Demographic Events and Evolutionary Forces Shaping European Genetic Diversity

Europeans have been the focus of some of the largest studies of genetic diversity in any species to date. Recent genome-wide data have reinforced the hypothesis that present-day European genetic diversity is strongly correlated with geography. The remaining challenge now is to understand more precisely how patterns of diversity in Europe reflect ancient demographic events such as postglacial expansions or the spread of farming. It is likely that recent advances in paleogenetics will give us some of these answers. There has also been progress in identifying specific segments of European genomes that reflect adaptations to selective pressures from the physical environment, disease, and dietary shifts. A growing understanding of how modern European genetic diversity has been shaped by demographic and evolutionary forces is not only of basic historical and anthropological interest but also aids genetic studies of disease.During classical antiquity, writers such as Herodotus chronicled the expansion and contraction of empires, as well as the traditions of the peoples associated with them. Julius Caesar''s memoirs from the Roman conquests of Gaul detail his encounters with foreign tribes such as the Helvetii and the Belgae. Such accounts were fascinating to peoples of that era as humans lived largely in ignorance of other cultures beyond their relatively small geographical vicinity. In the modern world, the barriers to acquiring knowledge of other contemporary societies are small; we can now easily learn about populations from across the world through an abundance of sources. Instead, the major challenge is to discern whom the peoples of the past were. From the perspective of genetics, we are especially curious about how past demographic and evolutionary events influenced the genetic diversity in humans today. However, peering into the past poses major challenges, and, in some ways, we stand much like Herodotus and Caesar, trying to piece together an understanding of distant populations from limited contact and partial experiences.For geneticists, Europe represents a uniquely well-studied region of the world. On the one hand, it has a richness of accessible sources. We have already mentioned historical accounts beginning with the ancient works of Herodotus; there has also been an abundance of archaeological, anthropological, and linguistic studies. More recently there has been substantial interest in understanding the genetic history of modern Europeans. Indeed, many of the largest studies of the genetics of human populations have taken place in Europe. This is, in large part, because of the availability of European universities and biomedical centers, which have provided the infrastructure for such “big science” studies that other regions have traditionally lacked. On the other hand, European human diversity has at various times been highly politicized, which has led to deeply misguided perspectives on the subject of genetic superiority and some of the most atrocious abuses to human life—the genocides and eugenics of the first half of the 20th century.Contemporary genetic studies in Europe still work under the shadow of such views that are now understood as being scientifically without merit as well as ethically wrong, and, as today''s scientists, we must be sensitive to the potential future misuse of findings regarding genetic diversity. That said, the field has been reinvigorated during the past approximately 50 years as perspectives on human diversity, both cultural and genetic, have matured. Scientifically, it is now appreciated that the genetic differences among humans are, in absolute terms, small as first identified by Lewontin (1972) (also see Chakravati 2014). Simplistic notions of genetic determinism have also fallen aside as most human traits are now thought to be driven by complex interactions between multiple environmental and genetic factors. Culturally, there is a wider appreciation that diversity makes a positive contribution to society. And finally, it is now recognized that understanding background patterns of genetic diversity is an essential component for combating heritable and infectious diseases.Thanks to the growing interest in human population genetics, the scale of recent studies of European genetic diversity has grown to a staggering extent. Studies involving Europeans are some of the largest to have been performed in any population, regardless of the species. As a result, research on genetic diversity in Europe is of interest not just to scientists examining other human populations around the world but to all students of genetic diversity.