Bilateral asymmetry of the humerus throughout growth and development

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Blackburn, Amanda
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This project investigates the development of asymmetry throughout growth by using bilateral asymmetry of the humerus as a proxy for handedness. A large skeletal sample of non-adults combined with a smaller sample of adults, primarily from British archaeological sites, was examined in order to detect when handedness appears in the human skeleton. Traditional measurements were combined with 3D data in order to provide a comprehensive picture of bilateral asymmetry. Results of this work indicate a striking trend from left to right-handedness during growth and development, with infants and toddlers exhibiting left-sided asymmetry and older children and adolescents demonstrating right-sidedness. Interestingly, this trend is consistent with what has been observed behaviourally in children, suggesting that biomechanical forces strongly influence bilateral asymmetry in the upper limb bones. In addition to examining handedness throughout growth, this research also explores bilateral asymmetry more generally as it is impossible to fully understand handedness without observing how asymmetry varies according to different factors. Although this work supports the hypothesis that all human populations are right-handed, there are subtle differences between groups. Results indicate that British populations became more asymmetrical over time, with this becoming most pronounced during the Industrial Revolution. Differences in degree of asymmetry between males and females was also noted, suggesting differences in activity between the two groups, as well as supporting the notion that the male and female skeleton differ in how they respond to biomechanical forces. Overall, this work provides a comprehensive analysis and discussion of how handedness presents in the human skeleton.
physical anthropology, handedness