The Whites Of The Eyes Suggest Early Humans Were Co-Operative

Aug 19, 2003
Human evolution

Eyeing up the collaboration

Nov 2nd 2006
From The Economist print edition

The whites of the eyes suggest early humans were co-operative

THE sight of a group of men standing round watching another man work on his car is familiar in cultures throughout the world. It is also an example of what seems to be a primal human interaction—the mutual direction of gaze. Indeed, being able to identify what someone else is looking at is thought to have been so important to humans that people evolved to have eyes surrounded by brilliant whites to assist with the process. Now new research from Germany backs up the idea.

People, more than any other primate, depend on their fellow humans to figure out where to direct their attention. Previous research has shown that human children are much more willing than chimpanzees to co-operate with a human adult in manipulating objects—for example, taking it in turns to drop a ball down a chute. And when the children do, they spend a lot more time looking at the face of the adult, monitoring where that person is looking.

Humans also happen to have scleras—the white part of the eye surrounding the iris—that are much bigger and brighter than the scleras of other primates. In fact, most other primates have scleras that are so dark that they camouflage which way the eyes are looking. The theory is that a white sclera surrounding a darker iris and pupil helps people work out where everyone else is looking. If this were correct, people might be expected to pay more attention to the eyes than do other primates.

So researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, decided to compare adult chimpanzees, gorillas and bonobos with human children of a year or 18 months in age. In the experiment, reported online in the Journal of Human Evolution, a human adult first attracted the attention of the non-human ape or the human child, and then looked up at the ceiling. The experimenter moved only his eyes, moved his head and his eyes, or moved his head and kept his eyes closed. In later versions of the experiment he also turned around so that only the back of his head was visible and then either moved his head up or stayed still.

Both the non-human apes and the human children tended to look where they thought the experimenter was looking. But the non-human apes paid the most attention to where the experimenter's head was pointing, in particular, looking up when the head was pointed up, no matter what the eyes were doing. Human children, on the other hand, paid the most attention to the eyes, and were relatively indifferent to where the head was pointed.

The idea that people evolved eyes that make it easy for others to see where they are looking suggests just how important sociability was for early humans. If human interactions were primarily competitive, it would be advantageous to camouflage eye movements, as other apes seem to have done. That way, it would be hard for a competitor to see someone eyeing a tasty banana or potential mate. Instead, people have evolved to make it easy for others to see where they are looking. The advantages of co-operation seem to have outweighed those of competition ... id=8103817
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Ephemeral Spectre
Apr 12, 2005
How interesting.

I was reading something similar the other day about "ostensible communication" or some such phrase, where what is being communicated is the desire to show someone something, or direct their attention in some way. The results were similar in that eye contact was essential for such communication, but the purpose was different.


I knew the job was dangerous when I took it ...
Staff member
Jul 19, 2004
Out of Bounds
This November 2018 article provides a fairly technical survey of research and results into gaze direction and interpersonal responses to averted gazes.
Adaptation to the Direction of Others’ Gaze: A Review

The direction of another person’s gaze provides us with a strong cue to their intentions and future actions, and, correspondingly, the human visual system has evolved to extract information about others’ gaze from the sensory stream. The perception of gaze is a remarkably plastic process: adaptation to a particular direction of gaze over a matter of seconds or minutes can cause marked aftereffects in our sense of where other people are looking. In this review, we first discuss the measurement, specificity, and neural correlates of gaze aftereffects. We then examine how studies that have explored the perceptual and neural determinants of gaze aftereffects have provided key insights into the nature of how other people’s gaze direction is represented within the visual hierarchy. This includes the level of perceptual representation of gaze direction (e.g., relating to integrated vs. local facial features) and the interaction of this system with higher-level social-cognitive functions, such as theory of mind. Moreover, computational modeling of data from behavioral studies of gaze adaptation allows us to make inferences about the functional principles that govern the neural encoding of gaze direction. This in turn provides a foundation for testing computational theories of neuropsychiatric conditions in which gaze processing is compromised, such as autism. ...