A study in Canada has found that women are more attracted to men who rarely smile.

According to research by the University of British Columbia females are more sexually attracted to brooding bad boys than happy-go-lucky lads.

Professor Jessica Tracy of UBC's Department of Psychology said: "While showing a happy face is considered essential to friendly social interactions, including those involving sexual attraction -- few studies have actually examined whether a smile is, in fact, attractive.

"This study finds that men and women respond very differently to displays of emotion, including smiles."