Secular changes in craniofacial dimensions of indigenous children in Southern Mexico

Abstract

Studies of adult European immigrants by Franz Boas early in the twentieth century indicated secular change in craniofacial dimensions, suggesting plasticity of the craniofacial skeleton. Subsequent analyses of the original Boas data and data for other populations have shown variation in the pattern of change in craniofacial dimensions and indices over time. Cranial length tends to increase while width tends to decrease, resulting in brachycephalization (increase in the cranial or cephalic index). A generalized trend toward brachycephalization and upper and lower facial narrowing has been noted across adult populations that were also experiencing a secular increase in height. Cranial height has also increased, resulting in a taller, narrower skull and cranial vault. Secular trends in craniofacial dimensions in a rural indigenous community in the Valley of Oaxaca in southern Mexico have followed the general population trends. Facial changes probably reflected environmental change associated with diet (softer, processed foods) while cranial vault changes were more likely associated with genetic variation. Although growth of the cranial vault is largely established prenatally, craniofacial remodeling extends throughout the growth period with major changes occurring in conjunction with rapid growth of neural tissues between birth and 5 years. Secular changes observed in indigenous children of school age (6-14 years) were extrapolated to young adulthood using a longitudinal component in the data set. Review of the limited literature suggests that environmental and genetic influences on craniofacial dimensions established early during growth are reflected in corresponding dimensions in young adulthood.