image: Evolved changes in pelvis shape allow the hamstrings muscles (red) to hyper-extend the hip in humans, but not in apes. view more
Credit: <i>PNAS</i>
A study examines the walking and climbing capabilities of human ancestors. Humans' straight-legged walking gait provides substantially improved walking economy, or distance traveled per unit energy consumed, compared with nonhuman apes. However, when and how human gait evolved remains unclear. Researchers have assumed that adaptations for improved walking economy require a corresponding reduction in climbing ability, but few studies have tested this hypothesis. Herman Pontzer and colleagues compared locomotor mechanics and pelvic morphology in humans and apes to determine how the force generated at the knee per unit hamstring tension varies with hip extension. Great apes had a greater maximum force generation than humans, resulting in enhanced climbing ability. However, ape pelvic orientation limited the hip extension angle to 160° or less, whereas humans could extend their hips beyond 180°, as required for upright walking. The authors used the results to estimate the locomotor capabilities of the early hominins Ardipithecus ramidus, Australopithecus afarensis, and Australopithecus africanus, based on pelvic morphology. All three early hominins had an estimated range of motion similar to that of humans. However, Ardipithecus also had an estimated maximum force generation similar to that of apes. Ardipithecus thus appears to have developed improved walking economy, compared with apes, without sacrificing climbing ability, according to the authors.
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Article #17-15120: "Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes, and fossil hominins," by Elaine E. Kozma et al.
MEDIA CONTACT: Herman Pontzer, Hunter College, New York, NY; tel: 212-772-5419; e-mail: hpontzer@hunter.cuny.edu
Journal
Proceedings of the National Academy of Sciences