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.

…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

…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 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.

…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.

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

hmmm

Men who lived on the Iberian Peninsula 4500 years ago …were replaced as new farming cultures swept into the region and drove them out of the gene pool. …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.

…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. …At first, the European farmers lived alongside the farmers already in Spain. ….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. …”The archaeological record gives no clear evidence of a burst of violence in this period.” 

…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.

Men who lived in Spain 4500 years ago left almost no male genetic legacy today | Science | AAAS

hmmm