"Why is it that men can be bastards and women must wear pearls and smile?" wrote author Lynn Hecht Schafran. The answer, according to an article in the Journal of Vision, may lie in our interpretation of facial expressions.

In two studies, researchers asked subjects to identify the sex of a series of faces.

The second study used male and female faces wearing expressions of happiness, anger, sadness, fear or a neutral expression. Overall, subjects were able to identify male faces more quickly than female faces, and female faces that expressed anger took the longest to identify.

"The present research shows that the association between anger and men and happiness and women is so strong that it can influence the decisions about the gender of another person when that person is viewed briefly," said Ursula Hess, PhD, from the Department of Psychology, University of Quebec at Montreal.

According to the report, the findings from this study as well as others lead to the idea that "the face is a complex social signaling system in which signals for emotion, behavioral intentions and sex all overlap."

Hess said that the same cues that make a face appear male - a high forehead, a square jaw and thicker eyebrows - have been linked to perceptions of dominance. Likewise, features that make a face appear female - a rounded, baby face with large eyes - have been linked to perceptions of the individual being approachable and warm.

"This difference in how the emotions and social traits of the two sexes are perceived could have significant implications for social interactions in a number of settings.

Our research demonstrates that equivalent levels of anger are perceived as more intense when shown by men rather than women, and happiness as more intense when shown by women rather than men. It also suggests that it is less likely for men to be perceived as warm and caring and for women to be perceived as dominant."

Source: Association for Research in Vision and Ophthalmology