Cooperative eye hypothesis

It suggests that the eye's distinctive visible characteristics evolved to make it easier for humans to follow another's gaze while communicating or while working together on tasks.

It is therefore unclear whether the cooperative eye hypothesis builds directly on Kobayashi & Kohshima's data, or whether it is based on Emery's 2000 article.

The cooperative eye hypothesis was tested by Michael Tomasello and others at the Max Planck Institute for Evolutionary Anthropology in Germany.

Other hypotheses include the proposal that white sclerae are a sign of good health, useful in mate selection, or that eye visibility promotes altruistic behaviour by letting people know they are being watched.

A study by the Max Planck Institute for Evolutionary Anthropology noted that "these hypotheses are not mutually exclusive, and highly visible eyes may serve all of these functions.