Illustration by Kristin Vogel

Many of us think we know which traits we want our ideal partner to have. Yet for some reason we often find ourselves attracted to people who possess none of those qualities. Sometimes we meet potential mates who seem perfect on paper but with whom we have no immediate spark. Other times we feel instant chemistry but end up with an incompatible long-term partner.

Attraction may feel natural, but that doesn’t mean it’s random. To figure out how we choose romantic partners, scientists have done everything from study symmetry of the human face to observe subconscious reactions to the smell of armpit sweat. If there were a formula for lasting love, what percentage of human compatibility can we credit to our behavior and what percentage is simple biology?

Surprisingly, research shows that attraction and compatibility can be predicted early on by interpreting some remarkable biological clues. Some signs of attraction and compatibility are obvious, but many may amaze you. Here are 6 surprising predictors that sparks will fly:

1. DNA: Your genes matter more than your jeans.

According to the biotechnology research company Instant Chemistry, up to 40% of physical attraction is determined by your genes. We are biologically programmed to feel that instant “spark” with someone who has a different genetic makeup than our own, and research shows that genetically compatible partners are more likely to make it work long-term.

“But not only do biologically compatible partners produce children with strong immune systems, these couples also enjoy more satisfying sex lives, greater marital stability, and increased fertility rates—and they find each other more attractive!” Instant Chemistry reports.

2. Facial features: The eyes (and more) have it.

The shape and angle of a person’s face provides insight into reproductive health. Evolutionary biologist Randy Thornhill of the University of New Mexico explains that estrogen influences bone growth in a woman’s face and chin, leading to moderately small and short facial features and prominent eyes. Men’s faces are shaped by testosterone, which results in a larger face and jaw and a more prominent brow. The prevalence of these traits advertises reproductive health, which makes a person seem more attractive to the opposite sex.

3. Smell: Your perfect match might be right under your nose.

Human odor preferences are shaped by sexual selection, and we are evolutionarily inclined to be sensitive to odor cues. Human sweat carries a lot of information about a person’s gender, genetic compatibility, and reproductive state. Those who maintain a good diet, an indicator of overall health, smell healthier and are more attractive to others. In fact, a team of biologists from the Czech Republic recently found that subjects who ate garlic, which is chock-full of antioxidants, smelled more attractive—ironically!

4. Language: What did you say?

Studies show that people who use the same kinds of function words (pronouns and conjunctions) when speaking are more likely to be a successful match. After looking at speed-dating results, researchers found a link between function-word similarity and the speed-daters’ odds of going on a second date, as well as couples’ odds of staying together three months after the experiment. Interestingly, language similarity turned out to be an even more accurate predictor of relationship success when compared to other factors such as “perceived similarity with one’s date, perceived relationship quality, and how many words people spoke to each other during conversation,” according to a study by Texas Tech University.

5. Color: Red is the new black.

There’s a reason why red is the color of love and passion. Research shows that both men and women perceive people wearing the color red as powerful, strong, and dominant. Studies also show that the color can produce physical responses like increased heart rate and heightened sense of smell. For women, the color red enhances a man’s attractiveness. Researchers from the University of Rochester found that female study participants even rated the same man as more attractive after seeing him against a red backdrop. Men in another study gave higher tips to waitresses wearing red.

But where does the link between red and sexual attraction originate? Scientists think it’s associated with physical signs of sexual excitement like redness in the erogenous areas and facial blushing. In addition, strong blood flow and high testosterone levels in men often produce a reddish tone to the skin. The color itself seems to have evolved into a sign of reproductive health and potential.

6. Voice pitch: It’s not what you say but how you say it.

If you’ve ever wondered why women swoon over men with low-pitched voices, it’s because we tend to associate men with deep baritones with larger bodies. In contrast, results of a study from University College London showed that male listeners preferred higher-pitched, breathier female voices, which they associated with a smaller body size. Deep male voices and high-pitched female voices are perceived as more attractive because of this association with body size.

Needless to say, the rules of attraction are complex, involving much more than good looks and a witty pickup line. Hot or not, research shows that your body knows what you’re attracted to better than you do! If you’re looking for love, you can put on a red shirt, eat some garlic, and hope for the best. Or you can follow the roadmap to love that’s already in your DNA. After all, while love is not an exact science, you may have had the clues to finding it all along.

Click here to see Rose’s tips for healthy and happy relationships