Opponens Pollicis Mechanical Effectiveness in Neandertals and Early Modern Humans

Abstract

Researchers have repeatedly noted a flange of bone along the distodorsoradial margin of the Neandertal first metacarpal diaphysis, marking the insertion of the opponens pollicis muscle. It has been argued that this flange represents both greater muscle volume and greater leverage for the opponens pollicis. Here we assess the poten-tial for increased mechanical effectiveness of the opponens pollicis in rotation and abduction in Neandertals as compared with Middle Paleolithic, Mid Upper Paleolithic, and recent modern humans. The radial displacement of the insertion for the opponens pollicis was assessed as a proxy for the moment arm for this muscle in rotation and abduction. Radial protrusion, both absolute and scaled to body size, was found to be greater in Neandertals and the Middle Paleolithic modern humans as compared with more recent humans, suggesting greater mechanical effectiveness of this muscle in Middle Paleolithic populations. This pattern may be the result of increased techno-logical advancement after the Middle Paleolithic, resulting in a decreased need for muscular strength.

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