Commentary on Sokal et al.'s “Historical Population Movements in Europe Influence Genetic Relationships in Modern Samples” (1996)

Abstract

The genetic history of Europe has been the focus of many studies looking at the relative influence of geography, language, and prehistoric and historic population movements on genetic differences between populations. Two groups of researchers have had a major impact on the evolution of these studies—Luca Cavalli-Sforza and colleagues (e.g., Cavalli-Sforza et al. 1994; Menozzi et al. 1978) and Robert Sokal and colleagues. The paper reprinted here is one of many of Sokal’s innovative approaches to population genetics, adroitly integrating anthropological data and hypotheses and genetic data in a rigorous and statistically precise manner. The focus of the paper is the use of ethnohistorical data to test the hypotheses of the influence of historical population movements over the past 4,000 years on the genetic structure of contemporary human populations across Europe. Sokal et al. used ethnohistorical data to construct a distance measure based on the likely relative ancestral contribution of different ethnic groups, which were defined in terms of language family membership. They found a significant correlation with genetic distance that was derived from a large sample of classical genetic markers. Further, they showed that this correlation remained even after controlling for geographic distance, thus showing that the expected relationship was not a byproduct of spatial autocorrelation. In addition, they found that the strength of the correlations increased over time, particularly during the past 400 years. This paper is an excellent example of the multidisciplinary approaches that Bob Sokal brought to investigations of genetic history. Ethnohistory is a key factor in the studies of anthropological genetics, because the origin of different groups and their contact with other populations, both near and far, affect genetic variation. Most often, the history of different populations is used to make indirect inferences regarding observed patterns of genetic similarity. For example, in my study of 19th-century Irish anthropometrics, the observed distinction of two island populations was explained by noting that their history pointed to a large influx of English soldiers (Relethford 1988). For many studies, historical hypotheses are treated in such an indirect fashion. What makes Sokal’s paper so innovative is that he and his colleagues quantified European ethnohistory through the compilation of a massive database on European-population movements (this