Birth Dilemma

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The birth dilemma deals with the hypothesis of an opposite evolutionary development that, as a result of the upright gait, the female pelvis narrowed in humans while the size of the skulls of newborns increased.

The human ancestors ( hominids ) developed the upright gait . This could have forced the human pelvis to become narrower in the course of evolution and thus the female birth canal . At the same time, our ancestors formed larger brains during embryonic development . The two developments are contrary to each other and make birth more difficult. The result was a high rate of infant and maternal mortality , which in the history of human evolution meant considerable fitness restrictions and an immense selection pressure with regard to head circumference and pelvic size. The birth dilemma hypothesis thus explains possible birth complications of modern humans that require the help of others. Such help is not necessary with our close relatives, the non-human primates. The English name for birth dilemma was first used in 1960 by the American anthropologist Sherwood L. Washburn . The hypothesis about the birth dilemma thus states that there were opposing selection pressures in evolution (narrower pelvis and large brain) and that constraints prevented the dilemma from being reduced or eliminated. The problem is compounded by the fact that the male pelvis does not have to meet the requirements of birth; it evolved solely for the motor demands of upright gait.

However, a 2015 study describes a covariation between female pelvic shape or size and head size of newborns. According to this, women with a large head have a modified birth canal that is better adapted for newborns with a large head. Small women at increased risk of a mother's pelvis and baby head imbalance have a more rounded entrance to their birth canal. This is more difficult at birth. The discovered pattern of covariation between mother and child contributes to an easier birth. It could have evolved as an adaptive response to the strongly correlated selection as a result of the birth problem and thus indicate a genetic-developmental morphological integration .

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Individual evidence

  1. ↑ a b c Barbara Fischer and Philipp Mitteröcker : Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma. PNAS, 2015, vol. 112, no. 18, 5655-5660 online
  2. ↑ Wittman, AB; Wall, LL (2007). "The Evolutionary Origins of Obstructed Labor: Bipedalism, Encephalization, and the Human Obstetric Dilemma". Obstetrical & Gynecological Survey 62 (11): 739. doi : 10.1097 / 01.ogx.0000286584.04310.5c
  3. ↑ Wells, JCK; Desilva, JM; Stock, JT (2012). "The obstetric dilemma: An ancient game of Russian roulette, or a variable dilemma sensitive to ecology?". American Journal of Physical Anthropology 149: 40-71