Anthropology: from a Sapienza study new insights into human diversity
Unlike what we might think, geographically and culturally isolated human populations are mines of genetic diversity. This is the conclusion of a study by an international research group coordinated by the Sapienza University of Rome, recently published in the prestigious journal Science Reports.
The research, which received a contribution from the National Geographic Society and funding from the European Research Council (ERC), involved Italy’s Alma Mater University of Bologna, University of Pisa, University of Sassari, University of Cagliari and the National Research Council.
The researchers’ conclusion challenge the generalized view: that human populations subject to geographical or cultural barriers that limit interaction with other human groups are confined to extreme environments, “impervious” to diversity. On the contrary, by comparing the genomic structure of European populations, the corresponding authors of the study published in Science Reports – Paolo Anagnostou and Giovanni Destro Bisol – observed in the isolated groups a variation up to sixteen times that found for “open” groups, such as Spanish, Russians or Greeks.
“Take the three German-speaking islands of Sappada, Sauris and Timau, which originated from nuclei that populated the adjacent areas of the Eastern Italian Alps in the Middle Ages”, said Giovanni Destro Bisol, explaining: “The genomic differences between these three communities were truly remarkable and absolutely similar to those observed by comparing groups that are historically and geographically very distant, such as the Basques in southern France and the inhabitants of the Orkney Islands, off the coast of Scotland”. The data can be explained with the levels of genetic drift – the random change in the frequency of a gene variant in a population – and inbreeding in these populations.
Unlike other Alpine groups, in the marriage patterns in Sappada, Sauris and Timau the bond of individuals with their communities of origin seems to have prevailed over that related to their common Germanic origin. This is not the case for the Cimbrians, another group of Germanic origin, settled on the Plateau of Asiago, in Veneto, between the 10th and 12th centuries, and the inhabitants of Carloforte on Saint Peter's Island, off the southern coast of Sardinia. The Cimbrians underwent a partial cultural assimilation that made them more “porous” to the linguistic and genetic influences of the local populations, whereas the isolation of Carloforte was mitigated over time by intermittent contacts with external populations during their wanderings from the area of Pegli, in Liguria, to the island of Tabarka, in Tunisia, and then to the southern edges of Sulcis. This would explain the weakening, in these two groups, of the typical signals of isolation in their genome, whose structure appeared to be more similar to that of open groups, such as the French and the north-western Italians, and to that of other isolated communities.
The results obtained, therefore, overcame the dichotomy between “open” and “isolated” populations in favour of a complex picture where DNA diversity tells different stories that only a synthesis between biological and cultural explanation can help recreate.