Yeganeh Sekhavati

YEGANEH SEKHAVATI, then a graduate student at Washington University, St. Louis, Missouri, was approved funding in October 2021 to aid research on “The Evolution of Bipedalism in Phylogenetic and Environmental Contexts,” supervised by Dr. David Samuel Strait. This study examines the evolutionary patterns and processes that shaped hominin foot evolution and the environmental conditions under which hominin feet evolved. Sixty-two discrete and 41 continuous foot traits were analyzed across early hominins and great apes. Results suggest that the last common ancestor (LCA) of humans and chimpanzees had an African ape-like foot morphology adapted to terrestrial heel strike plantigrady and vertical climbing. The earliest hominin foot adaptations involved ankle eversion and midtarsal stability. Findings support the hypothesis that lateral midfoot stability evolved before medial midfoot stability. Additionally, most traits evolved through stochastic processes and/or selective pressures with random components, though certain traits related to joint stability evolved under sustained selection. Finally, bipedal adaptations in the hominin feet first evolved in dry habitats, consistent with the Savannah Hypothesis. Yet, subsequent evolutionary changes in foot structure occurred primarily in wetter, more forested environments. A high level of ecological flexibility was evident in the LCA of Homo, who lived in both dry and wet environments. The results showed how the hominin foot evolved from an African ape-like foot morphology, driven by both random and selective processes and shaped by shifting environmental conditions.