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New Delhi, May 10: Masculinity, it turns out, is good only for short-term affairs. It’s men’s affinity for children that attracts women into long-lasting relationships, says a new study released on Tuesday.

The study by US scientists provides the first direct evidence that women’s judgements about how attractive men are depend on both men’s affinity for children and men’s concentration of testosterone, the hormone that determines masculinity.

The study, published in the Proceedings of the Royal Society: Biological Sciences, a British science journal, indicates that women subconsciously pick up cues of interest in children in men’s faces and then use them to determine attractiveness.

“This tells us that women can be quite accurate in judging men for their potential as short-term or long-term mates,” Dario Maestripieri, associate professor at the behavioural biology laboratory at the University of Chicago, told The Telegraph.

“Faces convey more information about attractiveness than previously thought,” said Maestripieri, a co-author of the study.

“Cues might be traits of the face ? such as shape ? that convey information about how interested men are in babies.”

In the study, University of Chicago scientists recruited 39 male undergraduate students from different ethnic backgrounds as volunteers.

These men were shown pairs of pictures ? an adult and an infant in each pair ? and asked which picture they preferred, while a digital camera captured the expression on each man’s face.

The researchers also took saliva samples from men to measure testosterone levels.

Then a group of 29 undergraduate women students at the University of California Santa Barbara were asked to rate the photographs on how much men liked children and whether they appeared masculine, physically attractive or kind. The scientists also asked the women to judge the men’s attractiveness for short-term romantic affairs or for long-term relationships such as marriage.

The men that women rated as being most interested in children were also the same men who had expressed the highest interest in photographs of the infants. Women’s judgement about masculinity also correlated well with men’s testosterone levels.

“Women are able to accurately detect a potentially important aspect of men’s biology in making mate preference selections,” James Roney, assistant professor at the University of California Santa Barbara, told The Telegraph.

“These results seem to suggest that different things are valued for sexual attractiveness than for long-term relationships,” Roney said. For short-term relationships, it is masculinity which correlates with testosterone and for long relationships, it is affinity for children which women infer from facial cues in men. “We’re not exactly sure what cues women are using,” Roney said.

But the men who scored high on the test involving infant pictures were also rated as having happier expressions. “This might be one cue that women are using to infer how much men like children,” Roney said.

Maestripieri said the accuracy of women’s judgements about men’s affinity for the infant pictures was surprising. The researchers caution that it would be premature to assume that similar results would be found across different cultures.

“Although several ethnicities were involved, most, if not all, the participants likely grew up in the US. We would need to see actual results in other cultures before we can be confident of generalising these results,” Roney said.