In a recent Guardian article , Simon Copland argued that it is very unlikely people are born gay (or presumably any other sexual orientation). Scientific evidence says otherwise. It points strongly to a biological origin for our sexualities. Finding evidence for a biological basis should not scare us or undermine gay, lesbian and bisexual (LGB) rights (the studies I refer to do not include transgendered individuals, so I’ll confine my comments to lesbian, gay and bisexual people). I would argue that understanding our fundamental biological nature should make us more vigorous in promoting LGB rights.

Let’s get some facts and perspective on the issue. Evidence from independent research groups who studied twins shows that genetic factors explain about 25-30% of the differences between people in sexual orientation (heterosexual, gay, lesbian, and bisexual). Twin studies are a first look into the genetics of a trait and tell us that there are such things as “genes for sexual orientation” (I hate the phrase “gay gene”). Three gene finding studies showed that gay brothers share genetic markers on the X chromosome; the most recent study also found shared markers on chromosome 8. This latest research overcomes the problems of three prior studies which did not find the same results.

Panel Discussion - Born that way: Is there a gay gene and should it matter? Read more

Gene finding efforts have issues, as Copland argues, but these are technical and not catastrophic errors in the science. For example, complex psychological traits have many causal genes (not simply “a gay gene”). But each of these genes has a small effect on the trait so do not reach traditional levels of statistical significance. In other words, lots of genes which do influence sexual orientation may fall under the radar. But scientific techniques will eventually catch up. In fact there are more pressing problems that I would like to see addressed, such as the inadequate research on female sexuality. Perhaps this is due to the stereotype that female sexuality is “too complex” or that lesbians are rarer than gay men.

Genes are far from the whole story. Sex hormones in prenatal life play a role. For example, girls born with congenital adrenal hyperplasia (CAH), which results in naturally increased levels of male sex hormones, show relatively high rates of same-sex attractions as adults. Further evidence comes from genetic males who, through accidents, or being born without penises, were subjected to sex change and raised as girls. As adults these men are typically attracted to women. The fact that you cannot make a genetic male sexually attracted to another male by raising him as a girl makes any social theory of sexuality very weak. Genes could themselves nudge one towards a particular sexual orientation or genes may simply interact with other environmental factors (such as sex hormones in the womb environment) to influence later sexual orientation.

The brains of gay and heterosexual people also appear to be organised differently. For example patterns of brain organisation appear similar between gay men and heterosexual women and between lesbian women and heterosexual men. Gay men appear, on average, more “female typical” in brain pattern responses and lesbian women are somewhat more “male typical”. Differences in brain organisation mean differences in psychology and study after study show differences in cognition between heterosexual and gay people. Thus gay differences are not just about who you fancy. They are reflected in our psychology and the ways we relate to others. The influence of biology runs throughout our sexual and gendered lives and those differences, that diversity, is surely to be celebrated.

Some writers tend to wave off the scientific evidence by urging us to look to the history of sexuality or claim that homosexuality is a social construction (cue Michel Foucault and the like). But these accounts are mere descriptions at best and not scientific theories. Social constructionist accounts generate no hypotheses about sexual orientation and are not subject to systematic testing. So why should we take their claims seriously? Social constructionism and postmodernist theory question the very validity of empirical science in the first place. That makes it no better than climate science denial.

Some will argue that our common sense experiences are full of people who are “fluid” in their sexual orientations or change their sexualities. This won’t do either because our experience fools us all the time. Change is widely used to argue against biological explanations. Critics will say that if behaviour changes, or is “fluid”, then surely it can’t have a biological basis? This is false because it is our biology that allows us to learn, respond to socialisation, and helps generate our culture. So showing evidence of change is not an argument against biology. There is indeed some fluidity in sexuality over time, predominantly among women. But there is no “bell shaped curve” to sexual orientation. People may change the identity labels they use and who they have sex with but sexual attractions seem stable over time.

Remember, sexual orientation is a pattern of desire, not of behaviour or sexual acts per se. It is not a simple act of will or a performance. We fall in love with men or women because we have gay, straight, or bisexual orientations and not because of choice. So let’s stop pretending there is choice in sexual orientation. Who truly “chooses” anything of substance anyway? Surely our choices are the result of things we didn’t choose (our genes, personalities, upbringing, and culture).

People worry that scientific research will lead to “cures” for homosexuality (which is an odd worry to have if you don’t believe in the “born this way” argument). They worry more about this than the consequences of choice or environmental explanations, which are not without risk either. But clearly none of the direst predictions have materialised. Sexual minority identities have not been medicalised nor has there been any genetic testing. Genetic tests would never result in 100% accurate identification of LGB individuals because, as I said, genes are less than one-third of the story. On the social policy and legal front we’ve gone in the direction of more rights and more freedoms for LGB people (at least in the West) and not less.

So should the causes of sexuality influence how we view sexual minority identities? No. The causes of a trait should not influence how we see it. But the science shows us that sexuality has a biological basis: that is simply how the science turned out. It’s no use denying it. So let’s use it to supplement, but not replace, a discussion about LGB rights and social policy. The biology of sexuality diversity tells the world to deal with it. We are who we are, and our sexualities are part of human nature.

My worry about the claims of social construction, choice and such like is that it plays into the hands of homophobic ideology, into the hands of the “aversion therapists”, and into the hands of a growing culture which seeks to minimise gay differences. It reminds me of something Noam Chomsky alluded to : if humans were entirely unstructured creatures we would be subject to the totalitarian whims of outside forces.

Dr Qazi Rahman is an academic at the Institute of Psychiatry, King’s College London. He studies the biology of sexual orientation and the implications for mental health and is the co-author of Born Gay? The Psychobiology of Sex Orientation