Models for the origin of the genus Homo propose that increased quality of diet led to changes in ranging ecology and selection for greater locomotor economy, speed, and endurance. Here, I examine the fossil evidence for postcranial change in early Homo and draw on comparative data from living mammals to assess whether increased diet quality has led to selection for improved locomotor performance in other lineages. Body mass estimates indicate early Homo, both males and females, were approximately 33% larger than australopiths, consistent with archeological evidence indicating an ecological change with the origins of our genus. However, many of the postcranial features thought to be derived in Homo, including longer hind limbs, are present in Australopithecus, challenging the hypothesis that early Homo is marked by significant change in walking and running performance. Analysis of energy budgets across mammals suggests that the larger body mass and increased diet quality in early Homo may reflect an increa...