Anthropology, Northwestern University
Thursday All day, Plaza Level
The ideal course of development in most organisms is characterized by a growth trajectory resulting in bilateral symmetry; an outward, perceivable signal of viability and fitness associated with genotypic and phenotypic quality. Previous research has established that though perfect bilateral symmetry is ideal, organisms commonly exhibit bilateral asymmetry (BA). Analysis of asymmetry in long bones is an important source of information concerning the impact of nutrition, pathology, and mechanical demands on the bilateral growth trajectory.
This study proposes that BA is exacerbated by external stressors encountered by an individual. BA may result when organisms experience these insults and must allocate additional energy away from symmetric growth and maintenance in order to buffer themselves from stress exposure. We explore this relationship between BA and external stressors through the analysis of the presence of fluctuating asymmetry (FA) and directional asymmetry (DA) in the long bones of individuals of an Ancestral Puebloan population (919-1640 CE) from infancy through adulthood.
Maximum length measurements of the humerii, radii, femura, and tibiae were assessed for individuals (n=198) divided into five age categories. Significant levels of BA were found in the humerii (p=0.0003) and tibiae (p=0.03). Frequency distributions reveal directional trends of asymmetry favoring the right side of both upper limb elements, with weaker trends seen for lower limb bones. Additionally, BA became more prevalent and exhibited greater percent difference as age increased. These results suggest that asymmetry in the long bones is influenced by environmental stressors that reduce an organism’s ability to produce symmetric morphological traits.