Is Being Gay Genetic? Unbiased Answers & Studies | PhysicsForums

[tahayassen]

Some background information: I had a really close friend of mine ask me if gays were born that way or if it's a choice. From the knowledge that I learned from the teachers at my school, I answered him saying that gays are just born that way, and they do not find out until they're teenagers.

Unfortunately, I was afraid that I may be misleading him so I told him I'll do some research to make sure that I am giving him right information, because my knowledge was pretty much from one health teacher from the ninth grade. Doing a quick good search led to a lot of biased information, so before I waste my time with a proper scholar search, I figured I'd ask PhysicsForums for their unbiased responses to the following questions:

Are gay people born the way they are? Or is it something they learn?
If you answer to "yes, gay people are born that way" to the previous question, is it still possible to be gay without being born that way?
If they are born that way, it it something they inherit?
If it's something they inherit, is there a particular gene?

I would really appreciate unbiased responses to the above information. It would be appreciated if you could enforce your arguments with credible studies. Please do not bring religion views or opinions into this.

 

[Simon Bridge]

As with anything humans do the answer is that "it's complicated".
http://en.wikipedia.org/wiki/Biology_and_sexual_orientation
... fwiw: should provide you with some idea as to why your questions don't have the kind of answers you are looking for.

 

[Simon Bridge]

Is there a verifiably unbiased source on this point?
I think the proper answer to the questions actually needs a little more information. We need to know the context of the debate - what do you want to know for?

If it is just intellectual curiosity then OP may have to settle for "we don't know enough yet". It does not look like there is much evidence to support the idea that there is a gene for homosexuality like there is a gene for blue eyes. However, there does seem to be evidence to support some genetic component to developing sexual orientation. There is a lot to suggest that orientation, once established, stays that way; and trying to alter it causes more problems than it solves.

But if the context is that if homosexuality is a mix of genes, hormones, and environment ... then you can bring up your kid to be heterosexual if you just avoid particular environmental factors -- then the resulting answer is a bit different.

When a question becomes politically charged, we need to be careful of how it is framed.
Having slept on it - I think I can manage a pretty neutral stance ... let's see...

* Are gay people born the way they are? Or is it something they learn?
... ans. it's complicated - it is unclear that you can be born gay the same way you are born right-handed. However, there is some evidence to support the idea that your sexual orientation is not very voluntary.

* is it still possible to be gay without being born that way?
... ans. yep - you can exhibit homosexual behavior without being homosexual just like homosexuals can exhibit heterosexual behavior (have children, get married, go to gay-hating churches etc) and have done in history. Another example would be practising so you can write with similar proficiency with either hand regardless of your preference. More controversially, it is possible to be a man without the Y chromosome ... in the sense that you exhibit the male human physical and behavioral traits. So it boild down to what you think of as "being" a particular way.

* If they are born that way, it it something they inherit?
... ans. if there is a gene for it, or a genetic predisposition, it would be a heritable trait.

If it's something they inherit, is there a particular gene?
... ans. it does not have to be the case: there could be a combination of genes which code of different things which give rise to a predisposition towards a particular sexual orientation.

 

[Pythagorean]

Its not unknown. There's genes associated with homosexuality, but having the gene doesn't mean you're going to be homosexual.

 

[Simon Bridge]

You have a reference to back that up of course?
ifaik no such gene has been isolated. Rather there is evidence to support a genetic component to sexual orientation.

 

[atyy]

http://news.bbc.co.uk/2/hi/science/nature/695142.stm
http://www.ncbi.nlm.nih.gov/pubmed/10761903 (Not free)

http://www.ncbi.nlm.nih.gov/pubmed/16815969 (Free)
http://www.ncbi.nlm.nih.gov/pubmed/16807297.1 (Free)

 

[Simon Bridge]

@atyy: that's actually pretty representative of the research.
You have a lot of correlations without a clear mechanism.
Probably time to hear from OP :)

 

[Pythagorean]

You have a reference to back that up of course?
ifaik no such gene has been isolated. Rather there is evidence to support a genetic component to sexual orientation.

I didn't mean to imply they were isolated or that there was only one. My point is out of context without Gabor Mate or Sapolsky's words. The point was that behavior (in general) is not about genes alone; it's about the interplay between genes and envrionment. You have a whole library of genes to choose from, you don't express them all at once, and you don't express them all in your lifetime.

The large problem is of course defining what constitutes the behavior, and once you do, you find degeneracy (the behavior can still arise without the underlying known genetic associations and the behavior can fail to arise in someone who has the underlying genetic associations).


Gonococcal strains from homosexual men have outer membranes with reduced permeability to hydrophobic molecules.
http://iai.asm.org/content/37/2/432.short

a statistical monozygotic twin study:
http://bjp.rcpsych.org/content/148/4/421.short

It's more likely to be associated with left-handers (who often have flipped brain symmetry):
http://www.sciencedirect.com/science/article/pii/002839328790100X

Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity:
http://rspb.royalsocietypublishing.org/content/271/1554/2217.short

 

[tahayassen]

This is much more complicated than I expected it to be. :|

 

[Ken Natton]

There may be some dispassionate evidence in support of the idea that homosexuality does have a genetic origin. There is undoubtedly also plenty of dispassionate evidence that human homosexuality is far more of a social phenomenon than a biological one. But it is abundantly clear that there is no gay gene. No more than there is an alcoholic gene, or a ‘thrill seeking’ gene. All of these ideas are founded on a misunderstanding. Behavioural traits, like morphological traits are not traced to individual genes. There are likely several genes involved and quite possibly dozens. But even identifying every single gene involved does not give you your answer for how that trait comes about. It is not just a question of the genes themselves but the sequence in which they are expressed during the embryological developmental process. The true explanation of how traits are genetically programmed is actually a deal more complex than that. But the point is made. There is no single, identifiable ‘gay’ gene.

 

[Hypercharge]

To be honest, your question made me doubt my knowledge about this topic.
AFAIK genes never determinate an attribute of a organism, their "data" just facilitate or inhibit a certain physical abilty of the organism (via biochemic factors), but being homosexual is something psycological.

 

[Ken Natton]

AFAIK genes never determinate an attribute of a organism, their "data" just facilitate or inhibit a certain physical abilty of the organism (via biochemic factors), but being homosexual is something psycological.

I think it is clear that some behaviours are genetically programmed. Obvious basic things like the instinct to turn and flee in the face of danger, for example, is a genetically programmed behaviour with a fairly obvious evolutionary purpose. But science has also demonstrated that much more complicated behaviours, such as altruism, are genetically program. Science has also demonstrated why altruism – as the term is defined in a purely biological sense – makes perfect sense in pure Darwinian evolutionary terms. But that does not mean that science has any real understanding of exactly how the genetic programming of behaviour actually works. I have never understood the obsession with the idea that homosexuality is founded in the genes and thus must have a Darwinian evolutionary explanation. It’s an idea that seems entirely false to me, but that feeling is based on observation of people and society rather than on genetic analysis. It is entirely possible that homosexuality is genetically programmed and thus has a Darwinian evolutionary explanation.

 

[Simon Bridge]

Yeah - the question amounts to whether sexual orientation is something you can "help being" or not. A genetic predisposition has been argued to put it in the "not something to be cured" category. ie. we can change peoples sex but we don't think of this as "curing" their sex and we don't think of our sex as something we can help being.

We can easily see that it is not as strongly predetermined as, say, sex or eye-color; nor as weakly determined as, say, a preference for pink or having short hair.

That preferences can be genetic is shown by the number of sexually selective characteristics in nature - where a genetic predisposition for, say, dramatic plumage in the male is paired with a preference for that plumage in the female. Here you have a psychological attitude, "stripey tails are sexy", being genetically determined.

 

[Ken Natton]

Yes Simon, unfortunately there is no escaping the undertone that this discussion always has. It is clear to me that even if it was ever proven that homosexuality has nothing whatever to do with genetic programming, that does not mean that it is something that anyone would want, or need, to be ‘cured’ of. To me, the suggestion that it is genetically programmed is actually the worst case. Another idea that I have encountered is that criminal behaviour is in the genes of those who commit crime. Nobody is going to suggest that criminal behaviour should be acceptable, indeed those who take this view want to use it to support the idea of permanently restricting the freedoms of such people. So the notion that homosexuality is something that you can’t help still leaves scope for it to be considered ‘bad’. If it is seen primarily as a lifestyle choice, then it is easier to support the idea that it is a choice that people should be free to make. For me, the prejudices against sexual orientation have nothing to do with the only question appropriate for consideration on this forum, which is whether or not it is genetically programmed because it serves an evolutionary purpose in terms of maximising replication of a given set of genes.

 

[Hypercharge]

Hmmm...just wondering: Let's assume there WAS a gay gene, how can someone be born with it while he/she was procreated by a non-homosexual man and a non-homosexual woman (in most cases)?

 

[Ken Natton]

Hmmm...just wondering: Let's assume there WAS a gay gene, how can someone be born with it while he/she was procreated by a non-homosexual man and a non-homosexual woman (in most cases)?

Okay, at that point, the issue does become much more subtle and more complex. I would reiterate the point that if homosexuality is genetically programmed then it will not be a question of a single ‘gay’ gene, it will be much more complex than that. However, there is an interesting parallel with the determinant of sex. Steve Jones’ book, ‘Y’ explains that the determination of male or female can be traced to a single gene that exists on the ‘y’ chromosome. Obviously, it takes a great deal more than one gene to govern all of the anatomical changes from female to male, and almost all of the genes involved are dotted all over the genome on various chromosomes, and thus females have them as well as males. It is just that the individual gene in question, located on the ‘y’ chromosome, is the one that triggers the sequence in embryonic development that drives the change from female to male. It does not even follow that females don’t use the genes in question. It is quite likely that the same genes serve many other purposes during embryonic development used by both females and males. But the particular sequence of maleness depends on a specific gene located on the ‘y’ chromosome.

There is another similar gene called ‘distalless’ because, before it was properly understood, certain alleles were known to cause distal elements to be absent in the fully developed organism. So one fascination of distalless is that it is a gene that is pretty universal across species – both humans and fruit flies have it for example. And certain alleles in fruit flies can cause then to be born without feelers of even legs. In humans it can cause serious malformations of a similar nature. Again, clearly one gene cannot govern the formation of an entire limb. The point is that distalless is critical in the triggering of the sequence that leads to the formation of a whole limb.

So it is possible that a single gene could be identified that a certain allele of that gene could trigger a sequence in embryonic development that leads to homosexuality in the mature organism. But it is also entirely possible for some organisms to have that allele and not be affected by it. In the way that, not everyone in a family known to have the gene that causes breast cancer actually develops breast cancer. Not everyone in a family known to have the gene that causes sickle cell anaemia necessarily have sickle red blood cells. The question I once posed is whether it is possible, if homosexuality is genetically programmed, for it to be maintained by evolution at a certain proportion in the population. And the answer came that yes it is. The suggestion is that the prevalence of a certain trait in a population could affect the selective pressure that acts on it, such that, in the manner of a closed loop control system, it finds a balance at a certain proportion in the population. And that then raises the possibility that other factors could also act on the selective pressure such that the balance point changes, thus explaining why that proportion is different at different times. See what I mean about more subtle and more complex?

 

[Simon Bridge]

whether or not it is genetically programmed because it serves an evolutionary purpose in terms of maximising replication of a given set of genes

There need be no "maximize" about it - even quite disadvantageous genesets can be passed on.

You'll notice that homosexual behavior is exhibited in animals besides humans, and that it is by no means a dominant characteristic. Also - being homosexual is not a barrier to having children since you don't have to be exclusive to the same sex just because you self-identify a particular way.

There is a rich variety of human sexual identification - beyond the black-and-white definitions that many people seem to want to saddle themselves with.

 

[Ken Natton]

There is a rich variety of human sexual identification - beyond the black-and-white definitions that many people seem to want to saddle themselves with.

I wholeheartedly agree with that Simon, that is exactly the point. I don't adhere to the belief that sexual orientation is in any way genetically programmed, but it is an idea that seems quite persistent on forums like these, and if a behaviour is genetically programmed, then it is reasonable to seek an evolutionary explanation for it. The usual theory I have seen offered is that homosexuals help to nurture the young of their hetrosexual siblings. I see very little evidence of that phenomenon in the human population.

And though I understand that there is homosexual behaviour observed in other species, I am much less than convinced that it is really exactly the same thing as occurs in human society. But to discuss my thought processes on that point would be way outside the normal discussion limits for a biology forum!

 

[Simon Bridge]

One of the problems talking about this is the idea that the genetic code is like a computer code ... that it is a set of instructions that determines everything about you.

This is basically untrue and yet the idea keeps getting circulated.

I like to tell people it is more like a recipe (also an oversimplifcation)... it takes a lot on context. You cannot put human DNA into a chicken egg and expect a human to hatch. It's the wrong context ... similarly a recipe may tell you to bring water to boil but neglect to tell you the altitude (air pressure) to do this at. Water boils at different temperatures in different circumstances but most cooking happens under predictable conditions so the recipe leaves that stuff out.

Each step at the genetic level is quite simple, but the possible variations in interactions mean the overall process of life is very very complicated.

I think there is a valid, bit tricky to pursue, scientific question about the extent to which genetic characteristics affect our social behaviors. It may lead to a more informed examination of our social structures. I somehow don't see this happening though.

 

[Hypercharge]

wow...again, I'm making things more complex.
Concerning homosexuality: I say it's a merely psycological attribute you decide for yourself, not your genes. ("Homosexuality has been observed in over 450 species, homophobia in only one.")

So, back to tahayassen's questions: (if anyone would answer differently, feel free to post and do so.

Are gay people born the way they are? Or is it something they learn?

I might answer "maybe" to the first, and "likely" to the second.

If you answer to "yes, gay people are born that way" to the previous question, is it still possible to be gay without being born that way?

Then they'd become it later in life (=learn)

If they are born that way, is it something they inherit?

Most likely not. (see Ken Natton's post

Spoiler

Okay, at that point, the issue does become much more subtle and more complex. I would reiterate the point that if homosexuality is genetically programmed then it will not be a question of a single ‘gay’ gene, it will be much more complex than that. However, there is an interesting parallel with the determinant of sex. Steve Jones’ book, ‘Y’ explains that the determination of male or female can be traced to a single gene that exists on the ‘y’ chromosome. Obviously, it takes a great deal more than one gene to govern all of the anatomical changes from female to male, and almost all of the genes involved are dotted all over the genome on various chromosomes, and thus females have them as well as males. It is just that the individual gene in question, located on the ‘y’ chromosome, is the one that triggers the sequence in embryonic development that drives the change from female to male. It does not even follow that females don’t use the genes in question. It is quite likely that the same genes serve many other purposes during embryonic development used by both females and males. But the particular sequence of maleness depends on a specific gene located on the ‘y’ chromosome.

There is another similar gene called ‘distalless’ because, before it was properly understood, certain alleles were known to cause distal elements to be absent in the fully developed organism. So one fascination of distalless is that it is a gene that is pretty universal across species – both humans and fruit flies have it for example. And certain alleles in fruit flies can cause then to be born without feelers of even legs. In humans it can cause serious malformations of a similar nature. Again, clearly one gene cannot govern the formation of an entire limb. The point is that distalless is critical in the triggering of the sequence that leads to the formation of a whole limb.

So it is possible that a single gene could be identified that a certain allele of that gene could trigger a sequence in embryonic development that leads to homosexuality in the mature organism. But it is also entirely possible for some organisms to have that allele and not be affected by it. In the way that, not everyone in a family known to have the gene that causes breast cancer actually develops breast cancer. Not everyone in a family known to have the gene that causes sickle cell anaemia necessarily have sickle red blood cells. The question I once posed is whether it is possible, if homosexuality is genetically programmed, for it to be maintained by evolution at a certain proportion in the population. And the answer came that yes it is. The suggestion is that the prevalence of a certain trait in a population could affect the selective pressure that acts on it, such that, in the manner of a closed loop control system, it finds a balance at a certain proportion in the population. And that then raises the possibility that other factors could also act on the selective pressure such that the balance point changes, thus explaining why that proportion is different at different times. See what I mean about more subtle and more complex?

)

If it's something they inherit, is there a particular gene?

Definitely there's not one, but several genes. Yet I'm not keen on finding out which ones( if they exist ) because I fear selection of people.

 

[Pythagorean]

Not peer-reviewed, but references peer review:

When homosexual men smelled the odor of male sweat—more specifically, a chemical in the male hormone testosterone—their brains responded similarly to those of women.

The findings suggest that brain activity and sexual orientation are linked. It also supports an opinion held by most scientists, that people are born—not bred—gay.

"This is one more line of evidence that there's a biological substring for sexual orientation," said Dean Hamer, a geneticist at the National Institutes of Health in Bethesda, Maryland.

http://news.nationalgeographic.com/news/2005/05/0510_050510_gayscent.html

 

[lisab]

Not to derail this thread, but it's very closely related - is there a straight gene?

 

[Ken Natton]

Not to derail this thread, but it's very closely related - is there a straight gene?

I am aware that you are not really interested in the answer to that question - that is not really your reason for posting - but for what it is worth, simple logic tells you that if there is a 'gay' gene then there is also a 'straight' gene. Of course the gay gene and the straight gene could actually be exactly the same gene. If it exists, it could be a matter of just different alleles of the same gene. It could be as subtle as a few different amino acids in the chain causing the protein to fold slightly differently.

It could be...

 

[Ryan_m_b]

I am aware that you are not really interested in the answer to that question - that is not really your reason for posting - but for what it is worth, simple logic tells you that if there is a 'gay' gene then there is also a 'straight' gene. Of course the gay gene and the straight gene could actually be exactly the same gene. If it exists, it could be a matter of just different alleles of the same gene. It could be as subtle as a few different amino acids in the chain causing the protein to fold slightly differently.

It could be...

It is extremely unlikely that a complex and varied personality trait is controlled by one gene.

 

[Ken Natton]

It is extremely unlikely that a complex and varied personality trait is controlled by one gene.

<Sigh> Yes Ryan, quite, I am aware of that. That issue has been discussed in detail further up this thread. I have also nmentioned how one gene can be critical in triggering different sequences of gene expression, and thus can appear to be pivotal in quite different traits in the organism. I doubt that lisab was really posing a question, I suspect she was only expressing her low opinion of this thread. But I was merely trying to point out that if something in the geneome does lead to homosexuality in the organism, then clearly there must be a contrasting feature that leads to hetrosexuality. It seems to me that does follow. That does not necessarily suggest any merit in the original premise.

 

[Ryan_m_b]

<Sigh> Yes Ryan, quite, I am aware of that. That issue has been discussed in detail further up this thread. I have also nmentioned how one gene can be critical in triggering different sequences of gene expression, and thus can appear to be pivotal in quite different traits in the organism. I doubt that lisab was really posing a question, I suspect she was only expressing her low opinion of this thread. But I was merely trying to point out that if something in the geneome does lead to homosexuality in the organism, then clearly there must be a contrasting feature that leads to hetrosexuality. It seems to me that does follow. That does not necessarily suggest any merit in the original premise.

I wasn't questioning that you didn't know that, simply reiterating it. Of more important note though is that it does not necessarily follow that there is a homosexual or heterosexual genotype at all. It could be that those phenotypes are determined by development perhaps with genotypes leading to predispositions.

Something that occurs to me is that we very well could be framing this question wrong by sticking with western concepts of homo/heterosexuality. The validity of such labels is disputed as being to categorical and unrepresentative of the spectrum of human sexual diversity (not to mention the confusion regarding whether or not a behaviour is homosexual and what that says about one's sexuality). I wonder if to tackle sexuality from a biological perspective at all we have to adopt a better way of talking about and viewing sexuality from a social perspective.

 

[lisab]

I am aware that you are not really interested in the answer to that question - that is not really your reason for posting - but for what it is worth, simple logic tells you that if there is a 'gay' gene then there is also a 'straight' gene. Of course the gay gene and the straight gene could actually be exactly the same gene. If it exists, it could be a matter of just different alleles of the same gene. It could be as subtle as a few different amino acids in the chain causing the protein to fold slightly differently.

It could be...

Actually it wasn't a rhetorical question. It was inspired by a conversation I had many years ago with a bio major. She said people had been looking for a long time for a left-handed gene but couldn't find anything definitive. Then someone thought to look for a right-handed gene and boom, there it was. She said people who don't have the right-handed gene are left-handed about half the time.

(Note: I have no idea if her story was correct, and my background is not in genetics so I don't have the knowledge or resources to research it properly.)

 

[Ryan_m_b]

Actually it wasn't a rhetorical question. It was inspired by a conversation I had many years ago with a bio major. She said people had been looking for a long time for a left-handed gene but couldn't find anything definitive. Then someone thought to look for a right-handed gene and boom, there it was. She said people who don't have the right-handed gene are left-handed about half the time.

(Note: I have no idea if her story was correct, and my background is not in genetics so I don't have the knowledge or resources to research it properly.)

As far as I'm aware the jury is still out on handedness with publications frequently cropping up detailing slight differences in various genes. Though there is a hypothesis similar to your story postulating that there is a specific allele that determines left-hemisphere dominance but it's not confirmed yet.

 

[Pythagorean]

As a left-hander, I'm apparently more likely to be homosexual, dyslexic, schizophrenic, creative and athletic... and president of the USA!

 

[CCWilson]

I suspect that there isn't a gay gene. If there were, it would be quickly eliminated by evolution. But I do believe that we have no choice in the matter of which sex we'd rather do the deed with. As a heterosexual guy, when puberty hit, the desires were focused and extreme and automatic. I think with some people it isn't that clear cut, but presumably for some homosexual men, it's also focused and automatic. The fact is that the plumbing allows any combination, so it's a matter of preference and desire. So if sexual orientation isn't genetically determined, why doesn't everybody turn out heterosexual, which is obviously better for spreading one's genes into future generations?

My opinion is that something is happening in the womb during development of the embryo. Sexual preference is a subtle thing. Men like other men as friends, women like other women as friends, it's just the sexual urges that differ from person to person. It may be that it was very difficult for evolution to devise a strategy that 100% of the time got the psychological urges right. Even the development of sexual organs, which is controlled by hormones, sometimes goes awry, and it must be much more complicated for genetics to control our psychological preference for vagina or otherwise. So my guess is that it's a hormonal thing during gestation. There probably are genetic variations in the control of those hormones, but I'm pretty sure that a gene which specifically causes homosexuality would be weeded out by evolution.

Regardless of the cause, I know that in my case sexual preference isn't something that I ever decided, it just was. For many homosexuals, probably likewise. We desire what we desire, and most of us could never change those tendencies.