>The paper is 25,000 words of very dense statistical reasoning; I often found myself struggling to read a paragraph, only to eventually realize it was saying something obvious in as many long words as possible.
Maybe science needs to be less hostile to comprehension
> They speculated that maybe (male) homosexuality came from genes for a sort of super-femininity which was bad for men but very good for women; under this model, female relatives of male homosexuals would have more children than normal. But in fact this study found the opposite: they had fewer.
At this point, it would probably be easier to make a list of the handful of human things where antagonistic pleiotropy is still a viable hypothesis than to list all the things like schizophrenia that someone has claimed might boost fertility in relatives (but never does approaching the necessary levels, if at all)...
> under this model, female relatives of male homosexuals would have more children than normal. But in fact this study found the opposite: they had fewer. This makes sense if they’re getting some of the gay genes and so have less interest in heterosexual sex than normal
Does this kind of conclusion really make sense in an environment with easily available birth control? Presumably the ancestral environment where these genes were selected for was quite different in that respect...
Three plausible-sounding reasons why evolution may support a non-zero level of being gay:
1) Gay uncles and aunts promote survival of their nieces and nephews - presumably more so in social animals.
2) In animals where sexual competition can be dangerous, the ability to defer the urge to procreate via gay sex may be pro-survival enough to outweigh the delayed or less-certain reproduction.
3) Bisexuality may be selected for for some reason (perhaps attracting more than one mate or child-raising partner), and people being purely gay is a side effect.
All of these seem somewhat testable by looking at animal species where homosexuality is observed, vs. biologically similar but socially different species where it's not observed, and checking the differences in social structure, investment in children, and mate competition.
Until these (and probably others) are ruled out, I'm going to think that there's no great evolutionary mystery in the existence of homosexuality. Absence of knowledge is very different from knowledge of absence.
Does the Dutch study control for time? Gen X is a little gayer than the baby boomers, Gen Y is a little gayer than Gen X. It seems like the more recent the birth, the more likely someone is to be gay, and younger siblings will tend to be born more recently.
I'd worry that the large-population studies are going to pick up unwanted demographic differences. For example, larger family size may correlate with religiosity or traditionalism, either of which might make people differently likely to get gay-married (regardless of actual sexual orientation).
Did the authors of the Danish and Dutch studies try to control for these effects at all?
I feel like I should clarify one of my thoughts. I sort of alluded to it here (https://twitter.com/cremieuxrecueil/status/1693811404845830377), but I really want AKP to do some triangulation. There are many variables they had access to that could have been leveraged to winnow down the DAG. That they didn't do this leaves us unclear on several viable alternatives I'm certain they had the power to address.
Personal numbers:
Sibling birth order effect on homosexuality is real: 90%
Real and biological: 75%
Real and of currently-estimated magnitudes: 40%
Real and explicable by current theory: 25%
Real, biological, and linked to NLGN4Y in particular: 10%
This makes far more sense. In utero, homosexual men have female responsiveness to testosterone, but only in specific parts of their brains that control attraction.
Seems straightforward to me. With fewer siblings you get more parental attention. More of your parents subjecting you to gender/sexual stereotypes, and less time to be yourself.
My hypothesis is that if homosexual behavior is culturally forbidden as in the case of past cultures, gay genes will increase cooperative behavior among males.
Given that women are more likely to identify as bisexual than men, I wonder how much of the differences in effect between gays and lesbians may be confounded by bisexuality – which these studies' methodologies could not control for (since they only observe monogamous marriages).
The sibling effect might be smaller for bisexuals and account for that sex difference?
My recollection from the early 2000s was that Blanchard's estimate was that FBOE accounted for 1/7th of all male homosexuals: in other words, not a trivial amount, but not a large fraction either, thus leaving most examples of male homosexuality unaccounted for.
All this talk of "gay genes" without acknowledging that the concordance rate among identical twins is so low that the twin of a homosexual most likely isn't one also. Psychology had a replication crisis because they had weak theories that led them to mine for noise. There's still no good theory for how gay genes could persist at a level higher than the rate of de novo mutations.
Is there a source that will disabuse me of what seems to be the obvious naïve parsimonious assumption that younger siblings are more submissive due to physical and intellectual inferiority during their childhood? Leading to higher rates of male homosexuality in particular when they learn to imprint on submission to another male (older brothers), but also leading to younger male siblings being less attractive to women due to a tendency to be submissive to females as well (older sisters) and thus finding themselves (on the margin) more likely to be both rejected by females for their submissiveness and accepted by male partners who seek submissive mates?
This seems really, really obvious to me. Males seek submissive partners and females seek dominant ones. Younger male siblings are more likely to be submissive.
>"if you’re gay, it means your parents had some of the genes for homosexuality, which means they weren’t as committed to the whole heterosexual-sex-for-procreation thing as usual, and we should expect them to have fewer kids, and therefore for you to have fewer siblings."
But the whole point of the theory, at least the NLGN4Y version, is that it explains how it could be passed down through evolution without a gay gene, because it's a gay gene wouldn't be adaptive. The way NLGN4Y explanation escapes that is that it's not a gene that causes homosexuality in the individual, but a gene that slightly increases the probability of older siblings to be gay, which means by the time you get a homosexual child, you probably already have some heterosexual children, which still carry the gene (because it doesn't directly make them gay) and pass it forward.
Maybe another complicating factor is the age difference between successive siblings, if changes in a mother's immune system gradually creep back to normal over time after the birth of a son. If so then perhaps the effect would be more pronounced and readily observable if results were weighted in inverse proportion to the interval between siblings (or better still based on typical functions of antibody levels over time following a male birth).
Parents pay far less attention to younger children of many, and are much more permissive and less controlling of them. The youngest are also going to be physically weaker and less able to physically compete with older siblings. The youngest is more likely to be the comedian of the family and more likely to reject the social paradigms around them- they’ve seen how they play out in their older siblings and can see the absurdity in them. My guess is this finding is more social than biological.
Let me try a simple cultural hypothesis. Éducation is very often more rigid on first childs since parents put more conscious efforts on « holding the frame » to avoid unwanted trajectories. They relax with younger ones.
It then become more acceptable for the the youngs to make their coming out.
It seems very possible to me that gay-married men are a significantly skewed portion of gay men.
“Strongly gay” men (i.e. men with more of the “thing that makes you gay”) might also be much more promiscuous (?) and keen on non- monogamous lifestyle.
So if homosexuality has an epigenetic cause, specifically an in-utero cause, does that mean that once we develop uterine replicators (a la Lois McMaster Bujold's sci-fi Vorkosigan saga books, setting aside "Ethan of Athos"), we would then be able to trigger or prevent homosexuality at will? And is there a reason to suppose that this would lead to anything other than an almost complete elimination of homosexuality?
(I'm asking because I'm curious. This isn't a veiled condemnation of technology. I personally view it like languages: humanity as a whole loses something every time a language becomes extinct, but at the same time it's obviously in a parent's interest to try to have their children be native speakers of [checks century] English.)
'Gay' vs 'Straight'. This Gay Younger Brothers post is doubtless an interesting and worthwhile area of research, although one of no particular interest to me personally. But something that does matter to me is that we should resist the English language being hijacked by propagandists. There is - I would guess -nothing particularly 'gay' about being homosexual. And 'straight' is a pointless and needless word as a description of the great majority of humans. It is a propagandist pitch.aimed at promoting a homosexual's illusory fantasist world in which there is no such thing as normal sexuality.
Actually I'd guess that for evolutionary reasons straight individuals who carry gay disposing genes would produce more offspring (or I'd expect the tendency to have been pushed out of the gene and meme pools).
For instance, esp in modern day, you might expect the prospect of uncles or aunts eager to assist w/o their own kids is more important in encouraging births than how much you want to fuck.
An idea that might help explain the unclear results: I remember having read many years ago (unfortunately I do not remember which book) the theory that there might be at the same time several reasons for (male) homosexuality. If I remember this correctly it was a) genetic, b) epigenetic (something about hormones during pregnancy I seem to remember?) and c) social (i.e. bisexuals that identify as gay). I found this theory also interesting as it would explain why there are from a young age very effeminate gays and gays that "pass", i.e. are not "read" as gay.
My father is gay, always has been. In terms of reproductive fitness throughout human history, I am not convinced that being gay would be a big disadvantage. Gay men make amazing parents, and want to have children. In prehistory there wouldn't be a gay culture or any distraction from having a family. Being gay you'd be content to hang out with all the manly warrior types, massage their muscles after a big hunt, braid their man locks. Gossiping with the ladies would come naturally too. And gays often assume that their gayness tracks with a set of genes for extra intelligence, a tendency for creativity, and a superior sense of aesthetics. Maybe this is true to some extent. Obviously there must be some benefit to being gay, even if the gayness is a sort of spandrel.
Denmark did not legalise gay marriage in 1989, and it's remarkable that you could think that, having lived through this last 15 years or so when this change has been introduced around the world.
Paternal age and offspring neurodivergence, presumably considered and dismissed long ago? "offspring of the fathers 45 years or older had a 34% increased risk" (of mental illness.) JAMA Psychiatry. Very large March 2014 Dutch study. A Comprehensive Assessment of Parental Age and Psychiatric Disorders. John J. McGrath, MD et al.
> Real, biological, and linked to NLGN4Y in particular: 40%
This would imply a 2/3 probability of being linked to NLGN4Y, conditional on it being real and biological, which seems very overconfident to me, given the uncertainty about the mechanism raised by Ablaza et al. Am I understanding Scott's statement here correctly?
> Even granting that the FBOE is true, why does adding more younger siblings make you less gay?
I don't know why we're considering only the genetic and in utero effects. To me it seems plausible that having more exposure to the other sex (or both sexes) during childhood and adolescence could increase the chances of adult heterosexuality. Chalk it up to pheromones or cultural effects, whatever.
To me the most interesting/confusing finding in the article is the huge difference between the <1% incidence of married homosexuality in Netherlands and 4-10% of gays in Scott's poll. Is it the subject or the marriage?
I wonder if abortion (including miscarriages, of course) has any impact on FBOE. How far along in the pregnancy does a mother have to be in order for the pregnancy to have an effect on future pregnancies? Finding that out might help clarify some things, but I imagine it's a much harder thing to measure than most.
Nine million sample? There's supposedly less than 18 million people in the Netherlands right now.
Also 2.36 siblings for opposite-sex and 2.14 siblings for same-sex means there's on average more than 3 children per family (or relationship I guess). In an age where everyone's saying that every country in western Europe has less than 2.1 children per family (a *lot* less), i.e. not replacing themselves?
Now maybe these have already been pointed out, and maybe I've missed something. Maybe the study ignored people who didn't form any relationship? But that sounds like it ignores a *lot* of people, enough to confound and even reverse their findings.
I think it’s interesting the effect was more observable with homosexual pedophiles, as that’s more likely to have a clear behavioral etiology. Very often they were themselves abused.
I’ve worked many child sexual abuse cases, and natural fathers almost never sexually abuse their own kids. The most common perpetrator is mom’s new boyfriend after the divorce. So the youngest siblings would have a higher chance of still being in the age range for the new boyfriend to groom and victimize them. Also a higher chance of an older step-brother or cousin being present in the house to abuse them.
If that point has been raised time & time again, I apologize for beating the dead horse. But...
Multiple people point out a supposed evolutionnary benefit to homosexuality in the form of "gay uncles" helping out with raising children, but isn't that ignoring the opportunity cost of that "gay uncle"? A non-gay uncle may not help with raising your 4-5 children, probably slightly worsening their outcome, but he'll have 4-5 children of his own, spreading their non-homosexuality-inducing genes.
I have a hard time believing a scenario where the effect of help raising the kids outweight a doubling of the offspring produced.
Were it socially acceptable to suggest that homosexuality can be caused by childhood sexual abuse, one would wonder if having older siblings might make that more likely.
Call me a philistine, but given the uncertainty pervading the literature, the smallness of the effect if it exists at all, the gap between statistical significance and real world significance, and the lack of useful an actionable takeaways, the word which springs to my mind is: nothingburger. Perhaps 50 years ago this might have inspired the thought that perhaps we should scale back the penalties for being gay on the grounds it might not be altogether their fault.
Also I generally like evolutionary explanations for things, but not here. Lefthandedness is heritable but evolutionarily neither here nor there. I'm happy to think the same about being gay.
Question for the mathiest among us: I have a feeling that there is something lacking in the way concordance is calculated. My understanding is that you calculate it by taking number of concordant twin pairs in your sample and dividing it by the total number of pairs. But it seems to me that the calculation needs to somehow take into account how rare or common the trait is that you are looking at. Being gay is not a common trait for males -- last figure I saw was about 5% of males. But think about calculating concordance for brown eyes, which 70% or so of people have. It seems like for a common trait like that, it's way "easier" to get concordance -- or you could think of it as you're getting a lot of "free concordance" for brown eyes from the commonness of the trait, and that totally blurs the picture if you what you are trying to figure out is the genetic contribution to brown eyes. My intuition is that you need to do some math that corrects for trait commonness if you are using trait concordance to figure out how genetic something is. One correction would be to calculate concordance on the trait for paired individual subjects in the pool -- i.e., not the concordance of identical twin pairs, but the concordance of random pairs of subjects with subjects in these pairs not being twin pairs but unrelated individuals. Then subtract this figure from the concordance for twin pairs.
Also, a related question: Scott says the usual concordance rate found for identical twins is around 50%, but most think that 80-90% of schizophrenia is genetic. How do you figure out what percent of a trait is genetic? Is there some other way to do it besides calculating concordance rates among identical twins?
Another possible cause, less dependant on a specific gene: pregnancy is hard on a mother's body. An ideal pregnancy requires a lot from a mother's body. A child developing inside a body that's already been pregnant multiple times is less likely to develop ideally. A mother who's had such rough pregnancies as to produce a gay child is less likely to have more children (either choosing not to when that choice is available, or to a lesser extent being unable to even if she can't choose not to).
How testable is this? Survey mothers of adults, and ask them on a scale to rate how difficult their pregnancies were. Then ask which of their kids are straight, bi, or gay.
I made this comment years ago on this subject (obligate homosexuality caused by an intragenomic conflict), and it got some interesting push back. I still think that this isn't a completely crazy theory.
Not that I look for a non-biological explanation for everything, and yes, I haven't read every single comment, but: has nobody really suggested that younger siblings are often under less pressure (from their parents, relatives, internalized paternal authority, etc.), conscious and unconscious, to continue the family line? And couldn't that expectation, or lack of it, affect sexual orientation?
> Remember how Frisch and Hviid managed to look at two million Danes? Well, the Dutch also have gay marriage and keep really good records. Ablaza, Kabatek, and Perales were able to obtain and analyze the data from nine million of them. They do more advanced statistics than any of their predecessors and are able to report basically every parameter of interest with high confidence.
This type of study seems impossible to do right. One thing I noticed immediately:
> We observe all maternal siblings who were alive and residing in the Netherlands after October 1994
In other words, diseased siblings don't count. All people, but especially old people, are more likely to have diseased older siblings than diseased younger siblings. (Old people die.) If a youngest sibling is old, their siblings are more likely to be diseased, excluding them from the study. As such, I expect the sample of oldest siblings in this study to be older than the sample of youngest siblings. This matters because old gays are much more likely to be closeted/unmarried/married to a woman.
Also:
> For example, 0.73% of [Dutch] men who are the youngest of five siblings entered a same sex union, compared to just 0.35% of men who are the eldest of five siblings . . . the share of men with four older brothers entering a same-sex union is 0.96%, more than twice the share among men with four older sisters (0.46%)
My impression is that by the 80s, most Dutch parents rarely chose to have 4+ children, so I expect most of this sample to either be very religious or of age.
A proper Dutch social scientist could probably think of many more ways this data is skewed.
Re: genes ('fitness') or germs, I want to again encourage everyone to read "The Goodness Paradox", by Richard Wrangham. And our 'scrambling' of sex could be a spandrel to self domestication. (Selecting for less violence, aggression... read the book.) There is no selection for spandrels, though they are open for later selection in the genome.
Why wouldn't the nation the samples are from have a major difference? Genetics or cultural.
Additionally the parental acceptance of homosexuality could increase the more children they have. Ongoing changes in cultural acceptance would vary over time and by decade causing self identification issues.
I'm not surprised it will be difficult to perfectly find the same results as the original paper.
If the biological effect is correct, does this mean that if child #1 had an identical genome to child #7 (thought experiment here) the environment in the mother's womb could result in children with identical genomes, one gay and one not? The chemical conditions in the womb affect how the genes are expressed, not the content of the genome itself, right?
There is another aspect which may be slightly relevant to this. I've heard it said that someone's sexual orientation is to a degree determined early in their life by the presence or otherwise of a parent of the same sex (whether actual or in loco parentis) during a certain critical period of their infancy.
I'm not sure if this is idea still supported and, if so, the strength of the effect. But it seems that a parent might be more likely to be around, and around for longer, during their eldest offspring's infancy than maybe during that of their subsequent children, what with death or divorce or simply working away more to support their growing family.
That said, I would expect the effect, if any, to apply equally to either biological or adopted younger siblings, assuming the latter were adopted soon after birth.
This really feels like "thumb on the scale" studies in all instances.
Among other problems: the obvious societal pushes both for generalized acceptance of "gay" as well as increasing promotion via celebration of "gay" (as well evidenced by Hollywood alphabet children percentages) provides a non-linear, non-constant baseline.
As someone with a young kid, an obvious explanation for the other birth order effects is that they have the same cause as increased allergies in firstborns: later born children get a lot more exposure to viruses, in utero and as babies, thanks to their older sibling(s) bringing them home. Covid, with it's school and nursery closures and isolation measures, provides the ideal opportunity to test this hypothesis.
OK I thought I made this comment so maybe I'm making it twice, but. I think even if the older sibling effect appears statistically stronger, it's the older brother (as opposed to sister) effect that is more trustworthy, because it's one of those rare cases where nature is doing randomization for you.
"the share of men with four older brothers entering a same-sex union is 0.96%, more than twice the share among men with four older sisters (0.46%)"
Whether the older sibling was a brother or a sister was decided by meiosis, as good as a coin flip.
>The paper is 25,000 words of very dense statistical reasoning; I often found myself struggling to read a paragraph, only to eventually realize it was saying something obvious in as many long words as possible.
Maybe science needs to be less hostile to comprehension
> They speculated that maybe (male) homosexuality came from genes for a sort of super-femininity which was bad for men but very good for women; under this model, female relatives of male homosexuals would have more children than normal. But in fact this study found the opposite: they had fewer.
At this point, it would probably be easier to make a list of the handful of human things where antagonistic pleiotropy is still a viable hypothesis than to list all the things like schizophrenia that someone has claimed might boost fertility in relatives (but never does approaching the necessary levels, if at all)...
> under this model, female relatives of male homosexuals would have more children than normal. But in fact this study found the opposite: they had fewer. This makes sense if they’re getting some of the gay genes and so have less interest in heterosexual sex than normal
Does this kind of conclusion really make sense in an environment with easily available birth control? Presumably the ancestral environment where these genes were selected for was quite different in that respect...
Three plausible-sounding reasons why evolution may support a non-zero level of being gay:
1) Gay uncles and aunts promote survival of their nieces and nephews - presumably more so in social animals.
2) In animals where sexual competition can be dangerous, the ability to defer the urge to procreate via gay sex may be pro-survival enough to outweigh the delayed or less-certain reproduction.
3) Bisexuality may be selected for for some reason (perhaps attracting more than one mate or child-raising partner), and people being purely gay is a side effect.
All of these seem somewhat testable by looking at animal species where homosexuality is observed, vs. biologically similar but socially different species where it's not observed, and checking the differences in social structure, investment in children, and mate competition.
Until these (and probably others) are ruled out, I'm going to think that there's no great evolutionary mystery in the existence of homosexuality. Absence of knowledge is very different from knowledge of absence.
Wow ... a real tour de force ... great article.
Does the Dutch study control for time? Gen X is a little gayer than the baby boomers, Gen Y is a little gayer than Gen X. It seems like the more recent the birth, the more likely someone is to be gay, and younger siblings will tend to be born more recently.
I'd worry that the large-population studies are going to pick up unwanted demographic differences. For example, larger family size may correlate with religiosity or traditionalism, either of which might make people differently likely to get gay-married (regardless of actual sexual orientation).
Did the authors of the Danish and Dutch studies try to control for these effects at all?
I feel like I should clarify one of my thoughts. I sort of alluded to it here (https://twitter.com/cremieuxrecueil/status/1693811404845830377), but I really want AKP to do some triangulation. There are many variables they had access to that could have been leveraged to winnow down the DAG. That they didn't do this leaves us unclear on several viable alternatives I'm certain they had the power to address.
Personal numbers:
Sibling birth order effect on homosexuality is real: 90%
Real and biological: 75%
Real and of currently-estimated magnitudes: 40%
Real and explicable by current theory: 25%
Real, biological, and linked to NLGN4Y in particular: 10%
There is no FBOE. It makes no evolutionary sense. The only plausible explanation is that (male) homosexuality traces back to a single mechanism. It’s a byproduct of an evolved mechanism: http://scottbarrykaufman.com/wp-content/uploads/2012/12/Rice-et-al.-2012.pdf
This makes far more sense. In utero, homosexual men have female responsiveness to testosterone, but only in specific parts of their brains that control attraction.
Seems straightforward to me. With fewer siblings you get more parental attention. More of your parents subjecting you to gender/sexual stereotypes, and less time to be yourself.
My hypothesis is that if homosexual behavior is culturally forbidden as in the case of past cultures, gay genes will increase cooperative behavior among males.
Given that women are more likely to identify as bisexual than men, I wonder how much of the differences in effect between gays and lesbians may be confounded by bisexuality – which these studies' methodologies could not control for (since they only observe monogamous marriages).
The sibling effect might be smaller for bisexuals and account for that sex difference?
My recollection from the early 2000s was that Blanchard's estimate was that FBOE accounted for 1/7th of all male homosexuals: in other words, not a trivial amount, but not a large fraction either, thus leaving most examples of male homosexuality unaccounted for.
All this talk of "gay genes" without acknowledging that the concordance rate among identical twins is so low that the twin of a homosexual most likely isn't one also. Psychology had a replication crisis because they had weak theories that led them to mine for noise. There's still no good theory for how gay genes could persist at a level higher than the rate of de novo mutations.
Is there a source that will disabuse me of what seems to be the obvious naïve parsimonious assumption that younger siblings are more submissive due to physical and intellectual inferiority during their childhood? Leading to higher rates of male homosexuality in particular when they learn to imprint on submission to another male (older brothers), but also leading to younger male siblings being less attractive to women due to a tendency to be submissive to females as well (older sisters) and thus finding themselves (on the margin) more likely to be both rejected by females for their submissiveness and accepted by male partners who seek submissive mates?
This seems really, really obvious to me. Males seek submissive partners and females seek dominant ones. Younger male siblings are more likely to be submissive.
You keep saying
>"if you’re gay, it means your parents had some of the genes for homosexuality, which means they weren’t as committed to the whole heterosexual-sex-for-procreation thing as usual, and we should expect them to have fewer kids, and therefore for you to have fewer siblings."
But the whole point of the theory, at least the NLGN4Y version, is that it explains how it could be passed down through evolution without a gay gene, because it's a gay gene wouldn't be adaptive. The way NLGN4Y explanation escapes that is that it's not a gene that causes homosexuality in the individual, but a gene that slightly increases the probability of older siblings to be gay, which means by the time you get a homosexual child, you probably already have some heterosexual children, which still carry the gene (because it doesn't directly make them gay) and pass it forward.
Before modern medicine, women had many more children (often 10+), and many children died in childbirth or at a young age.
If birth order effects were biological, this would predict many more gay men historically than today, but I'm pretty sure that was not the case.
Does the birth order theory have an explanation for this?
Maybe another complicating factor is the age difference between successive siblings, if changes in a mother's immune system gradually creep back to normal over time after the birth of a son. If so then perhaps the effect would be more pronounced and readily observable if results were weighted in inverse proportion to the interval between siblings (or better still based on typical functions of antibody levels over time following a male birth).
Parents pay far less attention to younger children of many, and are much more permissive and less controlling of them. The youngest are also going to be physically weaker and less able to physically compete with older siblings. The youngest is more likely to be the comedian of the family and more likely to reject the social paradigms around them- they’ve seen how they play out in their older siblings and can see the absurdity in them. My guess is this finding is more social than biological.
Let me try a simple cultural hypothesis. Éducation is very often more rigid on first childs since parents put more conscious efforts on « holding the frame » to avoid unwanted trajectories. They relax with younger ones.
It then become more acceptable for the the youngs to make their coming out.
It seems very possible to me that gay-married men are a significantly skewed portion of gay men.
“Strongly gay” men (i.e. men with more of the “thing that makes you gay”) might also be much more promiscuous (?) and keen on non- monogamous lifestyle.
Speculation.
So if homosexuality has an epigenetic cause, specifically an in-utero cause, does that mean that once we develop uterine replicators (a la Lois McMaster Bujold's sci-fi Vorkosigan saga books, setting aside "Ethan of Athos"), we would then be able to trigger or prevent homosexuality at will? And is there a reason to suppose that this would lead to anything other than an almost complete elimination of homosexuality?
(I'm asking because I'm curious. This isn't a veiled condemnation of technology. I personally view it like languages: humanity as a whole loses something every time a language becomes extinct, but at the same time it's obviously in a parent's interest to try to have their children be native speakers of [checks century] English.)
'Gay' vs 'Straight'. This Gay Younger Brothers post is doubtless an interesting and worthwhile area of research, although one of no particular interest to me personally. But something that does matter to me is that we should resist the English language being hijacked by propagandists. There is - I would guess -nothing particularly 'gay' about being homosexual. And 'straight' is a pointless and needless word as a description of the great majority of humans. It is a propagandist pitch.aimed at promoting a homosexual's illusory fantasist world in which there is no such thing as normal sexuality.
Actually I'd guess that for evolutionary reasons straight individuals who carry gay disposing genes would produce more offspring (or I'd expect the tendency to have been pushed out of the gene and meme pools).
For instance, esp in modern day, you might expect the prospect of uncles or aunts eager to assist w/o their own kids is more important in encouraging births than how much you want to fuck.
Could this be the entire effect?
Is such an effect enough to explain the outcome.
Interestingly, i would predict that birth control would make the gay uncle effect far stronger in increasing births.
That predicts that gays should be increasing in percentage since 60s.
Family sizes are much smaller now, shouldn't we be seeing less and less gays in the population? But we're not.
An idea that might help explain the unclear results: I remember having read many years ago (unfortunately I do not remember which book) the theory that there might be at the same time several reasons for (male) homosexuality. If I remember this correctly it was a) genetic, b) epigenetic (something about hormones during pregnancy I seem to remember?) and c) social (i.e. bisexuals that identify as gay). I found this theory also interesting as it would explain why there are from a young age very effeminate gays and gays that "pass", i.e. are not "read" as gay.
My father is gay, always has been. In terms of reproductive fitness throughout human history, I am not convinced that being gay would be a big disadvantage. Gay men make amazing parents, and want to have children. In prehistory there wouldn't be a gay culture or any distraction from having a family. Being gay you'd be content to hang out with all the manly warrior types, massage their muscles after a big hunt, braid their man locks. Gossiping with the ladies would come naturally too. And gays often assume that their gayness tracks with a set of genes for extra intelligence, a tendency for creativity, and a superior sense of aesthetics. Maybe this is true to some extent. Obviously there must be some benefit to being gay, even if the gayness is a sort of spandrel.
Denmark did not legalise gay marriage in 1989, and it's remarkable that you could think that, having lived through this last 15 years or so when this change has been introduced around the world.
Here is a comic that explains an evolutionary reason for homosexuality and also for the birth order effect: https://evolutions.thecomicseries.com/
Paternal age and offspring neurodivergence, presumably considered and dismissed long ago? "offspring of the fathers 45 years or older had a 34% increased risk" (of mental illness.) JAMA Psychiatry. Very large March 2014 Dutch study. A Comprehensive Assessment of Parental Age and Psychiatric Disorders. John J. McGrath, MD et al.
> Real and biological: 60%
> Real, biological, and linked to NLGN4Y in particular: 40%
This would imply a 2/3 probability of being linked to NLGN4Y, conditional on it being real and biological, which seems very overconfident to me, given the uncertainty about the mechanism raised by Ablaza et al. Am I understanding Scott's statement here correctly?
> Even granting that the FBOE is true, why does adding more younger siblings make you less gay?
I don't know why we're considering only the genetic and in utero effects. To me it seems plausible that having more exposure to the other sex (or both sexes) during childhood and adolescence could increase the chances of adult heterosexuality. Chalk it up to pheromones or cultural effects, whatever.
To me the most interesting/confusing finding in the article is the huge difference between the <1% incidence of married homosexuality in Netherlands and 4-10% of gays in Scott's poll. Is it the subject or the marriage?
I wonder if abortion (including miscarriages, of course) has any impact on FBOE. How far along in the pregnancy does a mother have to be in order for the pregnancy to have an effect on future pregnancies? Finding that out might help clarify some things, but I imagine it's a much harder thing to measure than most.
The Dutch study numbers seem odd.
Nine million sample? There's supposedly less than 18 million people in the Netherlands right now.
Also 2.36 siblings for opposite-sex and 2.14 siblings for same-sex means there's on average more than 3 children per family (or relationship I guess). In an age where everyone's saying that every country in western Europe has less than 2.1 children per family (a *lot* less), i.e. not replacing themselves?
Now maybe these have already been pointed out, and maybe I've missed something. Maybe the study ignored people who didn't form any relationship? But that sounds like it ignores a *lot* of people, enough to confound and even reverse their findings.
I think it’s interesting the effect was more observable with homosexual pedophiles, as that’s more likely to have a clear behavioral etiology. Very often they were themselves abused.
I’ve worked many child sexual abuse cases, and natural fathers almost never sexually abuse their own kids. The most common perpetrator is mom’s new boyfriend after the divorce. So the youngest siblings would have a higher chance of still being in the age range for the new boyfriend to groom and victimize them. Also a higher chance of an older step-brother or cousin being present in the house to abuse them.
Scott, Denmark had "registered partnership" (= civil unions?) for gay couples starting in 1989. They didn't have actual gay marriage until 2012.
If that point has been raised time & time again, I apologize for beating the dead horse. But...
Multiple people point out a supposed evolutionnary benefit to homosexuality in the form of "gay uncles" helping out with raising children, but isn't that ignoring the opportunity cost of that "gay uncle"? A non-gay uncle may not help with raising your 4-5 children, probably slightly worsening their outcome, but he'll have 4-5 children of his own, spreading their non-homosexuality-inducing genes.
I have a hard time believing a scenario where the effect of help raising the kids outweight a doubling of the offspring produced.
Has anyone considered this might be the impact of older siblings (particularly brothers) committing sexual assault?
Were it socially acceptable to suggest that homosexuality can be caused by childhood sexual abuse, one would wonder if having older siblings might make that more likely.
Call me a philistine, but given the uncertainty pervading the literature, the smallness of the effect if it exists at all, the gap between statistical significance and real world significance, and the lack of useful an actionable takeaways, the word which springs to my mind is: nothingburger. Perhaps 50 years ago this might have inspired the thought that perhaps we should scale back the penalties for being gay on the grounds it might not be altogether their fault.
Also I generally like evolutionary explanations for things, but not here. Lefthandedness is heritable but evolutionarily neither here nor there. I'm happy to think the same about being gay.
Question for the mathiest among us: I have a feeling that there is something lacking in the way concordance is calculated. My understanding is that you calculate it by taking number of concordant twin pairs in your sample and dividing it by the total number of pairs. But it seems to me that the calculation needs to somehow take into account how rare or common the trait is that you are looking at. Being gay is not a common trait for males -- last figure I saw was about 5% of males. But think about calculating concordance for brown eyes, which 70% or so of people have. It seems like for a common trait like that, it's way "easier" to get concordance -- or you could think of it as you're getting a lot of "free concordance" for brown eyes from the commonness of the trait, and that totally blurs the picture if you what you are trying to figure out is the genetic contribution to brown eyes. My intuition is that you need to do some math that corrects for trait commonness if you are using trait concordance to figure out how genetic something is. One correction would be to calculate concordance on the trait for paired individual subjects in the pool -- i.e., not the concordance of identical twin pairs, but the concordance of random pairs of subjects with subjects in these pairs not being twin pairs but unrelated individuals. Then subtract this figure from the concordance for twin pairs.
Also, a related question: Scott says the usual concordance rate found for identical twins is around 50%, but most think that 80-90% of schizophrenia is genetic. How do you figure out what percent of a trait is genetic? Is there some other way to do it besides calculating concordance rates among identical twins?
where they able to control for age of the mother? or the father?
Another possible cause, less dependant on a specific gene: pregnancy is hard on a mother's body. An ideal pregnancy requires a lot from a mother's body. A child developing inside a body that's already been pregnant multiple times is less likely to develop ideally. A mother who's had such rough pregnancies as to produce a gay child is less likely to have more children (either choosing not to when that choice is available, or to a lesser extent being unable to even if she can't choose not to).
How testable is this? Survey mothers of adults, and ask them on a scale to rate how difficult their pregnancies were. Then ask which of their kids are straight, bi, or gay.
I made this comment years ago on this subject (obligate homosexuality caused by an intragenomic conflict), and it got some interesting push back. I still think that this isn't a completely crazy theory.
https://slatestarcodex.com/2019/05/14/age-gaps-and-birth-order-effects/#comment-752266
An equivalent study on 1980s-‘90s AIDS victims might turn up interesting results.
Not that I look for a non-biological explanation for everything, and yes, I haven't read every single comment, but: has nobody really suggested that younger siblings are often under less pressure (from their parents, relatives, internalized paternal authority, etc.), conscious and unconscious, to continue the family line? And couldn't that expectation, or lack of it, affect sexual orientation?
> Remember how Frisch and Hviid managed to look at two million Danes? Well, the Dutch also have gay marriage and keep really good records. Ablaza, Kabatek, and Perales were able to obtain and analyze the data from nine million of them. They do more advanced statistics than any of their predecessors and are able to report basically every parameter of interest with high confidence.
This type of study seems impossible to do right. One thing I noticed immediately:
> We observe all maternal siblings who were alive and residing in the Netherlands after October 1994
In other words, diseased siblings don't count. All people, but especially old people, are more likely to have diseased older siblings than diseased younger siblings. (Old people die.) If a youngest sibling is old, their siblings are more likely to be diseased, excluding them from the study. As such, I expect the sample of oldest siblings in this study to be older than the sample of youngest siblings. This matters because old gays are much more likely to be closeted/unmarried/married to a woman.
Also:
> For example, 0.73% of [Dutch] men who are the youngest of five siblings entered a same sex union, compared to just 0.35% of men who are the eldest of five siblings . . . the share of men with four older brothers entering a same-sex union is 0.96%, more than twice the share among men with four older sisters (0.46%)
My impression is that by the 80s, most Dutch parents rarely chose to have 4+ children, so I expect most of this sample to either be very religious or of age.
A proper Dutch social scientist could probably think of many more ways this data is skewed.
Re: genes ('fitness') or germs, I want to again encourage everyone to read "The Goodness Paradox", by Richard Wrangham. And our 'scrambling' of sex could be a spandrel to self domestication. (Selecting for less violence, aggression... read the book.) There is no selection for spandrels, though they are open for later selection in the genome.
Why wouldn't the nation the samples are from have a major difference? Genetics or cultural.
Additionally the parental acceptance of homosexuality could increase the more children they have. Ongoing changes in cultural acceptance would vary over time and by decade causing self identification issues.
I'm not surprised it will be difficult to perfectly find the same results as the original paper.
"All of these differences are statistically significant . . ." Yay!
"Ablaza, Kabatek, Perales, And 9,000,000 Dutch People To The Rescue"
To me, this conjures up an image of a statistician rubbing their hands together and muttering: Power!, Power!, I must have more [statistical] power!
If the biological effect is correct, does this mean that if child #1 had an identical genome to child #7 (thought experiment here) the environment in the mother's womb could result in children with identical genomes, one gay and one not? The chemical conditions in the womb affect how the genes are expressed, not the content of the genome itself, right?
I just want to say that "Ablaza, Kabatek, Perales" sounds like a magical incantation.
There is another aspect which may be slightly relevant to this. I've heard it said that someone's sexual orientation is to a degree determined early in their life by the presence or otherwise of a parent of the same sex (whether actual or in loco parentis) during a certain critical period of their infancy.
I'm not sure if this is idea still supported and, if so, the strength of the effect. But it seems that a parent might be more likely to be around, and around for longer, during their eldest offspring's infancy than maybe during that of their subsequent children, what with death or divorce or simply working away more to support their growing family.
That said, I would expect the effect, if any, to apply equally to either biological or adopted younger siblings, assuming the latter were adopted soon after birth.
This really feels like "thumb on the scale" studies in all instances.
Among other problems: the obvious societal pushes both for generalized acceptance of "gay" as well as increasing promotion via celebration of "gay" (as well evidenced by Hollywood alphabet children percentages) provides a non-linear, non-constant baseline.
As someone with a young kid, an obvious explanation for the other birth order effects is that they have the same cause as increased allergies in firstborns: later born children get a lot more exposure to viruses, in utero and as babies, thanks to their older sibling(s) bringing them home. Covid, with it's school and nursery closures and isolation measures, provides the ideal opportunity to test this hypothesis.
OK I thought I made this comment so maybe I'm making it twice, but. I think even if the older sibling effect appears statistically stronger, it's the older brother (as opposed to sister) effect that is more trustworthy, because it's one of those rare cases where nature is doing randomization for you.
"the share of men with four older brothers entering a same-sex union is 0.96%, more than twice the share among men with four older sisters (0.46%)"
Whether the older sibling was a brother or a sister was decided by meiosis, as good as a coin flip.