There are two models concerning the peopling of Europe: multiregional evolution and Out of Africa. According to the multiregional hypothesis, the inhabitants of Europe migrated out of Africa around 2 mya (generally associated with the appearance of Homo erectus), and evolved in situ through Neandertals to modern humans. The Out of Africa hypothesis states that there were multiple migrations from Africa, the most recent of which resulted in the spread of anatomically modern humans into Europe and Asia, and the complete replacement of the more archaic hominins in the rest of the Old World.
Analysis of 5000 hominin teeth suggests that a third possibility exists, migration into Europe from Asia. Teeth are considered to have a strong genetic component (as opposed to environmental component), which is important in elucidating evolutionary relationships between species. A shared environment, or a strong environmental component for a given trait, could confound or obscure the true genetic relationship. Imagine constructing a cladogram of modern human groups based on body mass index (the ratio of weight/height2). While we know there is a genetic component in human weight and height, both traits are significantly influenced by environmental factors, including diet, exercise, and disease.
Teeth are also one of the most frequently preserved parts of the skeleton, and so provide a unique opportunity for comparing different fossil species. Martinón-Torres et al. examined 51 dental traits in 12 hominin species. Distinctions in dental morphology between Eurasian and African specimens suggests a long period of relative isolation.
