Sigmund Freud got many things wrong. In Three Essays on the Theory of Sexuality (1905), he argued that gay sons are the result of dominant mothers and absent or hostile fathers. He got things backward. There is now a huge amount of evidence that, as boys, many gay men show behaviour and interests more characteristic of girls - playing with dolls etc. The kids brought on the reactions by the parents, rather than conversely.
But Freud got things so massively right that his name should be honoured forever. He and others opened the way to regard gay people as human beings, not as deviates or sinners. He saw that adult sexual orientation is not a matter of free choice. Although admittedly he did think being gay is in a sense a sign of immaturity, in the celebrated "Letter to an American mother," he went so far as to say that being gay is no sickness. We are what we are, and there is no changing this - or need to.
A hundred years after Freud, we have made great progress in understanding. Neuroscientist Simon LeVay has written an absolutely superb book, aimed at the general reader, discussing in detail what we now know. Gay, Straight, and the Reason Why should be on everyone's reading list. Clearly the environment, culture, can be significant. Think of the Greeks and of the behaviours of people in prisons.
More basically, however, it turns out that biology is the key. It is a matter of hormones, more specifically, of hormonal levels in the mid-point of fetal development and how they affect that part of the brain called the hypothalamus. To produce heterosexuals, distinctively different hormonal cocktails are needed for men and women. Homosexual orientation seems to be a matter of (in the case of males) the cocktails being more typical of those that produce heterosexual females. Conversely for women.
Why exactly these atypical combinations should happen - and given that we are looking at around 5 per cent of the population, they are not rare - is still a matter of some debate. Gay orientations run in families. The genes are involved, but not that simply or inevitably. Which at once raises the question of why natural selection does not act against them strongly.
One interesting suggestion, with some evidence, is that gay men and their female siblings might both share genes that make them super attracted to males. Hence the sisters tend to have more children than other women, balancing out the fact that their gay brothers have fewer children than other men. Birth order also may be important. If you have older brothers, then, if male, the chances that you will be gay are raised. This could have something to do with the mother's biology affecting her sons so as to maximize her chances of grandchildren - younger sons tend to have features that complement those of older sons and so are not competing for the same kinds of mates. Sometimes this leads to gay orientation as a kind of byproduct.
Notice that these suggestions are about males. One thing LeVay stresses is that, although in some respects we can treat gay men and women as mirror images for causal factors, one should not assume that this is always the case. Indeed, we should not assume that all gay people of one sex are the same. For instance, there may well be significant differences in the factors making for rather dominant "butch" lesbians, as opposed to "femmes."
My gay son works at Toronto's Hospital for Sick Children, he is open about his sexuality, he is married, and he is loved and respected. Yet in Serbia there was a riot against a gay parade. The Anglican Church is ripping itself apart over gay priests. We have gone far. We have far to go.
Gay, Straight, and the Reason Why is a very good book. It is clear and comprehensive, looking at the widest range of research, and very balanced. Read it, and then pass on its message to others.
Michael Ruse teaches the history and philosophy of science at Florida State University. His next book is on philosophical questions arising out of human evolution.