• Certain psychological factors make it more likely — though not certain — that two people will fall in love.
  • Some factors are based in biology, like the way you smell.
  • Other factors are behavioral, like your body language.

Love is mysterious, but it’s probably not destiny.

According to the research, your hormones, interests, and upbringing all help determine who you fall for — and who falls for you.

Since your partner plays a significant role in your long-term health, happiness, and even your career prospects, we’ve scoured the studies and collected some of the psychological reasons two people click.

If you’re really, really alike

Decades of studies have shown that the cliché that “opposites attract” is totally off.

“Partners who are similar in broad dispositions, like personality, are more likely to feel the same way in their day-to-day lives,” said Gian Gonzaga, lead author of a study of couples who met on eHarmony. “This may make it easier for partners to understand each other.”

If you look like their opposite-sex parent

University of St. Andrews psychologist David Perrett and his colleagues found that some people are attracted to folks with the same hair and eye color of their opposite-sex parents, as well as the age range they saw at birth.

“We found that women born to ‘old’ parents (over 30) were less impressed by youth, and more attracted to age cues in male faces than women with ‘young’ parents (under 30),” the authors wrote. “For men, preferences for female faces were influenced by their mother’s age and not their father’s age, but only for long-term relationships.”

If you smell right

A University of Southern California study of women who were ovulating suggested that some prefer the smell of T-shirts worn by men with high levels of testosterone.

This matched with other hormone-based instincts: Some women also preferred men with a strong jaw line when they were ovulating.

If you keep your hands and torso open

Body-language experts agree that posture can speak just as loud as words.

Keeping your hands stuffed in your pockets and your shoulders turned inward sends the signal that you’re not interested. But talking with your hands and standing in an open stance shows that you’re available.

If you stare into each other’s eyes for two minutes

University of Massachusetts psychologist Joan Kellerman asked 72 unacquainted undergrads to pair off and stare into each other’s eyes for two minutes.

“They later reported they had increased feelings of passionate love and affection towards the other person,” Scientific American reports. “This suggests that long periods of eye contact can connect you to someone and even ignite feelings of love inside you for that person you have never previously met.”

If you literally ‘warm’ your date up

Yale psychologist John Bargh performed an experiment in which participants held warm or cold beverages and had to rate whether someone’s personality was warm or cold. Participants who held warm beverages judged the person to have a warm personality, because their minds were already primed to think that way.

If you take someone on a coffee date instead of an ice-cream date, they may feel more warmly toward you.

If you own a dog

In a University of Michigan experiment, women read vignettes about men. Whenever the story featured a person who owned a dog, women rated them with higher long-term attractiveness.

This is because, researchers have hypothesized, pet ownership could signal a nurturing person or one with a tendency toward relationship commitment. It could also make you appear more relaxed, approachable, and happy .

If they are considered equally desirable

The “matching hypothesis” suggests that people pair up with partners who are about as attractive and desirable as they are. A 2011 study , published in the journal Personality and Social Psychology Bulletin, suggests that’s only sort-of true.

The study found that most online daters do in fact try to date people who are “out of their league,” as in more attractive. However, that same study also found that online daters select other online daters who are about as popular as they are.

If you get Botox

In a European study about facial age and attractiveness, researchers wanted to determine whether Botox actually does help women find partners.

The women who went through facial procedures experienced a significant reduction in perceived age, and people rated them as much more attractive and healthy. The more treatments the women received, the more they were considered youthful, healthy, and attractive.

If you play music

Researchers in France found that musical practice is associated with sexual selection. In an experiment, a young man holding either a guitar case or sports bag asked 300 young women on the street for their numbers. When the man held the guitar case, more women were willing to give him their number.

If you wear the color red

In a Slovakian research study, women who wore the color red were more successful in mating-game scenarios. This can be attributed to sexual signaling, because women use the color red to attract potential mates.

Women are attracted to red on men, too, since, as HuffPost reports, it signals status .

If you have a certain type of facial hair

In an Australian experiment , researchers found that women consider faces with heavy stubble more attractive than heavy beards, light stubble, or clean-shaven faces.

Beyond attractiveness, researchers also found that facial hair affects perceived fertility as well. The more facial hair a man had, the more masculine a woman perceived him to be — especially when she was in the fertile phase of her menstrual cycle.

If you care about the environment

It’s easy being green — but only if you’re seeking something serious.

A 2016 study, published in the Journal of Social Psychology, found that men and women who make eco-friendly purchases are perceived as more desirable for long-term relationships, while those who make luxury purchases are perceived as more physically attractive and more desirable for short-term relationships.

If you play generally hard to get

A 2014 study, published in the Journal of Experimental Psychology General, found that men in a speed-dating experiment wanted a woman more when she played hard-to-get by acting disinterested in the men’s questions. But these findings only applied in certain situations.

Specifically, the men had to feel “committed” to the woman, which in this study meant that they’d chosen her as their partner, instead of being assigned to her.

It’s also worth noting that, even though the men wanted the woman more when she played hard to get, they liked her less.

Other research suggests that playing hard-to-get is a nuanced topic: A 1979 paper published in the Journal of Research in Personality found that people who are discriminating but indicate that they like you are seen as more appealing.

If you display the right facial expression

Happiness is generally attractive on women — but not so much on men.

In 2011, researchers conducted experiments on more than 1,000 people, showing them photographs of members of the opposite sex and asking them how attractive the people in the photos were.

Results, published in the journal Emotion, showed that men rated women most attractive when they looked happy and least attractive when they displayed pride. Women, on the other hand, rated men most attractive when they displayed pride and least attractive when they looked happy.

Interestingly, shame was pretty attractive in both men and women.

If they don’t know whether you like them

A little mystery might help you out on the dating front. 2011 research, published in the journal Psychological Science, suggests that people like you more when they don’t know if you like them.

For the study, some women saw photos of men who had seen their Facebook profiles and really liked them. Other women saw photos of men who had seen their Facebook profiles and rated them average.

A third group of women saw photos of men who had seen their Facebook profiles — but the researchers didn’t reveal whether the men had liked them or not. (In reality, the researchers had made up all this information about who liked who.)

Sure enough, women liked the men most when it was unclear whether the men had liked their profiles.

If you look similar enough to their current or last partner

We may all have a “type” — but women are more likely to adhere to it than men are.

In one 2011 study , researchers from the UK found that both men and women rated opposite-sex faces more attractive when they closely resembled their current or most recent partners. Men, however, were less attracted to faces that looked similar to their current partner than women were.

If you use a lot of hand gestures

Fill up the physical space around you with hand gestures and an expansive posture. In one 2016 study, published in the Proceedings of the National Academy of Sciences, researchers observed men and women in speed-dating sessions.

Results showed that people were twice as likely to say that they wanted to see their partners again when those partners moved their hands and arms, compared to when their partners sat still.

For the same study, researchers set up profiles for men and women on a GPS-based dating app, showing them in both expansive and contractive postures. Sure enough, people were selected more often when they were pictured in expansive postures.

If you share three basic compatibilities

According to the work of Canadian psychologist Eric Berne, the best-matched couples vibe on three different levels.

His popular books about the model became best sellers, namely ” The Games People Play .” Drawing somewhat on Sigmund Freud, his theory argued that every person has three ” ego states “:

The parent: What you’ve been taught

The child: What you have felt

The adult: What you have learned

When two people are really compatible, they connect along each tier. Couples therapist Peter Pearson gave us a few questions for figuring out compatibility at each level:

The parent: Do you have similar values and beliefs about the world?

The child: Do you have fun together? Can you be spontaneous? Do you think your partner’s hot? Do you like to travel together?

The adult: Does each person think the other is bright? Are you good at solving problems together?

If you respond to their ‘bids’ for attention and they do the same for you

Starting — and growing — a relationship seems to largely depend on how people attend to one another.

Over 40 years of studying couples, psychologist John Gottman says it’s a matter of “bids.” For example, if a bird-loving wife points out to her husband that a goldfinch just flew landed in a nearby tree, he can “turn away” from her by dismissing the remark or “turn toward” her by sharing her enthusiasm.

As Emily Esfahani Smith reported in the Atlantic , the results of the “bids” are staggering: in one of Gottman’s studies of marriage, couples who divorced after six years had the “turn toward” reply 33% of the time, and the couples that were still together had the “turn toward” 87% of the time.

Originally published at www.businessinsider.com.

This is an updated version of an article originally written by Drake Baer and Maggie Zhang.

More from Business Insider:

Science says people decide these 9 things within seconds of meeting you

How you know you’ve met ‘the one’ according to 3 relationship experts

7 physical and psychological changes that happen when you fall in love

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