When it comes to sex, we are quite the shallow bunch: Something as simple as the smell of your sweat, the dilation of your pupils or the proportion of your waistline can make all the difference.

Yet science also shows that personality traits matter at least some of the time, both in the long-term partners we choose and our shorter-term, umm, relationships.

So say you want to have more sex — hypothetically, of course. Should you offer flowers or act aloof?

The answer is complicated. Here’s just some of what science has figured out about the mating game and personality. The findings are as diverse — and as seemingly contradictory — as we humans.

Nice Men (and Women) Can Seal the Deal

Recent research published in the British Journal of Psychology showed that altruism may put you in the best position (ahem) to find a willing partner. The results of two trials conducted by Canadian researchers showed that men and women who scored higher on altruism also said they were more desirable to the opposite sex.

Men who scored higher on altruism also reported more sexual partners, and more casual hook-ups compared to female participants. If altruistic participants were in long-term relationships, those altruistic men and women said they had more sex over the last 30 days.

Researchers didn’t just take their word for it. Watch the video above for more.

Honesty Is Sexy

Let’s be real. Humans are drawn to other humans they find physically attractive. But there may be more going on than simple hotness, according to a study published in the journal Personality and Individual Differences.

Researchers from China divided 120 study participants into into three groups. Before the experiment began, all of these participants, 60 men and 60 women, were asked to rate 60 random Google photographs of Chinese women. The faces were unfamiliar to the study participants, and all the women in the photos had neutral expressions.

Two weeks later, the study participants were asked to look at the photos again. But this time, one group of participants was given the same photos with descriptions of positive personality traits such as decent and honest. Another group was given the photos that now contained negative personality traits including evil and mean. A third group was given no information about personality.

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The researchers found no difference among the groups during the first cycle of the experiment. But in the second cycle, those photos that contained positive descriptions of personality traits scored high on attractiveness. Those with negative descriptors scored lowest.

The researchers say “what is good is beautiful,” and this so-called “halo effect” shows that desirable personality traits are reflected in facial preference.

But We Like The Dark Side, Too

Men (and women) may say they like nice humans, but sometimes what we do tells a different story. When it comes to mating, both sexes seem to be drawn to (cue the theme from Jaws) “The Dark Triad.” That psych-speak for the personality traits of Machiavellianism, narcissism and psychopathy.

We know it’s true: Mean girls and bad boys can be pretty popular, at least for a while. It seems the Dark Triad may boost short-term mating prospects for men, and, importantly, women too, despite being “fundamentally callous, exploitative traits that deviate from species-typical cooperation,” explains Dr. Gregory Louis Carter, a lecturer in Psychology at York St John University.

Narcissism, for example, is related to good physical and mental health and longer life while Machiavellianism is linked to social flexibility. Psychopathy results in impulsivity and sensation-seeking, which can be extremely seductive, he says.

So men and women who score high on the Dark Triad scale may appeal to because they are confident, persistent, have a higher-ranking status and look pretty darn good.

The ‘Big Five’ Traits That Mean More Action

If you want to learn about your personality traits, most psychologists suggest looking at the “Big Five.” That’s a group of descriptors that include openness, conscientiousness, extraversion, agreeableness, and neuroticism. Taken together those Big Five can influence our health as well as our sex lives.

In a study of newlyweds, researchers from Florida State University shed some light on how a couples’ personalities influenced how often newlyweds had sex. Although the study did not look at non-married individuals, there is a good chance the results would hold true, says co-author Dr. Andrea Meltzer, Assistant Professor of Psychology at Florida State University.

The study included data on 278 newlywed heterosexual couples, all of whom were married less than six months. They kept a two-week journal detailing their life and how often they had sex. The couples also took a Big Five test to figure out their individual personalities.

Here’s what they found. There was absolutely zero link between the man’s personality traits and how often the couple had sex. But higher levels of the traits of agreeableness and openness among wives led to more frequent sex.

“Openness refers to the willingness to explore new idea and experiences,” says Meltzer, adding these folks tend to like art and abstract ideas, often try new and different foods, and love novelty.

Agreeableness means you can get along well with others and maintain social harmony. These folks are often perceived as kind, generous, and trustworthy, she says.

No surprise that husbands and wives who scored low on neuroticism were more satisfied with their sex lives. But husbands who scored low in openness also were more satisfied with their sex lives. Maybe these guys just weren't into novelty.

Make ‘Em Laugh

Humor always ranks near the top of seemingly any list of what men and women find attractive in each other.

Some research shows that humor gets us hot because it may reveal intelligence, a creative bent, and robust genes that equate to not only good health but also good parenting traits.

Although humor is almost universally appealing, there are sex differences. “Women want to be made to laugh more than men,” says Carter. “Men want to be able to induce laughter, though probably not in the bedroom.”