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Ancient DNA Details Bronze Age Population Shifts in Southern Iberia

NEW YORK – A team led by researchers from the Max Planck Institute for the Science of Human History and Autonomous University of Barcelona has identified significant genetic changes in Southern Iberia during the transition from the Late Copper Age to Early Bronze Age — a period known for dramatic archeological changes, including a shift from large enclosed "megasite" settlements to hilltop communities linked to groups such as the El Argar culture with distinct burial rituals, ornaments, pottery, and weapons.

As they reported in Science Advances on Wednesday, the researchers aimed to understand the population dynamics behind this Iberian Copper Age collapse, the rise and development of the El Argar culture, and the relationships between these processes and population patterns in other parts of western Europe, the Balearic Islands, and beyond before and during the Bronze Age.

After using shotgun sequencing to screen for usable DNA in more than 200 ancient individuals, the researchers relied on hybridization capture sequencing to target around 1.24 million ancestry-informative SNPs across the genome in 136 ancient individuals from Southern Iberia going back some 3,500 to 5,000 years, including 96 Bronze Age El Argar individuals, 34 Copper Age representatives, and six individuals from the Late Bronze Age. They also did further low-coverage genome sequencing on five of the ancient individuals.

Together with sequence data from more than 100 ancient representatives reported in past studies, the new data made it possible to pick apart population patterns during the transitional period that brought Bronze Age changes to the peninsula. In particular, the team's analyses highlighted pulses of European steppe ancestry into the region not long before the Bronze Age.

Although absent in the Copper Age, this steppe ancestry was found across the population by the time the El Argar culture formed, the researchers reported. The arrival of steppe-related ancestry appeared to be spread out over time, they explained, and eventually corresponded to widespread steppe-related ancestry and "a complete turnover of Y-chromosome lineages."

"[W]e can now conclude that the population movement starting in the eastern European steppe zones around 3000 BCE was not a single migratory event, but required over four centuries to reach the Iberian Peninsula and another 200 years to appear in present-day Murcia and Alicante," co-senior and co-corresponding author Roberto Risch, a researcher affiliated with the Max Planck and the Autonomous University of Barcelona, said in a statement.

"Whether the genetic shift was brought about by migrating groups from North and Central Iberia or by climatic deteriorations that affected the eastern Mediterranean around 2200 BCE is the million-dollar question," Risch added, cautioning that "[i]t would be foolish to think that it can all be explained by a simple, one-factor model."

Along with ancestry from Copper Age groups that were present in the southern part of the peninsula and Mediterranean populations they interacted with, the team's kinship analyses suggested the El Argar site was marked by the presence of females with lower levels of relatedness to other individuals compared to relative-rich male representatives at the same sites, pointing to a patrilineal population structure.

"Overall, we propose that El Argar has likely formed from a mixture of new groups arriving from north-central Iberia, which already carried central European steppe-related ancestry (and the predominant Y-chromosome lineage) and local southeastern Iberian [Copper Age] groups that differed from other regions in Iberia," the authors wrote.