Cliff-edge model of obstetric selection in humans

Bibliographic Collection: 
Publication Type: Journal Article
Authors: Mitteroecker, Philipp; Huttegger, Simon M.; Fischer, Barbara; Pavlicev, Mihaela
Year of Publication: 2016
Journal: PNAS
Date Published: 2016/12/05
Publication Language: eng

Compared with other primates, human childbirth is difficult because the fetus is large relative to the maternal pelvic canal. It is a long-standing evolutionary puzzle why the pelvis has not evolved to be wider, thus reducing the risk of obstructed labor. We present a mathematical model that explains the high rates of fetopelvic disproportion by the discrepancy between a wide symmetric phenotype distribution and an asymmetric, “cliff-edged” fitness function. Only weak selection for a large newborn, a narrow pelvis, or both is necessary to account for the high incidence of fetopelvic disproportion. Because the regular use of Caesarean sections has reduced maternal mortality, the model predicts an evolutionary response of fetal or maternal dimensions, increasing the rates of fetopelvic disproportion.

DOI: 10.1073/pnas.1612410113
Short Title: Proceedings of the National Academy of Sciences