Morphological and functional correlates of variation in the human longitudinal arch




Heard-Booth, Amber Nichole

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The human longitudinal arch has long been considered to be an important adaptation for proper foot function and efficient locomotion. The anatomy and evolution of the arch has been a topic of discussion in biological anthropology for nearly a century, as its appearance presumably marked an important shift in human evolution towards use of a gait that was biomechanically-similar to that of modern humans. However, recent studies have challenged the paradigm that has historically characterized human feet as stiff and having an arch, in contrast to the highly-mobile feet of non-human primates, which lack an arch. Increasingly, studies report that humans exhibit variation in arch height, including flat-footedness, as well as variation in midfoot mobility. These findings have important implications for how paleoanthropologists interpret fossil foot bones that exhibit “human-like” morphology. This dissertation uses a novel, yet straightforward approach to look for direct links among foot bone morphology, arch height, and pedal loading mechanics. Rather than comparing human foot bone morphology to that of apes (like previous studies), this dissertation examines how foot bone shape varies within humans, and seeks to determine whether that variation is directly related to differences in arch height between individuals. This dissertation also investigates how variation in foot shape is related to variation in midfoot loading. Using data collected from X-rays, magnetic resonance imagery, and human osteological remains, the chapters of this dissertation discuss whether variation in the morphology of the distal tibia, calcaneus, and metatarsals is related to variation in arch height. Here, it is argued that features of the distal tibia and metatarsals previously used to infer arch presence in fossil hominins cannot be used to draw such conclusions. A feature of the calcaneus does correlate with variation in arch height, however, and may be useful for reconstructing arch height. Finally, humans who have a low longitudinal arch and a relatively wide foot were found to experience greater loading of the midfoot, irrespective of age. Given that early hominins are estimated to have had relatively broad feet, these results suggest that early hominins may have experienced greater midfoot loading than modern humans.



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