PEOPLE'S attitude towards sex may be given away by the look on their face, according to new research.
The study into attraction, and how we find a mate, has confirmed that young heterosexual men and women are looking for complete opposites when it comes to relationships.
The survey of 700 heterosexuals in their early twenties found that men generally prefer women whom they perceive to be open to short-term sexual relationships, but women are usually interested in men who seem to have the potential to be a long-term partner.
It also found men picked out women who appeared open to sex as more attractive, while men looking for a one-night stand were deemed to be more masculine-looking, with a squarer jaw, smaller eyes and larger nose.
Scientists behind the study said people used their first impressions to make an informed decision quickly about their partner selection, and what kind of relationship they wanted.
The study, funded by the Medical Research Council and the Economic and Social Research Council, involved teams from St Andrews, Aberdeen and Durham universities.
Participants were asked to judge the attractiveness and attitudes to sex of the opposite gender from a photograph of their face.
This was compared to the real-life behaviour and attitude of the people in the photos – which they revealed in a detailed questionnaire.
The experiments found that the men and women taking part could generally judge who would be more interested in a short-term fling just by looking at their expression and features.
In one study of 153 participants, 72 per cent of people correctly identified the attitudes from photographs more than half of the time.
However, further questioning showed that the participants were not always confident their judgment was right.
The findings, published in Evolution and Human Behaviour, indicate that subtle facial expressions give away more than was previously thought.
Dr Ben Jones, from the University of Aberdeen's Face Research Lab, said: "Lots of previous studies have shown that people can judge a lot about a person from their face, but this really is the first study to show that people are also sensitive to subtle facial signals about the type of romantic relationships that others might enjoy."
Dr Lynda Boothroyd from Durham University's Psychology Department said: "Our results suggest that although some people can judge the sexual strategy of others simply from looking at their face, people are not always sure about their judgments.
"Yet preferences for different types of face were actually quite strong.
"This shows that these initial impressions may be part of how we assess potential mates – or potential rivals – when we first meet them.
"These will then give way over time to more in-depth knowledge of that person, as you get to know them better, and may change with age".
But Professor David Perrett, a psychologist at the University of St Andrews Perception Lab, said: "While faces do hold clues to sexual attitudes, men should not presume any kind of relationship is wanted from appearance alone since women's choice is what matters.
"Indeed, most women found promiscuous-looking guys unattractive for both short and long-term relationships."