The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

The relationship between cephalopelvic proportions and sexual dimorphism in the birth canal and non-obstetric pelvis in anthropoids


Pathology and Anatomical Sciences, University of Missouri

March 27, 2015 10:15, Grand Ballroom A/B Add to calendar

The extent to which obstetric selection has shaped the primate pelvis is poorly characterized. As important as birth is hypothesized to be in shaping pelvic morphology, we actually know relatively little about how birth affects the anthropoid pelvis, especially outside the birth canal. This study tests the hypothesis that large cephalopelvic proportions are related to dimorphism in the obstetric and non-obstetric pelvis. Landmark data for 118 anthropoid specimens were analyzed [Large cephalopelvic proportions: Ateles geoffroyi (n=4), Homo sapiens (n=13), Hylobates lar (n=17), Macaca fasicularis (n=10), Nasalis larvatus (n=13), Papio cynocephalus (n=10), Saimiri sciureus (n=14); Small cephalopelvic proportions: Alouatta palliata (n=5), Gorilla gorilla (n=13), Pan troglodytes (n=11), Pongo pygmaeus (n=8)].

Birth canal dimensions were significantly larger in females than males (p<0.05) within those species having large cephalopelvic proportions, but not in species with small proportions. Birth canal shape, quantified using principal components analysis of landmark data, was also dimorphic in species with large cephalopelvic proportions (all p-values <0.05), but not for species with small cephalopelvic proportions. Patterns of obstetrically-related dimorphism, quantified using Euclidean distance matrix analysis, were shared among phylogenetic groups (New World monkeys, Old World monkeys, and apes). Finally, using similar methods, dimorphism in the non-obstetric pelvis did not correspond predictably to either the presence of birth canal dimorphism or large cephalopelvic proportions. These results suggest that large cephalopelvic proportions influence dimorphism in birth canal size and shape, but not dimorphism outside the birth canal, and that patterns of dimorphsim are shared within phylogenetic groups.

Research supported by NSF BCS 0716244.