Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine
Saturday 2:45-3:00, Galleria North
Asymmetry in humans has both genetic and environmental origins. In adults, post-cranial bilateral asymmetry has been related to environment and mechanical loading, most notably in upper limb bone cross-sectional properties. However, few studies have addressed the ontogenetic timing of asymmetric diaphyseal cross-sectional properties specifically, with one problem being potentially large relative measurement errors in small juvenile bones when using radiography to reconstruct sections.
Measurement error for sub-adult humeral diaphyseal cross-sectional properties was assessed using a sample of archaeological juveniles (n=20) by comparing pQCT derived properties and those reconstructed using bi-planar radiography and external molds. Errors were acceptable and similar to those reported for adults (mean humeral %error: 1.92%; mean Coefficient of Reliability: 0.99).
The x-ray and molding technique was then used to examine the ontogeny of humeral directional asymmetry in humeral cross-sectional diaphyseal properties (n=103), as well as length (n=107), metaphyseal (n=60) and articular dimensions (n=53), from a well-age-distributed British cemetery assemblage, Barton-upon-Humber (ca. 950 AD to 1849 AD). The sample (perinatal to young adult) was subdivided into age cohorts for analysis. It was predicted that asymmetry would shift throughout growth, with right-biased laterality developing during childhood with the establishment of handedness.
Results indicate that left-sided humeral asymmetry is more prevalent during infancy and young childhood, with right-bias emerging during middle childhood for cross-sectional properties (5 –10 years; p<0.00001), while asymmetry in length (p<0.01), metaphyseal and epiphyseal dimensions emerge in later development (10-18 years; p<0.05).
Research supported by The Wenner-Gren Foundation (EMG) and National Geographic Society (CBR)