From The Science Will Set You Free (more or less) Department:

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 skeptical 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.

Exactly! No science, no knowledge. Only ignorance.

("Science is not taken in the restricted meaning of natural sciences, but in the general one given to the word by Aristotle and St. Thomas Aquinas. Aristotle defines science as a sure and evident knowledge obtained from demonstrations. This is identical with St. Thomas's definition of science as the knowledge of things from their causes." See science link above.)

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.