An ontogenetic approach to facial variation in three Native American populations.

Various explanations have been formulated regarding high levels of craniofacial variation among Native American populations but the contribution of developmental processes to the establishment of these patterns of variation remains unknown. In this study, we compare facial morphology in ontogenetic series of three Native South American populations, one hunter-gatherer group and two farmer groups, in order to test the null hypothesis that indicates that the pattern of facial differentiation between populations does not change during ontogeny. If diet-related factors contribute to outline facial morphology, it is likely to find greater differences between hunter-gatherer and both farmer groups than between two groups of farmers and this differentiation is expected to increase with age, especially in those structures that are influenced by the mechanical load of mastication. According to our results, hunter-gatherers clearly differ from the two groups of farmers. Non-heritable factors linked to diet, such as nutritional content of food, may increase differentiation across ontogeny in some cases. However, as hunter-gatherers were clearly separated from farmer populations during entire postnatal ontogeny, an important proportion of size variation may not necessarily reflect eco-sensitive changes. Consequently, the hypothesis cannot be completely rejected.