The human foot thus serves as a stable platform for bipedal locomotor behaviors. For humans, standing bipedally requires only slight activity of the calf muscles, and is highly efficient from an energetic standpoint. When nonhuman primates stand bipedally, they must recruit large blocks of lower limb and back musculature, partly because their feet do not provide a stable platform. The plantar ligament, a tough, fibrous ligament at the bottom of the foot, maintains the human arch. This is a thick ligament in humans, but in other primates, it takes the form of a either a weakly developed ligament or a muscle.
Diagrams represent, from upper row, left to right, chimpanzee, gorilla, and orangutan.
The bottom row, from left to right, includes feet representing humans, siamangs, and baboons. The evaluation of characteristics of the skull, hands, and feet for primate taxonomy. Classification and Human Evolution. The Wenner-Gren Foundation for Anthropological Research, Inc. pp. The derived nature of the human foot is obvious upon direct comparison.