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bipedalism - Courtney Peterson BAA 180S Ape-Human...

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Courtney Peterson BAA 180S – Ape-Human Transition This week’s articles regard hominid bipedalism, its origins, and its implications. The National Geographic article highlights how the locomotor mechanisms of modern humans, and likely our ancestors, are the very cause of many osteological morbidities, such as back pain and knee problems, as well as the long and arduous process of birth. Adaptations for birth, in particular, are puzzling. A woman’s pelvis, and indeed her skeletal structure from the pelvis down, is described as “a classic example of evolutionary compromise” (Ackerman 126). However, it leaves very little wiggle room. When changes favor an easier birth, the structural integrity of knee is compromised due to the increased lateral pressure on the knee (discussed below). When changes favor more efficient locomotion, birth becomes more difficult and more deadly, meaning that such changes are unlikely to be inherited if the progeny of such a mother dies or the mother dies herself. As a result, selective pressure has also been placed on the fetus: the human skull of an infant is four times as small as that of an adult (Ackerman126). These anatomical compromises help to explain why in most cultures assistance is sought after for birth.
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