The functional anatomy of Late Pleistocene and recent human carpometacarpal and metacarpophalangeal articulations

Four different models were tested to determine their ability to explain aspects of stasis and change in the carpometacarpal (CMC) and the metacarpophalangeal (MCP) two and five joint anatomies of Late Pleistocene humans from Europe and the Near East, and recent Holocene humans from the United States and Europe.; The robusticity model predicts that Neandertal metacarpals should have the highest levels of J (torsional strength), cortical areas, and the greatest proximal phalangeal base articular surface areas, indicating the transmission of significantly elevated levels of axial forces through their hands. The skeletal proportion model predicts that Neandertals maintained increased hand mechanical advantages, indicating that elevated somatic force levels were used during manipulatory tasks. The joint position model argues the Neandertal manipulatory repertoire differed significantly. If true, Neandertals peak-loaded their joints in contrasting positions, resulting in altered joint orientations and/or shapes. Thus, Neandertal joint shapes should differ from all other samples. The stochastic model argues that significant but functionally irrelevant between-sample morphological contrasts are produced by stochastic variation.; Univariate analyses of metacarpal cross-sectional properties derived from biplanar x-rays, and the proximal phalangeal base articular surface areas derived from digitized photographs, provides weak support for the robusticity model. The existing literature on mechanical advantages in the Neandertal wrist and thumb MCP joints supports the skeletal proportion model. The three-dimensional morphometric analysis of the CMC and MCP joints indicates there are numerous significant between-sample differences in joint morphologies. This supports the joint position model, indicating significant frequency shifts in Late Pleistocene human manipulatory repertoires. The morphological differences analyzed are argued to be adaptations to the predominance of axially, rather than obliquely directed forces through the Neandertal hand. The stochastic model is weakly supported.; The joint position and skeletal proportion models account for most of the morphological differences in Late Pleistocene and recent human hands. The Neandertal hand is morphologically distinct from the recent human hand, although it was fully capable of precision grips. Neandertals are less distinct, however, when other Late Pleistocene human samples are considered. Although mechanical advantages decrease significantly in non-Neandertal samples, the Early Upper Paleolithic sample possesses Neandertal-like metacarpal 1 base morphologies, while the Early and Late Upper Paleolithic samples have transitional metacarpal two and three base morphologies. The Skhul/Qafzeh sample is morphologically most similar to the Upper Paleolithic samples, and therefore must have been behaviorally similar.; This mosaic morphological transition is argued to be indicative of subtle, rather than abrupt frequency shifts in manipulatory behaviors at the Middle-to-Upper Paleolithic archeological transition. Further elucidation of this behavioral transition will require non-typological lithic analyses of Mousterian and Early Upper Paleolithic tools in conjunction with functional analyses of the skeleton.