MADISON, Wis. -- There is more to beauty than meets the stranger's eye, according to results from three studies examining the influence of non-physical traits on people's perception of physical attractiveness. The results, which show that people perceive physical appeal differently when they look at those they know versus strangers, are published in the recently released March issue of Evolution and Human Behavior.
In many studies evaluating physical attractiveness, people are often shown an array of strangers' photos, computer-generated images or line drawings and asked to identify which ones, based on differences in physical features, are most attractive. Results from these studies suggest that physically attractive traits include high degrees of bilateral facial symmetries, such as eyes that are identical in shape and size, and waist-to-hip ratios of 0.7 for women and 0.9 for men.

"You can find study after study that focuses on which waist-to-hip ratios or particular facial features people find physically attractive, and these studies have captured popular attention," says Kevin Kniffin, an honorary fellow in the anthropology department at the University of Wisconsin-Madison and an adjunct assistant professor at Binghamton University.
Kniffin co-authored the Evolution and Human Behavior paper with David Sloan Wilson, an evolutionary biologist at Binghamton University.
While these past studies do show which features people find physically appealing after just a glance, they overlook the non-physical traits that may influence a person's perception of another's beauty over time. In other words, people may see physical attractiveness differently when they know that person's other qualities, usually invisible to strangers, says Kniffin.

Pressures selecting for the influence of non-physical traits on the perception of physical beauty have operated across millennia. According to evolutionary theory, many animals, including humans, are attracted to those who are likely to increase their own fitness -- the likelihood of surviving and reproducing.
In the case of humans, "the fitness value of potential social partners depends at least as much on non-physical traits -- whether they are cooperative, dependable, brave, hardworking, intelligent and so on -- as physical factors, such as smooth skin and symmetrical features," says Wilson. "It follows that non-physical factors should be included in the subconscious assessment of beauty."

To systematically consider the influence of non-physical traits on how people who are familiar with each other perceive physical appeal, Kniffin and Wilson conducted three studies of beauty involving people who know each other and people who don't. For all studies, the participants were asked to rate physical attractiveness and non-physical traits such as liking, respect and talent. Strangers rated only physical attractiveness.

In the first study, the participants rated people photographed in high school yearbooks, including one that belonged to each participant. In the second, members of a college sports team, as well as strangers, rated each team member. Finally, students in a summer archaeological excavation course rated each other on the first day of class and six weeks later at the end of the course. "In each case, non-physical traits known only to familiars, such as how much the person was liked, respected and contributed to shared goals, had a large effect on the perception of physical attractiveness that was invisible to the strangers," says Wilson.

Each study provided an illustrative example of this finding. For instance, one middle-aged subject who had not seen the familiar person photographed in the yearbook for decades responded with absolute disgust when she recalled the person's character and described that person as ugly. In the sports team study, team members considered the slacker to be ugly and one of the leaders to be physically attractive, while strangers, blind to the members' relative contributions, rated them as equally attractive on the basis of photographs. And, after six weeks of working together on an archaeological dig, students' perception of physical attractiveness changed based on interactions during the course.

In a world where people are bombarded with messages about physical attractiveness from magazines, television and advertisements, the researchers say their results point to the influence of other traits on people's perception of physical beauty. Kniffin adds that he hopes these findings may encourage the consumers of this information to rethink the value of cosmetic surgery, especially if it involves risk.

At the end of their paper, the researchers offer this beauty tip: "If you want to enhance your physical attractiveness, become a valuable social partner."

Look at what that did for Abraham Lincoln. "During his lifetime, he was regarded as so ugly that he once quipped, 'If I were two-faced, do you think I would be wearing this one?'" says Wilson. "Yet his physical features have become beloved, not because of their physical qualities per se, but because of what they stand for."