The genetic inheritance of men living on the Iberian Peninsula 4500 years ago has been greatly reduced – all of their Y chromosomes, which are transmitted from men to men, were replaced as new agricultural cultures swept into the region and drove them out of the gene pool. It is one of the striking conclusions from the greatest analysis of ancient DNA from the Iberian Peninsula. The results suggest that Iberia, far from being an isolated Europe, experienced massive ancestral changes, as waves of hunter-gatherers, peasants, Romans and others mingled with the locals for thousands of years.
The work – a deep dive in the genomes of about 300 people who lived in Iberia from 13,000 to 500 years ago – is "extraordinary to get as 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 to early history," adds archaeologist Kristian Kristiansen from the University of Gothenburg in Sweden. Neither was involved in the new research.
Iberia was first determined by modern people 44,000 years ago. But little is known about how these pioneers contributed to later populations – the oldest DNA comes from hunter-gatherers dating back to 19,000 years in northern Spain. These early hunter-gatherers came in two separate groups who settled in northern and southern Spain and had close ties to hunter-gatherers in Poland and Italy, respectively, according to old DNA from 11 hunter-gatherers and early peasants living in Iberia from 13,000 to 6,000. years ago. Later, the DNA, which is slowly mixed with incoming farmers from Anatolia, which is today in Turkey, reported researchers led by population geneticist Wolfgang Haak of the Max Planck Institute for Human History Science in Jena, Germany, report today in Present biology .
Younger DNA, from two skeletons from between 3,600 and 4,500 years ago, reveals another element of the Iberian mix. One was North Africa 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 Genetics David Reich at Harvard Medical School in Boston and their colleagues.
Thereafter, central Europeans who were descendants of shepherds from grasslands in Eastern Europe and Russia appeared in Iberia, who began at the beginning of the Bronze Age 4500 years ago. They probably introduced an early indo-European language (the large family in more than 400 languages spoken in Europe and Asia today), according to Olalde. First, the European peasants, together with the peasants, already lived in Spain, based on old DNA from men buried about the same in the same places. But within a few hundred years, almost all Y chromosomes from the Iberian peasants were gone and replaced by the Central European agricultural DNA.
This meant that the new migrants somehow replaced 40% of the Spanish and Portuguese genetic heritage. "It would be a mistake to jump to the conclusion that the Iberian men were killed or forced to be displaced," says Olalde, "because the archaeological record does not provide any clear evidence of violent crime during this period." Perhaps the steppe migrants had far more children than the small population of local farmers, eventually their DNA sponges, Reich says.
Additional immigrants came in historic times: first Romans and then Muslim North Africans. At one time 500 years ago, far more people lived in North African ancestry in Spain than today, before the Christian Kingdom drove the Muslim states south and eventually expelled them. But DNA suggests the Muslim invaders and former immigrants did not penetrate the far-off Basque country into northern northern; 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 their arrival and blend with the central European peasants.
"The Basque Country is a very difficult place to conquer; there are quotes from French rulers in medieval times saying that this is a nasty place to come in an army," says population geneticist Mattias Jakobsson at Uppsala University in Sweden, not a part As a result, "The current Basques look like Iron Age people from Iberia," says Olalde, himself a Basque.