" [Evolutionary selection pressures for general communication] explain why humans are peculiar in having our rather small irises set against a white background—the sclera—in our eyes. Anyone watching us can infer where we are looking or whom we are looking at. Experiments with apes and infants show that apes watch the orientation of the heads of others while human infants watch the eyes. "

― Joseph Henrich , The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter