The “obstetrical dilemma” was born, so to speak, in 1960, not in a medical journal, but in the pages of Scientific American magazine. There, anthropologist Sherwood Washburn proposed that the ease with which most non-human primates give birth when compared to humans comes down to bipedalism. While a mother-to-be great ape will seek seclusion to give birth easily and quickly in solitude, human birth is typically complicated and painful, takes hours and generally needs assistance. Washburn’s hypothesis claims that:
• The adoption of bipedalism by our hominid ancestors some 4 or 5 million years ago resulted in a trade-off for females: the narrower the pelvis, the more efficiently a female could walk, but also the more difficult her birthing process through her bony pelvic opening.
• As hominid brains (and therefore craniums) grew larger, females evolved wider hips to give birth, putting them at a disadvantage when it came to walking and running …
• … thus making them more dependent on males for food, fundamentally shaping “how humans organize socially, with a firmly patriarchal slant,” according to Washburn.
It’s certainly true that the process of giving birth to a human baby is far, far more complicated and riskier than for most other primates, mostly due to the tight fit between the baby’s head and the pelvic opening. (A human baby at birth is about twice as large in relation to the weight of its mother as would be expected for a similarly sized non-human primate.) Whereas birth in other primates is a straight shot, a human baby must go through a series of overlapping biomechanical contortions, the “seven cardinal movements” (including descending, rotating and aligning) to get itself born, even with its very malleable head.
In earlier times, obstructed labor — when the baby’s head was simply too large for the mother’s pelvis — typically resulted in the death of both mother and baby. This occurred in about one percent of births, so that a woman having 10 pregnancies — not unusual back then — had a one in 10 lifetime chance of dying in childbirth. Today, obstructed labor can be avoided with Caesarean section births, which avoid the pelvis altogether. However, C-section rates — about one in three in the US — are far in excess of what would be expected for clinical reasons alone, and are often influenced by convenience, economics, racism and over-medicalization.
Washburn’s obstetrical dilemma hypothesis was generally accepted until about 20 years ago, but his purported link between fetal head size, width of the pelvic opening and a woman’s lesser ability to walk and run is now treated more skeptically. For instance:
A 2007 study showed that contemporary Stone Age society female foragers living in Southern Africa who had “high levels of terrestrial mobility” (they walked a lot!) typically had large pelvic openings. Maybe bipedalism wasn’t the culprit?
More recently, a Harvard University lab study on men and women concluded that “pelvic width does not predict … locomotor cost in either women or men [who] are equally efficient at both walking and running.”
While the obstetrical dilemma hypothesis argues that birth occurs early in humans (compared to other primates) so that large-headed babies can squeeze through female pelvises, a competing “energetics of gestation and growth” hypothesis maintains that babies are born at the optimum gestation length (266 days from conception). This is when it’s more efficient for a mother to nurture the baby with breast milk than with nutrients via the placenta.
Bottom line: The fact that there are more than 8 billion of us says that a woman’s clunky birth process works on a population level, if not always on an individual level.
Barry Evans (he/him, barryevans9@yahoo.com) learned, while researching this topic, that the most common way anthropologists identify biological sex in ancient human skeletons is by the size of the pelvic opening.
This article appears in Local Lit.