title: Reliance on head versus eyes in the gaze following of great apes and human infants: the cooperative eye hypothesis.
abstract: As compared with other primates, humans have especially visible eyes (e.g., white sclera). One hypothesis is that this feature of human eyes evolved to make it easier for conspecifics to follow an individual's gaze direction in close-range joint attentional and communicative interactions, which would seem to imply especially cooperative (mututalistic) conspecifics. In the current study, we tested one aspect of this cooperative eye hypothesis by comparing the gaze following behavior of great apes to that of human infants. A human experimenter "looked" to the ceiling either with his eyes only, head only (eyes closed), both head and eyes, or neither. Great apes followed gaze to the ceiling based mainly on the human's head direction (although eye direction played some role as well). In contrast, human infants relied almost exclusively on eye direction in these same situations. These results demonstrate that humans are especially reliant on eyes in gaze following situations, and thus, suggest that eyes evolved a new social function in human evolution, most likely to support cooperative (mututalistic) social interactions.
authors.affiliation: Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany. tomas@eva.mpg.de
authors.forename: Michael
authors.initials: M
authors.lastname: Tomasello
authors.forename: Brian
authors.initials: B
authors.lastname: Hare
authors.forename: Hagen
authors.initials: H
authors.lastname: Lehmann
authors.forename: Josep
authors.initials: J
authors.lastname: Call
mesh_terms: D000818:Animals; D001288:Attention / Q000502:physiology; D001522:Behavior, Animal / Q000502:physiology; D005075:Biological Evolution; D003299:Cooperative Behavior; D005133:Eye Movements; D005260:Female; D006071:Gorilla gorilla / Q000502:physiology*; D019416:Head Movements; D006801:Humans; D007223:Infant; D007398:Interpersonal Relations; D008297:Male; D019974:Pan paniscus / Q000502:physiology*; D002679:Pan troglodytes / Q000502:physiology*; D012590:Sclera / Q000033:anatomy & histology*