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The Causes of Male Homosexuality

A man develops a sexual preference for women because his brain develops in a certain way. It develops in a certain way because testosterone produced by his genetically determined testicles alter the brain inside his mother’s womb in such a way that later, at puberty, it will react to testosterone again. Miss out on the genes for testicles, the testosterone burst in the womb or the testosterone burst at puberty – any one of the three – and you will not be a typical man. Presumably, a man who develops a preference for other men is a man who has a different gene that affects how his testicles develop, or a different gene that affects how his brain responds to hormones, or a different learning experience during the pubertal burst of testosterone – or some combination of these.

The search for the cause of homosexuality has begun to shed a great deal of light on the way the brain develops in response to testosterone. It was fashionable until the 1960s to believe that homosexuality was entirely a matter of upbringing. But cruel Freudian aversion therapy proved incapable of changing it, and the fashion then changed to hormonal explanations. Yet adding male hormones to the blood of gay men does not make them more heterosexual; it merely makes them more highly sexed. Sexual orientation has already been fixed before adulthood. Then, in the 1960s, an East German doctor named Gunter Dörner began a series of experiments on rats that seemed to show that in the womb the male homosexual brain releases a hormone more typical of female brains, called luteinizing hormone. Dörner, whose motives have often been questioned on the grounds that he seemed to be searching for a way to ‘cure’ homosexuality, castrated male rats at different stages of development and injected them with female hormones. The earlier the castration, the more likely the rat was to solicit sex from other male rats. Research in Britain, America and Germany has all confirmed that a prenatal exposure to deficiency of testosterone increases the likelihood of a man becoming homosexual. Men with an extra X chromosome, and men exposed in the womb to female hormones, are more likely to be gay or effeminate and effeminate boys do indeed grow up to be gay more often than other boys. Intriguingly, men who were conceived and born in periods of great stress, such as towards the end of the Second World War in Germany, are more often gay than men born at other times. (The stress hormone, cortisol, is made from the same progenitor as testosterone; perhaps it uses up the raw material, leaving less to be made into testosterone.) The same is true of rats: homosexual behaviour is commoner in rats whose mothers were stressed during pregnancy. The things that male brains are usually good at gay brains are often bad at, and vice versa. Gays are also more often left-handed than heterosexuals, which makes a sort of sense because handedness is affected by sex hormones during development, but is also odd because left-handed people are supposed to better at spatial tasks than right-handers. This only demonstrates how sketchy our knowledge of the relationship between genes, hormones, brains and skills still is.26

However, it is clear that the cause of homosexuality lies in some unusual balance of hormonal influence in the womb, but not later on, a fact that further supports the idea that the mentality of sexual preference is affected by prenatal sex hormones. This is not incompatible with the growing evidence that homosexuality is genetically determined. The ‘gay gene’ that I will discuss in the next chapter is widely expected to turn out to be a series of genes that affect the sensitivity of certain tissues to testosterone.27 It is both nature and nurture.

It is no different from genes for height. Fed on identical diets, two genetically different men will not grow to the same height. Fed on different diets, two identical twins will grow to different heights. Nature is one side