Evolution of the Human Eye as a Device for Communication

Abstract

(from the chapter) Measured the external eye morphologies of nearly half of all the extant primate species with video camera and computer-aided image analyzing techniques to clarify the morphological uniqueness of the human eye and to understand these adaptive meanings of external eye-morphology in primates. In order to explain the close correlation of eye-shape parameters with habitat type or body size of the species examined, the authors tested the hypothesis that these features are adaptations for extending the visual eye field by eyeball movement, especially in the horizontal direction. This hypothesis was supported by analyzing the eye-movements of video-recorded primates and the developmental change of eye morphology in humans and olive baboons. The authors also tested the hypothesis that only coloration of the human eye is adapted to enhance the gaze signal while eye-coloration of primates is adapted to camouflage the gaze direction against other individuals. This hypothesis was supported by analyzing relationships among iris coloration, sclera coloration and facial coloration around the eye. These results suggest that unique features of the human eye started to evolve as adaptations to large body size and terrestrial life and were completed as a device for communication using gaze signal.