Functional Anatomy of the Knee and Development-Implications for Interpreting Early Hominin Locomotion

George Washington University, Washington DC

Investigators

Abstract

This project supports the training and education of a Mexican American Postdoctoral Fellow, an under-represented minority in science and especially paleoanthropology. As a Chicana and first generation college graduate, the Fellow is personally committed to broadening participation of under-represented individuals in STEM fields. The research project explores bipedalism in humans. Walking on two legs is a defining feature of the human lineage, and yet major questions remain about the origin and evolution of human gait. Bipedalism evolved early in the human lineage, possibly as early as six million years ago; however, major debate has persisted over whether the earliest hominins walked essentially like modern humans do today, or whether various hominin species differ in their gait biomechanics. The recent discovery of an unusually complete, 2 million year old skeleton belonging to Australopithecus sediba has inspired new inquiry into the development and function of the hominin lower limb. In particular, recent interpretations of Au. sediba have refueled the debate as to how different species of australopiths may have varied in their form of bipedalism. The only way to directly test those hypotheses relies on examining aspects of the skeleton are sensitive to biomechanical demands during growth, and thus provide evidence of the biomechanics of gait during growth. However, little is currently known about how gait biomechanics influences the development of the lower limb. This project combines experimental, ontogenetic, and comparative approaches to interpret and reconstruct early hominin bipedalism. First, the effect of locomotor regimes (vertical climbing, pedal grasping canopy climbing, and wheel-running) on lower limb morphology are studied in a mouse experimental model, addressing skeletal plasticity of the femur and tibia. In running this project, the Fellow recruits minority students to be trained as assistant researchers through minority student organizations at GWU such as the Bouchet Society. The Fellow continues to present her research to children through outreach programs targeting low-income and minority students interested in science. This relies on previous experiences implementing age-appropriate activities, piloted during graduate school. Other efforts to improve public understanding of science include engaging broad audiences through the Smithsonian Institution's National Museum of Natural History's outreach programs (e.g., Scientist Is In, Human Origins Today (HOT) Topics), based on presentations originally developed for the NC Museum of Natural Sciences during the final year of her dissertation. The Fellow continues to be active in Graduate Women in Science, supporting other female scientists across STEM fields as well as coordinating outreach and volunteer opportunities for these women. Intellectual Merit: The proposed project advances our understanding of how and when our modern style of upright, bipedal gait evolved. The current paradigm views all early human ancestors and relatives as essentially the same, when in fact there may be considerable adaptive diversity in the early phase of human evolution. This project therefore has the potential to transform the current paradigm in paleoanthropology, and integrates experimental, developmental, and comparative data to achieve a more rigorous understanding of the functional significance of knee anatomy in humans. The experimental component provides the context for interpreting the results of a comprehensive ontogenetic primate comparative study, which examines whether developmental trajectories are correlated with behavioral changes throughout development, and addresses whether deviations from the general mammalian and primate pattern of epiphyseal fusion are correlated with specialized locomotion. Finally, lower limb fossils belonging to early Homo erectus and other early hominin species are included to test and advance hypotheses about the functional significance of developing morphology in light of the aforementioned experimental and ontogenetic results.