Surprising trunk rotational capabilities in chimpanzees and implications for bipedal walking proficiency in early hominins
Nathan E. Thompson, Brigitte Demes, Matthew C. O’Neill, Nicholas B. Holowka & Susan G. Larson
Affiliations Contributions Corresponding author
Nature Communications 6, Article number: 8416 doi:10.1038/ncomms9416
Received 10 July 2015 Accepted 19 August 2015 Published 06 October 2015
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.
Subject terms: Biological sciences Zoology Evolution