Beyond the obstetric dilemma: evolutionary maternal-fetal conflict causes health problems in pregnancy and childbirth

Dakota E McCoy, Jennifer Kotler , Brianna Weir, Arvid Ågren

In excellent recent work, Webb and colleagues challenged the so-called “obstetric dilemma”—the long-standing hypothesis that human childbearing is particularly dangerous because we have a narrow pelvis but large infant heads (we are bipedal and smart). They showed that humans and chimpanzees have a comparable fetal-pelvic squeeze. What, then, causes risky childbirth in humans? Webb and colleagues describe a gradual series of physical obstetric compromises: e.g., our contorted birth canal allows bipedal movement but requires the fetus to rotate during birth. We propose an additional obstetric compromise between the evolutionary interests of mother and fetus, who experience genetic conflict over resource allocation. The fetus manipulates maternal vasculature to boost resources flowing to the placenta, benefiting itself but increasing the risk of maternal hypertension and hemorrhage. Following Haig, we suggest that maternal-fetal conflict harms human mothers more than other mammals because our cooperative infant care permits more damage to maternal health (when it grants some resource benefit to the fetus).