Nice guys have always suspected it but the confirmation is finally in -- when it comes to sexual attraction, bad boys always win.
A major study from the University of British Columbia in Canada has confirmed that women find "happy" guys significantly less sexually attractive than swaggering or brooding men.
And the research -- which may cause men to smile less on dates -- finds dramatic gender differences in how men and women rank the sexual attractiveness of non-verbal expressions of commonly displayed emotions, such as happiness, pride or arrogance.
In terms of basic attraction, women are drawn to moody, self-absorbed guys while men tend to look for open, apparently happy and confident women. But not too confident.
The bad news for independently minded ladies is that men are least attracted to women who appear "proud and confident".
The team found that men and women even respond differently to something as simple as a smile.
The study goes some way towards explaining the enduring allure of classic 'bad boys' and other iconic gender types (and why troubled-but-cute characters such as James Dean or Robert Pattinson's vampire in the Twilight movies are so enduringly hot).
Surprisingly, very few studies have explored the relationship between emotions and initial sexual attraction.
And this research is the first to report a significant gender difference in the attractiveness of smiles and also the first to investigate the attractiveness of displays of pride and shame.
"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," says Professor Jessica Tracy of UBC's Department of Psychology.
"This study finds that men and women respond very differently to displays of emotion, including smiles."
In a series of studies, more than 1,000 men and women rated the sexual attractiveness of hundreds of images of the opposite sex engaged in universal displays of happiness (broad smiles), pride (raised heads, puffed-up chests) and shame (lowered heads, averted eyes).
The study found that women were least attracted to smiling men, preferring those who looked proud and powerful or moody and ashamed.
In contrast, male participants were most sexually attracted to women who looked happy, and least attracted to women who appeared proud and confident.
That would seem to be bad news for strong women, but the research does come with something of a caveat.
"It is important to remember that this study explored first-impressions of sexual attraction to images of the opposite sex," says Alec Beall, a UBC psychology graduate student and co-author of the study.
"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."
The two academics say that other studies suggest that what people find attractive has been shaped by centuries of evolutionary and cultural forces.
For example, evolutionary theories suggest females are attracted to male displays of pride because they imply status, competence and an ability to provide for a partner and offspring.
"Previous research has shown that these features are among the most attractive male physical characteristics, as judged by women," he says.
The researchers say more work is needed to understand the differing responses to happiness, but suggest the phenomenon can also be understood according to evolutionary psychology, as well as socio-cultural gender norms.
For example, past research has associated smiling with a lack of dominance, which is consistent with traditional gender norms of the "submissive and vulnerable" woman, but inconsistent with "strong, silent" man.
"Previous research has also suggested that happiness is a particularly feminine-appearing expression," Beall adds.
"Generally, the results appear to reflect some very traditional gender norms in Western cultures," says Professor Tracy.
"These include norms and values that many would consider old-fashioned and perhaps hoped that we've moved beyond."
One overall finding of the study -- and one that might not surprise those who have watched guys operate in a nightclub setting -- is that men tend to have lower standards than women when it comes to ranking attractiveness.
Sex & Relationships
The study from the University of British Columbia is clear -- 'smiley' guys are at a serious disadvantage when it comes to initial attraction, while single girls need to turn on the charm and send out some happy vibes. Applying this research to some well known faces, the celeb role models men and women need to study include: