Multiple factors involved in sexual orientation: New study

A new study released online with Archives of Sexual Behavior and via press release today propose a relatively small role for family attitudes in the direction of sexual attraction, with more of the explanation being factors not shared by siblings.

Society’s attitudes have little impact on choice of sexual partner

[PRESS RELEASE 16 June 2008] A unique new study from the Swedish medical university Karolinska Institute (KI) suggests that the attitude of families and the public have little impact on if adults decide to have sex with persons of the same or the opposite sex. Instead, hereditary factors and the individual’s unique experiences have the strongest influence on our choice of sexual partners.

The study is the largest in the world so far and was performed in collaboration with the Queen Mary University of London. More than 7,600 Swedish twins (men and women) aged 20-47 years responded to a 2005 – 2006 survey of health, behaviour, and sexuality. Seven percent of the twins had ever had a same-sex sexual partner.

“The results show, that familial and public attitudes might be less important for our sexual behaviour than previously suggested”, says Associate Professor Niklas Långström, one of the involved researchers. “Instead, genetic factors and the individual’s unique biological and social environments play the biggest role. Studies like this are needed to improve our basic understanding of sexuality and to inform the public debate.”

The conclusions apply equally well to why people only have sex with persons of the opposite sex as to why we have sex with same-sex partners. However, the conclusions are more difficult to transfer to countries where non-heterosexual behaviour remains prohibited.

Overall, the environment shared by twins (including familial and societal attitudes) explained 0-17% of the choice of sexual partner, genetic factors 18-39% and the unique environment 61-66%. The individual’s unique environment includes, for example, circumstances during pregnancy and childbirth, physical and psychological trauma (e.g., accidents, violence, and disease), peer groups, and sexual experiences.

Publication:

Niklas Långström, Qazi Rahman, Eva Carlström, Paul Lichtenstein, “Genetic and Environmental Effects on Same-sex Sexual Behaviour: A Population Study of Twins in Sweden.” Archives of Sexual Behaviour, 7 June 2008, doi 10.1007/s10508-008-9386-1

This is more evidence that different factors operate differently for different people. In discussing sexual orientation, it may be that individual narratives have validity for the individual but cannot be generalized widely. Where have I heard that before?

Another news item is circulating today with what appears to be a mix of new and old research on brain structure and sexual orientation.

UPDATE – There is indeed new research from Ivanka Savic’s team in the Proceedings of the National Academies of Science. The study, titled “PET and MRI show differences in cerebral asymmetry

and functional connectivity between homo- and heterosexual subjects” by Ivanka Savic and Per Lindstrom is not yet published but I have a copy and am reviewing it.

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  • concerned

    Warren,

    This is why I have had such difficulty agreeing with those who want to continue to convince us that our attractions are so heavily determined by genetics when the experience we have growing up seem to play such an important role. These factors result in the development of our identity. My experience can change when I begin to think differently about what I have come to believe. Ultimately this leaves us to choices to make.

  • http://www.patheos.com/blogs/warrenthrockmorton/ Warren

    @concerned:

    The news release notes that unique environment can include pre-natal and biological factors unrelated to childhood experiences as well. It is unclear from this news release how much might relate to social factors and how much to unique events but still beyond anyone’s control. Nonetheless, what is striking about this paper is that the variance break down relates to choice of sexual partner, not SSA per se. Stay tuned…

  • Michael Bussee

    Well, waddya know? “Instead, hereditary factors and the individual’s unique experiences have the strongest influence on our choice of sexual partners” while “familial and public attitudes might be less important for our sexual behaviour than previously suggested”,

    Hello? This is kinda what gay guys have been trying to tell us all along — if only folks would listen to their narratives. It feels like being homosexual is who we are and that which gender we find attractive (not just who we “decide” to have sex with) is somehow hard-wired — and that our individual experiences shape that. (1-2-3-4-)

  • Drowssap

    The results show, that familial and public attitudes might be less important for our sexual behaviour than previously suggested

    More evidence that orientation and attraction are instincts folks. 8-) Nobody remembers learning orientation and men have an extremely, difficult time UNlearning it.

    As for societies that practice homosexuality as a form of birth control, or guys in prison who have sex with men, that’s a completely different phenomenon caused by socialization.

    Example:

    Mexicans in Mexico take siestas, Mexicans born in American don’t. That’s clearly socialization. If Mexicans physically HAD to take a siesta wherever they were born or lived that would suggest biology.

    Instead, genetic factors and the individual’s unique biological and social environments play the biggest role.

    No comment on what the unique, biological input is. I can’t wait for my Drudgereport flashing siren when the press release comes out. 8-) IMHO when it does come out most people’s head will spin because all they’ve ever heard is socialization, genes and hormones.

  • Drowssap

    Overall, the environment shared by twins (including familial and societal attitudes) explained 0-17% of the choice of sexual partner, genetic factors 18-39% and the unique environment 61-66%.

    That pretty much says it all.

    I used to think that SSA was almost certainly set in motion in the womb. However all the evidence points to something that happens in very, early life. For every different factor that twins experience in the womb they experience thousands, maybe millions of different variables after birth.

  • jayhuck

    Drowssap -

    I would bet that this applies to OSA as well as SSA – but we’ll have to wait and see

  • Evan

    Warren:

    Nonetheless, what is striking about this paper is that the variance break down relates to choice of sexual partner, not SSA per se.

    Where have I heard that before? The Santtila et al. study. They concluded in a similar note that what causes same-sex behaviour may partially overlap with what causes same-sex attractions, so there could be factors that work differently to produce different outcomes. That can raise a new theoretical question: the factors that underlie behaviour could be different from those that generate attractions, which might explain why some people may experience SSAs as an unwanted condition without being socially pressed not to act on them.

    Michael Bussee:

    Hello? This is kinda what gay guys have been trying to tell us all along — if only folks would listen to their narratives. It feels like being homosexual is who we are and that which gender we find attractive (not just who we “decide” to have sex with) is somehow hard-wired — and that our individual experiences shape that.

    Study quote:

    “The results show, that familial and public attitudes might be less important for our sexual behaviour than previously suggested”. “Instead, genetic factors and the individual’s unique biological and social environments play the biggest role.”

    Michael, this shows that family and public attitudes (pressure or encouragement) play a less important role in determining choice of sexual partners. It does not say anything about attractions, identity or how can a certain individual develop so that he may eventually settle with a certain sexual preference and behaviour. It may say though that greater exposure to acceptance or lack of acceptance in the social setting or parenting styles do not influence much behaviour, IF the genetic and non-shared environmental factors are present to influence that sexual preference.

  • Drowssap

    “PET and MRI show differences in cerebral asymmetry

    and functional connectivity between homo- and heterosexual subjects”

    This kind of work is interesting to me because it shows that on average there is a difference between straight and gay people. It’s kind of like left handedness or finger length.

    Huge overlap, but a noticable difference in the aggregate.

  • jayhuck

    There’s a difference between straight and gay people? Shocking! ;)

  • jayhuck

    Evan,

    This study is only saying what many on here have been suggesting all along – that orientation is determined by a combination of genetic, biological and environmental factors. – not really earth shattering or new. I think what Michael was trying to say focused on the genetic and environmental outcomes of the study.

  • Evan

    Jayhuck,

    You may be right. But until we see the study there’s not much to say. It confirms some previous studies: genetic contribution does not seem to be the deciding factor (that is important because genes have a continuous influence during one’s lifetime, more or less) and familial and social factors (either negative or positive) even less so. I don’t know: it’s either hormonal brain organisation or … Drowssap’s environmental hypothesis. The BUG. :)

  • jayhuck

    Evan,

    My theory – its bigger than either hormonal brain organization or “the BUG” – LOL – and far more complex. I think we tend towards the easy and neat explanations on here when what we are dealing with is highly, um, involved? – I need to get my thesaurus out and find another word for complex :)

  • Evan

    Although some sex differences in brain size are visible at birth, the brain continues to develop as the child matures, meaning that environmental factors could also play a role.

    I was thinking that hemisphere size differences do not say much about differences in attractions. It could be the result of a particular prolongued usage on a certain genetic and biologic background. Doctors have brains different from basketball players.

    The amygdala differences are more interesting, but, again, we have to see the study. The article does not mention any original author and the PNAS did not publish this paper yet.

  • Scott

    From a quick reading of the article, I can say that that confidence intervals are large! To me this suggests multiple factors and complexity.

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  • Drowssap

    Even (or anybody else)

    Tell me where I go crazy and miss something.

    I’ll start with the important quote

    Overall, the environment shared by twins (including familial and societal attitudes) explained 0-17% of the choice of sexual partner, genetic factors 18-39% and the unique environment 61-66%.

    Although there is no hard and fast line between gay and straight biology differences do show up in the aggregate. Gay people are more likely to be left handed, lesbians have more masculine finger lengths, there might be eye blink differences, brain proportion differences, etc. etc. etc.

    Alright, so gay and straight people are slightly different from each other.

    Now this massive Swedish study comes along and suggests that these differences are about 2/3rds the result of something in the environment.

    Sooo…. it’s something from the environment and it’s almost certainly a variable that occurs outside the womb. That sounds like The Bug! 8-) I’m sure there are alternate possibilities as to why so many men would be gay, but isn’t that one suddenly a reasonable contender?

    In Dr. Langstrom’s conclusion he even mentions physical illness as a potential cause of SSA.

    The individual’s unique environment includes, for example, circumstances during pregnancy and childbirth, physical and psychological trauma (e.g., accidents, violence, and disease), peer groups, and sexual experiences.

    Interestingly enough here is what Zucker said in his 2000 Meta Analysis

    It is very likely that the disruptive events modify sexual differentiation

    of the brain, perhaps through hormonal or immunological mechanisms. Future studies are necessary to determine if homosexuality in men and women is associated with other signs of developmental instability

  • jayhuck

    Drowssap -

    Isn’t it a bit of a stretch to assume that environmental factors are causing the differences you mention when genetic factors can be up to 40% of the influence – how in the world do you make that jump? There’s no reason your “differences” can’t be explained genetically

  • Evan

    Drowssap,

    Your hypothesis is plausible, though it may the most difficult to prove. I was not making fun of that possibility. My English is not that good when I try to be funny! :|

  • Drowssap

    Evan

    No, I liked what you said. I didn’t think you were making fun of it. 8-)

  • Drowssap

    jayhuck

    There’s no reason your “differences” can’t be explained genetically

    So what you are saying is that all of the minor physical differences between gays and straights are caused by genetics. These traits are susceptability factors.

    Actual homosexuality is the result of the 2/3rds input that comes from the environment?

  • Drowssap

    jayhuck

    Let me write this better…

    There’s no reason your “differences” can’t be explained genetically

    So what you are saying is that all of the minor physical differences between gays and straights are caused by genetics.

    Actual homosexual feelings are the result of the 2/3rds input that comes from the environment?

    I say genes make us susceptible to various things in the environment. It’s the environmental input that actually makes someone gay. A byproduct of this gene/environment interaction are the minor, physical anomolies that scientists find. Perhaps SSA itself creates a few brain differences over a long period of time. I’m sure OSA slowly alters brain structure over time.

  • jayhuck

    Genes and the environment can change each OTHER – I don’t disagree with you that genes can make us susceptible to things in the environment, but to unequivocally say that it is the environment and the environment alone that makes someone gay is to ignore the obviously strong pull that genes have in making this determination. You are trying almost too hard to be linear in your thinking about this issue.

  • John Weaver

    The only reason this issue even matters to the gay community is because evangelicals have used this environmental argument to argue that homosexuality is “unnatural”. This is not surprising, considering evangelicals have no other argument against homosexuality beyond the argument from nature (barring scriptural fiat). But if someone could prove one hundred percent that homosexuality was totally environmentally, or “not natural”, it would mean absolutely nothing. Just because something is unnatural doesn’t make it wrong, and just because something is natural doesn’t make it right. Unfortunately, I think the GLBT community plays right into evangelicals hands when they allow evangelicals to debate on these terms (though I realize, as Wayne Besen has noted, that popular perception of this issue revolves around biology, however wrongly).

    Frankly, the less genetic (or hormonal) links to homosexuality there are, the better off I’ll feel. I don’t want Al Mohler messing with my gay children’s DNA, pre-birth.

  • Evan

    Warren Throckmorton:

    UPDATE – There is indeed new research from Ivanka Savic’s team in the Proceedings of the National Academies of Science. The study, titled “PET and MRI show differences in cerebral asymmetry

    and functional connectivity between homo- and heterosexual subjects” by Ivanka Savic and Per Lindstrom is not yet published but I have a copy and am reviewing it.

    Thanks for the reference details. I just checked again and they did publish it.

  • Drowssap

    BTW, can I just add that the next time somebody mentions the 1991 Bailey Twin study (that’s nearly 20 years ago folks) I’m going to stop refering them to his better 2000 twin study and instead foward them to this massive, 2008 Swedish twin study.

    GEEZ people get with the program! 1991 is a long time ago.

  • jayhuck

    I just wanted to provide this quote from the New Scientist regarding this study:

    “Brain scans have provided the most compelling evidence yet that being gay or straight is a biologically fixed trait.

    The scans reveal that in gay people, key structures of the brain governing emotion, mood, anxiety and aggressiveness resemble those in straight people of the opposite sex.

    The differences are likely to have been forged in the womb or in early infancy, says Ivanka Savic, who conducted the study at the Karolinska Institute in Stockholm, Sweden.

    “This is the most robust measure so far of cerebral differences between homosexual and heterosexual subjects,” she says.”

  • Drowssap

    Jayhuck

    And from the same study…

    Genetic factors, therefore, appear less probable as the major common denominator for all group differences observed here.

    Gay men and women are wired up differently… but just like the other Swedish study the scientists involved believe the difference is not due to genetics.

    F A S C I N A T I N G!!!

    It looks like I’ve got something to think about all day while I’m working. 8-)

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  • Evan

    The Savic & Lindstrom paper is a very interesting piece of research.

    The subjects were distributed in almost discrete categories in terms of Kinsey scores and were positioned at the extremes. It is most likely that what we are seeing are correlates for exclusively heterosexual and homosexual people.

    The standard deviations for the right hemispheric volumetric measures are rather small, which shows that the spread was small too within each category. The coefficients of variation for each category have very close values, slightly greater in men ( cv(HoM) = 7.5%, cv (HeM) = 6.8%). But given that the relative differences by sexual orientation inside sex groups were not large in males, but significant, I wonder whether there is any overlap between the distributions (the same problem that we know from LeVay’s study). Homosexual women (HoW) show a greater difference in mean values from heterosexual women (HeW) than homosexual men (HoM) from heterosexual men (HeM). Also, the HoM mean of right hemispheric values is closer to the HeM than to that of HeW. But the authors do make a convincing point that the asymmetry is significant in HeM compared to HoM, although the magnitude is rather small, IMO.

    The amygdala data is the most interesting part of this study. The values for left amygdala covariation in size for HoM are closer to the those of HoW and HeM than to those of HeW. But the values for the right amygdala are really astonishing: the size in HoM is really larger by a great margin compared to all other categories (does this indicate some genetic predisposition for mood disorders and anxiety?).

    I will come back with more comments about the amygdala connectivity patterns. I have to run.

  • Drowssap

    (does this indicate some genetic predisposition for mood disorders and anxiety?)

    Don’t the scientists suggest tthat hese brain differences are caused by something in the environment?

  • Drowssap

    Whoops, last post was to Evan

  • Nick R

    The two new articles seem to support what I’ve thought for a long time. The sex you are attracted to is determined by birth. The characteristics in individuals you are attracted to are influenced by post-natal factors. This article supports the latter, the other article the former.

  • Michael Bussee

    Question: Why do we even care what “causes” homosexuality? Does anybody really care what “causes” heterosexuality? And don’t give me the “I just have an unbaised scientific curiousity”. I have heard all that before and I don’t buy it. What’s the real reason?

  • Patrick

    The real reason Michael is because they want to ‘fix’ us.

    The reasoning here is really obvious. Look at the close ties Cochran (gay germ proponent) has with the eugenics movement. Drowssap mentioned that there has been funding into researching the gay germ theory. I would be willing to bet the eugenics organizations are providing the funding (of course this is just speculation on my part).

    I certainly don’t want people to have to accept being gay because they have no choice – but what I think is fueling this research is not the ability to have a choice about ones sexual orientation – but rather eliminating homosexuals.

  • http://www.wthrockmorton.com Warren

    Patrick – I suspect Qazi Rahman and Nicklas Langstrom will be enlightened to know of their real reasons for pursuing one of the most interesting questions of our day.

    We have had discussions like this on other threads. This is not the thread for this. Please keep the discussion on the topic of the study.

  • Michael Bussee

    Patrick said: “I certainly don’t want people to have to accept being gay because they have no choice “

    But Patrick, as far as I can tell, there is no choice in being gay — that is, we do not choose whether we are attracted to men or women. That seems intrinisic, hard-wired, part of our natural temperatment.

    Before the pouncers get me, please notice the word “seems” — This is the way it seems. I am not stating fact. This is my opinion. I am talking about the phenomenology, the internal experience of being gay. That is involuntary. Instinctive.

    We do have choices when it comes to what we will do about being gay — whether or not to have gay sex, who we hang out with, how we percieve ourselves, what labels we apply. But I have never met a person who chose to be gay — or a straight person who chose to be straight. Have you?

  • Patrick

    Patrick – I suspect Qazi Rahman and Nicklas Langstrom will be enlightened to know of their real reasons for pursuing one of the most interesting questions of our day.

    1. I highly doubt Qazi Rahman and Nicklas Langstrom are reading this blog anyway.

    2. I hardly think scientists are above reproach – certainly it is fair to question anyones motives.

    3. The view that this is one of the most interesting question of our day – is horribly myopic. Surely there are far more interesting and important questions for scientists to be using their time on.

    4. If you are going to chastise about staying on topic – perhaps you should look at the thread drift that is occurring in the topic above this one.

  • Evan

    Michael Bussee,

    Question: Why do we even care what “causes” homosexuality? Does anybody really care what “causes” heterosexuality? And don’t give me the “I just have an unbaised scientific curiousity”. I have heard all that before and I don’t buy it. What’s the real reason?

    I’m interested in what causes all sexual orientations, including heterosexuality and asexuality. I think it’s good to know, because it helps us understand why we are the way we are and why other people are the way they are. Research is surely getting more interesting each year.

  • Evan

    Patrick,

    The real reason Michael is because they want to ‘fix’ us.

    The reasoning here is really obvious. Look at the close ties Cochran (gay germ proponent) has with the eugenics movement. Drowssap mentioned that there has been funding into researching the gay germ theory. I would be willing to bet the eugenics organizations are providing the funding (of course this is just speculation on my part).

    I certainly don’t want people to have to accept being gay because they have no choice – but what I think is fueling this research is not the ability to have a choice about ones sexual orientation – but rather eliminating homosexuals.

    It doesn’t look like anything liable to be ‘fixed’ by one shot, even in the unlikely case that your suspicions were right. You’ve seen the last papers, they point to some brain characteristics that can’t be switched on or off.

  • Michael Bussee

    It’s just that I don’t see people obsessing about what “causes” straightness. Most of the people I encounter who do obsess about what “causes” gayness are the same ones who think it can and should be fixed. Yes there are exceptions, those who for some reason just find this subject fascinating and have no agenda to “repair” it.

  • Evan

    Niklas Långström, Qazi Rahman, Eva Carlström and Paul Lichtenstein, Genetic and Environmental Effects on Same-sex Sexual Behavior: A Population Study of Twins in Sweden

    Abstract

    There is still uncertainty about the relative importance of genes and environments on human sexual orientation. One reason is that previous studies employed self-selected, opportunistic, or small population-based samples. We used data from a truly population-based 2005–2006 survey of all adult twins (20–47 years) in Sweden to conduct the largest twin study of same-sex sexual behavior attempted so far. We performed biometric modeling with data on any and total number of lifetime same-sex sexual partners, respectively. The analyses were conducted separately by sex. Twin resemblance was moderate for the 3,826 studied monozygotic and dizygotic same-sex twin pairs. Biometric modeling revealed that, in men, genetic effects explained .34–.39 of the variance, the shared environment .00, and the individual-specific environment .61–.66 of the variance. Corresponding estimates among women were .18–.19 for genetic factors, .16–.17 for shared environmental, and 64–.66 for unique environmental factors. Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment (social and biological) on same-sex sexual behavior.

    Source: SpringerLink

    Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world’s largest study of twins.

    Writing in the scientific journal Archives of Sexual Behavior, researchers from Queen Mary’s School of Biological and Chemical Sciences, and Karolinska Institutet in Stockholm report that genetics and environmental factors (which are specific to an individual, and may include biological processes such as different hormone exposure in the womb), are important determinants of homosexual behaviour.

    Dr Qazi Rahman, study co-author and a leading scientist on human sexual orientation, explains: “This study puts cold water on any concerns that we are looking for a single ‘gay gene’ or a single environmental variable which could be used to ‘select out’ homosexuality – the factors which influence sexual orientation are complex. And we are not simply talking about homosexuality here – heterosexual behaviour is also influenced by a mixture of genetic and environmental factors.

    The team led by Dr Niklas Långström at Karolinska Institutet conducted the first truly population-based survey of all adult (20-47 years old) twins in Sweden. Studies of identical twins and non-identical, or fraternal, twins are often used to untangle the genetic and environmental factors responsible for a trait. While identical twins share all of their genes and their entire environment, fraternal twins share only half of their genes and their entire environment. Therefore, greater similarity in a trait between identical twins compared to fraternal twins shows that genetic factors are partly responsible for the trait.

    This study looked at 3,826 same-gender twin pairs (7,652 individuals), who were asked about the total numbers of opposite sex and same sex partners they had ever had. The findings showed that 35 per cent of the differences between men in same-sex behaviour (that is, that some men have no same sex partners, and some have one or more) is accounted for by genetics. Rahman explains:

    “Overall, genetics accounted for around 35 per cent of the differences between men in homosexual behaviour and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared by twins) accounted for around 64 per cent. In other words, men become gay or straight because of different developmental pathways, not just one pathway.”

    For women, genetics explained roughly 18 per cent of the variation in same-sex behaviour, non-shared environment roughly 64 per cent and shared factors, or the family environment, explained 16 per cent.

    The study shows that genetic influences are important but modest, and that non-shared environmental factors, which may include factors operating during foetal development, dominate. Importantly, heredity had roughly the same influence as shared environmental factors in women, whereas the latter had no impact on sexual behaviour in men.

    Dr Rahman adds: “The study is not without its limitations – we used a behavioural measure of sexual orientation which might be ok to use for men (men’s psychological orientation, sexual behaviour, and sexual responses are highly related) but less so for women (who show a clearer separation between these elements of sexuality). Despite this, our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation.”

    Source: Eurekalert!

  • Drowssap

    Michael Bussee

    Patrick

    It’s just that I don’t see people obsessing about what “causes” straightness.

    Most scientists aren’t too concerned with the genetic and environmental factors that lead to dead, average height. But you can bet there are multitudes of researchers interested in both Dwarfism and Gigantism.

    As for funding Gay Germ Theory research I’ve got no inside track. I suspect yeah, there is probably a lot of relatively secret research going on around the world. But I don’t know any more than anybody else who has access to Google.

  • Drowssap

    Evan

    This study puts cold water on any concerns that we are looking for a single ‘gay gene’ or a single environmental variable which could be used to ’select out’ homosexuality

    I try to avoid disagreeing with a guy twice as smart as me about his own study but I feel I must on this point.

    Their study found that homosexuality was largely environmental and as near as I can tell that’s about it. There could be 1 main environmental factor, 3 or even 50. Which environmental factor or factors are involved nobody knows. All I’m saying is that this study points to environment and reading any more into the results involves more speculation than even MY posts. 8-)

  • Drowssap

    Evan

    Ok, maybe I should have written this simpler.

    What in this study rules out the possibility that SSA is triggered in every, single case by exposure to a common cold virus or cat fur or even licorice?

    I don’t personally believe that SSA is always, in every case set in motion by one thing. I’m just saying, what data in this study shows that it isn’t?

    My Wider Point:

    Just because we don’t understand something doesn’t mean it’s complex. Most things aren’t.

  • jayhuck

    Drowssap -

    Their study found that homosexuality was largely environmental and as near as I can tell that’s about it. There could be 1 main environmental factor, 3 or even 50. Which environmental factor or factors are involved nobody knows.

    This study SHOWED, what most of us on here have been saying for years – indeed, what a majority of the scientific community has been saying for years – that homosexuality is most likely a combination of genes and its environment – Its a bit misleading to simply say that the study shows homosexuality is largely environmental, because it ignores, what I would consider, a great deal that is due to genetics – I doubt that genetics plays any stronger a part in any other behaviors/orientation – but that is just me making a poorly educated guess

  • Evan

    Drowssap,

    Just because we don’t understand something doesn’t mean it’s complex. Most things aren’t.

    Agreed. About the brain hormonisation issue, which is the only big biological factor that could still be expected to play a decisive role, before the biology card is dropped or trumped by other cards. For more than half a century scientists studied brain hormonisation in mice and they were convinced that variations in the hormonal organisation of the brain accounted for variations in gender-typical behaviours, including sexual behaviour (they were not interested in mice, though). A few years ago Professor Dulac from the Harvard made the global news with what looked as a groundbreaking discovery that is poised to change paradigm in this field: female mice brain have circuitry for both sexes that is activated by a sensory switch (male mice brains are built from the same template). Marc Breedlove, who’s been studying brain hormonisation effects on both mice and humans said:

    “All the thinking until now was that female brains can produce feminine behaviors while male brains can produce masculine behaviors, with little or no cross talk between them,” “These results do suggest that, at least for mice, the brain retains circuitry to display both masculine and feminine behaviors into adulthood.”

    “What’s startling about the finding is that you make a tiny change and full-blown male behaviour comes jumping out,”

    So Breedlove, who is one of the biggest names in this area of research was surprised by the findings himself. Probably most scientists who study mice right now think that they wasted decades of research focusing on the trees and missing the whole point about the forest. Brain hormonisation is part of the environmental factors, but it may not have the decisive say in all sexually dimorphic behaviours. It may have a say in how you throw the ball or how you walk, but you don’t need a whole hormonised brain to tell the difference between mating partners. Some sex-atypical behaviours may be false positives for the study of sexual orientation.

    Caveats:

    - this was only proved in female mice

    - the olfactory sexually dimorphic switch is no longer working in humans

    - all these studies on mice and fruitflies use genetically engineered subjects, because neither species have same-sex oriented conspecifics in the wild

    - there is no confirmed effect in sheep or some primates, the only other mammal species that have significant numbers of inborn same-sex oriented conspecifics.

    However, these studies do have a strong heuristic value, precisely because research in the area of prenatal factors’ influence on the human brain organisation is mainly done by indirect measures, like studying rare conditions (congenital adrenal hyperplasia, androgen insensitivity syndrome, 5-alpha reductase deficiency). We also have the even rarer cases of genetic males born with less differentiated genitals (cloacal exstrophy) that keep their presumedly inborn orientation in spite of their being reared as a member of the opposite sex. This is the kind of strong evidence that they have about the inborn aspect of human sexual orientation — very marginal cases. In other words, scientists in the field of human sexual orientation still study the haystack or a few side straws, while researchers studying mice have found a needle.

    The other markers for any possible hormonal effects on humans’ sexual orientation: cerebral asymmetry (we’ve discussed on the Savic study topic), the sexually dimorphic brain areas (INAH3 is a candidate), otoacustic emissions (some effect in women, unclear effect in men) and some anthropometric measures (2D:4D ratio, skin ridges, etc) are still scattered correlates that do not predict anything yet.

    On the genetic evidence side, we know the poor track research has had in establishing any predictive linkage.

    This study, by Långström and collegues, actually lowers the chances of a decisive genetic influence on sexual behaviour, because previous studies set the bar for genetic effects a lot higher. The 34-39% interval of possible genetic contribution in men and almost two times lower effect in women does ring a bell, if we think about the lower prevalence of female homosexual behaviour. We will have this question confirmed or not once the genetic linkage study gets on the market. I think Alan Sanders said something similar, about a 40% genetic effect. But let’s not forget we are talking about behaviour here, which should exhibit the strongest genetic effect, compared to exclusive attractions not acted upon or some degree of attractions.

    OK, I’ll continue this in another post.

  • Evan

    Let’s play with the facts a bit.

    Let’s assume that a rough estimate of 40% genetic effects turns out correct in males and a lot less in women (20%). How does this effect fit the current data?

    The twofold genetic contribution to the male sexual orientation compared to the female one must have some significance. In Bem’s modal path of development gender-nonconforming sissies and tomboys were different in two respects: aggressiveness and activity levels. Also, girls were more likely to have mixed playmates than boys. A lesser genetic pull for same-sex preference in females would indeed be expected to produce less strong lifetime preference and greater flexibility. But it would not explain the striking similarities in brain patterns between heterosexual males and homosexual females. Those should be accounted for by similar factors, either genetic or hormonal, or a combination of them in relation to the same type of sexual object: females. So having some common genetic and hormonal factors should produce similar effects on heterosexual males’ and homosexual females’ brains. But this study points to “effects”, not to causes. We still don’t know if all these figures are actually factored in in the development of same-sex sexual orientation, whether they point to actual causes rather than incidental commonalities. We don’t know if all the same-sex oriented individuals were so for the same reasons. Some of the participants could be phenocopies. That’s why we can only trust studies that will make a simultaneous link between brain usage, neuroanatomical differences and genetic and hormonal contributions. But we are far from seeing that. We should also see studies of all orientations together, because this is the only way we can discern the link between genetic differences and brain patterns in all orientations. We cannot, for instance, understand why homosexual men have similar amygdala connectivity with heterosexual women if we only see genetic and environmental contributions to the former.

    As for the “different factors for different individuals leading to the same effect” idea, I can only see this if in some individuals:

    - the genetic factors are strongest, the hormonal factors are strongest – the social factors would not matter very much;

    - the genetic factors are strongest, the hormonal factors are moderate – social factors could have a small influence;

    - genetic factors: moderate, hormonal factors: moderate, social factors: likely to make a difference;

    etc.

    But, in the last analysis, the effects on the brains of people of the same orientation and gender must be similar, because we have the same biological organ producing the same effect: same-sex attractions. I would say research must start with the most confirmed brain patterns and look for the combination of causes that could lead to that effect.

  • Drowssap

    Evan

    Marc Breedlove, who’s been studying brain hormonisation effects on both mice and humans said:

    RIGHT ON!!!! Great find on the Breedlove quote. That makes me feel so good that scientists take this seriously. I knew when you posted that first “When Minnie Turns Mickey” link that this was a huge breakthrough.

    In other words, scientists in the field of human sexual orientation still study the haystack or a few side straws, while researchers studying mice have found a needle.

    Brilliant point and I think this is how SSA will be figured out. A research team that doesn’t care one way or the other about Homosexuality is going to find the switch for mate selection in mice or flies or some other animal. Once we understand mice, humans probably aren’t 180 degrees different. Obviously we won’t work the exact same way as mice but we aren’t from Mars either. 8-)

  • Drowssap

    But, in the last analysis, the effects on the brains of people of the same orientation and gender must be similar, because we have the same biological organ producing the same effect: same-sex attractions.

    Yup, no matter how you slice it, something is creating a predictable and reliable set of attractions, in this case SSA. Gay men share something in common, just like straight men must.

    2+2=4 and 1+3=4 but the final answer is always 4.

  • Drowssap

    jayhuck

    You are definitely correct, SSA has a measurable genetic component. How it works is the question.

    Scenario A)

    A gene creates the potential for SSA. Men with this gene, when exposed to the right set of early life, social circumstances become gay. Because our brains have a critical imprint period this fixes more or less for life.

    Scenario B)

    A gene, when combined with something natural like the right level of maternal hormones triggers SSA.

    Scenario C)

    A gene creates susceptability to something like a common, cold virus. If men with this gene are exposed to this virus before birth or early in life they become gay.

    It’s going to be a version of one of those scenarios. Actually it is probably all of those scenarios. We just don’t know which scenario is the most common. Realistically speaking there could be people who are gay EXCLUSIVELY due to a gene they carry. But everything points towards this group being very small.

  • Evan

    Drowssap,

    I think this is how SSA will be figured out. A research team that doesn’t care one way or the other about Homosexuality is going to find the switch for mate selection in mice or flies or some other animal.

    Well, we can’t blame scientists who study human sexual orientation for the poor results in the field. They don’t have the technology to see what’s going on in the womb and neither can they crack people’s skulls open and plug electrodes to see which circuits fire where and find some switches. Or worse, genetically engineer humans, wait until they grow up and see the results. Or the nightmare case scenario, surgically remove sexually dimorphic brain nuclei and watch people acting like opposite-sex sexual zombies. That’s like Dawn of the Dead!

    Now back to reality. :)

    Someone who does comparative evolutionary biology must have some knowledge on how these particular systems in the mammalian brain have been passed on from one species to another. They also have homology maps where they can see the correspondent genes across species. Large chunks of the mammalian species genomes have been preserved. Geneticists call them evolutionarily conserved regions (ECRs). There are almost 5000 ECRs conserved between humans’ X chromosome and that of species like mice and rats. Nature didn’t waste genetic material to create a new way to build a mammalian brain; it only refined the advanced species for some tasks, like visual recognition in primates and, later, language in humans. So the principle of “one brain, two-gender circuits flipped by a sexually dimorphic switch according to the physical gender” should apply to humans at least in one respect: the presence of both-gender circuits in the basic foetal template (the female one). Whether there really is a similar switch in humans or it’s related to vision, or has any comparable effects on sexual attractions, that is a matter of great debate. Humans might have left behind that dichotomising mechanism or might have resorted to a mechanism that created more diversity than in other species, actually a curve bell distribution. No ON/OFF positions for gender switching. After all, we are the only species on earth that has a teenage stage. That must have something to say about human sexuality too. Culture and environment must play a big role, especially if the gender switch mechanism has been left behind (:!: Daryl Bem’s idea: the effect of gender segregation on the development of reproductive sexuality). Or, to quote Breedlove again:

    “There’s plenty of room in society to influence sex differences,” “Yes, we’re born with predispositions, but it’s society that amplifies them, exagerates them. I believe that–except for the sex differences in aggression. Those differences are too massive to be explained simply by society.”

    So it could be as simple as variations in hormonal fixation of aggressiveness + predisposition to anxiety in males and only aggression variation in females. In this case, gender variance in humans might be exactly the effect of a gender switch gone extinct.

  • Drowssap

    Evan

    Humans might have left behind that dichotomising mechanism or might have resorted to a mechanism that created more diversity than in other species, actually a curve bell distribution. No ON/OFF positions for gender switching.

    Why would we expect to find a naturally occuring bell curve for male, sexual orientation? Hunter gatherer societies accounted for about 250,000 years of human evolution. Roughly 20% of the men had offspring vs. 80% of the females. The competition for women was intense for thousands and thousands of years. Shouldn’t we expect the genes and biological systems that create Kinsey 0 personalities to become fixed among males? That doesn’t mean homosexuality wouldn’t exist. But preferential, life-long homosexuality probably shouldn’t. In what primitive environment would SSA give a man an advantage when competing for women? Having sex with men never comes in handy for spreading DNA. Since women were largely responsible for childrearing we didn’t depend on secondary, male-male relationships to create a backup family structure for children.

    By Comparison:

    Why would we expect a bell curve in bird migrations? Some fly north, others east and west and some fly south. In reality pretty much all birds fly south for the winter because that system ensures success.

  • Evan

    Drowssap,

    Humans have some peculiarities compared to other species. A teenage phase is one very important for brain development. There is no need to have a perfect bell curve of sexual orientation. The actual bell curve would be that of hormonal factors, like aggresiveness. Throw in some genetic factors for amygdala patterns that predispose some males to anxiety (there is a whole spectrum) and you’ve got a composite bell curve of predispositions slightly amplified in sensitive men (anxiety, vigilance, avoidance). That is why there was a need for culturally enforced gender segregation: to fill the void of a gender switch advantage that was lost. So the bell curve of predispositions had to be adjusted by cultural nudging. You won’t see that in mice, because there is no same-sex oriented mouse in the wild. If they had no gender switch, they would have gone extinct.

    What evolutionary advantage gender variance may have had for humans? Well, greater anxiety or vigilance might have come handy in dangerous environments, it might be that sensitive men might have had to compensate their lower aggressiveness by greater inventivity. They could have become healers, shamans or very knowledgeable tribe members that did not need to reproduce as much as the other men. The only chance for a ‘gay’ set of genes to survive would be to have a normal distribution in the population, that maintained a marginal strong effect and a greater weak effect in the rest of the population. So each generation would have a statistical “tail”, but the greater populational effect would be preserved by differing mating strategies: masculine men would pick the best females and less masculine men would settle for females who have a harder time finding mates among the more aggressive males (because of being deterred by their aggressiveness).

    Another possibility is that the genetic effects would be the only ones that have been actually passed on, while the hormonal effects might be due to many environmental factors that could be variable at different points in time. Compound factors might be variable across evolutionary ages. I dunno, just a possibility. :)

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  • Drowssap

    Evan

    Well, greater anxiety or vigilance might have come handy in dangerous environments, it might be that sensitive men might have had to compensate their lower aggressiveness by greater inventivity.

    I think that’s the big question. Do traits like greater sensitivity lead to homosexuality or are these traits biproducts of whatever triggers homosexuality?

    My personal guess is that these traits are biproducts of the SSA trigger. The recent Swedish study that found greater amounts of “feminine” wiring in gay men concluded that this wasn’t the result of natural genetics. Something out of the ordinary was responsible. It could have been hormones but even in this case why would the hormones have spiked or washed out or whatever during development?

  • Evan

    Drowssap,

    Anxious personality is based on stable brain patterns that are probably the result of genetics, hormones and how these two factors conspired to influence someone to have certain behavioural tendencies, like avoiding aggressive games or confrontational situations. Actually a recent study shows that trait is manifested all the time as a form of vigilence even in quiet environments. Being that aggresiveness and competitiveness are male-typical characteristics, these anxious kids probably perceived their same-sex peers in a manner that is typical for the opposite sex (they could have been ‘kitchen boys’ or ‘sissies’). This might explain the same amygdala patterns in male homosexuals and female heterosexuals. They used their brain in the same way in relation to the male sex, but the causes might not necessarily be the same. It could be that some genetic factors predispose some men to greater anxiety which is atypical for their gender. This factor alone cannot cause atypical attractions, but it probably contributes to the final outcome. Still, the amygdala is involved in many cascading effects throughout the entire body. There are unexpected relations between these effects, like:

    –greater anxiety which can also increase pain sensation (hyperalgesia),

    –greater anxiety can increase physiological arousal,

    –greater amygdala activation can cause greater visceral sensitivity along the brain-gut axis – especially in the lower gastrointestinal tract (intestines and anus).

    But the amygdala does not play a role in these reactions by itself, it’s integrated in a number of specialised networks. For instance, a probable network for sexual behaviours includes the amygdala that makes the emotional assessment of stimuli, the ventromedial nucleus of the hypothalamus (which triggers lordosis in the females and mounting in the males) and the periaqueductal gray (involved modulation of pain, defensive behaviour, lordosis). If these areas are somehow less masculinised or too effeminised they might trigger body reactions that are atypical for an individual’s sex status.

    That can happen in many ways. A combination of genetically caused androgen receptors problems and how they interact with a certain level of hormonal exposure. Or it could only make a difference in a few specialised areas, regardless of the overal level of hormonal exposure.

    But as I said there must be another brain area that manages aggressiveness and allows a greater degree of stimuli input in the stress system, which overwhelms it. This is known as a sensory gating problem and has caused many disorders, which might also account for straight women’s and gay men’s greater vulnerability to stress and mood problems.

    So, differences in aggressiveness and sensitivity are probably correlated with gender feelings. But there are too many black boxes in the human system to be able to tell, like scientists who work on animal models, that there could be a switch, upstream the brain circuitry that governs gender-typical dimensions, that can awake different gender potentialities in the same brain. That might be a whole different issue than what scienstists in the field of sexual orientation study right now. Aggressiveness could be a by-product of a region that switches more or less the gender status of an organism. But then, again, why are there no same-sex oriented mice in the wild but there are same-sex oriented monkeys? Maybe humans and higher primates have lost that switch (the vomeronasal organ) and they only rely on the former by-products of gender-typical hormonisation and genetic sex status.

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  • RandomEffect

    One thing I’ve thought of that I bet nobody else has mentioned is that part of the chance of your sexual orientation may be what we think of as randomness. Of course nothing is really random if you look at it very closely. I’m talking about the Butterfly Effect. This will probably confuse a lot of people, but bare with me. The Butterfly Effect comes from the idea that if a butterfly flaps its wings it can cause a tornado on the other side of the world. Basically all the matter and energy in the world is physically connected somehow so a physical or chemical reaction that happens anywhere in the world will have some influence on all the other ones that happen in the future. If one was different it might in some cases change the whole outcome, but usually you’d probably have to many be different, maybe even millions for it to affect the outcome.

    The human body is basically matter and energy interacting together to somehow produce consciousness and everything that goes with it (desires, feelings, etc.), so there’s no reason why another chemical reaction, especially one that’s in your body wouldn’t have any impact on future ones. What ever chemistry produces attraction towards someone is the outcome of a very long, chemical equation containing all the chemicals that have ever interacted with your brain and all the chemicals that interacted with those chemicals and so on and so forth. So that would mean that had millions of seemingly unrelated factors been different (you ran one day instead of walking/vice versa, you eat a little more/less, how long you slept, what you watched on tv, even just stepping down your foot one inch forward/backward (since every action essentially sends out chemical signals)) your sexual orientation could be different. And it wouldn’t even be consistent like for example if everytime you overslept that increased your chances of being heterosexual. Instead it would be like you oversleep and that changes a variable in the chemical equation and how that affects your sexual orientation would depend on how it interacts with all the other variables so sometimes it could make you more likely to be straight, sometimes gay, and sometimes bi.

    Final note, what do you think caused you to like the foods you like or the smells you like? You probably just think you “just do”. Of course something determines that 2, millions of factors including a few ones where the relation can be easily seen and millions and even billions that would seem to have no logical reason to affect the outcome but still do through the Butterfly Effect.

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  • carole

    @Evan,

    The amygdala differences are more interesting, but, again, we have to see the study.

    Here’s an interesting article–for what it’s worth, once again, activity in the amygdala is the focal point.

    http://www.livescience.com/culture/090903-seizure-switch.html

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