Master of Arts
Stock, Jay T.
This thesis aimed to differentiate climatic and ‘neutral’ morphological signatures in the human femur, allowing anthropologists to improve their interpretations of behaviour in the past. A dataset of geometric morphometric data and traditional linear measurements for eleven globally distributed hunter-gatherer groups, measures of distance from an estimated African Origin, and a set of climatic variables were used to separate the relative effect of neutral demographic processes and climatic selection on femoral morphology. Within-population shape variance was not significantly predicted by any of the variables tested. Adherence to Bergmann’s rule was identified in the linear measurements on the individual and population level, while within-population variance in femoral length was found to be significantly associated with maximum temperature. These results suggest that climatic selection may have overwritten any neutral signatures. Future research should expand the sample to clarify if the interesting but non-significant patterns identified represent real relationships.
Summary for Lay Audience
The femur is important for inferring the activities/behaviours of past peoples. However, it is impacted by a complex set of influences. This research aimed to differentiate climatic and ‘neutral’ morphological signatures on an element commonly used to infer behaviour in the past, allowing anthropologists to improve their interpretations. Distributions of neutral traits, those traits which have little to no effect on an individual’s suitability to their environment, are shaped by evolutionary processes other than natural selection. Once such process is represented in the Out-of-Africa (OoA) model, the idea that serial founder effects (a type of genetic drift) produce a gradient of decreasing within-population variation in human traits (genetic, morphological, etc.) with increasing distance from Africa
In the following study, the morphology of the femur was examined via linear measurements and 3D models from eleven hunter-gatherer groups. Geometric Morphometrics (GM), the study of shape via landmarking, was used to quantify within-population shape variation. Correlation and regression analyses were used to determine the direction and strength of relationships between these measurements, measures of distance from an estimated origin in Africa, and climatic variables (including temperature, precipitation, and net primary productivity).
This thesis did not identify a statistically significant relationship between distance from Africa or the climate variables, and within-population shape variation, for any part of the femur. However, the small sample size may have impacted these results. For the linear measurements, adherence to Bergmann’s rule, that as temperature decreases, an animal’s body size will increase to deal with temperature stress, was identified on the individual and population level. Within-population variance in femoral length was found to be significantly associated with maximum temperature. These results suggest that a neutral signal is not evident in femoral morphology, or that one could not be identified using these methods. Instead, climate has an influence on femoral shape, potentially overwriting any neutral signals. Ultimately, femoral morphology is the result of a complex set of influences, including genetics, plasticity, population adaptation and more. Future research should focus on expanding the number of populations in the GM sample to clarify if the patterns identified represent real relationships.
Rutherford, Isabelle, "Investigating neutral and climate-linked morphological variation in human femora: A geometric morphometrics approach" (2023). Electronic Thesis and Dissertation Repository. 9362.
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