To Run or to Carry: Derived Traits in Early Members of the Genus Homo

Abstract

The purpose of this dissertation is to expand upon hypothesized selective pressures for three body acceleration and impact-resisting derived skeletal features seen in early members of the genus Homo. Historically, many of these skeletal structures (including enlarged lower limb joint surface areas, large anterior semicircular canal diameters, increased gluteal attachment sites, and robust heel bones) have been interpreted in the context of long-distance running and persistence hunting (typically adult male activities in modern hunting and gathering societies). However, many human locomotor activities can produce elevated impact forces, including high-speed walking and load carrying. For example, carrying infants during extended juvenile periods is a derived trait within primates and represents a significant energetic challenge, a large portion of which is the byproduct of transporting additional weight in the form of the dependent offspring. Furthermore, activities practiced in early life have significant impacts on adult skeletal morphology especially related to locomotion. Therefore, this dissertation seeks to explore loaded walking behaviors in humans in relation to running to determine if there is overlap in locomotor challenges between these two activities. To accomplish this goal, three studies were conducted to examine locomotor impact forces in children, head perturbations during load carrying, and gluteal muscle activation between load carrying and running. The results of this dissertation suggest that children deal with high impact forces early in the development of walking but can use non-heel-strike foot postures to reduce these impacts, that load carrying significantly increases head motion when compared to running, and that high gluteal excitation is specific to running. These data suggest that the human endurance running capacity may be the product of co-opting many early adaptations related to non-running behaviors.