Hipstory: The Evolution of Birthing

Childbirth is a biosocial event, meaning that it is an experience bound by both physiological and social realities. The human experience is exemplified by this combination of culture and biology. As bipedalism began to emerge in the Miocene, our ancestors came to depend on one another for physical and emotional support during birthing. The mechanical demands of bipedal locomotion acted as a selective pressure, altering the platypelloid early hominin pelvis by relatively reducing the mediolateral axis to form a round pelvic outlet. This reduced outlet area also allowed the formation of a pelvic floor that could both stretch to allow parturition and support the internal organs in a chronic/habitual vertical position. The pelvis flattened and the ilia rotated laterally, allowing for lumbar flexibility and complete

joint extension during the stride, both mechanisms to maximize energetic efficiency. As evidenced by the lack of significant sexual dimorphism in the pelvises of Australopithecines, locomotion rather than parturition was the major selective pressure acting on the pelvis until the emergence of the genus Homo. Critically, theories regarding the environmental conditions that would have provided a selective pressure for bipedalism have implications for early hominin child-rearing, and thus, community dynamics. To accommodate endurance running in an arid savannah, crucial for Homo erectus, the hominin pelvis narrowed, and the majority of body hair was lost. This adaptation restricted carrying strategies, rendering active carry the most viable. Hunting also provided the nutritional richness necessary for the development of larger hominin brains, meaning encephalization and locomotion became conflicting selective pressures. Along with high cephalopelvic indices, the birth of relatively immature infants was likely a subsequent evolutionary compromise. These factors yielded a perilous parturition process, in which the mother risks injuring her infant if she attempts to birth alone. Obligate midwifery and the long second altriciality period create a positive feedback loop that makes social interaction crucial to human survival. Over centuries, anthropogenically constructed systems have also begun to influence this biosocial phenomenon. Despite extensive historical evidence of the use of dynamic and upright birthing positions across the globe, the supine and lithotomy positions rose to prominence in the 17th century and have remained so in Western medicine, allowing for an interventionist revolution in maternal healthcare. Decentering the patient, these interventionist methods have significant negative physical and psychological effects. Poor health outcomes are only amplified by race-based healthcare biases, leading to high maternal death rates for women of color. Although a total return to ancestral methods is not productive, the use of midwifery and holistic medicinal practices is an effective tool to combat institutional discrimination and ensure better overall health outcomes.

Ansuya Noor Somashekar, 2024