05Pres - Habitual Bipedalism and Hand Precision Grip...

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Unformatted text preview: Habitual Bipedalism and Hand Precision Grip Comparative skeletal anatomy of humans versus extant apes with regard to bipedalism Functional anatomy of pelvis, femur, and gluteus muscles Sexual dimorphism of the human pelvis Evolution of hominin bipedalism and striding gait Possible benefits and risks of bipedalism Evolution of the hand Figure 5.1: Skeletal adaptations to bipedalism. From Lewin (1993a) Figure S5.a: The opening for the spinal cord (foramen magnum) in the skull is located posteriorly in chimps and centrally in humans. From Lewin and Foley (2004) Figure 5.2: The valgus angle between femur and tibia allows humans to center the body weight over one foot while the other leg is in motion. Australopithecus afarensis has a valgus angle similar to that of humans, in line with other indicators of bipedalism. Habitual Bipedalism and Hand Precision Grip Comparative skeletal anatomy of humans versus extant apes with regard to bipedalism Functional anatomy of pelvis, femur, and gluteus muscles Sexual dimorphism of the human pelvis Evolution of hominin bipedalism and striding gait Possible benefits and risks of bipedalism Evolution of the hand Figure 5.3: Stance Phase and Swing Phase of Human Walking. Right leg shown in color. The stance phase begins with the heel strike, and the swing phase begins with the push-off. From Lewin (1993a), p. 85) Figure 5.4: During walking, the gluteus medius and gluteus minimus muscles contract on the side that is in stance phase, preventing the pelvis from tilting down too far on the unsupported side, which is in swing phase. From Lewin (1993a) p. 88 Figure 5.5: Gluteus Muscles vs. Gravity The gluteus medius and minimus muscles originate on the outside of the ilium and insert laterally on the greater trochanter of the femur. Their force (angled arrow) balances the body weight (vertical arrow), with the hip joint (triangle) acting as a fulcrum. Note the shorter leverage of the gluteus muscles. Figure 5.6: Pelvic girdles shown from above (superior view) Top: Chimpanzee Middle: Australopithecus Bottom: Homo sapiens Note the laterally and ventrally directed bending of the iliac crest during hominin evolution....
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05Pres - Habitual Bipedalism and Hand Precision Grip...

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