Ker Than asks, Did evolution make our eyes stand out?:
Of all primates, human eyes are the most conspicuous; our eyes see, but they are also meant to be seen. Our colored irises float against backdrops of white and encircle black pupils. This color contrast is not found in the eyes of most apes.According to one idea, called the cooperative eye hypothesis, the distinctive features that help highlight our eyes evolved partly to help us follow each others’ gazes when communicating or when cooperating with one another on tasks requiring close contact.
A recent study examined how various primates followed a human experimenter’s head and eye movements:
Results showed that the great apes — which included 11 chimpanzees, four gorillas and four bonobos — were more likely to follow the experimenter’s gaze when he moved only his head. In contrast, the 40 human infants looked up more often when the experimenter moved only his eyes.