Smiling makes men more attractive to women as husbands, but not as short-term dating partners, a study published in Evolutionary Psychology reports.

Evolutionary Psychologists believe that humans have two different basic strategies available for selecting sexual partners. Short-term mating strategies focus on finding a partner with the best genetic material to contribute to a potential child, whereas long-term mating strategies focus on finding a partner who will also do the best job of raising offspring. As a result, people find different qualities attractive in a potential partner depending on whether they see them as a short-term or long-term relationship prospect. Physical attractiveness is very important to both men and women in selecting a short-term partner, because it indicates that a potential partner is healthy and has good genes.

Trustworthiness is more important for selecting a long-term partner, because it identifies a partner who is likely to remain committed and will do a good job of helping care for children.

Men tend to find women more attractive when they are smiling, but previous research has been inconclusive concerning whether women prefer smiling male faces or neutral ones.

Matia Okuba, of Shenshu University, headed a recent study of 218 female university students from Japan, Norway, and Italy aimed at determining whether women’s preferences for smiling men depend on the kind of mating strategy they are pursuing. The women in the study rated the attractiveness of a series of male faces that were either smiling or had a neutral expression. Half of the women were asked to evaluate the faces as a marriage partner, while the other half were asked to make the evaluation as a boyfriend going on a date.

Women evaluating men’s attractiveness for marriage rated smiling faces as more attractive than neutral faces, whereas women evaluating men’s attractiveness for a date rated smiling and neutral faces the same.

In a second part of the study, 71 female Japanese university students rated the same smiling and neutral faces on three qualities thought to be important for mate selection. Women rated smiling men as less masculine and less mature, but more trustworthy compared with men who had a neutral facial expression.

The authors of the study conclude that, smiling affects women’s perceptions of who is attractive when they are pursuing a long-term mating strategy, but not when they are pursuing a short-term mating strategy. Smiling detracts from a man’s appearance of masculinity and maturity, which are important qualities for male attractiveness to women in a short-term mating context, but smiling makes a man appear more trustworthy, which is an important quality in a long-term mating context.

Men interested in long-term relationships may want to practice their smiles, while those with short-term goals in mind may be better off playing it cool when it comes to making themselves most attractive to women.