Humans walk with an upright posture with 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. Researchers have compared the bipedal gait of humans and chimpanzees in an effort to better understand the evolution of habitual bipedalism in humans. In addition, previous researchers have used the paradigm of 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. A better understanding of the relationship between the structure and function of the musculoskeletal system during gait can help researchers better interpret the evolution of human bipedalism. The purpose of this dissertation was to investigate the impact of morphology and posture on gait mechanics in humans and chimpanzees. Specifically, we investigated how healthy, adult human subjects perform different types of crouched walking and the degree to which human crouched posture walking converges to that of bipedal chimpanzee gait. The results from the first study of this dissertation indicate that crouched posture human gait does become more similar to chimpanzee gait, with more chimpanzee-like hip and knee flexion patterns. One important finding of this first study was that the hip was more abducted in the human crouched posture conditions, suggesting that the crouched posture itself influences the hip abduction angles measured in chimpanzee bipedal gait. However, differences between species persisted as the humans walking with a crouched posture did not have a double-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. We also compared the function of muscles in human crouched posture walking to that of chimpanzee walking to try to better understand the role of morphology on muscle function during gait. 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. The soleus and gastrocnemius seem to have a trade-off in function between human crouched posture walking and normal walking, with the gastrocnemius inducing greater accelerations in the normal posture and the soleus inducing greater accelerations in the crouched postures. When comparing between species, we found that the chimpanzees rely less on their vastus muscle group in inducing vertical and posterior accelerations than humans walking with a crouched posture. Chimpanzees instead rely more heavily on their gluteus maximus to produce vertical accelerations than the human subjects. The distinct musculoskeletal structure between humans and chimpanzees, such as differences in pelvis shape and muscle moment arms, likely play a key role in determining the function of muscles throughout the gait cycle. 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.