Foot in Mammals, Primates, and Humans: A Functional-Morphological Overview

Abstract

The evolution of locomotor adaptation of the human foot was reviewed and compared with those of other mammals (Fig. 2). As a result, three kinds of structural adaptation were identified.
First, in the stage of primitive mammals, the human foot acquired a basic structure for terrestrial locomotion. That is, the foot acts as a lever, in which the ankle joint is a pivot, the triceps surae generates power, and take-off is made at the tips of the metatarsals (Figs. 6, 7, 8, 9; Table 1).
Second, in the stage of primates, the adaptation for arboreal locomotion (brachiation in a wide sense) occurred. Namely, the big toe became large for grasping and the foot was supinated (Figs. 11, 12). Because of the remnant of these structures, the human foot arch is high medially.
Finally, in the stage of (proto-) hominids, the human foot was rearranged for terrestrial fast walking (Figs. 2, 10, 13). That is to say, the calcaneus was expanded, which made the power arm relatively long, the toes became short losing grasping ability, and the rigid arch was developed in both transverse and sagittal directions (Fig. 1).
It can be said that the human foot is fundamentally adapted not for running but for fast walking, because its structure resembles that of elephant foot. In other words, to carry extra weight of the upper limbs, which are useful for tool-using, we have to employ graviportal locomotion as elephants do.