Ever wonder why you can see “the whites” of human eyes at all? File this under “Department of Who Knew”:
Human eyes are somewhat unique in the animal kingdom in that the sclera is very plainly visible at all times (except when the eye is closed). This is not just due to the white color of the human sclera, which many other species share, but also to the fact that the human iris is relatively small and comprises a significantly smaller portion of the exposed eye surface compared to other animals. It is theorized that this adaptation evolved because of our social nature as the eye became a useful communication tool in addition to a sensory organ. It’s believed that the conspicuous sclera of the human eye makes it easier for one individual to infer where another individual is looking, increasing the efficacy of this particular form of nonverbal communication. Animal researchers have also found that, in the course of their domestication, dogs have also developed the ability to pick up visual cues from the eyes of humans, making them one of only two species known to seek visual cues from another individual’s eyes. Interestingly enough, dogs do not seem to use this form of communication with one another and only look for visual information from the eyes of humans.