Postnatal Ontogeny of Tibia and Femur Form in Two Human Populations: A Multivariate Morphometric Analysis

Objectives: Adult population differences in relative and absolute limb size often are explained as adaptations to different climates. Less is known about other aspects of limb bone form and their population-specific growth patterns. Methods: We study postnatal ontogenetic development of tibial and femoral form by a multivariate morphometric approach in a cross-sectional sample of South African (N = 97) and European (N = 81) modern humans from 0 to 20 years of age. Because the epiphyses ossify and fuse to the diaphysis in this time period, we separately analyze two sets of variables. Average ontogenetic trajectories are computed to compare the growth patterns of the African and the European groups. Results: For both the tibia and the femur, we could show that Africans and Europeans have a very similar average length and average shape until about 10 years of age. During adolescence Africans have a higher growth rate leading to longer adult bones with narrower epiphyses relative to the diaphysis. Despite substantial individual overlap, the average crural index is higher in Africans than in Europeans, from birth on through adulthood. Conclusions: The prenatal origin of population differences in the crural index indicates a genetic determination of these differences whereas limb length and relative epiphyseal width likely are both genetically and environmentally determined