On a typical summer Saturday morning Matt Avery and his wife, Sheila (not their real names), cook breakfast with their two sons, ages five and eight. Then they get organized with towels, goggles and water wings and load the family into the car for an afternoon at the pool. "Weekends are all about family time," Matt says.

Matt and Sheila have been happily married for 11 years. "She's my soul mate," Matt says. "I wouldn't trade my life for the world."

But some people would claim that Matt's life is based on an illusion—that he could not possibly be a dedicated husband and father. Why? Because Matt used to be gay.

According to the National Gay and Lesbian Task Force and at least a few experts, gays do not have a choice about their sexual orientation. If a man or a woman is born gay, he or she will always be gay. Because Matt was gay for most of his young adulthood (ages 17 to 24), the thinking goes, he must still be gay. Pressured by a homomisic society—a society that dislikes and shuns gays—Matt has simply run back inside the closet. Gay activists favor this perspective at least in part because survey data show that people are more sympathetic to gay causes if they believe that sexual orientation is immutable.

The public disclosure by James McGreevey, who announced at an August 2004 press conference that he was resigning as governor of New Jersey, seems to support this view. With his beautiful wife at his side, McGreevey revealed that he was about to be sued by another male for sexual harassment. His announcement suggested, at least to some, that he had always been gay and that his two marriages and two children were somehow less than valid.

Does this perspective have merit? Or are religious conservatives correct in asserting that homosexuality is entirely a matter of choice? A wealth of scientific evidence provides an answer. It turns out that sexual orientation is virtually never a black-and-white matter. Rather it exists on a continuum, with both genes and environment determining where people end up.

Biblical Proportions
It is difficult for most people to think objectively about homosexuality, in large part because biases against it are literally of biblical proportions. According to the book of Leviticus, homosexuality—at least when practiced by males—is prohibited, punishable by death. Thousands of American pulpits to this day repeat the old biblical injunctions, which fuel discomfort with homosexuality at every layer of our society.

Until recent decades, prejudice against homosexuality has persisted even in the mental health professions. In the 1970s most therapists still held that homosexuality was a psychological disorder, akin to a disease. In the 1968 edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM)—the indispensable diagnostic tool used by therapists—homosexuality appeared in the section on sexual deviations as an instance of an aberration in which sexual interests are "directed primarily toward objects other than people of the opposite sex."

It was largely gays themselves—understandably tired of being viewed as freaks of nature—who began to assert that their orientation was not pathological. A defining moment came on June 27, 1969, after a police raid on a gay bar in Greenwich Village in New York City provoked a riot. Crowds continued to gather at the site for another five days, protesting discrimination and preaching gay rights. Now called the Stonewall Riots (named after the Stonewall Inn, which was at the center of the melee), they galvanized the modern gay-rights movement in America and initiated a shift toward greater cultural acceptance of homosexuality.

A mere four years later, in 1973, the nomenclature committee of the American Psychiatric Association (APA) set about reassessing the profession's dark characterization of homosexuality. Leading the charge was psychiatrist Robert L. Spitzer of Columbia University. As a result of his committee's recommendation, the term "homosexuality" disappeared from the next edition of the DSM. That hardly settled the matter, however. In a poll of psychiatrists conducted soon after the APA's leadership voted to make the change, 37 percent said they opposed the change, and some accused the APA of sacrificing scientific principles in the service of "civil rights"—in other words, of giving in to pressure.

Changing "Truths"
Matt Avery had no doubt about his orientation when he first became sexually active in his teens. During college in the early 1980s, he worked at a gay bar and had hundreds of sexual partners. He also had a four-year relationship with a man. Matt considered himself "feminine." "I was 140 pounds, had long fingernails, a blond ponytail and wore an earring," he reminisces. "I was a sight to be seen."

But when he was 24 his partner returned from a weekend retreat with some incredible news. Being gay, his partner said, "wasn't a truth" for him. Matt was distraught. "My whole life," he says, "was defined by whomever I was with—whomever I could use to make up for my own faults." After their sexual relationship ended, they stayed roommates and friends. But then, Matt says, "he started dating this woman." This change was another blow, especially because Matt was still seeing multiple men at the time. He was shaken but also curious. "One day," he recalls, "I decided homosexuality might not be a truth for me either, and I went on a date with a woman. It was pretty good."

Within two or three years he found himself involved exclusively with women. He made the shift without therapy and without the influence of religious groups. He was supported, he says, by friends who helped him deal with "issues involving his father." They helped him learn to be comfortable with his masculinity. Matt got to the point where even his sexual fantasies about men disappeared. In that respect, he probably became straighter than many heterosexuals. Although Matt made the switch without professional assistance, others—sometimes under tremendous social pressure from family members or religious groups—seek out "reparative" therapists to help them become straight.

Floyd Godfrey—himself formerly gay—has been a reparative therapist in Arizona for six years. His office has five clinicians, and they see 30 to 40 clients a week, many of whom are men struggling to overcome homosexual tendencies. Godfrey says they come because they are depressed, anxious and unhappy. "They feel out of place," he says. "They don't feel like one of the guys. When people feel like they don't fit in, that can produce depression."

Some, he says, are young men whose fathers were abusive or neglectful. "Their dad was never available for them to bond with. Or sometimes mom was controlling or overprotective. The bottom line," Godfrey says, "is that there was a disruption during childhood of the bond that normally develops between father and son." Deficient upbringing, Godfrey claims, can sometimes lead to same-sex attractions.

Let us set aside the obvious question for the moment—whether the therapy works—and consider a more basic issue. Why is it called "reparative"? Doesn't this term presume that homosexuality is somehow invalid—that gays are like broken washing machines that need to be repaired? In other words, isn't this therapy a retrenchment to the old disease model of homosexuality that Spitzer and his colleagues dispatched more than 30 years ago?

It seems so. Those deeply entrenched notions affect even the way we talk about homosexuality. Even the common term "sexual preference" reflects bias, suggesting that orientation is entirely a matter of choice. As for the claim made by Godfrey and others that homosexuality is the result of poor parenting, there is simply no legitimate scientific evidence to support it. Whereas it is true that some homosexuals had poor relationships with their fathers when they were growing up, it is impossible to say whether those fathers produced homosexual tendencies in their sons by rejecting them or, instead, whether some fathers simply tend to shun boys who are effeminate at the outset.

As for the effectiveness of reparative therapy—referred to by some as reorientation therapy—initial studies such as a small one published in 2002 by New York psychologists Ariel Shidlo and Michael Schroeder suggested that such therapy worked poorly or only occasionally.

In a landmark study published in the Archives of Sexual Behavior in October 2003, however, Spitzer interviewed 200 men and women who once considered themselves homosexuals but who had lived their lives as heterosexuals for at least five years. Most of the participants had undergone some form of reorientation therapy. In addition to determining whether such therapy actually worked, Spitzer wanted to know just how dramatically people could alter their orientation. To his surprise, most of his subjects not only reported living long-term (more than 10 years) as heterosexuals, they also declared they had experienced "changes in sexual attraction, fantasy and desire" consistent with heterosexuality. The changes were clear for both sexes.

Not everyone who sets out to change his or her sexual orientation is successful in doing so, however. How can we understand these dynamics—why many people want to change, why some can, and why some appear unable to do so?

Continuity Rules
At the heart of the controversy about homosexuality are some microscopically small objects: the strands of proteins that make up our genes. Two genetic issues are relevant to our understanding of homosexuality. First, do genes play any role in sexual orientation? And second, if genes do help determine orientation, do they actually create two distinct types of orientation—gay and straight, as most people believe—or do they create a continuum of orientation?

A variety of studies suggest that genes play at least some role in homosexuality. Although no one study is entirely conclusive, studies of twins raised together, twins raised apart and family trees suggest—at least for males—that the more genes one shares with a homosexual relative, the more likely it is that one will be homosexual—the hallmark of a genetic characteristic. But more interesting for our purposes is the question of a continuum. Sometimes, as with eye color, genes create discrete characteristics. But with many attributes, such as height and head width, genes create continuities. Whereas most people believe that "straight" and "gay" are discrete categories, there is strong evidence that they are not—and this fact has important implications for the way we understand the various controversies surrounding homosexuality.

Ever since the late 1940s, when biologist Alfred Kinsey published his extensive reports on sexual practices in the U.S., it has been clear, as Kinsey put it, that people "do not represent two discrete populations, heterosexual and homosexual.... The living world is a continuum in each and every one of its aspects." A recent position statement by the APA, the American Academy of Pediatrics and eight other national organizations agrees that sexual orientation falls along a continuum. In other words, sexual attraction is simply not a black-and-white matter, and the labels "straight" and "gay" do not capture the complexities.

For obvious evolutionary reasons, most people are strongly inclined to prefer opposite-sex partners, because such relationships produce children who continue the human race. But a few—probably between 3 and 7 percent of the population—are exclusively attracted to members of the same sex, and many are in the middle. If a person's genes place him or her toward one end of what I call the Sexual Orientation Continuum, he or she almost certainly can never become homosexual [see illustration]. If the genes place the person at the other end of the curve, he or she almost certainly cannot become straight—or at least not a happy straight. But if an individual is somewhere in between, environment can be a major influence, especially when the person is young. Because society strongly favors the straight life, in the vast majority of cases the shift will be toward heterosexuality.

The way sexuality plays out is eerily similar to the process by which people become left- or right-handed. It may sound contrary to common sense, but scientific studies suggest that genes play a relatively small role in handedness; its heritability—an estimate of what proportion of a trait's variability can be accounted for by genes—is only about 0.32, compared with, say, 0.84 for height and 0.95 for head width. Then why is more than 90 percent of the population right-handed? It is because of that cultural "push" working again. Subtle and not so subtle influences make children favor their right hand, and the flexibility they probably had when they were young is simply lost as they grow up. Although they can still use the left hand, their handedness becomes so well established that they would find it difficult, if not impossible, to become left-handed.

Preliminary studies by psychologist J. Michael Bailey of Northwestern University, Michael King of University College London and others suggest that the heritability of homosexuality is not much higher than that of handedness—perhaps in the range 0.25 to 0.50 or so for males and somewhat lower for females. This finding raises an intriguing question: If people were raised in a truly orientation-neutral culture, what sexual orientation would they express? Although it is unlikely that half of us would end up gay, without societal pressure it is clear that a much larger proportion of the population would express homosexuality than we see now.

Matt's Choice
As for Matt, it is likely that he, like most or all people who change sexual orientation, was not near an extreme end of the continuum to begin with. It is unreasonable to say that he has been returned to a "natural" state, however; with strong social support, he has simply chosen a new path for himself—one that his genes made possible but that is almost certainly not possible for every gay person. Someday I suspect that psychobiological research will allow us to find precise physical correlates of sexual orientation: genes, neural structures or perhaps more subtle physical characteristics. But no advances in science will ever completely resolve the moral and philosophical issues that Matt's conversion raises.

Do gays have a choice? Because of the enormous pressures pushing all of us toward the straight end of the Sexual Orientation Continuum from the time we are very young, it is reasonable to assume that most of the people who currently live as homosexuals were probably close to the gay end of the continuum to begin with; in other words, they probably have strong genetic tendencies toward homosexuality. Even though the evidence is clear that some gays can switch their sexual orientation, the vast majority probably cannot—or at least not comfortably. If you doubt that—and assuming that you are right-handed—try eating with your left hand for a day or two, and good luck with your soup.