According to a controversial new study, researchers say men's faces reveal their interest in having children, and women subconsciously pick up these subtle cues when choosing a partner.
The study was carried out by researchers at the University of Chicago and the University of California, Santa Barbara.
Jim Roney from the University of California, says the team used photographs of men who had been questioned on their fondness for children, to see if women could identify those more likely to want a family.
Researcher Dr. Dario Maestripieri says that women are surprisingly accurate in judging a man's masculinity and his interest in infants by looking at his face.
The researchers found that not only were women often able to rank men by their fondness for children, but those who appeared more keen on kids were rated as more attractive prospects for long-term relationships.
That says the researchers suggests that a man's perceived attractiveness might have more to do with his desire to have children than previously thought.
Women it seems are fine tuned subconsciously to detect the qualities they are looking for in a man just by looking at his face.
Maestripieri says the results also show that women value masculinity as a desirable trait for short-term relationships and interest in infants as a desirable trait for more stable long-term relationships.
Roney says their data showed that men's interest in children predicts their long-term mate attractiveness, even after physical attraction was taken into account and may very well be an underestimated influence on long-term mate attractiveness.
For the study, 39 men gave saliva samples that were used to measure their testosterone levels.
Each man was was then shown 20 pairs of pictures, with one image depicting an adult human or animal and the other showing a baby of the same species.
By stating which image they preferred in each case, the psychologists say they were able to rank the males by their interest in babies.
Twenty nine undergraduate women were then asked to judge the men's photos, rating each man on his fondness for children, masculinity, physical attractiveness and kindness.
They were then asked to judge which most appealed as a short-term romantic partner and which seemed the best long-term partner.
The tests showed that women were easily able to identify the most masculine men, who scored highest on testosterone levels and these men were often picked as the best short-term partners.
But the men chosen as the best long-term partner and considered to have marriage potential were consistently the ones who showed a greater interest in children.
Dr. Roney says that women's ability to estimate men's interest in infants from face photographs is perhaps the most novel finding to emerge from the study.
It appears say the researchers that evolution has made women very good at using every piece of information at their disposal when making decisions about mating and relationships.
The research is published in the Proceedings of the Royal Society B: Biological Sciences.