Social Structure Predicts Eye Contact Tolerance in Nonhuman Primates: Evidence from a Crowd-Sourcing Approach

In most primates, eye contact is an implicit signal of threat, and often signals social status and imminent physical aggression. However, in humans and the more gregarious species of nonhuman primates, eye contact is more tolerated and used to communicate emotional and mental states. What accounts for the variation in this critical social behavior across primate species? We crowd-sourced primatologists and found a strong positive correlation between eye contact tolerance and primate social structure. In more egalitarian social structures, eye contact is more tolerated. In addition to constituting the first generalizable demonstration of this relationship, our findings can inform the related question of why eye contact is deferentially avoided in some human cultures, while in others eye contact is both frequent and even encouraged.