Women are fine tuned subconsciously to detect the qualities they are looking for in a man - just by looking at his face, US research suggests.
An interest in children was rated as attractive
Women can spot subtle signs of interest in children in a man's face, and accurately assess his level of the sex hormone testosterone, it claims.
Child-friendly men were rated as good long-term bets, masculine men as ideal for a more short-term fling.
Details feature in Proceedings of the Royal Society B: Biological Sciences.
The study was carried out by researchers at the University of Chicago and the University of California, Santa Barbara.
Researcher Dr Dario Maestripieri said: "Our results show that women are surprisingly accurate in judging a man's masculinity and his interest in infants by looking at his face.
"Our 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."
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Dr Maestripieri said the results suggested there was more information in the face about the potential value of a man as a mating partner than previously thought.
"I don't think that evolution has given women a second sense in this area but has made them very good at using every piece of information at their disposal when making decisions about mating and relationships."
The researchers recruited male undergraduate students, who underwent saliva tests to determine their testosterone levels.
They were also shown a series of pictures of adults and babies, and asked which they preferred.
Pictures of the volunteers were then shown to 29 female undergraduates, who were asked to rate the men according to whether they thought they liked children, appeared masculine, physically attractive, or kind.
The women 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 the same men who had expressed the most interest in children in the photo test.
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The women also accurately rated the men with the highest testosterone levels as being the most masculine.
Most women said they were attracted to the men who tested high for testosterone.
However, the results also showed that they tended to opt for men with a greater affinity for children when considering who had the greatest potential as a long-term partner.
Dr James Roney, who also worked on the study, said: "The research suggests that men's interest in children may be a relatively underappreciated influence on men's long-term mate attractiveness."