The Biology Of Beauty

What, then, is beauty made of? What are the innate rules we follow in sizing each other up? We're obviously wired to find robust health a prettier sight than infirmity. "All animals are attracted to other animals that are healthy, that are clean by their standards and that show signs of competence," says Rutgers University anthropologist Helen Fisher. As far as anyone knows, there isn't a village on earth where skin lesions, head lice and rotting teeth count as beauty aids. But the rules get subtler than that. Like scorpion flies, we love symmetry. And though we generally favor average features over unusual ones, the people we find extremely beautiful share certain exceptional qualities.

WHEN RANDY THORNhill started measuring the wings of Japanese scorpion flies six years ago, he wasn't much concerned with the orgasms and infidelities of college students. But sometimes one thing leads to another. Biologists have long used bilateral symmetry -- the extent to which a creature's right and left sides match -- to gauge what's known as developmental stability. Given ideal growing conditions, paired features such as wings, ears, eyes and feet would come out matching perfectly. But pollution, disease and other hazards can disrupt development. As a result, the least resilient individuals tend to be the most lopsided. In chronicling the scorpion flies' daily struggles, Thornhill found that the bugs with the most symmetrical wings fared best in the competition for food and mates. To his amazement, females preferred symmetrical males even when they were hidden from view; evidently, their smells are more attractive. And when researchers started noting similar trends in other species, Thornhill turned his attention to our own.

Working with psychologist Steven Gangestad, he set about measuring the body symmetry of hundreds of college-age men and women. By adding up right-left disparities in seven measurements -- the breadth of the feet, ankles, hands, wrists and elbows, as well as the breadth and length of the ears -- the researchers scored each subject's overall body asymmetry. Then they had the person fill out a confidential questionnaire covering everything from temperament to sexual behavior, and set about looking for connections. They weren't disappointed. In a 1994 study, they found that the most symmetrical males had started having sex three to four years earlier than their most lopsided brethren. For both men and women, greater symmetry predicted a larger number of past sex partners.

That was just the beginning. From what they knew about other species, Thornhill and Gangestad predicted that women would be more sexually responsive to symmetrical men, and that men would exploit that advantage. To date, their findings support both suspicions. Last year they surveyed 86 couples and found that women with highly symmetrical partners were more than twice as likely to climax during intercourse (an event that may foster conception by ushering sperm into the uterus) than those with low-symmetry partners. And in separate surveys, Gangestad and Thornhill have found that, compared with regular Joes, extremely symmetrical men are less attentive to their partners and more likely to cheat on them. Women showed no such tendency.

It's hard to imagine that we even notice the differences between people's elbows, let alone stake our love lives on them. No one carries calipers into a singles bar. So why do these measurements predict so much? Because, says Thornhill, people with symmetrical elbows tend to have "a whole suite of attractive features." His findings suggest that besides having attractive (and symmetrical) faces, men with symmetrical bodies are typically larger, more muscular and more athletic than their peers, and more dominant in personality. In a forthcoming study, researchers at the University of Michigan find evidence that facial symmetry is also associated with health. In analyzing diaries kept by 100 students over a two-month period, they found that the least symmetrical had the most physical complaints, from insomnia to nasal congestion, and reported more anger, jealousy and withdrawal. In light of all Thornhill and Gangestad's findings, you can hardly blame them.