Nancy L. Segal, Aaron T. Goetz, and Alberto C. Maldonado in the NYTimes:
The clear visibility of the sclera is a uniquely human characteristic. Other primates, such as the African great apes, also track the gaze direction of others, yet their sclera are pigmented or, if white, not visible. The great apes appear to use head direction more than other cues when following another’s gaze.
Do humans have an instinctive preference for the whites of eyes, thus explaining the allure of the Squirtle? We conducted a study, to be published this year in the journal Evolution and Human Behavior, that suggested that the answer was yes.
Preferences for Visible White Sclera in Adults, Children and Autism Spectrum Disorder Children: Implications of the Cooperative Eye Hypothesis, Nancy L., Aaron T. Goetzemail, Alberto C. Maldonado: Published Online: July 02, 2015, Evolution and Human Behavior.
Abstract: Visible white sclera (i.e., the opaque white outer coat enclosing the eyeball) is a uniquely human trait. An explanation for why such coloration evolved has been put forward by the Cooperative Eye Hypothesis (Kobayashi and Hashiya, 2011; Kobayashi and Koshima, 1997, 2001; Tomasello et al., 2007), which states that visible white sclera evolved to facilitate communication via joint attention and signaling of gaze direction. Therefore, we hypothesized that viewers comprised of both typically developing children and adults would show reliable preferences for stimuli with visible white sclera. However, because autism spectrum disorder (ASD) individuals have impaired social cognition and show gaze aversion, we also hypothesized that ASD children would show no consistent preference for eyes with visible white sclera. We tested these hypotheses by obtaining participants’ preferences across six sets of stuffed animals, identical but for the manipulation of eye size, eye color, and presence of visible sclera. Both hypotheses were supported. In addition to providing evidence consistent with the Cooperative Eye Hypothesis, our results also suggest that eyes and gaze serve a central role in social cognition. Furthermore, our results from ASD children have practical applications for therapeutic practices and evidence-based interventions.