The Evolutionary Basis of Some Clinical Disorders of the Human Foot: A Comparative Survey of the Living Primates

Abstract

The living primates are a highly diverse group of essentially arboreal animals whose feet are variously adapted for grasping, climbing, and leaping in trees. One of the most remarkable aspects of the anatomical variation in the feet of the extant primates is that this diversity can be arranged in a graduated sequence ranging from the primitive transtarsal-opposition type of grasping foot found in the lemurs, through the specialized transmeta-tarsal-adduction type that characterizes the higher primates, to'the unique nongrasping foot of humans. The comparative study of this graded series makes it possible, without recourse to the fossil record, to appreciate the adaptive and functional stages through which the human foot passed in its evolution. It is hypothesized that the initial stage of human erect posture was characterized by a foot which was adapted to both hallucial grasping and short distance bipedal walking. In many respects, the structure of the foot of this primitive human was probably similar to that of the living highland gorilla. When compared with the feet of our closest living relatives, the African apes, the human foot is characterized by two major evolutionary specializations: the longitudinal and transverse arches, and the parallel first and second metatarsals. These two morphological adaptations, together with several associated specializations, are the structural basis of the bipedal human foot. Reconstructing the evolutionary and adaptive history of these specializations creates a better understanding of some of the more common clinical podiatric disorders. The modern human foot is structurally so well adapted to prolonged bipedal walking and standing that even slight deviations from its evolutionarily established pattern will produce debilitating clinical manifestations. In most cases, successful treatment of such disorders involves restoration of the foot's basic adaptive configuration.