The Whites of Their Eyes:
The 'Science and Technology' section of the latest edition of The Economist (Nov 4th-10th) has an interesting article entitled 'Eyeing up the collaboration'. The article reports on research done at the Max Planck Institute for Evolutionary Anthropology in Liepzig Germany. The researchers decided to compare adult chimpanzees, gorillas and bonobos with human children of either 1 year or 18 months in terms of their response to tracking where the experimenters were looking. The experimental parameters were moving only the eyes, moving the head and eyes or moving the head with the eyes closed. Later the experimenters tried showing the subjects only the back of the head and either tilting the head or keeping still.
The results were interesting. All of the apes, including the "yard apes" tended to look towards where they thought the experimenters were looking. The human children, however, paid the most attention to the direction of gaze of the experimenters' eyes and were relatively indifferent to the direction of the head. The other apes focused on the direction of the head and were indifferent to the direction of gaze. Unlike other apes human have evolved a prominently visible sclera- the white of the eyes that allows other humans to notice the direction of gaze much more easily. The authors correlate this with other findings such human children are much more willing that apes to cooperate with others in manipulating objects and that they children spend a great amount of time during these interactions in observing the adult's face to find the direction of gaze. The authors say that this is at least preliminary evidence that humans have evolved to have a sociobiology that is much more cooperative in comparison to the sociobiology of their near relatives. The idea is that the prominent sclerae of humans have evolved as a signalling device that aids in the highly cooperative social interactions of humans.
The study's main author was Michael Tomasello, and the results have already been published online at the site of The Journal of Human Evolution. They will see print in an upcoming edition of this journal.