Born gay or made gay ... which camp are you in?
Sexual orientation is fixed at birth and not nurtured, a new book claims. Anjana Ahuja reports on its theories
There are people who can 'cure' you of your sexual orientation. If you are a woman, your eyes will no longer linger on tall, dark, musclebound Lotharios. If you are a man, your heart will no longer flutter at the sight of a plunging cleavage or a smooth thigh - instead it will thump into action at the glimpse of a broad, taut torso or a neatly-trimmed moustache.
To at least 96% of readers - the heterosexuals - the idea that we can be persuaded to change something as fundamental as sexual orientation seems ridiculous. So it is to homosexuals, who make up the remaining 4% and who are often told that their 'deviant' behaviour is a lifestyle choice.
Science has so far trodden carefully in the controversial debate about whether gays are born or made. Disparate pieces of evidence - such as homosexuality running in families, and identical twins having more similar sexual preferences than ordinary siblings - have long suggested that biology rather than upbringing shapes sexual preference. Now two researchers are throwing out the caveats in an attempt to 'out' the bald scientific truth: we are born either straight or gay and nothing can be done to make us otherwise.
In Born Gay, Dr Glenn Wilson, reader in personality at the Institute of Psychiatry in London, and Dr Qazi Rahman, a psychobiologist at the University of East London, declare that "the accumulation of evidence from independent laboratories across the world has shown that the biological differences between gay and straight people cannot be ignored ... our sexual preference is a fundamental and immutable component of our human nature". Wilson and Rahman's account goes beyond whether there is a gay gene - there is no single gay gene but genes do contribute - and considers the effect of sex hormones to which foetuses are exposed in the womb.
The boldly-titled book says the research leaves absolutely no room for parental or societal influence on this intimate trait. Children cannot be seduced or otherwise led into homosexuality and, however overbearing the mother or absent the father, no amount of poor parenting can waylay a child born to walk the path of heterosexuality.
No serious, evidence-based scientist, they charge, would deny that sexual orientation is fixed at birth. The authors also speculate that we face an evolutionary future in which homosexuals become more prevalent. The genes that are implicated in gayness do not just influence sexual orientation - in low doses, they might confer personality advantages to heterosexual men (such as making them loyal, empathic and considerate), turning them into attractive mates and thus propagating those genes further.
Rahman says that his view of corrective therapies designed to turn gay men straight is simple - they will never work: "You just can't do it. If people suggest they can, I ask them 'Can you turn someone from straight to gay? Show me the evidence.' But it's never going to happen, is it?"
According to Wilson and Rahman, the biological origin of sexual orientation means that discriminating against gays and lesbians is as justifiable as discriminating on the basis of eye colour or ethnicity. The authors have declined to reveal their own sexual orientation.
So, why are some men born gay? Homosexuality tends to run in families, which has prompted a search for the so-called gay gene. Last month, biologists in Austria discovered that fruit flies can be turned gay by altering a single gene. It is almost impossible that a single gene determining human sexual orientation exists: identical twins, who have identical genes, do not always have the same sexual preferences. But it does point to genetic influence.
"Gay men tend to have more gay brothers than straight men," Rahman says. "Heritability is thought to be around 30 to 40% which means that around 30 to 40% of the variation in homosexuality is down to genes. Strictly speaking, it's better than zero (which would imply no role for genes) but that shows there's significant environmental variance."
And this, Rahman says, is where a "massive misunderstanding of the concept of environment" comes into play. Studies have shown that the popular idea of environment - parental upbringing, peer norms, the family home, schooling - have no effect whatsoever. For example, the psychoanalytical idea that distant fathers or overbearing mothers sabotage their sons' sexual development is not borne out by evidence. Wilson and Rahman dismiss such theories as "beyond the pale of science". In conversation, Rahman is more brutal, dismissing "95% of psychology as rubbish".
Initial sexual experiences do not appear influential - one study showed that boys educated at single-sex boarding schools, where early same-sex experiences are relatively commonplace, are no more likely to become gay than other boys. What about the seduction hypothesis? Men who, as boys, had gay encounters with older men have reported that they already knew they were gay before the encounter. Adopted children of gay and lesbian parents are predominantly heterosexual. The missing environmental link, the authors argue, is the womb. This would fit with findings in the early Nineties that the brains of gay and straight men differ slightly. Rahman explains: "We argue that genes produce differences in the brains of pre-straight and pre-gay foetuses and those differences might affect certain receptors in the brain that influence the activity of male sex hormones."
Put simply, Wilson and Rahman suspect that some male foetuses absorb low amounts of testosterone in certain parts of the brain; full absorption is needed for full masculinisation. "In a foetus which has a genetic predisposition to be gay, these receptors are not as effective at soaking up testosterone. The result is that this slightly insensitive part of the brain follows the default development route, which is female."
In other words, the neural circuit that promotes sexual desire towards women is never laid down; the result is a male who is attracted to other men. This also explains, the authors claim, why gay men show a 'mosaic' of female-like and male-like cognitive traits. In their handling of language and in their spatial awareness, for example, gay men are more similar to women than to heterosexual men.
The idea that the womb environment may have consequences for future siblings is interesting because researchers have noted a sibling pattern among gay men, called the 'big brother effect'. The more older brothers a man has, the more likely he is to be gay. It is possible that maternal antibodies developed in early pregnancies may cross the placenta in later pregnancies to disrupt testosterone absorption.
Lesbianism may also be due to hormonal conditions in the womb (although scientists stress that lesbianism cannot always be examined as a direct parallel of male homosexuality - there is no 'big sister effect,' for example). "There's a protein in the womb that protects female foetuses from excessive exposure to male sex hormones," Rahman says. "Perhaps this protein doesn't kick in early enough in lesbians."
Some brain circuits then follow the male development; a sexual preference for women may be a consequence.
As for bisexuality, there is no biological evidence that some people are turned on equally by both sexes. Physiological studies show that self-declared bisexuals exposed to straight and gay erotica are aroused by either one or the other but not both. Academics suggest that bisexuals may be omnisexuals with libidos so high that the gender of the target doesn't matter.
Homosexuality does not promote reproduction (for every gay father, there are between five and 10 straight fathers). So why haven't the relevant genes vanished from the human gene pool? One suggestion is that, on the ancestral plains, same-sex social bonding - for both men and women - was necessary to reduce aggression within societies and encourage the sharing of resources. Bonobos, the closest primate species to humans, engage in homosexual behaviour for social purposes.
Another intriguing theory is that gay genes feminise men just enough to make them attractive as potential fathers. "You have these very nice heterosexual men who are 'gay-enabled', who have a low dose of the gay gene," Rahman says. "It might make them more committed, more empathic, more charming and more attractive to women." The benefits of having empathic men would stop gay genes being weeded out of the gene pool - and thus maintain a gay population.
In fact, Rahman suggests, modern women may be altering their ideal of the perfect partner enough to influence evolution: "These days, women may not want these big guys to protect them - they're not necessarily looking for the macho type. We might even see homosexuality increase. It's an idea that Glenn and I have talked about. There's no reason to think that evolution won't change the goalposts - evolution changes us all the time."
Born Gay: The Psychobiology of Sex Orientation, by Glenn Wilson and Qazi Rahman, is published by Peter Owen at ?20.79