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Biomechanics of the human thumb and the evolution of dexterity

Citation

Karakostis, Fotios Alexandros et al. (2021), Biomechanics of the human thumb and the evolution of dexterity, Dryad, Dataset, https://doi.org/10.5061/dryad.fttdz08rs

Abstract

Systematic tool production and use is one of humanitys defining characteristics, possibly originating as early as >3 million years ago.13 Although heightened manual dexterity is considered to be intrinsically intertwined with tool use and manufacture, and critical for human evolution, its role in the emergence of early culture remains unclear. Most previous research on this question exclusively relied on direct morphological comparisons between early hominin and modern human skeletal elements, assuming that the degree of a species dexterity depends on its similarity with the modern human form. Here, we develop a new approach to investigate the efficiency of thumb opposition, a fundamental component of manual dexterity, in several species of fossil hominins. Our work for the first time takes into account soft tissue as well as bone anatomy, integrating virtual modeling of musculus opponens pollicis and its interaction with three-dimensional bone shape form. Results indicate that a fundamental aspect of efficient thumb opposition appeared approximately 2 million years ago, possibly associated with our own genus Homo, and did not characterize Australopithecus, the earliest proposed stone tool maker. This was true also of the late Australopithecus species, Australopithecus sediba, previously found to exhibit human-like thumb proportions. In contrast, later Homo species, including the small-brained H. naledi, show high levels of thumb opposition dexterity, highlighting the increasing importance of cultural processes and manual dexterity in later human evolution.

Methods

Trapezio-metacarpal joint torque calculations were generated through virtual biomechanical modeling (see Karakostis et al., 2021). Three-dimensional shape variables were generated based on landmark-based geometric morphometrics.

Funding

European Research Council, Award: ERC CoG no. 724703

Deutsche Stiftung Friedensforschung, Award: DFG FOR 2237

Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst, Award: Az: 33-7533.-30-20/7/2