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When it comes to romantic relationships, it’s difficult to overstate the importance of first impressions.

A recent study  explored how initial impressions predict relational outcomes, including how the dating market’s determinations of desirability shapes those initial opinions before couples even get a chance to see if they have any chemistry one-on-one.

“We found that the factors that mattered the most in predicting romantic interest were the extent to which people agreed that certain partners had desirable traits,” says Emily Impett, a professor of psychology at the University of Toronto Mississauga who was a member of a team of researchers involved in a study on the topic.

In other words, potential mates already had to present a good “resume” of qualities considered important by society – such as physical attractiveness – just to get to that first face-to-face meeting. This factor is known as “partner effects” or “mate value.”

Impett and her research partners drew data from more than 6,600 speed dates in the study.

Right behind the importance of the “partner effect” was the “relationship effect,” or “the extent to which people uniquely desired each other,” says Impett, who earned her PhD at University of California, Los Angeles. Known more plainly as compatibility, the relationship effect is the elusive quality that turns dates into relationships.

“Compatibility has been very hard to predict before people first interact – despite the popularity of dating apps which would make us believe that it's possible to predict compatibility before two people interact with each other,” says Impett, who is also the director of ��˾��ֱ��’s .

“We thought that once people have had an initial interaction with another person, compatibility would matter. And in fact, across our studies, we found that it did – it predicted how interested people were in another person and who they reached out to.”

The third factor the study considered was the “actor effect,” which examines if the grader tended towards high or low ratings overall.

The researchers organized three speed dating events that paired up university students of various gender identities: Two sessions were held at Northwestern University in Illinois, while the third was at the Toronto 2015 Anime North comic book convention. Surveys issued immediately after the speed dates – and again 24 hours later – asked participants to rate initial desire and interest in further interaction.

The researchers found that first impressions based on partner effects and relationship effects were the strongest predictors of romantic outcomes. Impett says the researchers believe there is a very good reason why humans put so much stock in first impressions: It’s good for our evolution.

“The mating of humans evolved in the context of monogamous pair-bonded relationships,” she says. “When choosing a potential mate or partner, humans needed to consider not just whether a potential mate had attractive qualities – had good genes, was fertile – but also whether that person would make a suitable partner to raise offspring and that they could have a lasting relationship with that person in the long term.”