Ilium morphological variation during growth in forager populations

Human pelvic morphology has often been described in terms of an evolutionary compromise between bipedalism, encephalization, and obstetrics; however, recent research has argued that the pelvis is more biologically plastic than previously thought. Variation in pelvic form exists among adult modern human populations, but the factors influencing this variation, and when it manifests during growth, remain to be understood. The aim of this study is to investigate patterns of growth and development of the ilium and to consider factors that may influence variation. The presence of variation in lower limb strength emerging during growth between populations with differing foraging strategies prompted an investigation into whether the same variation extends to the pelvis. Ilium morphology was examined using a geometric morphometrics approach in an ontogenetic sample of bony ilia from four forager populations, two of whom pursued terrestrial foraging strategies (Later Stone Age southern Africa, Indian Knoll) and two of whom pursued marine foraging strategies (Point Hope, Sadlermiut) (n = 161). Principal component analysis shows population-based patterning in ilium morphology from birth which may reflect a combination of climatic adaptation, body shape differences, and neutral evolutionary processes. Ontogenetic allometry also appears to be a driver of morphological variation in the ilium during growth. These results have implications for the study of ilium shape differences among fossil hominin ilia and demonstrate that global patterning in ilium morphology is present even in the youngest members of a population.