"As teenagers, dimorphism (systematic difference between sexes) increases in the nose, chin, mouth, jaw, eyes and general shape of faces," says Nicolas Dupuis-Roy, lead author of the study. "Yet we aren't conscious of how our brain recognizes those differences."
To discover those reference points, Dupuis-Roy and colleagues showed photos of 300 Caucasian faces to some 30 participants. Subjects were asked to identify gender based on images where parts of faces were concealed using a technology called Bubbles.
The investigation found that eyes and mouths, specifically their subtle shading or luminance, are paramount in identifying gender. Unlike previous studies, which found the gap between the eyelid and eyebrow as essential in gender ID, this investigation found the shades of reds and greens around mouths and eyes led to faster gender discrimination.
"Studies have shown that an androgynous face is considered male if the skin complexion is redder, and considered female if the complexion is greener," says Dupuis-Roy. "However, it is the opposite for the mouth. A woman's mouth is usually redder. Our brain interprets this characteristic as female."
"A man's face usually reflects less light around the eyebrows. This is because they are usually thicker. The same applies to the upper lip and chin, which are hairier areas," he adds, noting people clearly use colour to rapidly identify gender.