Outreach: Fresh insights on the Obstetrical Dilemma

A recent paper in Science by Vagheesh Narasimhan and his team from the University of Texas sheds new light on the 'Obstetrical Dilemma' – the long-debated conflict regarding the optimal pelvic structure for bipedalism and successful childbirth in humans. Christina Berndt of Süddeutsche Zeitung covers this new finding, along with perspectives and insights from international researchers in the field, including Barbara Fischer and Philipp Mitteroecker of the KLI.

Childbirth in humans is exceptionally risky compared to most other primates. As human infants evolved to have larger brains than previous hominins, the large head size of the human infant almost matches the size of the mother’s narrow birth canal. A narrow pelvis shape has also long been proposed to be related to the evolution of bipedalism or upright walking in humans. This conflict regarding the optimal pelvis shape and size, known as the 'Obstetrical Dilemma,' was initially proposed in the 1960s. In their recently published article, Vagheesh Narasimhan and his team added a big data perspective to the existing work on the obstetrical dilemma and identified relevant underlying genes by conducting a genome-wide association study. They used a deep learning model to extract a set of seven pelvic distances from radiological scans of more than 30,000 individuals in the UK Biobank. Using these measurements, they confirm that rather than just the efficiency of locomotion, the reduced width of the birth canal is, in fact, significantly related to pelvic floor health in our transition to bipedalism. The study also found no evidence of a connection between pelvic proportions and the length of pregnancy. This indicates that human infants are not born prematurely, as was previously believed.

In the article titled "Unter Mühen sollst du Kinder gebären" (Translation: "With pain you shall bear children"), dated 2^nd May 2025, both Philipp and Barbara, express their agreement with the findings of the Science paper, and provide deeper insights into how the new findings contribute to the current understandings of the evolution of pelvic structure in modern humans, especially in relation to childbirth and bipedalism. Philipp affirms that locomotion alone is not enough to explain the complexities involved in the evolution of pelvis shape and structure; the slight biomechanical disadvantage of a wide pelvis could be compensated by adjusting one’s gait. Barbara agrees with the Science article’s finding which rejects the theory that human babies are borne preterm. The findings of the new study also strongly support Barbara’s own research, which has long postulated an evolutionary trade-off between pelvic floor health and birth canal size as well as an evolved link between head size and pelvis form that evolved to ease human birth. Barbara points out that the pelvis and pelvic floor have to fulfil multiple contradictory functions such as keeping internal organs in place, carrying and giving birth to children; the obstetrical dilemma is, therefore, unlikely to be solved by anatomical evolution. Nevertheless, Philipp hopes that knowing these real evolutionary obstacles will, at least, console mothers who feel guilty about being unable to give birth naturally.

References:

Christina Berndt (2025) Süddeutsche Zeitung, 02 May.

Xu, L., Kun, E., Pandey, D., Wang, J. Y., Brasil, M. F., Singh, T., & Narasimhan, V. M. (2025). The genetic architecture of and evolutionary constraints on the human pelvic form. Science, 388(6743), eadq1521.