We've heard it before: nice guys finish last. And when it comes to sexual attraction, it appears the rule holds.

A new study finds that women are more attracted to the brooding, "bad boy" rather than happy-go-lucky guys.

Now before you go asking, "They needed a study to tell us that?!", hear us out. The University of British Columbia researchers who worked on the study say there's an inherent contradiction in this finding.

They note that in almost every social interaction -- including those involving sexual attraction -- smiling is actually considered essential. But when it comes to first impressions, women seem to prefer men who look either sullen or boastful.

The study from UBC's Deptartment of Psychology involved more than 1,000 men and women who were asked to rate how sexually attractive they found hundreds of pictures of people of the opposite sex.

The pictures showed men and women engaged in standard displays of happiness (broad smiles), pride (raised heads, puffed-up chests) or shame (lowered heads, averted eyes).

When they asked the women which images they found sexiest, the women tended to be least interested in the smiling, happy men. They instead preferred either those who looked proud and powerful, or moody and ashamed.

In contrast, men were most sexually attracted to women who looked happy, and least attracted to women who appeared proud and confident.

Alec Beall, a UBC psychology graduate student and one of the study's co-authors says it's important to remember that the study was meant to explore first impressions of sexual attraction.

"We were not asking participants if they thought these targets would make a good boyfriend or wife – we wanted their gut reactions on carnal, sexual attraction," he explained in a news release.

He notes that previous studies have found nice personalities and positive emotions are highly desirable in relationship partners. But when it comes to sexual attraction, women seem to like their men "complicated."

Why would women like men who looked ashamed? Prof. Jessica Tracy of UBC's Deptartment of Psychology, who also worked on the study, has a theory.

She says displays of shame suggest the men are aware of social norms and appeasement behaviors, which suggests they are trustworthy, a trait that is valued by both sexes.

As for why the women preferred the men who raised their arms in pride, that one was a bit easier to explain.

First off, the pride expression accentuated the men's physical features, such as upper body size and muscularity, which may have helped to make the men more sexually attractive.

As well, evolutionary theories suggest females are often attracted to male displays of pride because they imply status and competence. Smiling, on the other hand, is often linked with a lack of dominance.

Men may have preferred the smiling women because happiness is considered a particularly feminine-appearing expression.

And like it or not, traditional gender norms call for men to be dominant and strong, and women to be submissive and vulnerable.

"Generally, the results appear to reflect some very traditional gender norms and cultural values that have emerged, developed and been reinforced through history, at least in Western cultures," Tracy said in the news release.

"These include norms and values that many would consider old-fashioned and perhaps hoped that we've moved beyond."

The study appears in the online edition of the American Psychological Association journal Emotion.