There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form.

Compared to other primates, modern humans face high rates of maternal and neonatal morbidity and mortality during childbirth. Since the early 20th century, this "difficulty" of human parturition has prompted numerous evolutionary explanations, typically assuming antagonistic selective forces acting on maternal and fetal traits, which has been termed the "obstetrical dilemma." Recently, there has been a growing tendency among some anthropologists to question the difficulty of human childbirth and its evolutionary origin in an antagonistic selective regime. Partly, this stems from the motivation to combat increasing pathologization and overmedicalization of childbirth in industrialized countries. Some authors have argued that there is no obstetrical dilemma at all, and that the difficulty of childbirth mainly results from modern lifestyles and inappropriate and patriarchal obstetric practices. The failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions is sometimes interpreted as empirical support for discarding an obstetrical dilemma. Here we explain why these points are important but do not invalidate evolutionary explanations of human childbirth. We present robust empirical evidence and solid evolutionary theory supporting an obstetrical dilemma, yet one that is much more complex than originally conceived in the 20th century. We argue that evolutionary research does not hinder appropriate midwifery and obstetric care, nor does it promote negative views of female bodies. Understanding the evolutionary entanglement of biological and sociocultural factors underlying human childbirth can help us to understand individual variation in the risk factors of obstructed labor, and thus can contribute to more individualized maternal care.

Maturational timing as a factor in female fatness and obesity.

As shown in more than 16 000 white participants in two major studies, menarcheal timing is a major determinant of weight and fatness in early adulthood. Early-maturing women are slightly shorter than late-maturing women but weigh 4 kg more. Early maturers are 30% fatter than late maturers, approximately +0.46 Z scores for each of four different skinfolds. Early maturers are far more often obese than late maturers (risk ratio = 1.8). The data suggest that maturational timing has a greater long-term effect on the level of fatness than the level of fatness had on maturational timing.