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Are Two Legs Better than Four? Comparative Biomechanics & the Evolution of Human Walking & Running
Author(s) -
Raichlen David,
Pontzer Herman,
Sockol Michael
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.239.1
Subject(s) - bipedalism , quadrupedalism , energetics , energy expenditure , biomechanics , biology , evolutionary biology , physical medicine and rehabilitation , anatomy , ecology , medicine , endocrinology
The evolution of bipedalism is considered a defining event of early hominin evolution, however the selection pressures that led to upright walking remain unclear. One popular hypothesis is that bipedalism evolved to reduce energy costs in early hominins. To test this hypothesis, we used chimpanzees as a model of our pre‐bipedal ancestors. We measured bipedal and quadrupedal biomechanics and energetics in a sample of adult chimpanzees and humans. Chimpanzees use approximately 75% more energy than humans during walking, suggesting bipedalism may have been an attractive option for early hominins if selection were acting to reduce energy expenditure. Using inverse dynamics to estimate the amount of muscle volume activated per step, we found that chimpanzees’ flexed limb postures led to large amounts of active muscle volume at the hip and knee, which fully explain their high costs compared to humans. Using a modeling approach, we then assessed how changes in morphology and posture impact estimated energy costs in early hominins. We found that minor changes to either anatomy, posture, or both would have reduced walking costs compared to a chimp‐like ancestor. Therefore, it is increasingly likely that energetics played a major role in the evolution of bipedalism. Research supported by the Leakey Foundation and NSF.