Certain factors make it more likely — though not certain — that two people will fall in love.
Some factors are biological, 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 speaks louder than 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.