Skeletal Asymmetry within the New Lisbon Collection: Implications for Environmental and Mechanical Stress

The purpose of this research is to investigate bilateral asymmetry within the New Lisbon Skeletal Collection, and to correlate observed levels with demographic and socioeconomic variables. The New Lisbon Collection is a historic skeletal assemblage of birthdates spanning 1805 – 1975, sourced primarily from Lisbon, Portugal. Metric long bone measurements of length and dimension were taken on a juvenile subsample (n = 82) and an adult subsample (n=248), and asymmetry indices were calculated incorporating both right and left and scaling for size. For the juvenile samples the objective was to investigate lateralization during growth and development. No significant difference could be found between the sexes, suggesting that males and females were responding similarly to external stressors. Close correlation was found between age and clavicle and humerus asymmetry, which may be related to increasing participation in unimanual activities. Moderately differences in asymmetry between causeof- death categories, coupled with the presence of both directional and fluctuating asymmetry suggests a population experiencing environmental instability and/or scarcity. In the adult subsample, the main objectives were to examine difference in asymmetry between groups, and track temporal change in asymmetry. Mechanical loading stress appears to be the source of adult asymmetry. This is supported by higher asymmetry observed in manual laborers, and in comparison against modern skeletal material. No difference could be determined between the sexes, which may be attributed to high physical workloads recorded for all historic Portuguese. In temporal analysis, asymmetry significantly increases during years 1890 – 1919, coinciding with an era of significant socioeconomic and political transition in Portugal. Ultimately, bilateral asymmetry in the New Lisbon Collection reflects a population experiencing moderate to high levels of environmental and mechanical stress