DNA reveals that local men were replaced in Iberian gene pool thousands of years ago

Ancient DNA is uncovering the secrets of the unique populations of what are now Portugal and Spain. Two studies published this week include unexpected findings from the DNA of people who lived thousands of years ago on the Iberian Peninsula.

The rugged peninsula is positioned between North Africa, Europe and the Mediterranean on the westernmost edge of the continent, so the DNA of its ancient population shows how it was affected by migration over time.

Iberia was also relatively warm during the last Ice Age, between 18,000 and 24,000 years ago, presenting a more welcoming climate for animals and people who retreated from the rest of Europe.

A study published Thursday in the journal Current Biology analyzed the Iberian hunter-gatherer population between 6,000 and 13,000 years ago, and one published in the journal Science conducted an overview of the Iberian population over the past 8,000 years. The findings support some ideas about the area’s history while challenging others.

The researchers were surprised to discover that local men living on the Iberian Peninsula during the Bronze Age were replaced in the gene pool, their Y chromosomes supplanted by those of men who migrated to the area.

“This is one of the strongest pieces of evidence in ancient-DNA research of sex bias in the prehistoric period,” said Iñigo Olalde, study author and postdoctoral fellow at Harvard Medical School, in a statement.

Beginning in 2500 BC, the researchers discovered, Iberians were joined by people from central Europe whose showed genetic ancestry from the Russian steppe. And over a few hundred years, the locals and the central Europeans interbred.

Before this, there is no evidence that locals came into contact with anyone from outside the area. But that changed after 2000 BC, when 40% of Iberian ancestry and 100% of the fathers in the study could be traced back to central Europe.

The difference was obvious in the DNA. The remains of a man and a woman buried together at a Spanish Bronze Age site called Castillejo de Bonete showed that the woman was a local and the man’s most recent ancestors had come from central Europe.

“The results were astonishing,” Carles Lalueza-Fox, co-senior study author and principal investigator of the Paleogenomics Lab at the Institute of Evolutionary Biology, said in a statement. “The data suggest there was a major genetic change that is not obvious from the archaeological record.”

However, Olalde noted, “It would be a mistake to jump to the conclusion that Iberian men were killed or forcibly displaced as the archaeological record gives no clear evidence of a burst of violence in this period.”

The genomes of 403 ancient Iberians who lived between 6000 BC and AD 1600, 975 ancient people from other areas and 2,900 current people were analyzed. Modern-day Iberian men can still trace their paternal ancestry to these central Europeans.

But the genetic data will need a boost from what anthropology and archaeology can show about the underlying causes for why this Y chromosome shift happened, the researchers said.

The researchers also discovered that between 8000 BC and 5500 BC, Iberia’s hunter-gatherers were genetically different from each other. This suggests that they interacted with a different group of hunter-gatherers during the Mesolithic era before Anatolian farmers, or those from what is presently Turkey, moved to Iberia and transformed the area yet again. The farmers also mixed with hunter-gatherers, according to their DNA.

They uncovered another surprise. The DNA of one person they studied, buried in Iberia between 2400 and 2000 BC, had North African ancestry. Another who lived between 2000 and 1600 BC showed North African ancestry from a grandparent.

At the time, trade existed between Iberia and North Africa, but now the researchers know that people moved between Africa and Europe as well. The gene flow from North Africa and the eastern Mediterranean is apparent in the DNA when Greek and Roman settlements appeared in Iberia. Those multiethnic settlements transformed Iberia and its population even more.

The research also sheds light on why the language and culture of present-day Basques are so distinct from those of Iberians. The modern people of Basque Country, in northern Spain, are genetically similar to the Iberian Iron Age people with ancestry from the Russian steppe. While people around them mixed with different groups and changed, the Basques held on to their heritage.

“Beyond the insights this study provides about the history of Iberia itself, it highlights the potential of future studies that focus on ancestry changes over time using large sample sizes in relatively small regions of the world,” said David Reich, co-senior study author and professor of genetics at the HMS Blavatnik Institute, in a statement.

The researchers wanted to be able to connect their findings to our time, rather than letting things “end in midair.” Their findings address the historical era when written records were created.

“When I was a child, I used to read old history books on Iberia that were at home,” Lalueza-Fox said. “They essentially started with the Iron Age Iberians (Íberos), then the Punics, the Greeks, the Roman conquest, the Barbarian invasions, the Muslim invasion, the reconquest and so on. I always wondered who these people really were, what mark they left in modern people and what all these movements meant in terms of numbers. Now, for the first time, we are able to study the remains of such people genetically and to integrate the genetics not only with archaeology and anthropology but also with historical accounts.”


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