Humans walk with an upright posture, extended limbs during stance, and a double-peaked vertical ground reaction force. Our closest living relatives, chimpanzees, sometimes walk bipedally but do so with a flexed, abducted hind limb. Previous researchers have studied humans walking with a crouched, chimpanzee-like gait pattern to try to infer how extinct human ancestors walked. However, it is not clear if the way humans perform this crouched posture gait would be similar to the way a species that is adapted to walk with a crouched posture would walk. The purpose of this dissertation was to investigate the impact of morphology and posture on gait mechanics in humans and chimpanzees. We investigated how human subjects perform different types of crouched posture walking and the degree to which human crouched posture walking converges to that of bipedal chimpanzee gait. The results from the first study indicate that crouched posture human gait does become more similar to chimpanzee gait, with more chimpanzee-like hip and knee flexion, and hip abduction patterns. However, differences between species persisted as the humans walking with a crouched posture did not have a single-peaked ground reaction force or as much pelvis transverse plane rotation. In the second study, we investigated how the major muscle groups in the lower limbs induce center of mass accelerations across different human postures and between humans and chimpanzees. Our results showed that when humans walk with a crouched posture, they rely on their gluteus maximus and vastus group to a greater extent to produce vertical accelerations than when humans walk with a normal posture. When comparing between species, we found that the chimpanzees rely less on their vastus muscle group and more on their gluteus maximus to induce vertical accelerations than humans walking with a crouched posture. The differences between humans and chimpanzees that persist when humans walk with a crouched posture in gait kinematics, ground reaction forces, and muscle function suggest that human crouched posture walking does not approximate a gait pattern of a chimpanzee and therefore should be used with caution when trying to understand the evolution of human bipedalism.