The genetic legacy of men who lived on the Iberian Peninsula 4500 years ago has largely diminished—all of their Y chromosomes, which are passed from men to men, were replaced as new farming cultures swept into the region and drove them out of the gene pool. That’s one of the striking conclusions of the largest analysis of ancient DNA from the Iberian Peninsula. The findings suggest that far from being an isolated cul-de-sac of Europe, Iberia experienced massive changes in ancestry, as waves of hunter-gatherers, farmers, Romans, and others mixed with the local population over the course of thousands of years.
The work—a deep dive into the genomes of about 300 people who lived in Iberia from 13,000 to 500 years ago—is “extraordinary in getting so much genetic data from so many individuals in time and space,” says evolutionary biologist Jaume Bertranpetit Busquets of Pompeu Fabra University in Barcelona, Spain. It “represents the most detailed and long-term genetic documentation of a single region, Iberia, from prehistory into early history,” adds archaeologist Kristian Kristiansen of the University of Gothenburg in Sweden. Neither was involved in the new research.
Iberia was first settled by modern humans some 44,000 years ago. But little is known about how those pioneers contributed to later populations—the oldest DNA comes from hunter-gatherers who date back to 19,000 years in northern Spain. These early hunter-gatherers came in two separate groups that settled in northern and southern Spain and had close ties to hunter-gatherers in Poland and Italy, respectively, according to ancient DNA from 11 hunter-gatherers and early farmers who lived in Iberia from 13,000 to 6000 years ago. Later, the DNA shows, they slowly mixed with incoming farmers from Anatolia, which is in present-day Turkey, researchers led by population geneticist Wolfgang Haak at the Max Planck Institute for the Science of Human History in Jena, Germany, report today in Current Biology.
Younger DNA, from two skeletons dating from between 3600 and 4500 years ago, reveals another element in the Iberian mixture. One was North African and the other had a grandparent with North African ancestry, according to a study today in Science by Iñigo Olalde, a postdoc in the lab of population geneticist David Reich at Harvard Medical School in Boston, and their colleagues.
Then, central Europeans who were descendants of herders from the grasslands of Eastern Europe and Russia, appeared in Iberia, starting in the early Bronze Age 4500 years ago. They probably introduced an early Indo-European language (the major family of more than 400 languages spoken in European and Asia today), according to Olalde. At first, the European farmers lived alongside the farmers already in Spain, based on ancient DNA from men buried at roughly the same time in the same places. But within a few hundred years, nearly all the Y chromosomes from Iberian farmers were gone—and replaced by the central Europeans farmers’ DNA.
This meant that somehow, the new migrants replaced 40% of genetic heritage of the Spanish and Portuguese. “It would be a mistake to jump to the conclusion that Iberian men were killed or forcibly displaced,” says Olalde, “as the archaeological record gives no clear evidence of a burst of violence in this period.” Perhaps the steppe migrants had far more children than the small population of local farmers, eventually swamping out their DNA, Reich says.
Still more immigrants came in historical times: first Romans and then Muslim North Africans. At one point 500 years ago, far more people of North African ancestry lived in Spain than today, before Christian kingdoms pushed the Muslim states south and eventually expelled them. But the DNA suggests the Muslim invaders and earlier migrants didn’t penetrate 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 retained their own non–Indo-European language even after the arrival and mixing with the Central European farmers.
“The Basque country is a really difficult place to conquer; there are quotes from French rulers in medieval times saying that this is a nasty place to get in an army,” says population geneticist Mattias Jakobsson of Uppsala University in Sweden, not part of either team. As a result, “The present-day Basques look like Iron Age people from Iberia,” says Olalde, himself a Basque.