God destroyed Sodom and Gomorrah, and he is going to destroy you and a lot of others.

I've often wondered if a network would have given Dr. Laura a talk show if she had said that Jews and non-whites are "biological errors."

I think homosexuals cursed, and I am afraid I mean this quite literally, in the medieval sense of having been struck by an unexplained injury, an extreme piece of evil luck whose origin is so unclear as to be, finally, a mystery.

If I had the power to do so, I would wish homosexuality off the face of the earth. I would do so because I think that it brings infinitely more pain than pleasure who are forced to live it; because I think there is no resolution for this pain in our lifetime, only, for the overwhelming majority of homosexuals, more pain and various degrees of exacerbating adjustment; and because, wholly selfishly, find myself completely incapable of coming to terms with it.

They are different from the rest of us. Homosexuals are different, moreover, in a way that cuts deeper than other kinds of human differences—religious, class, racial—in a way that is, somehow, more fundamental. Cursed without clear cause, afflicted without apparent cure, they are an affront to our rationality....

Pieces of the Puzzle

Researchers are finding tantalizing clues about what causes homosexuality and what signs may indicate its likelihood early in life.

By MELISSA HEALY, Special to The Times

It is not the most cherished childhood photo in his mother's collection, but it may be the most prescient.

The little boy, not quite 2, is perched on a potty seat. A mop of brown hair frames a face with delicate features and big brown eyes. He is wearing a pretty white sundress purloined from his older sister's closet, a "very girly" frock, according to his mother, that is one of his two favorites. Secreted away elsewhere in the house are the little boy's other passions: his mother's fancy shoes and jewelry, his sister's Barbie doll. And behind the lens is mom, a college professor from Toronto, "collecting evidence" that she can take to the pediatrician.

The boy in the photo, now nearly 15, is contemplating his sexual orientation with the same secretiveness that he once used to hide his penchant for cross-dressing. On the phone, he gabs with his many girlfriends about their current crushes, adopting their incredulous, eye-rolling gestures and their distinctive, sing-song mode of speech. About his own crushes, however, he is mum.

His mother, who demanded anonymity in the interests of her son's privacy, has no doubt about the young man's future sexual orientation. "I'm sure he'll end up being gay," she says matter-of-factly. As a parent, she wishes it were otherwise; being straight is simply an easier life for a young adult, she said. But she loves her son, and it's clear to her that even before she and her husband adopted him 20 days after the child's birth, this, simply, was the way he was made.

While scientists have pondered the mystery of homosexuality for centuries, the secret of how homosexuals are made is only now beginning to yield to their inquiries. Long branded a mental illness, attraction to those of the same sex was expunged in 1973 from the list of psychiatric disorders recognized by practicing clinicians. And American society has fitfully followed suit, emboldening many in this long-closeted minority to declare and celebrate their sexual orientation openly.

The drive toward societal acceptance has not dampened many scientists' zeal to explain one of evolution's most curious mysteries: Why has a trait that inhibits sexual reproduction endured? To these researchers, homosexuality remains an evolutionary oddity that demands to be explained. Intriguing new research is finding there may be many different pathways to gayness. Those seeking to explain homosexuality traditionally looked for instances of early sexual abuse, emotionally distant parents and other socialization factors to explain a child's later same-sex attraction.

But researchers from unexpected disciplines such as brain science and audiology are bringing new perspectives to a field long dominated by Freudians, social workers and, more recently, by gay activists. They are uncovering a wide range of possible physical markers for homosexuality—from the way one's inner ear responds to sound to the shape of one's hand—that are evident from a child's first days. These insights not only point to the mechanisms at work in homosexuality: They offer the intriguing and controversial prospect that perhaps in the not-too-distant future, parents like the mother in Toronto could do more than brace for a child's sexual awakening; they could do something about it.

Still, the science of homosexuality remains in its infancy. For now, there exists only one childhood trait—often exhibited before a child can walk—that strongly predicts homosexuality later in life. It is early behavior that departs markedly and persistently from the boys-and-trucks, girls-and-dolls stereotypes of years past.

For the cross-dressing toddler in Toronto and other boys who show "pervasive and persistently" effeminate behavior, the odds of being gay lie at about 75%, according to J. Michael Bailey, a psychologist and sexuality researcher at Northwestern University in Evanston, Ill. That is a probability of homosexuality 20 times as high as that in the broad population of boys; it is estimated (though hotly disputed) that 3% to 4% of males will grow up to be gay. Among girls, this so-called gender-atypical behavior also is a good predictor of later lesbianism, though the pattern is weaker.

That may disappoint those who hoped science would have disproved a painful stereotype. But strong and sustained gender-crossing behavior is, says Bailey, "about as strong a predictor as exists in the developmental literature."

Strong as the relationship may be, however, it has major limitations. Most important, researchers stress there is no evidence that early gender-bending behavior is the cause of later homosexuality: In fact, many argue, the early onset of such predictive behavior suggests that for many, sexual orientation may be fixed at birth. The fact that such behavior is more likely to be greeted with horror than encouragement by family and friends is seen as further evidence for that position.

Beyond that, researchers caution, such behavior is far from conclusive. Many adult gay men and lesbians were gender-conformers as children. And many boys derided as "sissies" and girls labeled as tomboys grow up to be straight.

Consistently Fighting Traditional Roles

The distinction, say researchers, is gender-bending behavior that is neither subtle nor temporary. It isn't "just a phase," say parents like Angela and James, a couple who spoke on condition their last names not be used.

By the time he was 18 months old, their son, now almost 7, was drawn to his mother's shoes and scarves. From 3 years old, he "'would obsess" about the Little Mermaid and Cinderella, mimicking their dresses, their songs and their gestures, according to his parents.

"Being the progressive, modern-thinking parents we were, we thought, 'Let's not stereotype,' " said Angela, explaining why the couple bought their son a Barbie doll (and a Ken, whom the child pointedly ignored) when he asked for it.

It was a poignant moment of epiphany—the day their then-4-year-old son stood up in a shopping cart and wept at the realization that he would not grow up to be a mommy—that drove the couple to seek treatment for the child's "gender-identity disorder." A certain type of treatment, called "reparative" or "conversion" therapy, seeks to steer a gay person toward heterosexual behavior. By contrast, however, treatment for gender-identity disorder focuses on an individual's confused sense of self, seeking to make them comfortable with their actual gender.

The American Psychiatric Assn. continues to view it as a mental disorder. But because it affects many in the homosexual community, gay activists object sharply to the labeling and treatment of what they call "transgender" behavior, denouncing clinicians' efforts as "genocide."

All of which underscores a key point: As a field of research, homosexuality lies at the dangerous intersection of science and minority politics. In this world, every new finding carries added weight. Both gay activists and their detractors—largely Christian conservatives who view homosexuality as contrary to biblical teachings—dissect the work of researchers for political meaning. If gays and lesbians are "born that way"—if homosexuality can definitively be traced to genes or prenatal environment—is being gay a choice? Do lesbians and gay men follow the same pathways to homosexuality? And if scientists can uncover how homosexuals are made, will they not be an important step closer to finding how they can be unmade?

To homosexuals struggling to protect and extend their rights, the answers to these questions may mean the difference between acceptance and intolerance, cultural vibrancy and decline—life and death, even. For even as a majority of Americans tell pollsters they believe homosexuals should enjoy job protections and basic human rights, roughly half of Americans, according to the Gallup Poll, continue to believe homosexuality "should not be considered an acceptable alternative lifestyle." And only 29% say they would like to see homosexuality "more accepted" in this nation.

Worry for a Child's Status in Society

For parents in particular, the dilemma of anticipating a child's homosexuality can be acute. The Toronto mom, whose son started playing with her fancy shoes at about 10 months, is typical: Like many who see the early glimmerings of a child who will grow up to be gay, she insists that as an intellectual, ethical and political matter, she would never consider trying to change her son's sexual course. But as she assesses the social challenges a gay son will face in life, she echoes the sentiment of virtually all parents interviewed for this article: If her child could magically be remade, she would wish a heterosexual life for him. "It's tougher to be a gay kid in high school," said James, whose 7-year-old has been treated for gender-identity disorder. "Geez, it's not easy being a straight adolescent!"

Although hypothetical for today's parents, the possibility that future parents may be able to take a pill or tinker with a gene to steer their offspring toward heterosexuality is no pipe dream.

"It's not a matter of whether" we'll find homosexuality's basic mechanisms, "it's a matter of when," said Dennis McFadden, a University of Texas specialist on auditory perception. "And parents are going to rush to influence them, possibly before a child is born."

Indeed, scientists are finding that an individual's sexual orientation may be most powerfully shaped before birth—both by genes and, as more recent research is showing, by prenatal environment.

In the last two decades, researchers have established beyond much doubt that, like high intelligence, green eyes or a propensity for certain diseases, homosexuality runs in some people's genes. Northwestern's J. Michael Bailey, who has conducted much of this research, notes that a male with a gay brother is three to seven times more likely to be gay himself; and a woman with a gay sister is four to eight times likelier to be a lesbian than a female drawn from the broader population.

"The data definitely are not as strong as for other traits such as intelligence or schizophrenia," said Bailey. But he added that researchers from various disciplines are nearing consensus on this point: Some genetic component to homosexuality clearly exists.

Studies of identical twins—siblings with the same DNA—illustrate both the power and the limitations of genes in homosexuality. A man or a woman is at least 10 times likelier to be gay if his or her identical twin is homosexual; in other words, his or her probability of being homosexual lies between 20% and 50%. But flip that figure over, and it looks far less impressive: Those probabilities still mean that, among identical twins in which one is homosexual, between half and 80% have a heterosexual twin. Having a "gay gene," if such a thing exists, carries no certainty of being gay.

How else, then, to account for homosexuality?

In the last several years, a welter of new research has begun to point strongly to a developing fetus' intrauterine environment as a possible incubator of gayness. This new line of research has been scattered broadly across the peer-reviewed journals that collectively make up science's bazaar of evidence and ideas. But it all started with a little-understood birth-order peculiarity long observed among adult gay men: They tended to be little brothers, frequently in a household full of older boys.

"When I first encountered these early studies, I thought they were so preposterous that I dismissed them out of hand," said Ray Blanchard, a psychologist at the University of Toronto's Department of Psychiatry. "It struck me as the most bizarre example of pseudoscience."

Later, "by accident," Blanchard said, he happened upon evidence in his work that there might be something to this anecdotal oddity. He began scouring dozens of databases containing data on both birth order and sexual orientation. By the late 1990s, he had established one of the strongest associations with homosexuality in the field.

For a male child, Blanchard found, the more older brothers in his family, the higher the probability that he would be gay. A firstborn male has a likelihood of homosexuality of about 2%. But for a boy with four older brothers, those odds jump to 6%, Blanchard found. In all, he estimated, one in seven gay men owed his sexual orientation to this "fraternal birth order" effect.

An Immune Response That May Grow Stronger

What force was at work here? An intriguing parallel suggested an explanation. "Blue babies," or babies born with anemia due to incompatibilities with their mother's blood type, were much more likely to be latter-born males, too. And researchers had established that the "blue baby" effect was the result of a maternal immune reaction to the presence of foreign cells—male cells—in her blood during pregnancy. With each male child a woman carries, that immune reaction grows stronger and so does the probability of a maternal reaction to the blood incompatibility that causes a newborn to look blue from low oxygen.

Blanchard hypothesized that a pregnant woman carrying a male child has an analogous kind of immune response, which grows stronger with each subsequent male fetus she carries. While he is unclear how, exactly, that immune response affects the baby, many researchers coming to the same conclusion surmise that it affects the chemistry of the amniotic soup in which a fetus develops. At a crucial period of fetal brain development, a higher-than average concentration of certain hormones—say, the powerful hormone estradiol—could cause changes in the way the developing baby's brain is wired. The implications of that chemical shift would likely be evident early. And they would likely last a lifetime.

By the end of the 1990s, other researchers were beginning to posit similar hypotheses on the bases of wildly different data. Researchers already had established that compared with their heterosexual counterparts, gay men and lesbians were more likely to be left-handed. But in Berkeley and in Liverpool, England, a psychologist and a biologist, working independently, were finding that the shape of the hands—a key measure of in-utero exposure to sex hormones—tended to be different too.

Simply put, the ring finger of a heterosexual man's right hand tends to be much longer than his index finger; in straight women, the two fingers typically appear nearly the same length, with the pointer dipping just slightly below the ring finger.

But John T. Manning, a biologist at the University of Liverpool, found that as a group, lesbians have a hand pattern that looks more like a man's than like that of a typical straight female, though still not quite as pronounced. "The finding, Manning concluded, "strongly tells us that female homosexuals have had high levels of exposure to testosterone before birth."

Texas Researcher Takes Another Tack

Manning seemed to be zeroing in on a defining moment in the development of sexual orientation. In the meantime, in Austin, Texas, a very different route brought psychologist Dennis McFadden to the same conclusion.

A psychoacoustics specialist, McFadden has studied group differences in two measures of hearing: otoacoustic emissions—tiny clicking sounds produced by the auditory system in response to stimulus—and auditory-evoked potential, the brain-wave peaks that an individual produces when presented with sound.

From their earliest days, boys and girls score differently on each measure—no surprise, perhaps, since a fetus' auditory system develops at the same time that hormonal differences peak in the womb and gender differences emerge. But McFadden found that lesbians fell between heterosexual men and women on both measures—a strong sign that they were exposed to higher-than-normal levels of male hormone in utero.

But like Manning in Liverpool and University of California psychologist Marc Breedlove, McFadden turned up a confounding pattern when he tested gay males. In one auditory measure, but not both, homosexual men were "hypermasculinized" compared with heterosexual men: Essentially, their brain wave peaks produced in response to sound were more "manly" than those of the average straight man.

Breedlove, surveying hand shapes with a portable photocopy machine at a San Francisco street fair, had come up with a similar finding. Writing in the journal Nature last year, Breedlove reported that he had been unable to establish a direct relationship between the overall average finger lengths of men and their sexual orientation. But on the basis of their finger lengths, he found that some gay men appeared to have been exposed to greater-than-normal levels of male hormones prenatally.

McFadden and Breedlove had run headlong into one of homosexuality's most entrenched stereotypes and some of its strongest research. In many cognitive measures, gay men tend to fall between men and women on the continuum of gender differences—they are, according to researchers, "feminized." Gay men tend to have better language skills, an area where girls generally fare better than boys. And they tend to be weaker in activities that take great spatial acuity, like maze-running and mathematics—areas where boys, as a group, outperform girls.

But here, by contrast, was evidence that some gay men were more "male" than the average male. And it tracked with other, sketchy indications of "hypermasculinization" among a group of male homosexuals: Their average number of sex partners was greater than that of their straight counterparts, the levels of testosterone that circulated in their blood was higher and their genitalia were larger. "This calls into question all of our cultural assumptions that gay men are feminine," said Breedlove.

Evidence like this has confounded and unsettled the community of researchers as well. With new findings scattered across many disciplines and, at best, a patchwork of explanations for homosexuality emerging, little is settled in this most incendiary of fields.

Within the gay activist community, the jumbled state of research is greeted with conflicting reactions: There is fascination "because these studies help us understand who we are," said David Smith, a spokesman for the Human Rights Campaign, a Washington-based gay-rights group. And there is a kind of grudging sympathy for the challenges facing researchers, since gay men and lesbians know how complicated and diverse they are. And finally, Smith added, there is a sense that whatever the outcome of research, "it shouldn't matter, because everyone deserves to be treated with dignity and respect."

Indeed, the fact that no one researcher has unlocked the mystery of all homosexuals' orientation suggests there may be many different factors at work.

Gay men and lesbians, in short, come in all varieties, scattered widely across our conventional notions of masculinity and femininity, said Northwestern's Bailey. "That suggests possibly that there are different bases for homosexuality" in different people, he said.

If they are to continue to uncover homosexuality's roots, scientists acknowledge, they increasingly will have to look at gay men and lesbians not just as groups, but as individuals. In that sense, they say, they are mirroring the challenges of the larger society. And the sentiments of parents like Angela and James.

"It's not on my mind that I'm watching our son grow up gay," said James. His 7-year-old is, he added, simply who he is: a shy child with a backyard fort and, yes, an attraction to Barbie dolls. If he ends up being gay, they will not worry so much about whether it was the fraternal birth order effect or an infancy traumatized by premature birth and kidney problems.

"If he decides he wants to come out," said Angela, "I'll simply be the biggest advocate out there."

Copyright © 2001 Los Angeles Times

The answer to "one of evolution's most curious mysteries: Why has a trait that inhibits sexual reproduction endured" seems quite simple to me. The earth is a finite piece of land that can only support life for so many life forms. With the population constantly growing, with all of the Earth's resources being depleted, homosexuality seems to me nature's way of curbing the population. So, heterosexuals need not be afraid; it just creates more space and resources for everyone.

Other than "to carry on the family name," why would we want to change anyone's sexual orientation, even if we could? We will always have enough breeding couples to more than sustain the species.

I think we would lose more than we would gain. We are just beginning to recognize the rich diversity brought to society by persons who, by our very nature, tend to think and feel outside the machismo of the straight-white-male-dominated-box.

So what is it we fear, really?

I am appalled at the continuing efforts of pseudo-Christian organizations, such as the Salvation Army, to further discrimination against lesbian and gay citizens. Jesus did not preach the laws of Leviticus; his was a gospel of love, compassion and forgiveness. Those who use his name to further agendas of hate and prejudice are truly the "anti-Christ."

As a gay man, I pray that I will not be dependent upon these organizations for social services in the future.

Sunday, June 19, 2005, 12:00 A.M. Pacific

Born gay? How biology may drive orientation

By Sandi Doughton
Seattle Times science reporter

As the culture wars rage over gay rights, a flock of sheep at Oregon State University may help answer a key question behind the controversy: Is homosexuality a matter of choice or biology?

The Corvallis herd includes a group of rams that scientists delicately refer to as "male-oriented." These animals consistently ignore females and bestow all their amorous attentions on members of their own sex.

Researcher Charles Roselli says a decade of study suggests sexual orientation is largely hard-wired into the sheep's brains before birth. Now, he's trying to figure out how that happens, zeroing in on genes and hormones. In a bold test of his ideas, he hopes to engineer the birth of gay rams by altering conditions in the womb.

Sheep aren't people, but the Oregon work adds to a growing body of research that bolsters biological explanations for sexual orientation across species — including humans.

Despite those scientific findings, some religious groups say homosexuality is a lifestyle that can be treated, if not prevented. One such group, the conservative Christian organization Focus on the Family, is sponsoring a one-day conference in Bothell Saturday.

The social and political implications of the research are impossible to ignore, leading to unease on both sides of the gay-rights debate. If science proves homosexuality is innate, is there any basis to deny gays equal treatment — including the right to marry? But if scientists unravel the roots of sexual orientation, will it some day be possible to "fix" people who don't fit the norms or abort fetuses likely to be born gay?

Much of the cutting-edge research is being conducted in other countries, because the political pressure cooker in the United States makes it difficult for scientists to get money, said Brian Mustanski, who juggles studies of the genetics of homosexuality with his main work on HIV prevention at the University of Illinois, Chicago.

But controversy can't obscure the facts, he said.

"It's pretty definitive that biological factors play a role in determining a person's sexual orientation."

Austrian scientists reported this month that switching a single gene was enough to make female fruit flies rebuff males and attempt to mate with other females. Swedish researchers recently found the sexual center of gay men's brains lit up when they sniffed a pheromone-like chemical from men's sweat, but didn't respond to a chemical from women.

And last fall, Italian scientists offered a possible explanation for the persistence of gay genes — even though evolution tends to weed out traits that discourage reproduction. The team from the University of Padua found that mothers and aunts of gay men had more offspring than female relatives of heterosexuals, suggesting genes that influence homosexuality in men may increase fertility in females.

That the evidence comes from such disparate directions leads scientists to suspect several different biological pathways may lead to homosexuality. Both genes and hormones appear to be important. Nor do researchers discount the possibility that social factors may play a role.

"I tend not to be a nature-versus-nurture kind of dichotomist," said Roselli, of the Oregon Health & Science University School of Medicine in Portland. "I think there's probably a very complex interaction that's going on between both biology and the environment that is involved in determining these types of behaviors."

Though they don't talk about it much, ranchers have long known that about 8 percent of rams never father offspring because they only have eyes for other males. Australian sheepherders call them "shy breeders," Roselli said.

Upbringing doesn't seem to make a difference. Domestication and captivity aren't responsible, because rams with same-sex proclivities occur in the wild.

Roselli's rams come from the U.S. Sheep Experiment Station in eastern Idaho, where federal researchers keep a herd of 3,000 to study genetics, breeding and grazing impacts.

They've also been quietly looking into sexual orientation, a subject so touchy the lab's U.S. Department of Agriculture boss won't allow his staff to discuss it with the press.

Roselli and his colleagues at OSU are using the gay rams to test what is called the neurohormonal theory of sexual development: that hormones from a developing fetus fix its sexual identity by orchestrating brain organization. Too much or too little of these powerful chemicals, or shifts in timing, may lead to homosexuality, the theory predicts.

Last year, Roselli found that a brain region linked with sexual behavior was twice as big in heterosexual as homosexual rams. The difference seems to exist even before birth, he said. The gay rams also had lower brain levels of an enzyme that activates testosterone and promotes typical male sexual behavior.

A 1991 study reported similar differences in the brains of gay and heterosexual men, but the findings haven't been confirmed. Human brain studies are problematic for another reason: Brain structures can guide behavior, but behavior also can cause brain structures to enlarge or shrink, making it difficult to say which comes first.

So in addition to brain studies, Roselli is waiting for a group of lambs born last spring to reach sexual maturity. Their mothers were dosed with drugs to block the action of male hormones in the fetuses. If Roselli's hypothesis is correct, rams born of this experiment will be disproportionately gay.

Hormones have long been suspect in homosexuality. Doctors used to treat gay men with testosterone injections, until it became clear adult homosexuals don't have blood hormone levels that differ significantly from heterosexuals.

But rats, hamsters, ferrets and other lab animals flip-flop their sexual behavior when scientists manipulate the hormones they're exposed to before birth. Such experiments would be unethical in people, but some rare medical conditions offer human parallels.

A high proportion of girls with a disorder that causes them to secrete male hormones before birth grow up to be lesbian. About 40 case studies have shown boys who are surgically altered and raised as girls because of genital deformities are overwhelmingly attracted to females once they reach puberty — indicating sexual orientation is determined very early in life and is difficult to alter.

That view is supported by a series of studies in the 1980s that found nearly 75 percent of young boys who dress up like girls, play with dolls and consistently choose stereotypical female pursuits will grow up to be gay. A similar, though less pronounced, pattern is found in girls who prefer trucks over tea sets.

Still, most gay people don't have gender-bending childhoods. As in heterosexuals, the majority say they became aware of their orientation at puberty.

"I just knew," said Seattle attorney Andrew Kamins, who is gay. "It's as simple as that."

Those who argue homosexuality is a choice haven't been able to dispute that fundamental point, said Michigan State University neuroscientist Marc Breedlove.

"If you're going to say people choose a sexual orientation when they reach puberty, you're going to have to find some people who remember making that choice, and there aren't any," he said. "The evidence is starting to look pretty good that hormones early in life influence the probability of who you will be attracted to 10 years later, when people start to get their first crushes," he said.

Breedlove found support for the neurohormonal theory by photocopying hands at gay street fairs.

In heterosexual women, the index and ring fingers are usually about the same length. In heterosexual men, the index finger is shorter, on average, than the ring finger. It's one of several differences between the sexes that seem to be set before birth, based on testosterone exposure.

Breedlove found lesbians' finger lengths were, on average, more like men's. The same holds true for other traits, like eye-blink patterns and inner-ear function.

"Every time you find a body marker that gives an indication of prenatal testosterone exposure, lesbians on average are more masculine than straight women," Breedlove said. "This can't be a fluke."

Patterns aren't as clear in gay men, with some hints they may be exposed to either less or more testosterone before birth.

All of the neurohormonal studies also leave a major puzzle unanswered: If hormones shape the brain and the brain directs behavior, what is controlling the hormone levels in the first place?

When Vince Healy finally came out as gay, his disapproving Catholic family was familiar with the story. His older brother had been living with a man for several years. It didn't make things any easier, the 45-year-old Ballard man recalled.

"I was very unhappy at the prospect of being gay," he said. "I kept thinking: I must be a late bloomer."

As the youngest of three brothers, one of whom is straight, Healy illustrates the two most robust findings in the science of homosexuality: It runs in families, and the number of older brothers a man has can increase his chances of being gay.

About 3 percent of American men and 1.5 percent of women describe themselves as gay or bisexual, according to the National Institutes of Health. Those percentages are three to five times higher among people who have a gay brother or sister.

Of course, family dynamics might be the reason, not biology.

What scientists call slam-dunk proof that genes are part of the equation comes from twin studies.

Genetically influenced traits are more likely to be shared among the closest relatives, and that pattern holds for homosexuality.

For fraternal male twins, the gay-gay concordance rate is about 22 percent. For identical twins, it's 52 percent.

Based on those results, scientists conservatively estimate homosexuality is about 40 percent due to genes, said Alan Sanders, director of behavior genetics at Northwestern Healthcare Research Institute in Illinois.

But genes clearly are not the only factor, or identical twins would always share the same sexual orientation.

"That means there's a significant environmental contribution," said Sanders, who is leading a five-year, $2.5 million project for the National Institutes of Health to try to identify the genes involved.

Earlier research has pointed to several possible gene regions, but those studies were small and not definitive. With DNA from 1,000 pairs of gay brothers, Sanders' project will be much more powerful.

It's very unlikely to uncover a single "gay" gene, he said. As in most complex traits, multiple genes and environmental factors probably work together.

So far, scientists can only speculate how genes linked with sexual orientation might work. Perhaps they dictate the size of brain structures, which in turn regulate hormones before birth. Perhaps genes directly adjust prenatal hormone levels, or merely predispose people to a gay orientation.

Environmental factors could be exclusively biological, like chemical exposure or infection. One theory, backed by some evidence in rats, is that the chemical and hormonal milieu of the developing fetus can be disrupted when pregnant mothers are stressed.

Social factors may ultimately prove to play a role as well, Sanders said.

None of the psychosocial theories for homosexuality have panned out so far, including Freud's distant-father/domineering-mother dynamic.

"There have been psychological and social explanations for homosexuality for 100 years, and they haven't come up with anything concrete," said Ray Blanchard, head of Clinical Sexology Services at the Centre for Addiction and Mental Health in Toronto.

A few studies suggest a higher rate of childhood sexual abuse in gays and lesbians, though there's no evidence such experiences trigger homosexuality, said Mustanski, the University of Illinois geneticist.

Blanchard's work on gay brothers offers an alternative explanation so odd he originally dismissed it as "obviously bogus."

But when he looked into scattered reports that many gay men have older brothers, he was astounded. The findings now have been confirmed by more than a dozen studies, including several of his own: Every older brother a man has increases his chances of being gay. A man with four older brothers is three times more likely to be gay than a man with none. Blanchard estimates one out of every seven gay men owes his orientation to this "fraternal birth order" effect.

It's possible to argue for social explanations — bullying by big brothers, indulgent mothers. But Blanchard believes it's biology. Gay males with older brothers weigh less at birth than heterosexual males with older brothers, hinting that something different is happening to them in the womb.

A possible explanation lies in the mother's immune system, which can be activated by cells from a male fetus.

For first sons, the effect would be slight. But subsequent boys could cause the immune response to ramp up until it somehow affects a baby's sexual orientation.

The idea is feasible, Blanchard cautioned, but still unproven.

Not all gay men have older brothers. Not all lesbians have short ring fingers. For some people, genes may be the dominant factor in sexual orientation. For others, it could be hormones. Just as sexual orientation spans a spectrum, scientists suspect there may be a range of mechanisms to explain it.

Over the next few years, scientists will begin to fit the divergent lines of evidence into a comprehensive picture of the way sexual orientation arises in both gays and heterosexuals, Mustanski predicts.

"We have these converging lines of evidence that are pointing to the importance of biology. Now we have to connect the dots."

The Gay Metropolis: Introduction

As the great architectural historian Vincent Scully pointed out, ours is "a time which, with all its agonies, has...been marked most of all by liberation." In the Jefferson lecture of 1995 Scully declared I think especially of the three great movements of liberation which have marked the past generation: black liberation, women's liberation, gay liberation. Each one of those movements liberated all of us, all the rest of us, from stereotypical ways of thinking which had imprisoned us and confined us for hundreds of years. Those movements, though they have a deep past in American history, were almost inconceivable just before they occurred. Then, all of a sudden, in the 1960's they all burst out together, changing us all.

America's best instincts have always been toward equality and inclusiveness. Especially in this century, the idea of a steadily widening embrace has been the genius behind the success of the American experiment. The main effects of these multiple liberations have been more openness, more honesty and more opportunity—changes which have benefitted everyone.