The genetic heritage of men who lived on the Iberian Peninsula 4,500 years ago has largely diminished – all of their Y chromosomes, those of men were transferred to men, were replaced when new agricultural crops were swept into the region and expelled them from the gene pool. This is one of the impressive conclusions of the largest analysis of the ancient DNA of the Iberian Peninsula. The findings indicate that Iberia, far from being an isolated impasse in Europe, has undergone massive changes in lineage. Hunters, collectors, farmers, Romans and others mingled with the local population over the millennia.
The work – a deep immersion in the genomes of about 300 people who lived in Iberia 13,000 to 500 years ago – is "extraordinary because it gets so much genetic data from so many people in time and space," he says Evolutionary biologist Jaume Bertranpetit Busquets of the University Pompeu Fabra in Barcelona, Spain. It "represents the most detailed and long-term genetic documentation of a single region, Iberia, from prehistory to early history," adds archaeologist Kristian Kristiansen of the University of Gothenburg in Sweden. None of them was involved in the new research.
Iberia was first populated by modern humans 44,000 years ago. However, little is known about how these pioneers contributed to later populations – the oldest DNA comes from hunters and gatherers from 19,000 years in northern Spain. These early hunters and gatherers came in two separate groups, which settled in northern and southern Spain, and had close ties with hunters and gatherers in Poland and Italy. This is evident from the ancient DNA of 11 hunters and early peasants who lived in Iberia from 13,000 6000 years ago. Later, the DNA, they slowly mingled with the incoming farmers from Anatolia, now Turkey. Researchers of population genetics Wolfgang Haak at the Max Planck Institute for the Study of History in Jena report today in Current Biology .
The younger DNA from two skeletons dating from 3600 to 4500 years ago reveals another element in the Iberian mix. One was North African and the other had a grandparent with North African ancestors, according to a recent study in Science by Iñigo Olalde, a postdoctoral fellow in the laboratory of population geneticist David Reich at Harvard Medical School in Boston.
Then Central Europeans emerged in Iberia, descendants of shepherds from the meadows of Eastern Europe and Russia, 4500 years ago in the early Bronze Age. They probably introduced an early Indo-European language (the main family of today more than 400 languages spoken in Europe and Asia), according to Olalde. First, European farmers already lived in Spain alongside farmers, based on ancient DNA of men who were buried in the same places at about the same time. But within a few hundred years, almost all Y chromosomes had disappeared from Iberian peasants – and been replaced by the DNA of the Central European peasants.
This meant that the new migrants somehow replaced 40% of the Spanish and Portuguese hereditary heritage. "It would be a mistake to conclude that Iberian men were killed or expelled," says Olalde. "Since the archaeological reports provide no clear evidence of an outbreak of violence at this time." Perhaps the steppe migrants had said much more empire, children were less children than the small population of local farmers, who eventually flooded their DNA.
More immigrants came in the past: first Romans and then Muslim North Africans. At one point 500 years ago, Spain had far more people of North African descent than today before Christian kingdoms pushed the Muslim states south and eventually expelled them. However, the DNA suggests that Muslim invaders and former migrants are not entering the remote Basque country in the far north. The Basque people, whose origins have long been a mystery, are one of the few groups in Europe that has retained its own non-Indo-European language even after arriving and mingling with the Central European farmers.
"The Basque Country is a really difficult place to conquer; There are quotes from medieval French rulers saying that this is an awkward place for an army, "says population geneticist Mattias Jakobsson of Uppsala University in Sweden, who is not a member of either team. "Today's Basques look like Iberian Iron Age people," says Olalde, even Basque.