The case of Chris Birch seems to have raised some questions for the gay community. Some of the comments on a news story covering his story have raised prejudices and fears about its implications. If someone can be “made gay” by the brain damage caused by a stroke, what does that mean for who we are?

The causes, consequences and cures of homosexuality have been debated on and off since before the subject first got its “scientific” name in 1869. Clearly same-sex relationships existed prior to that, but with the publication of Psychopathia Sexualis, the causes of homosexuality became scientific subject worthy of explanation. (It’s worth noting that the word heterosexual wasn’t coined until nearly 20 years later.)

For a long time, the explanation that held the most sway were the Freudian psychological theories about the unconscious influence of events in early life on behaviour later in life. Since it was thought homosexuality was a mental disorder, people attracted to the same sex were considered treatable. This attitude led to the death of Alan Turing who was subjected to aversion therapy (being given electric shocks associated with photos of naked men to associate pain with same-sex arousal) and hormone therapies.

Although psychoanalysis is generally considered to be unscientific today, the Freudian theories still hold sway amongst some groups of people, particularly by evangelical groups who want to advocate the ability to change from being gay. However, the consensus of the psychological community today is that homosexuality is not a disease, it’s an example of normal variation in human behaviour. Homosexuality was removed from the American list of mental health problems in the seventies although it wasn’t removed from the international list until 1990.

As the focus shifted away from psychological explanations of homosexuality, in the nineties, news started covering the exciting developments in genetics. As a result, a number of papers were written in the mid-nineties which linked genetics to sexuality. A paper published in 1993 linked a specific gene on the X chromosome (in men, this comes from the mother) with male homosexuality.

For the gay community this reinforced what they already felt: they were born gay. There were public meetings at which researchers told families that their children were normal, that homosexuality was a genetic trait just as much as left-handedness. However, the research couldn’t explain all cases of male homosexuality, and the links with female sexuality were even less clear. In short, genetics explained some cases, but is incomplete.

Focus then shifted to foetal environmental explanations: factors which change the expression of genes as the baby develops. An example of this is that children with a low birth weight tend to be more obese and have more heart disease later in life. It is thought that such children’s “famine” genes are turned on in the womb, so they tend to store more fat later in life.

There’s some evidence that there are developmental links to homosexuality. For example, levels of testosterone in the womb have been associated with both male and female sexuality. There’s also evidence that the more older brothers a man has, the more likely he is to be gay. Yet again, this is insufficient to explain all cases; it’s a part of the picture, but it’s not all of it.

Recently, it’s neuroscience which has dominated science in the news. Back in 1848, Phineas Gage had an accident when working on the railway which resulted in a iron bar being blown explosively into his head. As a result, he experienced a complete change I’m personality, and since then there has been a fascination with how brain damage can alter behaviour. High resolution magnetic scanners mean we’re gaining more insights into the structure of the brain, and some research has shown a link between specific neurological structures and sexuality.

Instead of gay and straight, these brain structures suggest that straight women and gay men share common structures, and that lesbians and straight men also have common structures which look the same. The suggestion here is that people have the structure for male-attraction or female-attraction. In such a light, it’s easy to see that brain damage, which results in the brain rewiring itself to recover, could result not only in personality changes but also in other fundamental behavioural changes.

However, again this is not a complete explanation. For starters, it doesn’t provide an explanation about bisexuality, but neither do psychological, genetic or foetal explanations. There are also people who move between sexualities, and thus engage in relationships with people of both sexes, without ever being attracted to both genders at the same time. How can any of these explanation account for such flexible and fluid expressions of sexuality?

The fact is, sexuality is not simple. Psychological explanations are no longer generally accepted, but may well be useful in some people. Genetics is inadequate to explain sexuality in all individuals, but definitely has some explanatory power for some. Foetal environment is also influential for some, but not for all. Neurological structure also shows explanations for some people, but doesn’t tell the whole story.

Given this complexity, if one wanted to eliminate gay men and women from society, one would have to generate such a multi-factorial model of sexuality that identifying us would be – and indeed is – impossible for all practical purposes. Organisations which claim that people can be cured of their homosexuality – as if homosexuality were disease – are claiming that purely by their psychological therapies (often along with the power of prayer of course) can affect genetic, developmental and neurological factors, an assertion simply not born out in reality.

Even if modifying brain structure were shown to be effective in “treating” homosexuality (or, for that matter, heterosexuality), as a society we learned lessons about allowing indiscriminate use of brain modification with the lobotomy scandals of the twentieth century. I don’t believe society today would allow such procedures.

I don’t know what made Chris Birch gay: I have no reason to disbelieve his story, and I think brain injury is as plausible as anything else. However, projecting our fears onto him and his story just gives the people who want to deny our existence power. We should be proud that, whatever the cause, Chris has felt able to come out and establish his new identity. Society has moved on so far in the last twenty years, and whilst we’re still fascinated by why we are the way we are, being gay is no longer the burden that it used to be.

David Waldock graduated with a degree in life sciences, and has a post-graduate diploma in how people relate to science and technology.