There’s a fascinating opinion piece by psychologist Michael Tomasello in The New York Times arguing that humans, unlike other apes, have evolved to have the whites of our eyes showing to make social cooperation easier.
The idea is that this allows us to easily work out where other humans are looking, and this can help us to work out focus of attention and intention.
It has been repeatedly demonstrated that all great apes, including humans, follow the gaze direction of others. But in previous studies the head and eyes were always pointed in the same direction. Only when we made the head and eyes point in different directions did we find a species difference: humans are sensitive to the direction of the eyes specifically in a way that our nearest primate relatives are not. This is the first demonstration of an actual behavioral function for humans’ uniquely visible eyes.
Link to NYT article ‘For Human Eyes Only’.