The largest study to date on the genetic basis of sexuality (2019)

My SO wrote a blog post that touched on the fraternal birth order effect which I thought was great (though I am biased): https://obscuredinosaurfacts.com/blog/post/2021/01/27/bayes....

She expands on it and I think her writing breaks it down well (just make sure to check out the appendix correction too!)

That weird caveat about right handedness actually makes me think this is a spurious correlation.

Are there any studies looking for genetic differences in mothers of gay men? Is it possible for the mothers to have a genetic trait that increases the chance of a gay son, but doesn’t get passed down to that gay son?

Remember that heritability is a measure of a population, not an individual. So you're measuring the amount that genes vs environment contributes to a trait within that population. It's not an absolute number.

Identical twin studies point away from genetics very hard. Pretty much all genetic anomalies will affect both identical twins 100% of the time. The fact that it's less than 40% points much more to environmental effects rather than genes.

The same goes for a cause we'd consider purely environmental, such as an illness caused by an infection. There will still be lots of associated genes with small effect determining how resilient a person is to the infection. Twins share environmental causes from early stages of development (like an infection during pregnancy) so that angle gets potentially confounded too.

Tangential to your point, but I enjoy the comparison you draw between DNA mechanisms and Rube Goldberg machines. It’s an apt metaphor because DNA, and the body as a whole, is constructed quite randomly according to the demands of the environment.

The best you could probably do would be to match twins, so about 65%[1].

[1]: https://pubmed.ncbi.nlm.nih.gov/8494487/

Neural nets for genetics are probably a good fit, and perhaps arguably, a better biological analogy than actual neurons. But they're likely already getting the gist here. They actually say that with genetic analysis (implying more than one gene at a time), they could explain 25% of sexual behavior. To be honest, that's a lot more than I would have expected. In biology, that's a pretty high predictive power, and I think is a way more interesting headline than "no single gene controls sexual orientation".

At the end of the day though, many other factors will contribute, so genetics can only explain so much. With aggressive data collection during development, I would wager we could get sexual orientation prediction much higher. Probably not high on the proverbial bio-ethicist's wishlist of things to make broadly available.

This is an interesting idea. I wonder if we could then use something like [0] to trace back "gay-ness" as well as other "personality features" (I'm not sure what the correct term is here) to the exact genes.

One potential issue I see is that the DNA of any person has an arbitrary length, which poses some challenges in the design of a neural network. Traditionally, this has been solved with LSTMs or RNNs, but as far I know these are designed for data with a temporal dimension (such as text or speech, which progress with time). I'm not sure if that's true for DNA.

[0] https://arxiv.org/abs/1509.06321

For complex traits, I believe people think that linear effects dominate. Which is another way of saying that they see no advantage to adding a hidden layer, which encodes interactions, compared to adding up individual effects.

The caveat here "for complex traits" means things like height, for which we know there are hundreds to thousands of common variants which matter. Some things aren't like that, e.g. simple recessive gene effects are interactions! And, with more data, this may change.

I don't think it is entirely genetic. There are other factors like development within the mother's body, levels of hormones / chemicals, and so on which could contribute to a different sexuality later on.

This doesn't mean you can change it, and messing with chemical levels in the hope of finding a configuration which leads to "normality" would be very unethical in my eyes.

This sort of approach is known as Genome Wide Association study, finding the correlation of hundreds or thousands of genes that will predict a trait: https://en.wikipedia.org/wiki/Genome-wide_association_study

If you are interested in the topic, I recommend https://en.wikipedia.org/wiki/Blueprint_(book)

Seems more likely that the causality is in the opposite direction

I suppose it depends on causality - do otherwise "str8" men who experiment with other men "turn" gay, or do "queer" men self select themselves for such experimentation?

Regarding your hypothesis, I'd suggest that perhaps queer kids are more likely to be targeted by older male relatives for sexual abuse.

Sexually antagonistic pleiotropy perhaps.

https://en.m.wikipedia.org/wiki/Antagonistic_pleiotropy_hypo...

I think this is called a Spandrel: https://en.wikipedia.org/wiki/Spandrel_(biology)

Kin-selection hypothesis also allow for some fraction of asexual or homosexual population being a positive overall (from an evolutionary perspective).

Not sure if nipples are the best analogy here. Formation of nipples is largely down to how fetuses develop; i.e. nipples form before sexual differentiation. And I believe in some mammals, males in fact do not have visible nipples.

https://www.livescience.com/32467-why-do-men-have-nipples.ht...

But we do measure a person by their reproductive success. Where would one see otherwise?

Umm... Men have nipples because they form before sexual differentiation occurs.

> We don't measure the worth of a person by their reproductive success.

We don't measure human worth that way, but evolution measures nothing else!

Harsh bucket boundaries are always the catch with studies like this. If you grew up in a smoky house or have had at least one cigarette in your life, you fall into a gray area of studies where you don't qualify as a smoker or a non-smoker.

My understanding is that people who self identify as gay are a much smaller subset within the group of people who engage in homosexual activities. For example, in my Asian country a large segment of the guys you meet cruising are married men (to women) who identify as completely straight. Perhaps the wife is unwilling to engage in acts you enjoy, and sex with men is low effort high reward. I also knew many guys who preferred sex with men but couldn't fathom a romantic relationship with one, and identified as mostly straight. It's highly likely that most (though not all) of these men were truly gay/bi/pan, but unable to accept it due to social conditioning.

I agree that a single encounter probably shouldn't count for the terms of the study.

Not necessarily, as long as it's recessive.

Not an expert either here though.

Also not if for most of humanity the mates with this hypothetical gene were repressed into heterosexual relationships.

Not if it is recessive. Example with a recessive "gay gene": Both parent have one normal allele and one "gay" allele. The repartition of the offspring will be:

- 25% both normal alleles (normal phenotype) - 50% one normal allele (normal phenotype) - 25% both gay alleles (gay phenotype)

But homosexuality is not a gene. I believe that the [fetal androgen exposure theory](https://en.wikipedia.org/wiki/Prenatal_hormones_and_sexual_o...) is the one currently preferred.

A common analogy here is that in lots of insects, you see whole groups of non-reproductive members, and yet the idea of a "non-reproductive worker insect" hasn't "evolved into extinction."

(I'm not commenting on whether being gay has a genetic basis or whether it's an example of kin selection, because honestly, I have no idea.)

There is also the 'beneficial sibling' theory where a homosexual sibling improves the reproductive success of their siblings/close family via being able to devote more energy to their siblings offspring instead of their own or are able to gather/utilize more resources that leads to a familial advantage.

Common mutations are inescapable.

It might persevere through kin selection. For siblings who share the gene, such an individual would have all the benefits of a male/female (security, hunting, care-giving), but none of the mating competition. One could argue if such a gene existed, it would be quite an altruistic one.

A lot of the musings I've seen in this direction have been along the lines of

(1) some people are bisexual and thus would occasionally reproduce and

(2) if sexuality promotes "togetherness" and "group cohesion", then having "our gay uncle who 'has connections' and is always willing to help out the family group" is still beneficial for the family unit and thus a gay gene would not be selected against within that family lineage.

Probably not a majority of the population, but there's no reason for such a "gay gene" (if it were to exist) to be driven to zero.

Not neccessarily. Humans are social creatures, our genes' survival is not solely dependent on our individual ability to pass them on, since we share genes with our siblings and parents as well as offspring. For example, families with some non-reproducing offspring may fair better due to having a higher adults/children ratio.

If such a gene existed (which perhaps it doesn't), it might benefit families who had members carrying it.

This is the same reason some species have evolved alarm-calling when a predator is nearby. It benefits the collective (who share the gene), but at an obvious detriment to the individual's ability to pass on their genes in this case.

The argument around this is that it's of social benefit rather than individual. Particularly when child/infant mortality is high and women have lots of children, it could be helpful to have a pool of adults supporting the child-rearing of others, especially their immediate siblings.

Not necessarily.

* the same gene can have different phenotypes in different individuals. One phenotype may be net negative but the benefit from the other makes it net positive.

* in social animal gene can be carried by relatives. Extreme example is ants and bees, most of them are not fertile but they help to spread their genes by helping those who are.

Not necessarily. If the gene is recessive, it will be passed on. The question then is: what happens when that gene expresses itself?

The naive reaction is: individuals with the "gay gene" won't reproduce and it will eventually die out. A more nuanced perspective is that while that individual won't reproduce, their presence in the community helps the clan's survival, so a community with the gene is overall stronger, so the gene will stay around.

Depending on other conditions (environmental and genetic), a particular gene may not be expressed in the same manner (or at all). You can find simple examples in recessive alleles. The phenotype of such genes will only be expressed when both alleles are of a compatible type.

Another striking example: Sickle cell disease will only be deadly if both alleles carry the unfortunate mutation. But the unhealthy allele is unlikely to be eliminated by evolutionary pressure because carrying one allele provides significant protection against malaria.

The interactions between genes and their environment is usually more complicated that these simple examples, but I hope it illustrates that evolutionary pressure may not suffice to erase some apparently unsustainable alleles from the population.

I would think that being "gay" doesn't 100% prevent someone from fathering / mothering children.

Well yes and no. It might actually give a benefit to other siblings. It could manifest itself only in certain circumstances in the womb or in the environment if something helps the phenotype manifest itself...

For example there is a correlation with sibling order and homosexuality. The more boys your mother had before you the more chance you have of being homosexual. We're talking about a non-negligible increase of over 30%: https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male...

What if the "gay gene" is tied to the "sexually attracted to our parents gene" ?

And evolving out the former would cause the later to go which is detrimental to the overall health of the species.

The trouble with that argument is that it also works with,

"If there was a genetic cause for shortsightedness, why is it still around?"

"If there was such a thing as a genetic disease, why haven't they evolved out?"

"If not having X-ray vision was genetic, wouldn't the absence of X-ray vision have been selected out?"

You really can't expect evolution to accomplish its "goals," per se. It is sort of a gentle flow down a lazy river, towards adaptation.

Interestingly, I've heard about many people who went from "straight", married with children to leaving their families because they've found out they're gay. I even knew one whose first sexual experiences were with women, and he decided he was gay later. In his "straight phase" he could have had fathered children if he weren't careful. Curiously, I've never heard about opposite cases (spontaneous [1] gay -> straight transition). Make of it what you want.

[1] Spontaneous = ignoring attempts to "cure" gay orientation.

The other posts cover possible reasons why being gay may be actually good for the utility function of a gene.

There is another hypothesis for why this hypothetical gene might not evolve into extinction. Being gay may just be a side effect of it, with some other benefits being the reason this gene stays in our gene pool.

If you take a simplistic view of genetics where you draw Punnet squares and check if the offspring has GG alleles, maybe. Even if there are social benefits to there being some gay people around, that would still make those alleles pretty unlikely to be passed on. That doesn't imply there isn't a genetic component. Real genetics is a lot more complicated than that.

The fact that something is genetic doesn't imply there is no social component. Genetic factors could lead to a predisposition for a certain behavior that would still be altered by environment. There could be many genes that each has some small effect but none of which is an on/off switch. Those would lead to more complicated selection pressures.

We are pretty sure there is a genetic component. We are pretty sure that it isn't just "if you got the gay allele then you's gay".

Also, some gay (or mostly gay) people have children. This is because a) most people are at least a little bit bisexual, b) people may want to have children even if the sex act isn't appealing, and c) there are social pressures to conform.

There are several possibilities.

1. If having gay relatives improved the chances that you will have children and they would survive to themselves reproduce, then evolution could favor maintaining a gay gene.

Remember that for nearly all of our species' existence, and that of the pre-humans we evolved from, we've lived most of our lives in arrangements where our close relatives lived near us and most people in the region were also related to us.

Your children have half your genes. Your siblings' children have a quarter of your genes. So in effect two of your siblings children are equivalent to one of your own as far as getting your genetic material into the next generation goes.

If being gay meant that your sibling does not have their own kids to take care of and so they devote effort that would have gone to raising their own kids to helping their straight siblings' with their kids or to doing things that help the village that those with kids don't have the time for, that might greatly increase the survival rate of those kids enough to make up for not having kids of their own.

2. Being gay doesn't mean you can't have kids. Throughout most of our history, many many people have had kids with people they have not been attracted to. That goes for both gay people and straight people.

3. What if it were a bisexual gene rather than a gay gene? Having people in your tribe that can form with both men and women the kind of close bonds the people form for the sexual partners has some obvious advantages.

I view this question - and the deliberation over it - as coming from present-day society's latent homophobia.

Doesn't the question apply to straight people, and anyone else, who don't reproduce?

If homosexuality provided a species or community benefit, it could be selected for in that way.

Perhaps akin to aging phenomena that benefit the species through mortality.

> But that's always been a fucked up idea. It shouldn't matter whether it was predetermined or otherwise not in your control. If it's constructed then it's constructed. If it's not then it's not. People shouldn't be oppressed for their sexuality full stop, regardless of reason.

You are right, I think, to root the conflict in religion. The dominant religion in the West, Christianity, treats the human body as a given. That is to say that while you are more than just your body, you are certainly not less: there is a union of mind and body that separates only at death. If they disagree, a reconciliation must be attempted from the outside (i.e., by God).

Of course today we have technology that puts a veneer of science on what is really a religious idea: we are essentially our mind and not our body. When the two disagree, we needn't change our minds because we can alter the body through hormones and surgery.

On the face of it, I don't see how you could reconcile these two positions. I think the use of genetic predestination was used as an attempt to do this: if I'm made this way then how can it be wrong to be {gay, trans, etc.}? But in general I think the denominations that were predisposed to blessing homosexuality (for example) were unlikely to need scientific persuasions like that. When it became clear that rigid denominations weren't going to budge, it feels like genetic predestination became unfashionable.

I agree that one shouldn't support the genetic predetermination theory of sexuality just as a defense for oppression. That's not how science should be done.

That being said, I still doubt that people really have a choice over their sexuality. Otherwise there would be far more stories from people who have "successfully" turned straight or something, instead of stories from people who have tried to suppress their true sexuality for years and who just turned sad in the process.

It might not be genetically determined, but there are so many more immutable determinants to our behaviour that are outside of our control. The brain is a giant state machine and not all of that is plastic all of the time. It might be determined before you are even born, in the womb. It might be determined in your first few years of life. Or it might actually be genetically determined but through a complex interplay from multiple genes, something that our statistical tools can't catch yet, especially as we don't have an objective measure for gayness. Last, there might be multiple ways someone turns gay.

I think there's also an element of constructed boxes to put people into as well.

Would I rather say to you, some random person, "I'm gay" and move on? Or do I want to get into "I'm gay, it's complicated" and have to explain more? Most of the time I just don't want to get into it further.

And I've had conversations with some folks who outwardly say they're straight but privately have described themselves pretty similarly to "Well mostly straight, it's complicated."

It's tiring, and I'd like it if we all came to an agreement that it's complicated, the edges don't line up nicely, and we should all just accept that it's weird. It'd make my life way easier

Amusingly, before I moved to America and understood it, I thought "sexuality is a choice" was a defence of homosexuality because I believed Americans believed "humans should be free to make choices about themselves". Funny, eh?

But it seemed obvious to me. After all, maybe some people are genetically predisposed to eating babies. Doesn't mean I'm going to be okay with that. Sucks for them but they can either suppress the baby eating or go to prison.

> But that's always been a fucked up idea. It shouldn't matter whether it was predetermined or otherwise not in your control.

Yep, that’s why I simply don’t care anymore what rhetoric modern social movements use. Not only usually it makes zero sense, they are ready to ditch it anytime it benefits them.

There is no point in having a serious discourse with anyone who treats it only as a weapon to achieve their goals.

> People shouldn't be oppressed for their sexuality full stop, regardless of reason.

Completely agreed. I don't think we should shy away from trying to understand and explain it though. It's been a puzzling question that people have tried to grapple with for a long time now. I think it would be interesting to understand humans better.

And.. if it is definitively proven that it is nature and not nurture, it might make the lives of individuals easier by not having to deal with as many attacks from those that were intolerant but have changed their minds when exposed to the science. I agree that ideally, those individuals wouldn't be discriminated against in the first place, but that's not the world we live in right now. I would argue that if anyone could do anything to alleviate some of that discrimination with science, it would be an incredibly worthwhile endeavor.

There's also the other side: if someone is a homicidal psychopath due to their genetics, then I still do not want them to roam free. So genetically predetermined is not a good argument to use in favor of gay rights. People should be allowed to determine their own sexuality, regardless of whether that determination was preset by their genetics or not, just as people should not be allowed to commit murder regardless of whether that was preset by their genetics. (Same goes for other possible sources of determination.)

You're collapsing a huge societal design space into a narrow, ultra-individualistic western viewpoint. Your point only makes sense in societies that take it as a given that individual autonomy trumps the right of society to enforce behavioral, moral, and social norms. That approach is not morally required and almost no non-western society embraces that viewpoint. Almost all of Asia and Africa accepts that requiring conformity in voluntary lifestyle and personal expression is legitimate. There is nothing special about sexuality in that respect--nearly everyone in the world thinks its perfectly legitimate for societies to, for example, impose taboos on sexual activity outside the bounds of some marriage-like relationship. By your reasoning, modern western sexual permissiveness is morally required--even when it comes to voluntary choices. That's a radical (and quite ethnocentric) claim.

In that context, whether something is a choice, versus a characteristic that cannot easily be changed, is tremendously important. It elevates the issue from ordinary policing of norms into the realm of human rights.

And of course, it's ridiculous to say that people "latched on" to sexual orientation being immutable to appease "bigots." Sexuality being immutable (or at least not easily changed) is an observation that rests on the experience of countless individuals who suffered tremendous pain and suffering trying to deny their sexual orientation. And the article, of course, nowhere suggests that sexual orientation is a choice. Many things are immutable characteristics, or at least not easily changeable--without being traceable to a specific gene.

I read this as well intentioned but ultimately poor reasoning. Things that are intrinsic about a person are a good baseline, no-question quality that we should not antagonize people for. Sexual orientation, race, disabilities, gender, appearance etc. These seem like important issues to get right on civic protections.

Saying we must offer respect to everyone's choices is just wrong. We certainly don't want to ensure someone's right to be a homophobic asshole in a workplace for example. And it's not as simple as just saying being LGBTQ is a private thing that doesn't affect others either. Trans bathroom rights, marriage license rights, adoption rights, etc.. The argument to ban gay conversion camps seems much harder to make if one believes identity is purely a choice. If homosexuality is perceived as a choice, then onlookers will wonder who influenced someone to make a choice to be gay, which muddies the perception of being gay being a personal private thing.

Homophobia is bad, but wishing it weren't a thing doesn't change the reasoning that intrinsic qualities are a lot more important to protect than choices.

Sexual orientation is more deserving of protection than, say, holocaust denialism. Religion is the only protected class that is a choice, but for many people, it's not so much a choice as an inherited identity and similarly fixed.

The big question that this viewpoint misses is what to do with fears that certain things "turn people gay" and the flip side of that fear: that the straight community might use successful conversion therapy to eliminate the gay community.

All of a sudden both of those camps have ammunition for their points.

Saying that it's "genetically determined" (or at least innately determined) very nicely sidestepped that. To the extent that that is not true, then you have to grapple with those other questions.

People have very strong feelings about self-categorization, whether or not the person's feelings are "accurate". We struggled with accepting gay people. We're struggling now with accepting transgender people. In twenty years the big culture war might be about people who think they were born the wrong ethnicity, or otherkin, or some other area in which our failure to produce an indiscriminate society runs up against the rules of behavior to which we've limited them.

It never made sense. Hitler (yes, sorry to go there) also thought that homosexuality was genetic, which is why it made sense to him to mass murder homosexuals.

Something being genetic/inherent has very little to do with whether it should be viewed as morally acceptable.

Of course, I am well aware of how troublesome it is to find empirical grounding in morality, but it always seemed to me that sexual relationship between two consenting partners was nobody else's business, least of all mine. Choice, genetics, curiosity, etc: what difference does it make?

I am about as "straight" as it comes: I for the life of me can't figure out the sexual appeal of men, but it also isn't at all obvious to me why I should be offended by the idea that there are people that think otherwise. And even if tomorrow Casanova came out and decided publicly that he is making a conscious choice to from now own only sleep with men, after decades of sexual adventures with women--well, what difference does it make?

It’s very common for people to make decisions that they regret for the rest of their lives.

If someone is straight and they have a gay experience that is something that could haunt them for the rest of their life. This seems to be less of a thing in the other direction. Maybe this is societies fault though. The lack of acceptance causes the inner shame.

But the notion of letting people be free to choose is pretending that there is nothing that will influence the choices they make. Most people will be straight genetically and that is the way society leans today.

Encouraging experimentation can have negative consequences.

The biggest danger of using genetics as a reason is that at some point someone is going to say, "we have unequivocally ID'd the genes involved and we can ensure your offspring are of the orientation of _your_ choice". Or in more authoritarian regimes, the state's choice.

> - internal development and expression of sexuality does not happen at the same pace and at the same amplitude for everybody (some people really are asexual their whole life) and of course the familly, sister/brotherhood, socio-economical environment influence it too

Some people IS asexual. Asexuality it's a valid sexual orientation like being bi/pan/homo or heterosexual. It isn't lack of sexual development or sexual expression or result of family, socio-economical environment influences.

Perhaps, you should inform about it better : https://www.asexuality.org/?q=overview.html

That would be ideal, but some people need to be convinced that it is not a choice before they will consider treating gay people with respect. So long as they think it's just a behavioral decision, they can rationalize their bigotry.

could still be a mix of genes. agree with your last sentence.

If you want people to be treated equally, wouldn't you want their existence to be justified?

It's difficult to think of a PC analogy here, so maybe... super villain mind control device strapped to someone's head. Provably unjustified behaviors due to the mind control device implies the ethical thing to do is try to remove the device. Treating someone normally implies an implicit belief that they're normal. Sound biological evidence that being queer is just how some people are feels like the best way to reinforce that belief and remove requirements for heteronormativity.

There are two meanings to "gene" here. What you describe as lego blocks are segments which code for a protein, which is one meaning.

The other is just any code which affects the phenotype, including promotors etc. The SNPs mentioned in TFA are just known fairly common single-point differences, but aren't necessarily in coding DNA. Of course these are still heritable, just like coding changes.

I think it's a mistake to see homosexuality as a binary on/off switch; in many cases it's a gradient.

I'm generally heterosexual, but I've also had sex with a man. It's was okay, I guess, but I'd prefer women. On a scale of 0-100 my "gayness score" is probably about 10-20. A hard strong 0 or 100 is probably a lot less common than it's often portrayed: it's more of a bell curve.

One explanation I've read is that gay men are more likely to be left alone with women as they're perceived to be less threatening; giving the gay man a chance to propagate his genes through infidelity (infidelity is fairly common throughout human history). The ever-eqloquent Richard Dawkins once called this "the sneaky fucker strategy".

Something similar could also apply to women.

It's hard to be sure of these kind of things, since it's, well, pre-history, but there are some models which can explain the propagation of homosexual genes and/or behaviour.

You can view homosexuality as an identity or as a behavior.

Recently the identity option has been emphasized. Part of those is because it offers more legitimacy: if I can convince you that:

1. Gay people exist 2. I am gay

Then, my homosexual behavior is more legitimate. Without the identity, Western legal codes were able to ban homosexual behavior.

> For straight men it seems mostly tied to women’s ability to carry children

I think this is far from clear

An innate desire to form an atypical pairing in a non-reproductive fashion.

Honestly i have no idea but this might be one of the last places left on the internet you can ask a question like this without getting dogpiled.

I've batted for both teams in my life and i still can't tell you.

When I was in middle school, one day I noticed that this one girl was the most amazing person on the planet and I couldn't stop thinking about her.

I imagine being gay would be a lot like that, except it would've been a boy.

Usually refers to romantic and/or sexual attraction to the same sex.

> Is it dislike, fear(?) of opposite sex?

Not generally, no, just like most straight people don't dislike members of their own sex.

In the simplest terms, it’s seeing a beautiful naked body of the opposite sex and getting zero sexual pleasure out of it. That’s it. Being gay doesn’t stop you from forming close bonds with the opposite sex just like being straight doesn’t stop you from having best friends of the same sex.

Both. It is not fear-based. It's the full package when it comes to sexuality and romance.

I would suggest asking yourself "what is being straight?", assuming that you identify as such.

I assume it’s a physical attraction to members of the same sex, with the emotional dimension developing in the same way as it does between any two individuals in a mated pair.

If this question is strictly about the study in OP and not a broader philosophical question, then it's worth pointing out that the study doesn't actually use the word gay but instead:

> In this study, we use the term “same-sex sexual behavior,” which is defined as having ever had sex with someone of the same sex.

https://science.sciencemag.org/content/365/6456/eaat7693

> Is there any trait that is strongly linked to a single gene?

Sure.

Sickle-cell anaemia is one classic case, one (recessive) gene.

Huntington's disease is another, it's about a specific repeat number.

But, as you say, most complex traits (such as height) aren't like that, and involve hundreds or thousands of different genes. IIRC eye color is actually fairly simple, not one gene but much of the control in just a handful? Maybe hair color too? (But not super-sure.)

ABO blood group gene

https://en.wikipedia.org/wiki/ABO_%28gene%29

Yes. MC1R which people with red hair carry. It's a very strongly associated gene. Also "People with freckles and no red hair have an 85% chance of carrying the MC1R gene that is connected to red hair. People with no freckles and no red hair have an 18% chance of carrying the MC1R gene linked to red hair."

https://en.wikipedia.org/wiki/Melanocortin_1_receptor

What they're describing is a very broad range of variations across multiple genetic loci with subtle effects that do not predict, only relatively vaguely correlate with, sexual behavior. They say as much, too, although at much greater length and complexity.

I get the concern for potential risk around selective abortion, IVF, etc; I was around for the "gay gene" debate in the 90s. This isn't that. This disproves that. And what they're reporting could not be used in that way.

Tangentially related; question to those who are pro-choice: why is regular abortion okay but sex-selective abortion, aborting downsies, etc. not? My understanding of the pro-choice argument is that if a fetus is not yet a person, it's not wrong to kill it. Why is it more wrong to abort a fetus because it is a boy/girl? I am pro-life and so view this differently, hence not understanding the reasoning here.

Intelligence or height is a spectrum too, yet we can probably explore existence of such genes. You just need to think in probabilities.

Yes, this study indicates that human sexuality is a trait more complex than many other aspects of humans, i.e. height, eye color, hair color, skin color, etc.

This would be evidence of your argument then.

To be fair the LGBT movement purposefully pushed that misconception because it was more convenient for civil rights purposes.

Agreed - “no gay gene” is akin to saying “no intelligence gene” or “no autism gene”.

My understanding is that most psychological traits are now thought of as polygenic, so a statement like “there is no gay gene” is really misleading, because genetics simply doesn’t work that way.

Not sure why you're being downvoted. You're right that human sexuality is nowhere near as clear cut as blonde/brown hair, or spotted fur on animals.

Still, that doesn't mean genetics do not play a role in determining human sexuality, binary or otherwise.

Indeed. Many people on HN talking on this thread are forgetting bisexuality, demisexuality, etc. Even comments as simple as "you see a beautiful [x of opposite sex] and feel no attraction" miss a lot of vitals.

“Same with gender”, but not (in my opinion) sex.

Sex is bimodal, and genetic - though there are are rare chromosomal disorders, and disorders of sexual development, these are not normal variants and shouldn’t be considered a distribution.

There’s a suggestion that gender is innate and therefore (I assume) genetic, but do we really want to recreate the once anachronistic belief that most men and women are genetically predisposed to behave in masculine and feminine ways?

(Not intended to be flame bait, but I thought someone ought to express the now rarely heard gender critical position)

I mean, yes, of course. But the fact that it's not fluid in so many individuals is part of what fascinates me! The supposed binary split is not real of course, but you note yourself a rather strong bimodal distribution. And that distribution is itself, fascinating and hard to explain.

I am gay, and I have been since I hit puberty. It's completely stable, a fixed personality trait my whole life. It's so... exact. That one little thing, completely inverted from a good majority of men. It's like someone flipped one little switch, that affected only that, at least as far as I can tell.

Bisexuality or pansexuality or whatever you want to call it, on the other hand, seems to fit many of the proposed origins, far better than exclusive homosexuality would. E.g., fuzzy pattern matching gone awry for finding a suitable mate, triggering a bunch of false matches. But it's not like that. It's very precise. That has always struck me as ever so strange.

> equally

citation needed

Hopefully, no. Because if true then it legitimizes conversation therapies.

There's some strong data that suggests it has to do with the interplay of hormones between the mother and fetus.

If this theory is proven correct, it wouldn't be either socialization or genes.

No, it means they haven't found a gene. There is ample evidence of a genetic link, even if we never find a specific gene or set of genes.

Not entirely. The idea of a gay/straight binary, though, is pretty outmoded.

Some people probably do have agency over their sexuality, or respond to incentives other than gender/sex. And part of that’s probably social.

No, it just means that within the population they studied, the variation in whether individuals identified as gay could be explained more with environmental factors than genetic ones. It doesn't say that being gay is 25% genetic and 75% environmental, that's a huge misconception. If parents all treated their kids the same way, and they all had the same treatment in schools, etc, then you'd probably see more influence of genetics than environment. That's how heritability works, it's relative to the population and how homogeneous it is.

Why do you think it would be a parasite, as opposed to any other environmental factor? I don't know of any parasite that affects behavior in that way, but if you have some further information, I'd be interested in hearing it.

Year added. Thanks for catching that.

I changed the title earlier to the first sentence of the article because it seemed more factual and neutral.

Narrowing things down is easier when you control for one aspect instead of multiple ones.

If, hypothetically, being trans inverted the expression of the gene for being gay, you'd have a harder time finding the gene until you accounted for it. By eliminating the possibility, you make it easier to find the gene you're looking for.

If you can't find the gene in the smaller pool of subjects, you weren't going to find it in the larger one. But if you did find it, you can learn how it affects everyone in a different study.

Last time I checked gay wasn't a gender.

So they likely excluded transsexual men (biological women) who are attracted to men and vice versa.

Looking inwards, attraction feels like pattern recognition combined with catecholamine release. So perhaps genes, but also hormones/environment would be responsible.

Given the number of comfortably-masculine gay men I've known, I have a feeling the womb isn't necessarily trying to ensure it eventually creates a Disney Princess. It feels a bit far-fetched, to be honest.

That... seems unlikely. That implies a woman's reproductive system knows and remembers or at least keeps a tallies of the sex of the offspring it has produced...

It seems more likely for it to be an emergent property of children serving as hunter/gatherer resources but not competing for procreation. It is either a novel mutation or something that is selected for.

> effeminate male

> gay son

This is a dangerous stereotype that is equally harmful to people of any sexuality, I'd encourage you to correct it. Most of the gay folk I know personally tend towards the athletic end of the spectrum

>To me this sounds like the mother's body is trying to "nudge" the odds towards a daughter

But if that were true, it must succeed sometimes. Evolution doesn't select for things that don't work. We should see an equally strong correlation with sex of offspring and birth order. We don't.

One possibility is that the effect reduces the harmful effects of sibling rivalry by making second sons more empathetic. However, this is basically a random guess — there are so many variables in biology that it could be a million other things instead.

> Fascinating! To me this sounds like the mother's body is trying to "nudge" the odds towards a daughter after several sons, but sometimes the process "fails" and produces an effeminate male instead - a gay son.

You know that a homosexual not are "effeminate males" ? Man, try to revise these stereotype that you have.

The only way to 'nudge' the chances of a girl baby is to select the sperm based on which sex genes they carry. Any hormonal or such changes induced in the fetus down the line is too late to have any effect on genetic gender.

That doesn't seem to make any sense as gender is determined by the sperm cell reaching the egg. Unless gay-dna sperm are somehow faster...

We detached this subthread from https://news.ycombinator.com/item?id=26070754.

That is a pretty self-contradicting statement in multiple ways.