" The sclera—the white of the eye—affects attraction. No other primates have white scleras. Their scleras are dark, hiding their direction of gaze from predators, and from members of their own species—for whom a stare can be a threat.40 The white sclera of the human eye advertises gaze direction, making it a tool for social communication. It also advertises emotion and health. "

― Donald D. Hoffman , The Case Against Reality: Why Evolution Hid the Truth from Our Eyes