Genetic evidence for prehistoric demographic changes in Europe

Objectives: Two main models have been proposed to explain the origins of the patterns of genetic variation in Europe, one emphasizing Paleolithic and the other Neolithic immigration from the Southeast. In this paper, I summarize how the models developed and how they can help address some open questions. Methods: The rationale of the methods traditionally supporting the Neolithic and the Paleolithic models is discussed, and the evidence supporting either of them is reviewed. Results: Ancient DNA evidence proves for good that the studies traditionally supporting the Paleolithic model had serious methodological flaws. This does not imply that the alternative model is right, but rather calls for further analyses explicitly testing the two models against the genomic information now available. Conclusions: Questions that need to be addressed include whether the two main models differ enough to be discriminated by analyses of modern DNA diversity, and to what extent inferences from ancient mitochondrial DNA can be trusted in the absence of sufficient datasets of ancient nuclear DNA. The time seems ripe for the construction of a more complex (and hence more realistic) model, incorporating the possibility of different processes affecting different geographic locations at different times