By BENEDICT CAREY Published: July 5, 2005
Some people are attracted to women; some are attracted to men. And some, if Sigmund Freud, Dr. Alfred Kinsey and millions of self-described bisexuals are to be believed, are drawn to both sexes.
But a new study casts doubt on whether true bisexuality exists, at least in men.
The study, by a team of psychologists in Chicago and Toronto, lends support to those who have long been sceptical that bisexuality is a distinct and stable sexual orientation.
People who claim bisexuality, according to these critics, are usually homosexual, but are ambivalent about their homosexuality or simply closeted. "You're either gay, straight or lying," as some gay men have put it.
In the new study, a team of psychologists directly measured genital arousal patterns in response to images of men and women. The psychologists found that men who identified themselves as bisexual were in fact exclusively aroused by either one sex or the other, usually by other men.
The study is the largest of several small reports suggesting that the estimated 1.7 percent of men who identify themselves as bisexual show physical attraction patterns that differ substantially from their professed desires.
"Research on sexual orientation has been based almost entirely on self-reports, and this is one of the few good studies using physiological measures," said Dr. Lisa Diamond, an associate professor of psychology and gender identity at the University of Utah, who was not involved in the study.
The discrepancy between what is happening in people's minds and what is going on in their bodies, she said, presents a puzzle "that the field now has to crack, and it raises this question about what we mean when we talk about desire."
"We have assumed that everyone means the same thing," she added, "but here we have evidence that that is not the case."
Several other researchers who have seen the study, scheduled to be published in the journal Psychological Science, said it would need to be repeated with larger numbers of bisexual men before clear conclusions could be drawn.
Bisexual desires are sometimes transient and they are still poorly understood. Men and women also appear to differ in the frequency of bisexual attractions. "The last thing you want," said Dr. Randall Sell, an assistant professor of clinical socio-medical sciences at Columbia University, "is for some therapists to see this study and start telling bisexual people that they're wrong, that they're really on their way to homosexuality."
He added, "We don't know nearly enough about sexual orientation and identity" to jump to these conclusions.
In the experiment, psychologists at Northwestern University and the Center for Addiction and Mental Health in Toronto used advertisements in gay and alternative newspapers to recruit 101 young adult men. Thirty-three of the men identified themselves as bisexual, 30 as straight and 38 as homosexual.
The researchers asked the men about their sexual desires and rated them on a scale from 0 to 6 on sexual orientation, with 0 to 1 indicating heterosexuality, and 5 to 6 indicating homosexuality. Bisexuality was measured by scores in the middle range.
Seated alone in a laboratory room, the men then watched a series of erotic movies, some involving only women, others involving only men.
Using a sensor to monitor sexual arousal, the researchers found what they expected: gay men showed arousal to images of men and little arousal to images of women, and heterosexual men showed arousal to women but not to men.
But the men in the study who described themselves as bisexual did not have patterns of arousal that were consistent with their stated attraction to men and to women. Instead, about three-quarters of the group had arousal patterns identical to those of gay men; the rest were indistinguishable from heterosexuals.
"Regardless of whether the men were gay, straight or bisexual, they showed about four times more arousal" to one sex or the other, said Gerulf Rieger, a graduate psychology student at Northwestern and the study's lead author.
Although about a third of the men in each group showed no significant arousal watching the movies, their lack of response did not change the overall findings, Mr. Rieger said.
Since at least the middle of the 19th century, behavioural scientists have noted bisexual attraction in men and women and debated its place in the development of sexual identity. Some experts, like Freud, concluded that humans are naturally bisexual. In his landmark sex surveys of the 1940's, Dr. Alfred Kinsey found many married, publicly heterosexual men who reported having had sex with other men.
"Males do not represent two discrete populations, heterosexual and homosexual," Dr. Kinsey wrote. "The world is not to be divided into sheep and goats."
By the 1990's, Newsweek had featured bisexuality on its cover, bisexuals had formed advocacy groups and television series like "Sex and the City" had begun exploring bisexual themes.
Yet researchers were unable to produce direct evidence of bisexual arousal patterns in men, said Dr. J. Michael Bailey, a professor of psychology at Northwestern and the new study's senior author.
A 1979 study of 30 men found that those who identified themselves as bisexuals were indistinguishable from homosexuals on measures of arousal. Studies of gay and bisexual men in the 1990's showed that the two groups reported similar numbers of male sexual partners and risky sexual encounters. And a 1994 survey by The Advocate, the gay-oriented newsmagazine, found that, before identifying themselves as gay, 40 percent of gay men had described themselves as bisexual.
"I'm not denying that bisexual behaviour exists," said Dr. Bailey, "but I am saying that in men there's no hint that true bisexual arousal exists, and that for men arousal is orientation."
But other researchers - and some self-identified bisexuals - say that the technique used in the study to measure genital arousal is too crude to capture the richness - erotic sensations, affection, admiration - that constitutes sexual attraction.
Social and emotional attraction are very important elements in bisexual attraction, said Dr. Fritz Klein, a sex researcher and the author of "The Bisexual Option."
"To claim on the basis of this study that there's no such thing as male bisexuality is overstepping, it seems to me," said Dr. Gilbert Herdt, director of the National Sexuality Resource Center in San Francisco. "It may be that there is a lot less true male bisexuality than we think, but if that's true then why in the world are there so many movies, novels and TV shows that have this as a theme - is it collective fantasy, merely a projection? I don't think so."
John Campbell, 36, a Web designer in Orange County, California., who describes himself as bisexual, also said he was sceptical of the findings.
Mr. Campbell said he had been strongly attracted to both sexes since he was sexually aware, although all his long-term relationships had been with women. "In my case I have been accused of being heterosexual, but I also feel a need for sex with men," he said.
Mr. Campbell rated his erotic attraction to men and women as about 50-50, but his emotional attraction, he said, was 90 to 10 in favour of women. "With men I can get aroused, I just don't feel the fireworks like I do with women," he said.
About 1.5 percent of American women identify themselves bisexual. And bisexuality appears easier to demonstrate in the female sex. A study published last November by the same team of Canadian and American researchers, for example, found that most women who said they were bisexual showed arousal to men and to women.
Although only a small number of women identify themselves as bisexual, Dr. Bailey said, bisexual arousal may for them in fact be the norm.
Researchers have little sense yet of how these differences may affect behaviour, or sexual identity. In the mid-1990's, Dr. Diamond recruited a group of 90 women at gay pride parades, academic conferences on gender issues and other venues. About half of the women called themselves lesbians, a third identified as bisexual and the rest claimed no sexual orientation. In follow-up interviews over the last 10 years, Dr. Diamond has found that most of these women have had relationships both with men and women.
"Most of them seem to lean one way or the other, but that doesn't preclude them from having a relationship with the nonpreferred sex," she said. "You may be mostly interested in women but, hey, the guy who delivers the pizza is really hot, and what are you going to do?"
"There's a whole lot of movement and flexibility," Dr. Diamond added. "The fact is, we have very little research in this area, and a lot to learn."