Chimpanzee Locomotor Energetics and the Origin of Human Bipedalism

Department of Anthropology, University of California, Davis, CA 95616, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2007; 104(30):12265-9. DOI: 10.1073/pnas.0703267104
Source: PubMed


Bipedal walking is evident in the earliest hominins [Zollikofer CPE, Ponce de Leon MS, Lieberman DE, Guy F, Pilbeam D, et al. (2005) Nature 434:755-759], but why our unique two-legged gait evolved remains unknown. Here, we analyze walking energetics and biomechanics for adult chimpanzees and humans to investigate the long-standing hypothesis that bipedalism reduced the energy cost of walking compared with our ape-like ancestors [Rodman PS, McHenry HM (1980) Am J Phys Anthropol 52:103-106]. Consistent with previous work on juvenile chimpanzees [Taylor CR, Rowntree VJ (1973) Science 179:186-187], we find that bipedal and quadrupedal walking costs are not significantly different in our sample of adult chimpanzees. However, a more detailed analysis reveals significant differences in bipedal and quadrupedal cost in most individuals, which are masked when subjects are examined as a group. Furthermore, human walking is approximately 75% less costly than both quadrupedal and bipedal walking in chimpanzees. Variation in cost between bipedal and quadrupedal walking, as well as between chimpanzees and humans, is well explained by biomechanical differences in anatomy and gait, with the decreased cost of human walking attributable to our more extended hip and a longer hindlimb. Analyses of these features in early fossil hominins, coupled with analyses of bipedal walking in chimpanzees, indicate that bipedalism in early, ape-like hominins could indeed have been less costly than quadrupedal knucklewalking.

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    • "Humans are decidedly the outlier among catarrhine primates, having relatively short arms and long legs relative to each other and to trunk length. This unique pattern primarily reflects selection for bipedalism on hindlimb length (Bramble and Lieberman, 2004; Sockol et al., 2007; Pontzer et al., 2009), but also potentially selection for shorter forelimb elements in the Homo, perhaps due to demands associated with increased tool use and manipulation and/or reduced reliance on arboreal behaviors. "
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    • "Humans are unique among apes and other primates in the musculoskeletal design of the pelvis and hind limbs. 1 Our short, wide pelvis and long, heavy hind limbs reflect both our evolution from an arboreal ape as well as selection pressures for an economical, two-legged walking stride (Rodman and McHenry, 1980; Sockol et al., 2007). The common chimpanzee (Pan troglodytes ) e a facultative biped and our closest living relative e uses a more expensive, flexed-limb gait when moving on two legs. "
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    • "Although the selective factors underlying the evolution of both walking and running are debated, it is likely that locomotor economy played a key role. Hypothesized energysaving features for walking include long legs and dorsally oriented ischia (Crompton et al., 1998; Pontzer et al., 2009; Robinson, 1972; Sockol et al., 2007). Energy saving features for running in the genus Homo include a long, compliant Achilles tendon and a spring-like median longitudinal arch, which are known to store and recover elastic energy during running in other vertebrates (Biewener, 2003; Ker et al., 1987; Roberts, 2002). "
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