Although attractive people do tend to select other attractive people in many romantic relationships, new research by Lucy Hunt, Paul Eastwick, and Eli Finkel indicates that there are predictable exceptions. Couples who spark a romantic relationship shortly after meeting are most likely to match in physical attractiveness; however, when people get to know each other well over an extended period of time before dating, it’s not unusual to see greater disparity in their physical appeal.

The tendency to pair with someone who is similar in physical, behavioral, and psychological characteristics is known as assortative mating, and this phenomenon has intrigued experts in psychology, sociology, genetics, and even economics for over a century. While assortative mating is a robust finding, scientists disagree about why it occurs. One popular theory argues a market-based explanation: Individuals compete for the most desirable mates, and those who are themselves very desirable are the most successful in this competition. Highly appealing people thus pair with other very appealing people, while moderately appealing people pair with other fairly appealing people, and so forth.

Hunt and colleagues speculated that assortative mating patterns may attenuate as the time a couple spends together before engaging in a romantic relationship increases. Why? Their belief is that romantic desirability is both objective and subjective.