An international study, co-led by the Higher Council for Scientific Research (CSIC) and Harvard University (USA), has drawn up the first genetic map of the Iberian Peninsula covering the last 8,000 years. One of their conclusions is that between 4,000 and 4,500 years ago, an invasion of descendants of steppe shepherds from Eastern Europe replaced about 40% of the population and almost 100% of the men of the Peninsula.
Since the beginning of human migration, the Iberian Peninsula, home to present-day Spain and Portugal, has been a place where the cultures of Africa, Europe and the Mediterranean have mixed.
Now, in the study published in the journal Science , a group of 111 population geneticists and archaeologists recorded 8,000 years of genetics in the region. The resulting map shows great genetic complexity, but alludes to a unique and mysterious migration some 4,500 years ago that completely shook the DNA of the ancient Iberians.
The team searched DNA evidence for clues as to how and when various populations became part of the genetic heritage of the Iberian Peninsula. They sequenced the genomes of 271 ancient Iberians and then combined that information with previously published data on 132 other inhabitants of the ancient peninsula.
The men of the steppes
Starting in the Bronze Age, the genetic makeup of the area changed dramatically. Beginning around 2,500 BC, much of the population’s DNA was replaced by that of the people of the steppe. The “Steppe Hypothesis” holds that this group spread eastward into Asia and westward into Europe around the same time, and the current study shows that they also reached the Iberian Peninsula. Although 60% of the total DNA in the region remained the same, the Y chromosomes of the inhabitants were almost completely replaced in 2,000 BC. C. This suggests a massive influx of men from the steppes, because the chromosomes are carried only by men.
Who were these men?
The current inhabitants of the Basque Country, who speak the only non-Indo-European language in Western Europe, have genetic markers closely related to those of the men of the steppe. And unlike modern Spaniards, Basques today do not display the same amount of genetic mixing that took place on the peninsula over the centuries.
Did they come in peace?
The study presents a complex picture of the genetic history of Spain and, as we have seen, the DNA of the local male lineages disappeared and was replaced by a foreign lineage called R1b (which is still the majority lineage in the Iberian Peninsula). However, it is not known how it happened or what processes generated this genetic pattern.
“The genetic results are compatible with several explanations and more research in archeology and anthropology will be needed to understand the social processes that may have resulted in the loss of local paternal lineages. The most simplistic hypothesis is that these foreign men violently eliminated the locals and reproduced with the women. The problem with this hypothesis is that it does not fit with the archaeological record, since there is no evidence of generalized violence during that period ”, explains Íñigo Olalde, co-author of the work.
“ We still don’t know how it happened and our results encourage other disciplines to continue investigating in this fascinating period ”, Olalde remarks.
Reference: Iñigo Olalde et al. The genomic history of the Iberian Peninsula over the past 8000 years. Science. DOI: 0.1126 / science.aav1444
Image credit: LUIS BENÍTEZ DE LUGO / J. LUIS FUENTES
