic Iberians than with those from Central Europe) almost disappear and are replaced by the populations from the Beaker culture from the Netherlands and Germany," Lalueza-Fox said, noting that "backward [Beaker culture] flow also reaches other places such as Italy (at least in the north) and Iberia."

In a related Nature study, Harvard's Reich and co-senior authors from the University of Vienna, University College Dublin, and the University of Pennsylvania described analyses of more than 200 ancient European genomes to get a look at human migrations associated with the spread of farming from Anatolia to southeastern Europe and beyond.

"Southeastern Europe was the beachhead in the spread of farming from Anatolia into Europe," co-first author Songül Alpaslan-Roodenberg, an anthropology and genetics researcher at Harvard, said in a statement. "This study is the first to provide a rich genetic characterization of this process by showing how the indigenous population interacted with incoming Asian immigrants at this extraordinary moment in the past."

Members of that team again enriched targets with more than 1.2 million SNPs and sequenced them in remains from 225 individuals, between 2,500 and more than 14,000 years old, including 215  not profiled previously. The samples spanned more than 100 Paleolithic, Mesolithic, or eastern European Neolithic representatives, the authors explained, and the latter group encompassed individuals with a range of western hunter-gatherer and eastern hunter-gatherer ancestry.

Through comparisons with 274 more ancient samples, 777 genotyped individuals from current populations, and some 300 high-quality genomes from present-day populations, the researchers were able to start clustering the populations and teasing apart historical relationships between them.

As it turned out, the ancient interactions accompanying the introduction of agriculture were not homogeneous, they reported, but varied depending on the specific population and region considered in southeastern Europe.

"In some places, hunter-gatherers and incoming farmers seem to have mixed very quickly," co-first author Iain Mathieson, a genetics researcher at Harvard, said in a statement, "but mostly the two groups remained isolated, at least for the first few hundred years." 

The team noted that sex-mixed admixture was limited during the earlier interactions in Europe's southeast, but became more prominent in other parts of Europe, with admixture events in central Europe and Iberia during the Copper Age typically involving more male hunter-gatherers.