Surprising trunk rotational capabilities in chimpanzees and implications for bipedal walking proficiency in early hominins.

Bibliographic Collection: 
Publication Type: Journal Article
Authors: Thompson, Nathan E; Demes, Brigitte; O'Neill, Matthew C; Holowka, Nicholas B; Larson, Susan G
Year of Publication: 2015
Journal: Nat Commun
Volume: 6
Pagination: 8416
Date Published: 2015
Publication Language: eng
ISSN: 2041-1723
Keywords: Adult, Animals, Biomechanical Phenomena, Female, Gait, Hominidae, Humans, Male, Pan troglodytes, pelvis, Range of Motion, Articular, Rotation, Spine, Thorax, Torso, Walking, Young Adult

Human walking entails coordinated out-of-phase axial rotations of the thorax and pelvis. A long-held assumption is that this ability relies on adaptations for trunk flexibility present in humans, but not in chimpanzees, other great apes, or australopithecines. Here we use three-dimensional kinematic analyses to show that, contrary to current thinking, chimpanzees walking bipedally rotate their lumbar and thoracic regions in a manner similar to humans. This occurs despite differences in the magnitude of trunk motion, and despite morphological differences in truncal 'rigidity' between species. These results suggest that, like humans and chimpanzees, early hominins walked with upper body rotations that countered pelvic rotation. We demonstrate that even if early hominins walked with pelvic rotations 50% larger than humans, they may have accrued the energetic and mechanical benefits of out-of-phase thoracic rotations. This would have allowed early hominins to reduce work and locomotor cost, improving walking efficiency early in hominin evolution.

DOI: 10.1038/ncomms9416
Alternate Journal: Nat Commun
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