Research supporting that homosexuals are born homosexuals

December 16, 2009 3:35 AM

What exact research has been done to support the notion that homosexuals are born gay?

I’m a person who believes that homosexuals are not born gay. I believe that it’s a choice they make. This often brings me into heated arguments with some of my friends who do believe gay people are born gay. During our arguments they often say that there is research out there to back this up, but they’ve never actually presented me with any of it. This leads to my question. I would like to see what research there exists, both for and against the notion that homosexuality is something you’re born into, preferably showing the methodology that was used, results concluded and researcher/s involved. I’d like to see this research not only to be better prepared for future debates, but to actually understand this topic. Is anybody here aware of anything I should be reading, preferably online but offline is fine also? My own Google searches have turned up the usual for/against arguments, but nothing with the more rigorous approach I’m looking for.

posted by Prunedish to science & nature (40 answers total)

You might want to start here. It's Wikipedia, but it summarizes and links to a great many academic texts.
posted by sueinnyc at 3:43 AM on December 16, 2009

Biological differences between brains (specifically size of the hypothalamus and suprachiasmatic nuclei) of hetero/homo/transsexuals have been shown; this finding is more than 15 years old and now considered pretty robust, if I'm not mistaken (but IANABiologist). From this paper (assuming you don't have an academic library to back you up):

Sexual orientation is influenced by quite a number of genetic as well as non-genetic factors (Table 2). Genetic factors appear from studies in families, twins and through molecular genetics
(follows technical discussion about crosslinks on specific gene locations...)
This controversy will undoubtedly continue.

Sex hormones during development also have an influence on sexual orientation, as appears from the increased proportion of bi- and homosexual girls with congenital adrenal hyperplasia [27, 71 and 75]. Then there is diethylstilboestrol (DES), a compound related to estrogens that increases the occurrence of bi- or homosexuality in girls whose mothers received DES during pregnancy [29 and 71] in order to prevent miscarriage (which it does not do). Whether environmental estrogens, e.g. from plastics can influence sexual differentiation of the human brain and behavior is, at present, in debate but certainly not established. In addition, phytoestrogens, such as resveratrol, present in grapes and wine and an agonist for the estrogen receptor should be considered in this respect [38].

Prenatal nicotine exposure has masculinizing/defeminizing effects on sexual orientation of female offspring and increases the probability of lesbianism [31].

Maternal stress is thought to lead to increased occurrence of homosexuality in boys, particularly when the stress occurs during the first trimester [30 and 31], and in girls [8]. As an interesting case history of this potentially environmental factor, Weyl [113] has mentioned that Marcel Proust’s mother was subjected to the overwhelming stress of the Paris commune during the fifth month of her pregnancy in 1871 and that Mary, Queen of Scots, the mother of the homosexual king of England, James I, toward the end of the fifth month of pregnancy had the terrifying experience that her secretary and special friend Riccio was killed. Although postnatal social factors are generally presumed to be involved in the development of sexual orientation [15], solid evidence in support of such an effect has not yet been reported. The observation that children raised by lesbian couples or by transsexuals generally have a heterosexual orientation [40, 42 and 58] does not support the possibility of the social environment in which the child is raised as an important factor for determining sexual orientation, nor is there scientific support for the idea that homosexuality has psychoanalytical or other psychological or social learning explanations, or that it would be a ‘lifestyle choice” [30]. ...

Not to get into a heated argument, but personal beliefs and powers of imagination are a bad measure for the actual state of things, in general. Yes, please read up, with an open mind.
posted by gijsvs at 4:14 AM on December 16, 2009 [5 favorites]

I do not dispute that homosexuality may be genetic. But I never understand this question put into such morally weighted terms. Why is it a dichotomy between flat-out "born that way" vs. "choice" anyway? Many aspects of our deepest selves are the result of an interaction between our genetic dispositions and the environmental stew of factors we happen to be born into -- which are still not a choice in any way. "Choice" is an overused word that is meaningless, in practical terms, when we are talking about desire and affect. Part of our hard wiring is genetic, but part of our hard wiring is laid into place as we grow up, and it really doesn't matter -- you still just are who you are.
posted by keener_sounds at 4:41 AM on December 16, 2009 [17 favorites]

Here's a good summary [PDF] of the arguments in this debate, published in the Scientific American.

Basically, it argues that sexuality exists on a continuum. You could be entirely gay, or entirely straight, in which case you don't have much choice about which gender you're attracted to. But you could also be somewhere in the middle, which means you can 'choose' to express your sexuality with one people of the same or opposite gender, or both, during your lifetime. You can't choose where you end up on the continuum - that's down to genes and environment. And the fact that some people can shift their sexual orientation during their lifetimes does not negate the experience of people who were born gay and are certain they always will be.

The debate around this question has historically been influenced by moral arguments about sexuality. People who believe homosexuality is immoral tend to believe that it is an immoral choice; if it were innate, it would be (even more) unjust to vilify someone because of his or her sexuality. When evidence began to emerge in the 80s that homosexuality was innate, some gay rights activists seized on what they saw as a defence against that kind of disapproval. If being gay is natural, they argued, then nobody can tell us that our sexuality is immoral - it's just the way God made us. Since then, the research has become more nuanced and the debate has widened - it's become accepted that while some people are hard-wired to be straight or gay, others experience their sexuality as fluid and changeable.

I guess my question is, why are you so convinced of your position? By clinging to your argument that homosexuality is a choice, what underlying beliefs are you trying to support? And if you're straight, when did you make that choice?
posted by embrangled at 4:52 AM on December 16, 2009 [16 favorites]

..to express your sexuality with one people of the same or opposite gender...
posted by embrangled at 4:53 AM on December 16, 2009

Ok, a few distinctions need to be made here. First, I have seen no evidence that "genetics" has anything to do with it--i don't think it is a heritable trait. Instead, my reading of the literature is that sexuality is set in the womb by hormone levels. Second, a distinction has to be made between sexual behavior and orientation. Prisoners will often engage in homosexual behavior because of a lack of opposite-sex outlets. This does not mean they have a homosexual orientation.

The first thing I ever saw on this was a study showing that Germans born during wartime (Second World War) were more likely to be gay. This is called the "prenatal stress" theory. Other peer-reviewed studies have shown a link between birth order and being gay.

More importantly, do a thought experiment--just ask yourself about your orientation. If it was a choice, when did you make it? Do you remember at any time, thinking that the same sex was attractive? Do you remember making a choice? Was there ever a time when you thought men's bodies sexually attractive? This straight man hasn't, ever.
posted by Ironmouth at 5:41 AM on December 16, 2009 [3 favorites]

Ironmouth is correct that "hormone levels in womb" or any number of other early/natural causes are not the same as "genetic" and we should be less sloppy with our language here.

And by "we", I mean of course me.
posted by rokusan at 6:03 AM on December 16, 2009

I don't know how the "choice" part would apply, if at all, but homosexual behavior (including pair-bonding) has been observed in many, many species of animals. I'm not a biologist, but it would be weird if homosexual behavior in, say, lions was the result of genetics/hormones, but in humans it's a choice, and not the result of genetics/hormones. More here.
posted by rtha at 6:04 AM on December 16, 2009 [3 favorites]

Seconding same-sex behavior in animals. When penguins, dolphins, bonobos, and lions engage in same-sex pair-bonding and sexual activity, it's hard to see how it could be a uniquely human "choice."
posted by Tomorrowful at 6:21 AM on December 16, 2009

I recommend watching the2008 BBC documentary The Making of Me. In it actor John Barrowman "sets out to unearth what the latest scientific research can tell him about the origins of his homosexuality." He travels to different science centers in Europe and the U.S and meeting with the scientists who are focused on this question. It's compelling what the studies show.

YouTube - 1 | 2 | 3 | 4 | 5 | 6.
posted by ericb at 6:26 AM on December 16, 2009 [10 favorites]

Ironmouth: First, I have seen no evidence that "genetics" has anything to do with it--i don't think it is a heritable trait.


Certainly not meaning to contradict you, but I think I've read some articles linking male homosexuality with large numbers of brothers, with a possible genetic link (not just one gene, of course, but a ...cluster? IANA biologist). There is some idea that this could be why homosexuality has not been, as it were, bred out of the human race. Can't look up links as I'm at work.

I agree with other commenters who said it's great that the OP is looking for logical/rational/scientific background about this issue :).
posted by daisyk at 6:30 AM on December 16, 2009

[A few comments removed. Like the setup or not, the asker is looking for research citations, and a general debate about beliefs doesn't really belong here.]
posted by cortex at 6:33 AM on December 16, 2009

Also, take a look at the animal kingdom at large:

The Fabulous Kingdom of Gay Animals.

The Gay Animal Kingdom.

Gay Animals: Alternate Lifestyles in the Wild.

Gay Animals Out of the Closet.

A first-ever museum display, ‘Against Nature?,’ opened in October 2006 at the University of Oslo's Natural History Museum in Norway, presenting 51 species of animals exhibiting homosexuality.

posted by ericb at 6:33 AM on December 16, 2009

Previous related MeFi thread: "The 'Darwinian Paradox' [PDF] of homosexuality presents the conundrum of how a potential genetic basis for homosexual behavior could provide a survival benefit to offpsring and extend through generations, when sexual reproduction would seem to place strong selection pressure against such a 'gene.'"
posted by ericb at 6:39 AM on December 16, 2009 [1 favorite]

A central problem here is that neither developmental psychologists or biologists think in either/or terms about his issue. Rather, the question is how much proportion of variance can be attributed to environmental vs. genetic factors. Behavioral genetics is still a fairly weak field, and due to ethical considerations its extremely difficult to assess genetic influences on human behavior.
posted by KirkJobSluder at 6:41 AM on December 16, 2009 [2 favorites]

CBS NEWS | 60 Minutes: The Science Of Sexual Orientation

"There are few issues as hotly contested — and as poorly understood — as the question of what makes a person gay or straight. It's not only a political, social, and religious question but also a scientific question, one that might someday have an actual, provable answer.

The handful of scientists who work in this under-funded and politically charged field will tell you: That answer is a long way off. But as Lesley Stahl reports, their efforts are already yielding tantalizing clues. One focus of their research is twins." [more]

Video.
posted by ericb at 6:43 AM on December 16, 2009

This doesn't answer your question directly, but it's (more) evidence for a biological basis for sexual orientation. Plenty of cites there.
posted by s0ckpupp3t at 6:45 AM on December 16, 2009

In addition to the false dichotomy of "choice" vs "born that way", there's also an important point about the status of different types of evidence here. Like all psychological phenomena, the experience of becoming aware of (or even, for the sake of this discussion) choosing sexual orientation is an entirely internal one, that can quantitative scientists can only analyze via proxies — in the examples above, either by correlating certain circumstances during pregnancy with self-reports of orientation, or in animals by observing homosexual behavior. So there's a very real sense in which anecdotal accounts — the fact that any gay person you ask will tell you they were never conscious of having a choice — are equally valid as evidence here, albeit in a non-quantitative way. What I am saying in short is that there is a built-in limit to the degree to which "research papers", in the sense of quantitative controlled studies, are ever going to be able to address this question.
posted by game warden to the events rhino at 6:47 AM on December 16, 2009 [2 favorites]

that quantitative scientists can only analyze via proxies
posted by game warden to the events rhino at 6:47 AM on December 16, 2009

Gay twin brothers may hold genetic clues -- "They are among 1,000 pairs of gay brothers taking part in the largest study to date seeking genes that may influence whether people are gay."
posted by ericb at 6:48 AM on December 16, 2009

New York Times | June 2005: A single gene answers question of sex.
posted by ericb at 6:54 AM on December 16, 2009

I've only had time to scroll through the first page, but this article in New Scientist might be a good place to start. Lots of names/ideas to follow up on.

New Scientist is a good site in general. I found this piece by searching gay+brothers.

Hope that helps.
posted by daisyk at 6:55 AM on December 16, 2009

The Independent | July 1993: Homosexuality linked to genes.
posted by ericb at 6:57 AM on December 16, 2009

Slate | June 2008: A genetic theory of homosexuality.
posted by ericb at 6:59 AM on December 16, 2009

PBS | Frontline: 'A Gay Gene?'

The documentary looks at various studies, such as those conducted by neuroscientist Simon Levay who has been doing research on brain structures and sexual orientation for quite some time. Dr. Levay's website.
posted by ericb at 7:06 AM on December 16, 2009

Thanks, ericb, that Slate article summed up exactly what I meant earlier but couldn't recall well enough to describe.
posted by daisyk at 7:10 AM on December 16, 2009

anecdotal accounts — the fact that any gay person you ask will tell you they were never conscious of having a choice — are equally valid as evidence here, albeit in a non-quantitative way.

I want to second this. If you are focusing on the notion of "choice," then individual, narrative accounts of sexuality should figure in to your evidence. For that, you could read coming out stories, as well as stories by self-identified ex-gays.

Ultimately, though, I am curious as to how you would you prove that any feeling (as opposed to behavior) is a volitional "choice"?
posted by yarly at 7:10 AM on December 16, 2009

I've always found this paper interesting: Finger-length ratios and sexual orientation.
posted by 6550 at 7:13 AM on December 16, 2009

When you're researching the socialization aspects, don't forget to take into account the similarities in sexuality between straight and gay folks. Heterosexuals engage in the same process of "choosing" whether or not to acknowledge and act on their sexual orientation...we call it a "coming of age" story.
posted by desuetude at 7:19 AM on December 16, 2009

A couple points:

Genetic predispositions to behavior, as opposed to simple physiological traits like eye color, are rarely simple and straightforward. For instance, some people have a genetic predisposition to shyness. The predisposition, though, consists of a longer-duration startle response. Being startled is unpleasant. If it takes you slightly longer to calm down after something startles you, that makes it slightly more unpleasant. People learn avoid things that are unpleasant for them. One thing that can scare kids, among other things, is the sudden appearance of strange people. So people who have this trait are more likely to learn avoid strangers. However, which allele a person has doesn't determine whether people's interactions with strangers are generally positive or not. People who don't have a longer than usual startle response can still learn from experience to avoid talking to people they don't know well, and people with the trait don't necessarily learn to avoid strangers. So there isn't actually a shyness gene. It's just that people learn from experience, and the genetic difference in question is a factor in how people experience things. It also wouldn't make sense to say that people chose to be shy.

For homosexual attraction to potentially be directly genetically determined, you have to establish that people have an innate ability to tell sexes apart, rather than this being something they have to learn, and that they innately know which one to try to mate with. Although this seems plausible enough, and little kids do catch on to gender very quickly, research in this area is actually inconclusive. (It's a tricky thing to try to study.)
posted by nangar at 7:22 AM on December 16, 2009 [1 favorite]

Ironmouth: First, I have seen no evidence that "genetics" has anything to do with it--i don't think it is a heritable trait.


Certainly not meaning to contradict you, but I think I've read some articles linking male homosexuality with large numbers of brothers, with a possible genetic link (not just one gene, of course, but a ...cluster? IANA biologist). There is some idea that this could be why homosexuality has not been, as it were, bred out of the human race. Can't look up links as I'm at work.

I agree with other commenters who said it's great that the OP is looking for logical/rational/scientific background about this issue :).

Just to be clear, my understanding from the science is that it is about gene activation, not gene heritability, meaning that we all have the genes for it, but they are only activated in certain circumstances, such as when there are a whole load of male children around in the matrilineal line or there is a great deal of prenatal stress.

There is a huge difference between passing on a gene that others do not have and passing on a gene that is not activated on and then circumstances activate it. Otherwise, homosexuality would be fast disappearing--those not having children would not pass it on.
posted by Ironmouth at 7:34 AM on December 16, 2009

I'm as much a stickler for hard, quantitative, reproducible, peer-reviewed evidence as you're likely to find. By all means, review the links presented here. I think it's great that you're willing to revise your beliefs if and when the evidence requires you to do so. The world could use a lot more of that.

But let's assume, just for the sake of argument, that you perform a full review of the available literature, and the best thing you can say about the scientific evidence is that it's inconclusive—i.e., there is no compelling evidence either way.

So science can't help us answer this question. But we can ask gay people themselves whether they've chosen to be gay. Sure, it's testimonial evidence, and therefore not as reliable as quantitative studies. But I hope you have enough faith in humanity to believe that most people tell the truth, most of the time. Lacking scientific evidence, I think that personal testimony from those who live every day of their lives as gay people is an important kind of evidence to consider.

You can conduct your own survey along these lines, if you like. I think I know the answer you'll get. Maybe all of your informants are lying. But that seems pretty unlikely, doesn't it?

Try a simple experiment: can you choose to be gay? Can you just decide to be sexually aroused by the same gender, in equal degree and kind to the way you're currently aroused by the opposite gender? Try it now. Try as hard as you can to be gay for fifteen minutes (you don't have to act on your urges). Conjure up a gay fantasy that's as erotic to you as your favorite heterosexual fantasy. Find some gay porn on Google Image Search and masturbate to it. I'm not being crass; I'm being serious. If, as you suggest, people can just choose to be attracted to one gender or the other, this shouldn't be a problem for you. (Remember, this is only for fifteen minutes, for the purposes of experiment. You can just choose to be straight again when the experiment is over.)

If you find that you can't choose to be gay, then why are you so convinced that other people can, especially when they're telling you that it's not the case?
posted by s0ckpupp3t at 7:40 AM on December 16, 2009 [15 favorites]

Firstly, it's worth pointing out that the whole "nature vs. nurture" debate is almost always a false dichotomy. Everywhere I've heard of people searching for genetic causes to phsychological phenomena has turned up with the answer "actually, it's a bit of both". Think of it like height: your parents' genetic information plays a big role in your height, and so does your diet, excercise, exposure to disease, etc. It's very rare for things to be purely nature or purely nurture.

I'm not an expert on this stuff, but it's something I've done a bit of reading around.

Finger length ratios are correlated with birth order, levels of sex hormones you were exposed to in the womb and your eventual sexual orientation. So it looks pretty certain that something that happens in the womb influences a person's sexuality. [Nature paper, free version, BBC News writeup]

As regards the birth order, it's not just the case that being raised with lots of older brothers makes a man gay. Being born to a mother who has already given birth to boys increases a boy's odds even if he's not raised with that family, so it really does seem to be a pre-natal event rather than post-natal (nature, not nurture). [PNAS paper]

About 8% of male sheep exhibit homosexual tendencies, suggesting that if homosexuality is purely cultural then sheep have a lot more culture than we previously thought. Further, brain scans and dissection show different brain structures in homosexual sheep as compared to heterosexual sheep, in areas of the brain thought to be formed very early in development (probably before birth, maybe in infancy). [Endocrinology paper, Endocrinology Editorial (more readable, better background), Medical News writeup, New Scientist]

Also noted in that Endocrinology paper is that stright men's "interstitial nucleus of the anterior hypothalamus (INAH3)" is bigger than straight women's, but that gay men's INAH3s are indistinguishable from women's, showing that this part of brain anatomy is strongly linked with orientation. (Big = attracted to women, small = attracted to men?) Science paper, New Scientist] Again, this brain development usually finishes before birth, strongly suggesting that this isn't due to a choice or a learned response.

There's a nice twin study in this Biological Psychology paper, which suggests that genetic factors account for a proportion of "potential for homosexual response" (in which they asked about hypothetical responses to various scenarios rather than actual sexual activity) - 37% in men, 46% in women. So genetics seems to play a big role, then womb conditions can be added to that, then environmental conditions on top of that.

So it might be (and probably is) the case that environmental conditions play a role in determining sexuality. But a person's genes, prenatal conditions (birth order, exposure to hormones) and pre-natal or infant brain development all play important roles in determining sexuality.

As a final note, even if you want to ignore this evidence and believe that homoseuality is not physiological on origin, can I suggest a change in your terminology? Calling it a "choice" would still only be true in the same sense that people "choose" to become depressed, or to have a New York accent, or to be phobic of something. You'd be talking about the way that someone's personality has developed in a given environment (generally shorthanded as referring to "nurture"). Talking about it as a "choice" implies to a lot of people that they just woke up one morning and thought "hey, from now on I'd be attracted to dudes!". As well as strawmanning your own argument, it also carries the implication that they're just doing it to be obstinate, for attention or whatever, and could snap out of it if they "chose", which is very insulting. I'm sure this isn't what you mean, but please bear in mind that it's what many people will think you mean which, in a conversation, is more important.

Ironmouth, daisyk et al. - Even if it is about gene activation rather than just inheriting the gene, gene activation levels can be heritable too, thanks to the miracle of epigenetics. This is simultaneously very exciting and tremendously depressing for a load of geneticists who realise how much more work they need to do on heritability than they had previously thought.
posted by metaBugs at 7:47 AM on December 16, 2009 [5 favorites]

Ironmouth: Your statements rely on a number of sloppy and simplistic assumptions about genetics and natural selection. First, mendelian dominance/submission describes only a small portion of what we know about genetics. And secondly, it rests on the assumption that the genetic factors influencing human sexuality are binary characteristics and maladaptive to reproductive success at any level of expression.

The bottom line is that there is reasonable evidence out there that hereditary factors do play a role in sexual orientation. That is to say that multiple LGB people among genetic kin is more likely than can be expected from environmental factors. While genes alone probably don't determine sexual orientation (which we don't have a rigorous definition of anyway), they almost certainly bias the odds.
posted by KirkJobSluder at 8:19 AM on December 16, 2009 [2 favorites]

s0ckpupp3t makes a good point, but I'd like to add that being gay isn't just a matter of which sex physically arouses you. While I've met plenty of attractive men over the years (I'm a lesbian), none of them have given me the same physical and emotional ZING that I feel when I meet an attractive woman. This isn't true for all self-identified gay people, of course, but it's true for a lot of us.
posted by rtha at 8:33 AM on December 16, 2009 [2 favorites]

And it's critically important to note that when geneticists identify a trait as influenced by genes, what they mean is that they have strong evidence that the trait appears more frequently among genetically-related families and populations than can be expected by random chance. How much the genes influence the resulting trait is a related but different question.
posted by KirkJobSluder at 8:42 AM on December 16, 2009

Sadly, you probably need to hit your library, but this article on Evolutionary Biology: Genetics and Bisexuality is rather interesting, as it takes the next step of the 'if it is genetic' question. The summary:

"A population-genetic model indicates that if there is a gene responsible for homosexual behaviour it can readily spread in populations. The model also predicts widespread bisexuality in humans."

The article can bring up some interesting thoughts. If it's genetic, and it's prevalent in the population, then the next step becomes is how should a society respond. Personally, here's where the fight over the language about 'choice' is both fascinating and horrifying to me, as I almost always associate the concept of 'choice' and 'freedom of choice' as a positive. Yet I recognize here the usage of 'choice' often implies something else; an accusation that people are just being 'petulant' and 'willful' in their stated sexual preference - like they're just being difficult.

For me, socially, the scientific evidence (so it it genetic or not?) would do nothing to change my mind about how folks with homosexual and bisexual preferences should be treated (which is: equal in the eyes of the law). What's interesting is that when I have conversations with some folks, the science (homosexuality: genetic and prevalent in population), does nothing to change their view either (they still think it should not be tolerated in society, regardless of prevalence). Just something to consider as you are using this data for debate purposes.

Anyway, best of luck on your search for information!
posted by anitanita at 8:54 AM on December 16, 2009

It seems like the most promising research on this is in identical twins as mentioned above by several others. Much like fingerprints, which are never the same, identical twins can often have non-identical sexual preferences. The current theory, as I understand it, is that the balance of hormones available to the two fetuses in utero is skewed leading to two "identical" individuals whose sexuality falls on different points of the spectrum.

National Geographic touched on the research that's being done in this area in their documentary on twins (which is fascinating and worth watching for all sorts of other reasons too).

That's not to say that only identical twins can identify as gay, it's just that with identical twins you've got a great laboratory of nature genetic vs. nature non-genetic vs. nuture.
posted by togdon at 8:56 AM on December 16, 2009

"My own Google searches have turned up the usual for/against arguments, but nothing with the more rigorous approach I’m looking for."

Um really?

The first google scholar query that came to mind, "genetics homosexuality" returned quite a few papers on the subject.

http://scholar.google.com/scholar?q=genetics homosexuality
posted by zentrification at 11:57 AM on December 16, 2009

gijsvs: "
Prenatal nicotine exposure has masculinizing/defeminizing effects on sexual orientation of female offspring and increases the probability of lesbianism [31]."

I would like to read more about this, as I have PCOS which is characterized by excess masculine hormones and I am straight. I want to know how they'd explain that.

Not to play devil's advocate, but have you considered that perhaps some people are born with a sexual preference and perhaps others (who might actually be bisexual) make the choice to be gay?
posted by IndigoRain at 9:16 PM on December 16, 2009