I summarized this once before in a previous thread - it’s an excerpt from an article by John Derbyshire:
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What causes homosexuality?
In the first place, the main point I was making was not about homosexuality, but about current attitudes, and the metaphysics that underlies them. Whether homosexuals are indeed “born that way” is one question; whether it is “taken for granted” in modern society that they are is a separate and independent question. Either could be true without the other’s being true. That the second is true seems to me too obvious to be worth arguing. Even the Roman Catholic Church, while condemning homosexual acts as sinful, concedes that the predilection to such acts may be inborn, in which case homosexuals “are called to chastity.” (Article 2359 of the current Catechism.)
Leaving that aside, what are the causes of homosexuality �?? the predilection, not the acts (which I assume to be caused by free will prompted by the predilection)? I can list a baker’s dozen of theories that I have heard or seen written up at one time or another. In very approximate order of scientific respectability, as best I can judge it, the theories are:
u Satan.[/u] Homosexuality may be a manifestation of Satan’s work. While the least scientific of current theories, this one is probably the most widely believed, taking the world at large. Most devout Muslims, for example, believe it, and so do many Christians.
u Social Construction.[/u] There is no such thing as homosexuality. There are only heterosexual and homosexual acts, which different cultures regard differently. The notion of “homosexuality” as a personality attribute is a 19th-century invention.
u Brain damage.[/u] Some insult to the tissues of the brain, perhaps at birth or in infancy, causes homosexuality.
u Choice.[/u] People choose to prefer their own sex over the other.
u Family influences in childhood.[/u] The Freudian belief is that having a weak father and/or dominant mother can form the child’s personality in the direction of homosexuality.
u Social stress.[/u] Rats kept in overpopulated environments, even when sufficient food and access to females are available, will become aggressively homosexual after the stress in the environment rises above a certain level.
u Imprinting.[/u] The individual’s early sexual history can “imprint” certain tendencies on animals and humans. Many homosexuals report having been same-sexually molested in childhood or youth.
u Socialization theories.[/u] The high levels of homosexual bonding in some ancient and primitive societies suggests that the common mores of a culture have some power to socialize large numbers of people into homosexuality.
u Genetics, direct.[/u] Homosexuality is the expression of some gene, or some combination of genes.
u Womb environment - too much of a good thing.[/u] The presence of certain hormone imbalances during critical periods of gestation can have the effect of hyper-masculinizing the brain of a male infant. Paradoxically - there are plausible biological arguments - this might lead to the infant becoming homosexual.
u Infection.[/u] Homosexuality may be caused by an infectious agent - a germ or a virus. This is the Cochran/Ewald theory, which made a cover story for the February 1999 Atlantic Monthly.
u Genetics, indirect.[/u] Homosexuality may be an undesirable (from the evolutionary point of view) side effect of some genetic defense against a disease �?? analogous to the sickle-cell anemia mutation, a by-product of genetic defenses against malaria, negative to the organism but nothing like as negative, net-net, as susceptibility to malaria.
u Womb environment - too much of the wrong thing.[/u] Here the effect of the rogue hormones is to feminize the brain of a male infant. (I assume that there are theories corresponding to 10 and 13 for female infants, though I have never seen them documented.)
Note that theories number 9, 10, 12, 13, and conditionally (depending on the age at injury or infection) 3 and 11, could all be taken as saying that homosexuality is “inborn,” while only two of these six theories have anything to do with genetics. The confusion between “genetic” and “inborn” is epidemic among the general public, however, to the despair of science writers. To readers suffering from that confusion - an actual majority of those who wrote to me suffer from it - I recommend the purchase of a good dictionary.
Which is it?
Which of these theories is true? In the current state of our understanding, I don’t believe that anyone can say for sure. From what I have seen of the scientific literature, I should say that numbers 12 and 13 currently hold the strongest positions, with much, though I think declining, interest and research in 9 and 10, modest but growing interest in 11, and some lingering residual attachment to 6, 7, and 8. The other theories are not taken seriously by anyone doing genuine science, so far as I know. If anyone has information to the contrary, I should be interested to look at it �?? though I should only be interested in research written up in a respectable peer-reviewed journal of the human sciences.
My own favorite is the infection theory, number 11. I favor it because it seems to me to be the most parsimonious �?? always a good reason for favoring a scientific theory. Until an actual agent of infection can be identified, however, the infection theory must remain speculative and the evidence circumstantial.
The theories involving genetics all suffer from mathematical problems. Homosexuality imposes such a huge “negative Darwinian load” on the affected organism that it is hard to see how genes inclining to homosexuality could persist for long in any population. Various ingenious theories have been cooked up in attempts to finesse the issue, but nobody has been able to make the evolutionary math work. Which is baffling, because there are persistent nagging hints, in identical-twin studies for instance, that homosexuality does have some genetic component. Science is full of conundrums like this, to the delight of unscientific cranks, who leap on them as evidence of supernatural intervention. History shows that these puzzles always get resolved sooner or later in a natural way, however, sending the “God of the Gaps” traipsing off to find a new place where he can hang his starry cloak for a while.
The “socialization” theories, while not scientifically contemptible, do not hold up well under rigorous examination. It is indeed true that large numbers of men and women, deprived of the companionship of the opposite sex by confinement or social custom, will form erotic bonds with their own sex. As soon as the constraints are removed, however, the great majority revert to heterosexuality. Graduates of English boys’ boarding schools marry and raise families; the convict who spent his sentence bullying weaker inmates into giving him sexual gratification will, upon his release, immediately seek out old girlfriends. Lab studies �?? measuring sexual arousal caused by various kinds of images, for instance �?? confirm that the great majority of people everywhere are, in their inner lives, heterosexual, however they may express themselves under the constraints of their immediate environment.
The “choice” theory, which most of my correspondents seem to cleave to, has as its main supporting evidence the fact that some people have been “converted” from a homosexual lifestyle to a heterosexual one, usually by counseling, often by religious conversion. I don’t myself find this very impressive. The numbers involved are small, and these conversions seem to fall into the category of fringe phenomena you are bound to get when investigating something as complex and variable as the human personality. [/i]