Migration, selection, and spatial differentiation determine the patterns of geographic variation in the gene frequencies of human populations. Inferences about past processes must be made from current patterns. The use of language differences as a variable concomitant to gene frequencies allows such inferences despite the complex relationship between language and genetics in populations. Seven methods that test varying aspects of this relationship show genetic differences among speakers of different language families in Europe, in addition to differences among the populations due to geographic differentiation. A model, based on the known history of each language-family boundary, was constructed to predict the likelihood of genetic differences at the boundaries. The model is in good agreement with the observed results. The genetic-linguistic patterns observed in Europe are consistent with the combined operation of spatial differentiation and aboriginal genetic differences among speakers of different langua...