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For couples, time can upend the laws of attraction

Experts say more dates often make that schlub or plain jane appealing

After decades of studying the concept of “mate value,” social scientists finally have the data necessary to explain the romantic choices in “Knocked Up” and “Pride and Prejudice.”

The flabby, unkempt Seth Rogen is no one’s dream date, especially when he’s playing the unemployed guy in “Knocked Up” who spends his days smoking pot and ogling naked celebrities. He has none of the obvious qualities that make a mate valuable: good looks, money, social status.

Yet somehow this slacker eventually winds up with a successful television journalist, played by the gorgeous Katherine Heigl. You could dismiss this as a pathetically absurd fantasy by male screenwriters, but the film is plausible enough to audiences to have grossed over $200 million.

The schlub-gets-babe is a reliable formula at the box office —Adam Sandler has made a career of it. And the mismatched couple isn’t just a male dream.

There are hundreds of romance novels in a category that some have named “Plain Jane and Hot Stud,” a theme that was equally popular when Jane Austen wrote “Pride and Prejudice.” Tall and good-looking, endowed with a “noble mien,” Mr. Darcy initially denigrates Elizabeth Bennet’s appearance: “She is tolerable, but not handsome enough to tempt me.” He notes “more than one failure of perfect symmetry in her form.”

Even worse for the rich Mr. Darcy, her family’s social status is “so decidedly beneath my own.”

His initial reactions make perfect sense to evolutionary psychologists, because these preferences can improve the odds of passing on one’s genes. Beauty and physical symmetry are markers of a mate’s health and genetic fitness; status and wealth make it more likely that children will survive to adulthood.

It seems logical for people with high mate value to insist on comparable partners, and there’s some evidence that they do. By observing singles pursuing one another at online dating sites and in speed-dating experiments, researchers have found that people tend to end up with those of similar mate value.

That pattern also occurs in married couples: Attractive, well-educated, high-earning people tend to marry people like themselves. In fact, economists say that this growing trend of “assortative mating” is a major cause of income inequality, because a household with two high earners makes so much more money than a household with two low earners (or only one earner).

But just how ruthlessly superficial are people in assessing the value of potential mates? To investigate, psychologists at the University of Texas at Austin asked students to rate the romantic appeal of their opposite-sex classmates.

At the start of the semester, the students pretty much agreed on who in their class was most desirable. But when they were asked again three months later, after spending a semester in a small class together, their judgments varied widely on who was hot and who was not.

“Perceptions of mate value change the more time that people spend together,” said Lucy Hunt, a graduate student who published the study last year with Paul Eastwick, an assistant professor of human development and family sciences.

“Sometimes you get that Seth Rogen happy story, where an unattractive person comes to seem more attractive to one person in particular,” Hunt said. “But the opposite is just as likely to happen, too. Someone can become less attractive.”

These changes in attitudes, Eastwick noted, should mean that there are fewer losers in the mating game, because everyone isn’t vying for the same Mr. or Ms. Right. “As the consensus about who is attractive declines, competition should decline, because the person I think is especially desirable might not be the person you think is especially desirable,” he said.

To test this effect, the Texas researchers joined with Eli Finkel, a professor of psychology at Northwestern University, in a study of couples that was published online this month in Psychological Science.

Some of the couples had been married for five decades; others had been dating for just a few months. Some had known one another for a while before starting a romantic relationship; others had started dating as soon as they met. After being videotaped talking about their relationships, all were rated for physical attractiveness by a group of judges who viewed each partner separately.

When the ratings for partners were compared, there was a clear pattern based on how long the people had known one another before they had begun dating.

If they’d begun going out within a month of meeting, then they tended to be equally attractive physically. But if they’d been acquaintances for a long time, or if they’d been friends before becoming lovers, then someone hot was more liable to end up with someone not so hot.

This gradual change in feelings seems to occur quite often, said the anthropologist Helen Fisher of the Kinsey Institute, who works with on its annual survey of a representative sample of single adults in America.

In the 2012 survey, people were asked a version of the famous question in Christopher Marlowe’s 16th-century poem: “Who ever loved, that loved not at first sight?”

A great many, it turns out. In the survey, 33 percent of men and 43 percent of women answered yes when asked if they had ever fallen in love with someone they did not initially find attractive. Fisher terms this process “slow love,” and says it is becoming more common as people take longer to marry.

“Everyone is terrified that online dating is reducing mate value to just a few superficial things like beauty — whether you swipe left or right on Tinder,” she said in an interview. “But that’s just the start of the process. Once you meet someone and get to know them, their mate value keeps changing.”

When the survey respondents were asked what had changed their feelings, the chief reasons they gave were “great conversations,” “common interests,” and “came to appreciate his/her sense of humor.” All of those factors contribute to Mr. Darcy’s change of heart in “Pride and Prejudice.”