A Novel Human Sex Difference: Male Sclera Are Redder and Yellower than Female Sclera

A Novel Human Sex Difference: Male Sclera Are Redder and Yellower than Female Sclera. Sarah S. Kramer & Richard Russell. Archives of Sexual Behavior, May 4 2022. https://link.springer.com/article/10.1007/s10508-022-02304-9

Abstract

In a seminal study, Kobayashi and Kohshima (1997) found that the human sclera—the white of the eye—is unique among primates for its whitish color, and subsequent work has supported the notion that this coloration underlies the human ability to gaze follow. Kobayashi and Kohshima also claimed that there is no significant sex difference in sclera color, though no data were presented to support the claim. We investigated sclera color in a standardized sample of faces varying in age and sex, presenting the first data comparing male and female sclera color. Our data support the claim that indeed there is a sex difference in sclera color, with male sclera being yellower and redder than female sclera. We also replicated earlier findings that female sclera vary in color across the adult lifespan, with older sclera appearing yellower, redder, and slightly darker than younger sclera, and we extended these findings to male sclera. Finally, in two experiments we found evidence that people use sclera color as a cue for making judgements of facial femininity or masculinity. When sclera were manipulated to appear redder and yellower, faces were perceived as more masculine, but were perceived as more feminine when sclera were manipulated to appear less red and yellow. Though people are typically unaware of the sex difference in sclera color, these findings suggest that people nevertheless use the difference as a visual cue when perceiving sex-related traits from the face.