This project will study a particular feature of walking and foot anatomy that may provide new insight about the evolution of bipedalism (walking upright) in humans. Humans and our closest living relatives, the African great apes, use a unique foot strike pattern in which they strike the ground with the heel first, before the rest of the foot (heel strike) when walking. Yet the factors influencing the evolution of a specialized foot posture and the first appearance of our unique (human) footfall patterns are still poorly understood. It is unknown to what degree heel strike is similar across humans and African apes, how it develops throughout an individual's lifetime, and how different patterns of heel strike are reflected in the anatomy of foot bones. This study tracks the development of foot posture in African apes and provides a unique opportunity to understand why African apes and humans heel strike, and to explore how fossil hominin foot bones might tell us about walking patterns during hominin evolution. This project will support an early career female scientist and provide numerous research opportunities for graduate and undergraduate students, with a specific focus on female and minority students. At the end of the project, all video and image data will be made available to other scientists and educators, and used to promote the research and education goals of public zoological facilities and sanctuaries. Information on heel strike can be applied not only to the fossil record but also to studies of foot development and injuries in humans.
The objective of this project is to quantify patterns of heel strike functional morphology throughout ontogeny in African hominoids. The study will quantify the range of variation in pedal mechanics and anatomy among living primates who use a heel strike through an experimental, comparative, ontogenetic approach, and ask: (1) are the mechanics of heel strike the same in all contexts in which it occurs?, (2) how do body size, behavior, age, and hind limb dynamics influence heel strike mechanics?, and (3) can heel strike be detected in external and internal calcaneal anatomy? To test hypotheses regarding the effect of hind limb mechanics on heel strike, kinematic data are analyzed from non-invasive video recordings of infant and adult chimpanzees and gorillas walking. To investigate how foot inversion and associated ground reaction forces that load the calcaneus change during locomotor development, the center of pressure and ground reaction forces incurred by the foot are recorded with a pressure mat mounted on top of a force platform. These data are compared with previously collected video data of wild chimpanzees. Magnetic resonance imaging (MRI) and medical computed tomography (CT) are used to model how the African ape heel pad attenuates impact forces in the absence of a calcaneal lateral plantar process. These data are compared with microCT data of calcaneal trabecular architecture in captive and wild extant apes and humans and then applied to early fossil hominin calcanei (A. afarensis, and A. sediba). This integrative project is transformative because it investigates an entire functional chain: locomotor behavior and gait mechanics (kinematics, kinetics, and plantar pressure) throughout ontogeny, internal and external calcaneal structure in extant apes, and interpretation of fossil foot bone functional morphology. A comprehensive understanding of heel strike variation in living apes and its evolution in fossil hominins is an essential first step toward a broader understanding of the evolution of heel strike in hominoids.