Obstetrical dilemma

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The obstetrical dilemma is a hypothesis to explain why humans often require assistance from other humans during childbirth to avoid complications, whereas most non-human primates give birth unassisted with relatively little difficulty. This occurs due to the tight fit of the fetal head to the maternal birth canal, which is additionally convoluted, meaning the head and therefore body of the infant must rotate during childbirth in order to fit, unlike in other, non-upright walking mammals. Consequently, there is an unusually high incidence of cephalopelvic disproportion and obstructed labor in humans. The obstetrical dilemma claims that this difference is due to the biological trade-off imposed by two opposing evolutionary pressures in the development of the human pelvis: smaller birth canals in the mothers, and larger brains, and therefore skulls in the babies. Proponents believe bipedal locomotion (the ability to walk upright) decreased the size of the bony parts of the birth canal....

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