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.

 

[2AlphaMales?!]

Intrauterine hormone dosing causing homosexuality is almost as evolutionarily counterintuitive as a gay gene, and although there is a medium strength correlation for some hormonal conditions/some genes and homosexuality there has only ever been at most a medium strength correlation demonstrated AFAIK. Hardly deterministic. There is only a 20% concordance for monozygotic twins and homosexuality (Bailey et al 2000). Many such twins would also have shared very similar environments of course - still only 20% however.

If it were frequently the environment which causes homosexuality (seems likely) it would not be politically correct to disseminate that information with certitude however because then various...unpalatable cultural groups would force their members, and society at large, to undergo experimental, possibly damaging and certainly unethical practices in order to try and ensure heterosexuality.

There is also the problem that if environmental factors which lead to an increased likelihood of homosexuality were widely known then most parents would do their bit to try and ensure the heterosexuality of their kids, for whatever reason, thereby validating the politically incorrect view that there's something wrong with homosexuality.

The important thing is that it doesn't matter if people are gay or not, and that view is far from universally accepted, so official pronouncements that homosexuality could be avoided through environmental manipulation would cause problems. The AP(sychological)A's glaring omission/dismissal of all the individual psychotherapeutic reports of successful SOCE (sexual orientation change efforts) from their “definitive” 2009 report is testament to that.

It seeems scientific analysis has to take a back seat about this one for now – it’s one of the areas where psychology (and, indeed, biology) isn't allowed to be a proper science for political reasons. Black books indeed…no need to go so far as to actually burn the books however, ergo the comment.~Bailey, Michael J., Michael P. Dunne and Nicholas G. Martin (2000). Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology, 78, 3, 524-536.

 

[CCWilson]

Alpha, when you say that you believe it's environment that causes homosexuality, do you mean parenting and childhood experiences, without including intrauterine environmental factors? Possible, but in many of us sexual preference is so powerfully one-sided that I don't think anything could have changed us. In others, sexual preference is less focused, and those folks might be able to go either way; I can see that they might be influenced by outside factors.

It's interesting to think about how genetics could lead us, through specific wiring in the brain, to find one sex or the other sexually stimulating. Are there connections in our brains between the sexual stimulation center and images of our mother or of some kind of representation of generic female or male secondary sexual characteristics? How does genetics do that? Strange to contemplate.

Are there differences in sexual preference among those who are breast fed or had more intensive mothering? How about sexual preference percentages between those raised in a heterosexual two-parent home and those raised by one parent or by two homosexual parents or in an orphanage? I think in general there aren't big differences in outcome, although I don't believe the definitive studies have been done. If it turns out that sexual preference isn't affected by the sexual orientation of the parent(s), that would suggest - but not prove - that social environment outside the womb is not the determining factor.

I don't agree that intrauterine hormones as a cause of homosexuality is counterintuitive. My suggestion was that sexual preference, presumably genetically engineered through brain structure and connections, must be a difficult thing to get right, and easy to screw up. So it's possible that the best that evolution could come up with as a mechanism isn't perfect and only gets it right 90% of the time, using hormones (and who knows what else) as drivers for the brain changes that tell a person, "This is what turns you on."

 

[OmCheeto]

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

A topic about sexuality, and sheep haven't been brought into the conversation yet?

BIOLOGY BEHIND HOMOSEXUALITY IN SHEEP, STUDY CONFIRMS

Researchers ... have confirmed that a male sheep's preference for same-sex partners has biological underpinnings.

...researchers discovered an irregularly shaped, densely packed cluster of nerve cells in the hypothalamus of the sheep brain, which they named the ovine sexually dimorphic nucleus or oSDN because it is a different size in rams than in ewes. The hypothalamus is the part of the brain that regulates sex hormone secretion, blood pressure, body temperature, water balance, and food intake, while it also plays a role in regulating complex behaviors, such as sexual behavior.

The oSDN in rams that preferred females was "significantly" larger and contained more neurons than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of aromatase, a substance that converts testosterone to estradiol so that the androgen hormone can facilitate typical male sexual behaviors. Aromatase expression was no different between male-oriented rams and ewes.

The study was the first to demonstrate an association between natural variations in sexual partner preferences and brain structure in nonhuman animals.

Typical incomprehensible biology babel, but I think it implies that they're born that way.

ps. Lots of interesting articles can be found by googling "gay sheep"

pps. I'm still in the market for lesbian tree climbing milk goats. If anyone see's some for sale, please contact me immediately.

 

[CCWilson]

What we don't know is why the hypothalamus was different in straight and gay sheep - was it genetic, or was it something that happened in the womb?

There was a study which showed that the more older brothers a boy has, the higher the likelihood he'll be homosexual. That suggests that maybe the mother's supply of hormones available for the fetus gets depleted or altered somehow. But who knows. http://www.dailymail.co.uk/health/article-173878/Boys-big-brothers-likely-gay.html

 

[Ken Natton]

I suspect that there isn't a gay gene. If there were, it would be quickly eliminated by evolution.

I have always had the strongest feeling that the certainty that some people seem to have that homosexuality is genetically programmed and thus has an evolutionary explanation is wrong. It seems to me that you might as well search for an evolutionary explanation for why some people like White Snake and others prefer John Denver. But your dismissal of the possibility of an evolutionary explanation for homosexuality is naïve. The logic that says heterosexuality = reproduction = evolutionarily good, homosexuality = no reproduction = evolutionarily bad is hopelessly simplistic. And your faith in the unwavering nature of your own heterosexuality might also be open to challenge. Plenty of film makers and other artists have done just that, with great skill, to plenty of others who felt just as certain as you are.

There is a clue in your post to just where you are going wrong. You have a common view that heterosexuality or homosexuality is primarily about an urge that you can barely control. We won’t go into all the flaws and potential pitfalls about that view. But the human reality is that, for the most part, expression of sexuality is something that follows the arousing of the emotions, and it is not always so clear cut just who might arouse your emotions.

 

[2AlphaMales?!]

What we don't know is why the hypothalamus was different in straight and gay sheep - was it genetic, or was it something that happened in the womb?

Many brain structures develop in later life. The medium strength correlation in similarities between cerebral hemisphere "gay brains" of humans and those of stright people of the opposite sex seeming the most pertinent example:

...noted in the article is that even though the scans suggest
similarities in how the brain functions between the aforementioned
groups, it doesn’t really tease out whether these findings are the
result of biology, environment, hormones, etc.

http://www.wellsphere.com/mental-health-article/certain-brain-scans-show-similarity-between-gay-men-heterosexual-women/413862

There also seems some significant confusion (no pun intended) as to whether the "gay rams" were always in fact bisexual. I've yet to read a study reporting non-human animals as being exclusively homosexual in anything approaching 8% of the population. Perhaps the full text of the study is online somewhere...

Overpopulation as a cause of some homosexuality has also received some support in the past, and sheep often live in artificially dense/engineered communities which could perhaps be causing this possible "neurological predisposition toward homosexuality" to become evident behaviourally.

Given the number of studies involving human brains and sexual orientation I'm not sure looking to sheep for answeres is entirely expedient in any case.

 

[CCWilson]

I have always had the strongest feeling that the certainty that some people seem to have that homosexuality is genetically programmed and thus has an evolutionary explanation is wrong. But your dismissal of the possibility of an evolutionary explanation for homosexuality is naïve.

What you are saying is that probably there's no evolutionary explanation for homosexuality, but that I dismiss the possibility is naive. Odd logic. I guess what you're saying is that we shouldn't be too sure of our opinions on this subject, which is true, but there's nothing wrong with drawing tentative conclusions from existing evidence. Without opinions, we wouldn't have anything to talk about.

Of course homosexual men are capable of mating with women. But there's an obvious evolutionary reason that heterosexual men have an intense desire for women - because it promotes sexual congress that will send his genes forward. There can't be many characteristics more important than that in terms of evolutionary success. Evolution works by making more prominent those features which give slight survival or reproductive advantages, and eliminating those features which are even slightly disadvantageous. What trait would be worse in terms of genetic spread than a lack of interest in heterosexual copulation? Granted, it's possible that there's some complicated combination of factors that are at play that we haven't considered, but in terms of basic evolutionary theory, what characteristic would be more disadvantageous than homosexuality? Sometimes we overthink things and overlook the obvious. Again, to me the most likely explanation is that evolution wasn't able to devise a totally reliable scheme for ensuring heterosexuality, and sometimes errors (from an evolutionary standpoint) are made. Nobody's perfect.

 

[Ken Natton]

What you are saying is that probably there's no evolutionary explanation for homosexuality, but that I dismiss the possibility is naive. Odd logic.

I doubt that homosexulaity is genetically programmed because my observation of real human behaviour does not seem to fit that idea. But dismissing the possibility on the basis that you did so is what I see as naive. When scientists first started to observe the behaviour of hymenoptra, it seemed absolutely impossible to imagine that there could be any evolutionary advantage to sacrificing your own life for the good of others. But then they looked a bit closer and found that there really is such an evolutionary advantage, and that behaviour is indeed, genetically programmed.

 

[CCWilson]

With bees and ants, the DNA is so close in all members of a colony that it isn't difficult at all to see how sacrificing oneself can send copies of your own genes forward.

Look, without further evidence we have to make intelligent, informed guesses as to how evolution ended up with the present system of sexual preference determination. But logic tells me that a suicide gene would be weeded out, and a gene for infanticide would be weeded out, and a sexual disinterest gene would be weeded out, and a gay gene would be weeded out. What genetic tendencies would be more important to eliminate than those, from the standpoint of one's ability to send his genes into the next generation? I'll be happy to reevaluate my position if a good argument against it comes along.

 

[Ryan_m_b]

But logic tells me that a suicide gene would be weeded out, and a gene for infanticide would be weeded out, and a sexual disinterest gene would be weeded out, and a gay gene would be weeded out. What genetic tendencies would be more important to eliminate than those, from the standpoint of one's ability to send his genes into the next generation? I'll be happy to reevaluate my position if a good argument against it comes along.

You're looking at this too simplistically. Individual genes rarely map directly to physical traits, let alone behavioural ones. But leaving that aside and assuming that there existed a genotype that causes suicide before sexual maturity there are plausible reasons for its existence. Remember evolution favours species, not just indivudual organisms and a genotype that confers a tendency for suicide may also confer a tendency in others that causes them to proliferate more. In the case of homosexuality from an evolutionary perspective if we ignore kin selection, assume no homosexual individual reproduces and assume that there is no sociological advantage to having a percentage of the population as homosexual then it could still persist if the mechanism that gives rise to homosexuality some of the time has a greater effect on the rest of the population than without it. What I'm getting at here is that if a species were "programmed" for sexuality then they would have a greater advantage even if a fraction of them are rendered "infertile" by it.

 

[Monique]

Remember evolution favours species, not just indivudual organisms and a genotype that confers a tendency for suicide may also confer a tendency in others that causes them to proliferate more.

Indeed, seemingly detrimental traits can have positive influences as well. For example sickle cell anemia in malaria-infested regions.

The idea that natural selection weeds out detrimental traits is flawed as well, just look at all the illnesses that humans suffer from. For a trait to disappear there needs to be a strong negative selection, otherwise it will persist in a population (Hardy-Weinberg equilibrium). Just since how long has it been acceptable to lead a homosexual lifestyle? Before that people with homosexual feelings were in heterosexual relationships and had children. Today people in homosexual relationships can have children as well.

 

[CCWilson]

Indeed, seemingly detrimental traits can have positive influences as well. For example sickle cell anemia in malaria-infested regions.

Actually sickle cell anemia is not a positive for survival; those people die early. It's sickle cell trait - the heterozygous version - that offers some protection against malaria, probably because of alterations of the red cells. There are some American football players with sickle cell trait, which is usually asymptomatic but is associated with a slight risk, especially with prolonged extreme physical activity without time for recovery. Off subject.

 

[Evo]

With bees and ants, the DNA is so close in all members of a colony that it isn't difficult at all to see how sacrificing oneself can send copies of your own genes forward.

Look, without further evidence we have to make intelligent, informed guesses as to how evolution ended up with the present system of sexual preference determination. But logic tells me that a suicide gene would be weeded out, and a gene for infanticide would be weeded out, and a sexual disinterest gene would be weeded out, and a gay gene would be weeded out. What genetic tendencies would be more important to eliminate than those, from the standpoint of one's ability to send his genes into the next generation? I'll be happy to reevaluate my position if a good argument against it comes along.

First, you need to provide peer reviewed studies that back you up. Personal opinions don't suffice in the science forums.

 

[CCWilson]

Evolution is different from most of the sciences. You can't do experiments to test hypotheses, except maybe to a very limited degree with bacteria and such. Let's be honest. Evolutionary science is mostly a matter of logic. Darwin's theory was based on a lot of observations, not of evolution in action, but of its end results. It was really a brilliant, logical conclusion with no peer reviewed studies to back it up. We know more and more about some of the details of how inheritance works, and how some genes accomplish their tasks, but when it comes to personality traits and how genes affect those changes, we don't know very much. As far as I know, we don't have a clue about how genetics and particular alleles affect the structure of the brains and its chemicals and connections to cause aggressiveness, sexual preference, empathy, selfishness, altruism, and so on. Let's be a little modest in our certainty that peer reviewers have anything useful to tell us about all that.

Bottom line, we don't have the tools yet to investigate the functioning of the brain at the neuronal level. The discovery of mirror neurons was extremely cool but I don't think it's been the major breakthrough we hoped it would be, except as an suggestion of what the mechanism might be for empathy and learning - maybe. Until we get a lot further in our ability to understand how genetics affects the structure and functioning of the brain, we're stuck with using logic, based on what we do know. All this discussion that we're reading now about whether morality and religion are determined by what's in our genes - fascinating subjects - do you think that's come about because of scientific breakthroughs? No, it's the result of people trying to put two and two together based on what we do know.

The best peer reviewers can do when an evolution hypothesis is presented to them is pass judgment on whether it logically fits the facts.

What happened when somebody suggested that maybe homosexuality was selected for, or at least not eliminated, because an extra caregiver might increase survival of kin? Were experiments conducted to demonstrate its truth? If they were, we should have the results in 2000 years or so. No, presumably peer reviewers, if there were any for that idea, would have tried to figure out if that made more sense than other theories, would have tried to fit the possibilities into Hamilton's equation or some such, and they would have published their opinion, which might be right. Or not.

 

[atyy]

But logic tells me that a suicide gene would be weeded out, and a gene for infanticide would be weeded out, and a sexual disinterest gene would be weeded out, and a gay gene would be weeded out.

Here's some discussion in the literature which may be helpful for this thread.

http://www.ncbi.nlm.nih.gov/pubmed/20141266
http://homepage.psy.utexas.edu/homepage/group/busslab/pdffiles/evolutionary_psychology_AP_2010.pdf
"Exclusive homosexual orientation seems to defy evolutionary logic since it presumably fails to increase an individual’s reproductive success. Although evolutionary hypotheses have been proposed for homosexuality, as discussed earlier, none have received empirical support thus far (e.g., Bobrow & Bailey, 2001)."

http://www.ncbi.nlm.nih.gov/pubmed/19539396
http://www.faculty.ucr.edu/~mzuk/Bailey and Zuk 2009 Same sex behaviour.pdf
"Previous work has emphasized the apparent paradox of selection acting on non-reproductive individuals [1,2],"

"Over the past two decades, Drosophila researchers have examined a multitude of candidate genes implicated in the genetic and neurological control of sexual behavior. These studies have provided insights into sexual behavior in general, and as a byproduct have illustrated different mechanisms that can independently produce same-sex sexual behavior. What are these mechanisms, and what can we learn from them? Mutations in a Drosophila gene called fruitless have been known for nearly half a century to cause males to court other males [4]."

 

[EagleNebula]

Speaking from my own knowledge (which is quite limited on this subject) I think so. If we are talking about male sexuality that is, because that's where the most research has been made. For example, let's take a family. There is one father, one mother and four boys. The fifth is on it's way (and he'll be gay in this scenario). Is there any rational explanation to why the chances of getting a gay son would increase? Yes. But wait, so what is happening biologically to the baby boy?

When a mother is pregnant with a boy, the female body sees the male fetus as a foreign object. For protection, the female body sends out antibodies to the boy in the womb. The more antibodies the mother have, the more adapt her body becomes at feminizing the male fetus. Thus, giving birth to gay son.

Of course this not enough to say with 100% confidence that there is something as a gay gene, but I see result like these to be of value. At least we can see that it's not totally a decision for everyone. Maybe I'm talking total rubbish, but that's my opinion right now.

 

[Ryan_m_b]

Speaking from my own knowledge (which is quite limited on this subject) I think so. If we are talking about male sexuality that is, because that's where the most research has been made. For example, let's take a family. There is one father, one mother and four boys. The fifth is on it's way (and he'll be gay in this scenario). Is there any rational explanation to why the chances of getting a gay son would increase? Yes. But wait, so what is happening biologically to the baby boy?

When a mother is pregnant with a boy, the female body sees the male fetus as a foreign object. For protection, the female body sends out antibodies to the boy in the womb. The more antibodies the mother have, the more adapt her body becomes at feminizing the male fetus. Thus, giving birth to gay son.

Of course this not enough to say with 100% confidence that there is something as a gay gene, but I see result like these to be of value. At least we can see that it's not totally a decision for everyone. Maybe I'm talking total rubbish, but that's my opinion right now.

Welcome to the forums. I'm afraid to say that this is mostly total rubbish. Genes are sequences of DNA that are transcribed into RNA, they are not created or altered on the basis of antibodies in the womb. In fact if the mother rejected the embryo in the manner you describe it would not result in a viable pregnancy.

Whilst it has been reported that birth order and sibling sex and number have a statistically significant effect on a child's sexuality the mechanism is likely to be far more subtle and complex than simply a case of genetics.

 

[Antiphon]

Not rubbish at all. The probability of a homosexual male offspring increases dramatically with the number of offspring.

It seems to me the evolutionary function is obvious- it prevents anyone set of parents from monopolizing the gene pool by creating too many boys.

Suppose a couple decided to have 20 children and they all turned out boys. In a small clan this would greatly reduce the diversity if they all took wives. By ensuring that only the first 3-4 of the males are interested in reproducing the diversity is maintained.

 

[Ryan_m_b]

Not rubbish at all.

Aside from the mention that number of siblings has an effect on sexuality I don't see how you can say this.

 

[Borek]

From The Red Queen: Sex and the Evolution of Human Nature by Matt Ridley:

How could such a gene survive, given that gay men generally do not have children? There are two possible answers. One is that the gene is good for female fertility when in woman, to the same extent that it is bad for male fertility when in men. The second possibility is more intriguing. Laurence Hurst and David Haig of Oxford University believe that the gene might not be on the X chromosome after all. X genes are are not the only genes inherited through the female line¹. So are the genes of mitochondria, described in chapter 4, and the evidence linking the gene to a region of the X chromosome is still very shaky statistically. If the gay gene is in the mitochondria, then a conspiracu theory springs to the devious minds of Hurst and Haig, Perhaps the gay gene is like those "male killer" genes found in many insects, It effectively sterilizes males, causing the diversion of inherited wealth to female relatives. That would (until recently at least) have enhanced the breeding success of the descendants of these female relatives, which would have caused the gay gene to spread.

¹Earlier he wrote that there is some kind of evidence that the gay gene is inherited from the mother and not from the father.