While conservatives continue to stoke the fires of homosexuality as a curable dereliction, folks like New Jersey Gov. James McGreevey and a significant percentage of some animals are still compelled to boff, bed, bang or – gasp! – form lifelong bonds with members of the same sex.

Until recently, science didn’t appear to be losing sleep trying to determine whether this predilection is due to biological or social factors – or a confluence of both.

Why are some people more attracted to a particular gender? It’s an ancient conundrum in which the answer is as elusive as the origins of the universe or the existence of god.

The reason science remains stumped is multifold: funds for this type of research are usually less than forthcoming; the question itself is politically charged (with both gay rights advocates and religious fundamentalists arguing for and against particular outcomes); and a general lack of scientific accoutrements needed to solve the puzzle.

However, with support for embryonic stem cell research gaining new momentum, and the discovery of the human genome, a renaissance of research into the origins of sexual orientation may be just around the corner.

In 1991, Simon LeVay, then a researcher with the La Jolla-based Salk Institute, published the first significant data on sexual orientation. Comparing the brains of both gay and straight men, LeVay found a considerable size difference in a portion of the hypothalamus (which regulates certain metabolic processes and sexual response). Though this portion of the hypothalamus is generally three times larger in men than in women, LeVay found that its size was about the same in gay men and women.

In 1993, a team at the National Institutes of Health (NIH), led by researcher Dean Hamer, became the first to publish data finding a genetic link to sexual orientation. In the study, they found that in families with two gay brothers, 33 out of 40 pairs shared a distinctive marker in one region of the X chromosome.

Though another group at NIH was said to have later replicated the study, a team at the University of Western Ontario failed to reproduce the findings after studying close to 400 families.

Over the past decade, other researchers have posited that considerable stress during a mother’s second trimester could cause a male fetus to become gay, and that a variation in the length of the index fingers of men and women could indicate a person’s sexual orientation.

Alan R. Sanders is the principal investigator of a new “linkage” study at Evanston Northwestern Healthcare Research Institute, near Chicago. Sanders and his team hit the Pride circuit this summer (including San Diego LGBT Pride) to recruit 1,000 pairs of fraternal gay brothers for a molecular genetics study of sexual orientation.

Researchers at Northwestern will be looking at the genetic map of gay brothers for markers that may determine sexual orientation.

The study is funded by a five-year NIH grant of over $1 million, said Sanders, who hopes to recruit his sample within a three-year period.

While Hamer’s earlier study only looked at a portion of the X chromosome, researchers at Northwestern will be scanning the entire human genome, or DNA code, to look for evidence of a genetic link to homosexuality. (A similar, though more modest linkage study of 150 pairs of gay brothers was conducted in Hamer’s lab and is expected to be published in the near future.)

Sanders said the discovery of the human genome has made the process of identifying genetic markers less time consuming and more straightforward.

“It’s helped a lot,” he said. “Knowing the DNA sequence tells you exactly where all these different genetic markers are…. It’s much easier to find them than it was 10 years ago.”

A former NIH researcher, Sanders was involved in the study that sought to replicate Hamer’s 1993 findings, though he called the results somewhat ambiguous.

“We didn’t really fully replicate what Hamer found,” he said, “but our study was not nearly as negative as the [Canadian] group’s study.”

Sanders said the biggest problem with prior research might be the modest sample size of the studies, or their low “statistical power.” If Sanders and his team succeed in recruiting 1,000 pairs of gay brothers, their statistical power would be an average of 10 times larger than that of most previous studies.

“With these small samples, a lot of times the findings are somewhat unstable,” Sanders said. “If you have poor or low statistical power, even if there’s something there, you don’t have a very good chance of finding it.”

While the headlines have grabbed the attention of readers with news of a so-called “gay gene,” most researchers believe a combination of several genetic and environmental factors are responsible for a person’s sexual orientation.

“The pattern they see in families and the information we have for twin studies seems to indicate that this is not a one-gene, one-trait kind of thing,” Sanders said.

If no environmental factors were involved, he noted, studies on identical twins, which possess the same genetic makeup, would show that both twins were gay nearly 100 percent of the time, rather than around 50 percent, which previous studies show.

Sven Bocklandt, a postgraduate research fellow at the University of California Los Angeles (UCLA), is involved in several new sexual orientation studies; most notably, he is studying the brains of gay male sheep.

Having worked with Hamer for over three years at NIH, Bocklandt came to UCLA last year when Hamer began studying molecular therapies for HIV/AIDS.

UCLA researcher Eric Vilain had obtained the ram samples through Charles Roselli, a professor at the Oregon Health and Science University School of Medicine, who began the study several years ago.

To the chagrin of the United States Department of Agriculture, which first isolated the phenomenon, eight percent of all male sheep are believed to be exclusively homosexual.

“In Dean Hamer’s lab, we only had access to the DNA of gay men and their family members,” Bocklandt said. “There’s very little you can actually do with people; [you] can ask them questions and draw their blood. Having these rams was an exciting idea for me because by combining the possibilities we had with the sort of DNA database that Dean Hamer had, … we actually had a much higher chance of finding something.”

While there had been some doubt cast on LeVay’s 1991 research, initial studies done on the gay rams by Roselli found the same size difference in they hypothalamus of homosexual and heterosexual rams that LeVay found in the brains of gay and straight men.

“It shows that maybe these rams are a good animal model for human sexual orientation,” Bocklandt said.

With the gray matter of gay rams at hand, Bocklandt is testing his own hypothesis, which takes a revolutionary approach to the genetic theory of homosexuality.

“My idea is that being gay is not a matter of what genes you have, but what genes you use,” he said.

“As a man, you have all the genes in your body to make a vagina and a womb and become a woman,” he added. “Men don’t have vaginas and wombs because they don’t use these genes, … but basically the genetic material that’s there is almost identical for men and for women. It’s a matter of which genes you activate.”

Bocklandt calls his theory “genetic imprinting.”

“When parents make their baby, their genes carry, not just the genetic information, but they also carry labels that tells these genes whether they are going to be used or not in certain tissue and certain moments,” he explained. “[These labels] sits on top of that DNA…. What I’ve been doing with these rams is looking at which genes are being used and which genes are not being used.”

One distinct advantage Bocklandt’s ram tissue holds over LeVay’s human hypothalamus samples is particularly significant to his research.

Regrettably for the rams, in order to preserve an accurate record of their brain at the time of same-sex activity, they must be killed shortly after copulating.

“Chuck Roselli put these rams through their preference tests and, pretty much as they were done mounting the males, he just decapitated them and scooped out their brain,” Bocklandt explained.

“I can ask my subjects whether they want to donate their hypothalamus to me, but few gay men have been willing to do that…. With people, even if you get access to the brain, like Simon LeVay did, dying does mess with your head. These things change quite quickly and so you need fresh tissue.”

To determine which genes are being activated in the rams that cause same-sex impulses, Bocklandt looks at the RNA, as opposed to their DNA (which can be obtained by a blood sample).

“[RNA] is sort of the temporary copy of the DNA, but only of those genes that are actually being used at that point,” he said. “It indeed gives you a snapshot of what’s going on in that specific cell or tissue.”

According to Bocklandt’s theory, straight and gay labels are devoid of meaning.

“The whole hypothesis that I’ve been working on is that there’s no such thing, from a biological point of view, as homosexuality or heterosexuality,” he said. “The only thing that exists is being attracted to men or being attracted to women…. I have some results that indicate that at least that is partially true.”

Bocklandt’s genetic imprinting theory will also be conducted on identical twins, he said. His team recently attended an annual twins festival in Twinsburg, Ohio, to recruit samples.

Bocklandt is also researching the potential for genetic differences in various types of gay men.

“The problem with all the research that’s been done, which is not all that much, is that we researchers look at gay men as one group, and I think that there are a whole lot of types of gay men,” he said. “You see that there are very feminine men and very masculine men and everything in between. Maybe there are genetic differences between these groups.”

Michael Bailey, a psychiatric researcher at Evanston Northwestern Healthcare Research Institute, has arguably done more groundwork on the genetics of sexual orientation than any researcher to date, studying families, siblings and twins.

The Northwestern study will build upon his previous research, which suggested that homosexuality may run in families, with 8 to 12 percent of the brothers of gay men also being gay, as compared to 2 to 4 percent of men in the general population.

Bailey’s studies on identical twins have shown that in 52 percent of gay men with an identical twin, their twin is also gay. Similarly, a 48 percent concurrence rate was found for lesbians with an identical twin – showing that the pattern may be due to heredity.

Beyond the current study at Northwestern, Bailey is continuing a study looking at the difference in response to sexual stimuli between men and women, both gay and straight.

“I’m looking at what happens in the brains of these people as they look at different kinds of sexual stimuli,” Bailey explained. “For men, we begin by measuring the circumference of the penis and erection.”

To accomplish this, Bailey and his team attach a sort of rubber band with a thin wire inside.

“As the penis expands, the wire stretches and that changes the current, [which] you can measure with electrical equipment,” he said.

The same process is conducted on women, using an instrument that measures the amount of light reflected in the vagina during arousal.

To get the best stimuli, Bailey said, all study participants, gay or straight, are shown a scene of two women having sex and one of two men having sex.

“I would say the most interesting finding with respect to sexual orientation so far is that men are very specific in their arousal responses,” Bailey said. “If a guy is gay, he’s going to get erections to watching two men; if he’s straight, he’s going to get erections from watching two women.

“What’s interesting,” he continued, “is that, for women, no matter what their sexual orientation, they tend to respond to both. Straight women show arousal to watching two women, and gay women show arousal to watching two men, so women are not very specific in their arousal.

“Not all women get equally aroused to everything,” Bailey noted, “but generally, what it means is that sexual arousal plays a much different role in sexual orientation for women than it does for men. For men, I think sexual arousal patterns are one’s sexual orientation – what you get erections to determines what you are.”

By and large, Sanders said male homosexuality has been studied more than female homosexuality because there is more of a foundation of research, and also because of differences in male and female sexual response.

Sanders said Northwestern researchers hope to conduct a study exclusively on female sexual orientation in the near future.

“We would have a similar approach, but we would analyze our sample differently,” he said. “There’s a pretty good chance that different genes contribute to sexual orientation in males versus females…. Male homosexuality is a little more common than female and the pattern seems somewhat different too.”

Looking at Alfred Kinsey’ seven-point rating scale for sexual orientation, which identifies various gradations between exclusively homosexual and exclusively heterosexual, Sanders said men tend to be much more polarized between straight and gay, whereas, after a considerable heterosexual spike, women tend to be more evenly distributed.

Sanders said research has also shown the number of families in which there are more than one gay male offspring or more than one lesbian offspring are far greater than families containing a combination of both gay and lesbian offspring.

Another well-established study, Bailey noted, was conducted by Canadian researcher Ray Blanchard, who showed that gay men tend to have more older brothers than straight men.

“It has found that gay men tend to be later born in a series of brothers,” Bailey said. “[Blanchard] has a biological hypothesis that it has to do with an immune response to testosterone over successive pregnancies – that eventually a mother produces antibodies to testosterone that interfere with the masculinization of the brain in some way.”

Some in the GLBT community have a personal interest in a biological basis for sexual orientation being established, which would debunk the assertion of religious conservatives that homosexuality is a choice.

Still, others worry that locating a genetic cause could lead to a genetic eradication of sexual diversity.

Should homosexuality be attributed to hormonal factors, and screened for during a pregnancy, what’s to say parents wouldn’t opt to alter a homosexual orientation through hormone therapy, or even opt to abort a predetermined “gay fetus”?

German researchers have raised concerns over the issue, and some countries have even considered imposing a moratorium over sexual orientation research.

While most researchers would not outwardly advocate a complete distinction of science and ethics, Bailey, Bocklandt and Sanders say the concerns are largely speculative at this point.

“I don’t think anyone can tell whether we will be able to do good prenatal testing or whether we ever will be able to change these genes or control them somehow and choose the sexual orientation of our kids,” Bocklandt said. “I do think, though, that once we get to the point that we have the technology to actually change the genetic material of our kids and control them, that will be the time that we can change any genetic variable that you want to effect…. But that is a huge political or societal discussion; it’s not a scientific discussion. I don’t believe that we should not do the research because we are afraid of how it’s going to be used. I don’t think ignorance as a strategy makes any sense.”

“I think the main reason [we study sexual orientation] is legitimate,” Bailey said, “and that that’s because it’s a damn interesting question. Any causative factor, whether it be biological or social, could conceivably allow the manipulation of sexual orientation…. I don’t approve of homophobia, but I think that it’s a misallocation of concern to wring hands about this very speculative thing when all you have to do is look out there and see lots of gay people mistreated every day.

“As a general rule,” he continued, “I think that the more we know about sexual orientation, the more tolerant people will be.”

Bocklandt admitted that the type of research he is involved in is at the eye of a political storm.

“From both sides, there’s politics involved,” he said. “The religious right is basically keeping an eye on what we’re doing. They’re writing articles on our research if you look at the Family Research Council or Focus on the Family [websites]. They obviously don’t like what we’re doing.

“Then there’s the gay organizations themselves,” he added. “For example, PFLAG has always been very, very helpful with live studies. They helped us recruit a lot of the samples because they are very eager to show that they weren’t bad parents somehow, because that’s the language that they sometimes hear when they find out that their kids are gay.”

Furthermore, unveiling the origin of sexual orientation is far too important to be ignored, the researchers say, given its potential application in a variety of related disciplines.

“We’ve started to understand things about memory and how our memory works; we’ve started to understand things about language, but we don’t understand anything about attraction, we don’t understand anything about love,” Bocklandt said. “We really have no clue how it works. It’s such a fundamental question and it’s so important to our evolution that it seems weird that you wouldn’t want to know how that works.”