The multifactor pelvis: An alternative to the adaptationist approach of the obstetrical dilemma

Abstract

The obstetrical dilemma describes the competing demands that a bipedally adapted pelvis and a large‐brained neonate place on human childbirth and is the predominant model within which hypotheses about the evolution of the pelvis are framed. I argue the obstetrical dilemma follows the adaptationist program outlined by Gould and Lewontin in 1979 and should be replaced with a new model, the multifactor pelvis. This change will allow thorough consideration of nonadaptive explanations for the evolution of the human pelvis and avoid negative social impacts from considering human childbirth inherently dangerous. First, the atomization of the pelvis into discrete traits is discussed, after which current evidence for both adaptive and nonadaptive hypotheses is evaluated, including childbirth, locomotion, shared genetics with other traits under selection, evolutionary history, genetic drift, and environmental and epigenetic influences on the pelvis.

Prevalence of sacroiliac joint fusion in females and males depending on parity status

“…However, it is important to note that the current literature around the OD suggests a much more complex model of human pelvic evolution than simply the conflict between bipedalism and birth. Many different factors, such as epigenetics and nutrition, impact an individual's pelvic dimensions (Warrener, 2023). Sociocultural factors such as advancements in midwifery and obstetrical care can also impact difficulty in labor (Grunstra et al, 2023).…”