Some people sleep around, but others are proudly chaste. Why would evolution have thrown up such a wide range of strategies? (Image: Alan Powdrill/Getty)

SOME people revel in a reputation as a Casanova and others proudly proclaim their chastity. But most of us probably prefer not to advertise our sexual proclivities. Still, if you think your attitudes to sex are a private affair consider this. Earlier this year, Lynda Boothroyd of the University of Durham, UK, and colleagues published a study showing that the majority of men and women were able to accurately judge whether a person would be a good bet for a committed relationship or were more interested in a fling, just by looking at a photograph of their face.

How exactly we make this assessment based on such minimal information is up for debate, though Boothroyd’s study did yield one clue. She found that men who were judged to be more “masculine” and women who were considered more “attractive”, were likely to be seen as more inclined towards casual sex – and to actually be so (Evolution and Human Behavior, vol 29, p 211).

This surprising talent for accurately reading people’s attitude to sex has an obvious benefit – it allows us to hook up with a partner who is likely to want the same out of a sexual relationship as we do. It also raises the more fundamental question of why individuals have such widely varying attitudes to sex in the first place. The answer is not simply that beautiful people have more opportunity. So what does make one person sexually restrained and another outrageously promiscuous? And how much do our attitudes …