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Human bipedal instability in tree canopy environments is reduced by "light touch" fingertip support

Johannsen, L.; Coward, S. R.L.; Martin, G. R.; Wing, A. M.; Casteren, A. Van; Sellers, W. I.; Ennos, A. R.; Crompton, R. H.; Thorpe, S. K.S.

Authors

L. Johannsen

S. R.L. Coward

G. R. Martin

A. M. Wing

A. Van Casteren

W. I. Sellers

A. R. Ennos

R. H. Crompton

S. K.S. Thorpe

Abstract

© 2017 The Author(s). Whether tree canopy habitats played a sustained role in the ecology of ancestral bipedal hominins is unresolved. Some argue that arboreal bipedalism was prohibitively risky for hominins whose increasingly modern anatomy prevented them from gripping branches with their feet. Balancing on two legs is indeed challenging for humans under optimal conditions let alone in forest canopy, which is physically and visually highly dynamic. Here we quantify the impact of forest canopy characteristics on postural stability in humans. Viewing a movie of swaying branches while standing on a branch-like bouncy springboard destabilised the participants as much as wearing a blindfold. However "light touch", a sensorimotor strategy based on light fingertip support, significantly enhanced their balance and lowered their thigh muscle activity by up to 30%. This demonstrates how a light touch strategy could have been central to our ancestor's ability to avoid falls and reduce the mechanical and metabolic cost of arboreal feeding and movement. Our results may also indicate that some adaptations in the hand that facilitated continued access to forest canopy may have complemented, rather than opposed, adaptations that facilitated precise manipulation and tool use.

Journal Article Type Article
Publication Date Dec 1, 2017
Journal Scientific Reports
Print ISSN 2045-2322
Electronic ISSN 2045-2322
Publisher Nature Publishing Group
Peer Reviewed Peer Reviewed
Volume 7
Issue 1
Article Number 1135
Institution Citation Johannsen, L., Coward, S. R., Martin, G. R., Wing, A. M., Casteren, A. V., Sellers, W. I., …Thorpe, S. K. (2017). Human bipedal instability in tree canopy environments is reduced by "light touch" fingertip support. Scientific reports, 7(1), https://doi.org/10.1038/s41598-017-01265-7
DOI https://doi.org/10.1038/s41598-017-01265-7
Keywords Biological anthropology; Evolutionary ecology; Experimental evolution; Human behaviour
Publisher URL https://www.nature.com/articles/s41598-017-01265-7

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