Sexual orientation revealed by body type and motion, study suggests

"We already know that men and women are built differently and walk differently from each other and that casual observers use this information as clues in making a range of social judgments," said lead author Kerri Johnson, UCLA assistant professor of communication studies. "Now we've found that casual observers can use gait and body shape to judge whether a stranger is gay or straight with a small but perceptible amount of accuracy."

Johnson and colleagues at New York University and Texas A&M measured the hips, waists and shoulders of eight male and eight female volunteers, half of whom were gay and half straight. The volunteers then walked on a treadmill for two minutes as a three-dimensional motion-capture system similar to those used by the movie industry to create animated figures from living models made measurements of their motions, allowing researchers to track the precise amount of shoulder swagger and hip sway in their gaits.

Based on these measurements, the researchers determined that the gay subjects tended to have more gender-incongruent body types than their straight counterparts (hourglass figures for men, tubular bodies for women) and body motions (hip-swaying for men, shoulder-swaggering for women) than their straight counterparts.

In addition, 112 undergraduate observers were shown videos of the backsides of the volunteers as they walked at various speeds on the treadmill. The observers were able to determine the volunteers' sexual orientation with an overall rate of accuracy that exceeded chance, even though they could not see the volunteers' faces or the details of their clothing. Interestingly, the casual observers were much more accurate in judging the orientation of males than females; they correctly categorized the sexual orientation of men with more than 60 percent accuracy, but their categorization of women did not exceeded chance.

The findings build on recent research that shows that casual observers can often correctly identify sexual orientation with very limited information. A 1999 Harvard study, for example, found that just by looking at the photographs of seated strangers, college undergraduates were able to judge sexual orientation accurately 55 percent of the time.

"Studies like ours are raising questions about the value of the military's 'don't ask, don't tell' policy," Johnson said. "If casual observers can determine sexual orientation with minimal information, then the value in concealing this information certainly appears questionable. Given that we all appear to be able to deduce this information to some degree with just a glance, more comprehensive policies may be required to protect gays against discrimination based on their sexual orientation."

The findings also are part of mounting evidence suggesting that sexual orientation may actually be what social scientists call a "master status category," or a defining characteristic that observers cannot help but notice and which has been scientifically shown to color all subsequent social dealings with others.

"Once you know a person's sexual orientation, the fact has consequences for all subsequent interactions, and our findings suggest that this category of information can be deduced from subtle clues in body movement," Johnson said.