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,” Ms. Hunt said. “But the opposite is just as likely to happen, too. Someone can become less attractive.”

These changes in attitudes, Dr. 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.