Form and Function: An Ontogenetic Study of Adaptive Responses in Human Pelvic Morphology




MacKinnon, Marla

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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 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 pelvis, and to consider how ecological factors, including activity, may affect this growth. Pelvic morphology was examined using a geometric morphometrics approach in an ontogenetic sample of pelvic bones 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) (juvenile n=169; adult n=88). Principal components analysis shows population-based patterning in ilium morphology from birth, but a similar pattern is not apparent in the ischium. This may imply a greater degree of adaptive response in the ilium to environmental stimuli or may reflect body shape differences. Age-related changes appear to be the most prominent source of variation in ischium morphology. Cross-sectional geometric (CSG) measures of long bones (humerus, femur, and tibia), representing habitual activity patterns, were used to examine the impact of loading on pelvic morphology. No relationship was found between pelvic shape and CSG measures, suggesting that pelvic morphology is not influenced by habitual behaviours. As has been hypothesized for epiphyseal morphology, it may be that the functional significance of the pelvis has led to a form that is more canalized and less plastic than the cross-sectional parameters of long bones. Instead, it seems that group differences, which may be driven by climate-related directional selection or neutral evolutionary processes (or, most likely, a combination thereof), as well as ontogenetic allometry, are the strongest drivers of morphological variation in the ilium and the ischium during growth.



Bioarchaeology, Ontogeny, Pelvis, Evolution, Adaptation