The research also shows that women's judgments of men's facial masculinity accurately reflect individual men's testosterone levels. Accordingly, women are attracted to those men for short-term relationships.

"The study provides the first direct evidence that women's attractiveness judgments specifically track both men's affinity for children and men's hormone concentrations," said Dario Maestripieri, Associate Professor in Comparative Human Development, and co-author of "Reading Men's Faces: Women's Mate Attractiveness Judgments Track Men's Testosterone and Interest in Infants" published on-line in today's (May 9) issue of Proceedings of the Royal Society B: Biological Sciences, a British scientific journal.

Women are surprisingly accurate in being able to determine interest in children and testosterone levels, said James Roney, Assistant Professor at the University of California, Santa Barbara, the lead author of the paper. "Our data suggest that men's interest in children predicts their long-term mate attractiveness even after we account for how physically attractive the women rated the men," he said.

Joining the two in the study are Katherine Hanson, a graduate student in anthropology at the University of California, Santa Barbara, and Kristina Durante, a graduate student in psychology at the University of Texas, Austin.

For the study, researchers at the University of Chicago recruited male undergraduate students from a variety of ethnic backgrounds who were tested for testosterone and for their interest in children. Researchers took saliva samples to measure testosterone levels.

To determine interest in children, researchers showed the 39 men in the sample pairs of pictures, each of an adult and a baby. They were asked which picture they preferred. Five of the men expressed no interest in the baby pictures, while the rest expressed a range of interest, up to preferring the baby pictures exclusively.

The researchers then took pictures of each man, asking them to display a neutral expression. An oval frame was placed around each photo to focus attention to the faces and the photos were shown to 29 undergraduate women from diverse backgrounds at UCSB.

The women were asked to rate the men according to whether they thought the men liked children, whether they appeared masculine, physically attractive, or kind. They were then asked to determine men's attractiveness as short-term romantic partners or as long-term partners for relationships such as marriage.

The men women chose as being most interested in children were also the same men who had expressed the most interest in children in the photo test. The women were also able to determine from their pictures which men had high on testosterone levels because they perceived the men as looking masculine.

Although women said they were attracted to the men who tested high for testosterone, an important factor in their attraction to men for a long-term relationship was their perception of a man's affinity for children, even after accounting for their perceptions of men's general kindness.

"The research suggests that men's interest in children may be a relatively underappreciated influence on men's long-term mate attractiveness." Roney said.