POSTCRANIAL ROBUSTICITY IN HOMO .2. HUMERAL BILATERAL ASYMMETRY AND BONE PLASTICITY

The analysis of humeral asymmetry in Recent human skeletal samples and an extant tennis-player sample documents minimal asymmetry in bone le ngth, little asymmetry in distal humeral articular breadth, but pronou nced and variable asymmetry in mid- and distal diaphyseal cross-sectio nal geometric parameters. More specifically, skeletal samples of norma l modern Euroamericans, prehistoric and early historic Amerindians, an d prehistoric Japanese show moderate (ca. 5-14%) median asymmetry in d iaphyseal cross-sectional areas and polar second moments of area, wher eas the tennis-player sample, with pronounced unilateral physical acti vity, exhibits median asymmetries of 28-57% in the same parameters. A sample of Neandertals with nonpathological upper limbs exhibits simila rly low articular asymmetry but pronounced diaphyseal asymmetries, ave raging 24-57%. In addition, three Neandertals with actual or possible post-traumatic upper limb alterations have the same low articular asym metry but extremely high diaphyseal asymmetries, averaging 112-215%. T hese data support those from experimental work on animals, exercise pr ograms of humans, and human clinical contexts in establishing the high degree of diaphyseal plasticity possible for humans, past and present , under changing biomechanical loading conditions. This lends support to activity-related functional interpretations of changing human diaph yseal morphology and robusticity-during the Pleistocene. (C) 1994 Wile y-Liss, Inc.