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Born this way? An evolutionary view of ‘gay genes’

The claim that homosexual men share a “gay gene” created a furore in the 1990s. But new research two decades on supports this claim – and adds another candidate gene. To an evolutionary geneticist, the…

Rather than there being a single ‘gay gene’, there may be many which contribute to sexual preference. Sasha Kargaltsev/Flickr, CC BY

The claim that homosexual men share a “gay gene” created a furore in the 1990s. But new research two decades on supports this claim – and adds another candidate gene.

To an evolutionary geneticist, the idea that a person’s genetic makeup affects their mating preference is unsurprising. We see it in the animal world all the time. There are probably many genes that affect human sexual orientation.

But rather than thinking of them as “gay genes”, perhaps we should consider them “male-loving genes”. They may be common because these variant genes, in a female, predispose her to mate earlier and more often, and to have more children.

Likewise, it would be surprising if there were not “female-loving genes” in lesbian women that, in a male, predispose him to mate earlier and have more children.

Evidence for ‘gay genes’

masterdesigner/Flickr, CC BY-SA

We can detect genetic variants that produce differences between people by tracking traits in families that display differences.

Patterns of inheritance reveal variants of genes (called “alleles”) that affect normal differences such as hair colour, or disease states such as sickle cell anaemia.

Quantitative traits, such as height, are affected by many different genes, as well as environmental factors.

It’s hard to use these techniques to detect genetic variants associated with male homosexuality, because many gay men prefer not to be open about their sexuality. It is even harder because twin studies show that shared genes are only part of the story; hormones, birth order and environment play roles too.

In 1993, American geneticist Dean Hamer found families with several gay males on the mother’s side, suggesting a gene on the X chromosome. He showed that pairs of brothers who were openly gay shared a small region at the tip of the X, and proposed that it contained a gene that predisposes a male to homosexuality.

Hamer’s conclusions were extremely controversial. He was challenged at every turn by people unwilling to accept that homosexuality is at least partly genetic, rather than a “lifestyle choice”.

Dean Hamer talks about the gay gene study.

Gay men were divided: it vindicated the oft-repeated claims that “I was born this way” but also opened frightening new possibilities for detection and discrimination.

Similar studies gave contradictory results. A later search found associations with genes on three other chromosomes.

This year, a larger study of gay brothers, using the many genetic markers now available through the Human Genome Project, confirmed the original finding, and also detected another “gay gene” on chromosome 8. This has unleashed a new flurry of comment.

But why such a furore when we know of gay gene variants in species from flies to mammals? Homosexuality is quite common throughout the animal kingdom. For instance, there are variants that influence mating preference in mice and a mutation in the fruit fly makes males court other males instead of females.

Is the ‘gay gene’ really a ‘male-loving allele’?

The puzzle is not whether “gay genes” exist in humans, but why they are so common (estimates from 5-15%). We know that gay men have fewer children on average, so shouldn’t these gene variants disappear?

There are several theories that account for the high frequency of homosexuality. A decade ago I wondered if gay gene variants have another effect that boosts the chances of leaving offspring (“evolutionary fitness”), and passing the gay allele on.

A normal blood cell behind a human blood cell of a sickle cell anaemia patient. Wellcome Images/Flickr, CC BY-NC-ND

This is a well-known situation (called “balanced polymorphism”) in which an allele is advantageous in one situation and not in another. The classic case is the blood disease sickle cell anaemia, which leads to disease and death if you have two alleles, but to malaria resistance if you have only one, making it common in malarial regions.

A special category is “sexually antagonistic genes” that increase genetic fitness in one sex, but not in the other; some are even lethal. We have many examples across many species. Maybe the gay allele is just another of these.

Perhaps “male-loving” alleles in a female predispose her to mate earlier and have more children. If their sisters, mother and aunts have more kids who share some of their genes, it would make up for the fewer children of gay males.

And they do. Lots more children. An Italian group showed that the female relatives of gay men have 1.3 times as many children as the female relatives of straight men. This is a huge selective advantage that a male-loving allele confers on women, and offsets the selective disadvantage that it confers on men.

I am surprised that this work is not better known, and its explanatory power is neglected in the whole debate about the “normality” of homosexual behaviour.

How ‘normal’ are gay alleles?

darcyandkat/Flickr, CC BY-NC-SA

We have no idea whether these genetic studies identified “gay alleles” of the same or different genes.

It is interesting that Hamer detected the original “gay gene” on the X, because this chromosome has more than its fair share of genes that affect reproduction, but I would expect that there are genes all over the genome that contribute to mate choice in humans (female-loving as well as male-loving).

If there are male-loving and female-loving alleles of tens or hundreds of genes battling it out in the population, everyone will inherit a mixture of different variants. Combined with environmental influences, it will be hard to detect individual genes.

It’s a bit like height, which is influenced by variants in thousands of genes, as well as the environment, and produces a “continuous distribution” of people of different heights. At the two extremes are the very tall and the very short.

In the same way, at each end of a continuous distribution of human mating preference, we would expect the “very male-loving” and the “very female-loving” in both sexes.

Gay men and lesbian women may simply be the two ends of the same distribution.

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83 Comments sorted by

  1. Stephen Ralph

    carer at n/a

    Lifestyle choice....paleese.

    So laughable, it is just pathetic. Just think about it.

    Who would choose to swim against the raging tide?

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    1. Michael Shand

      Software Tester

      In reply to Stephen Ralph

      I wouldn't use the "Who would swim against the tide" argument as you don't have to look very far to find someone who wants victimhood and a certain type of fame and is willing to ruin their lives and everyone they love to achieve it

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    2. Josh Godda

      logged in via Facebook

      In reply to Stephen Ralph

      As Lenin said: "it all depends on who is swimming against whom..."

      http://en.wikipedia.org/wiki/Who,_whom%3F

      Who whom is the best maxim to defer to when you don't understand why an outlet like "the conversation" states a certain proposition. Just think "who whom."

      Gay genes piss of Christians (good)
      Intelligence genes piss of blacks (bad)

      The very same tools that are being used, and will be used, to determine the genetic contribution to homosexuality have been used to show that intelligence is highly genetic. So why then does intelligence research get shunned by an outlet like "the conversation" and gay gene research get propelled to "most read" here? It's simple: who whom. Who is doing what to whom. Gay genes piss of Christians (good). Intelligence genes piss of blacks (bad). Who whom. Who Whom. Who Whom. Got it?

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  2. Preman Tilson

    logged in via Facebook

    Excellent article. One comment: clicking on the link for "environment" takes you to an abstract for a paper in which it is clear that the only environment being referred to is pre-natal uterine environment.

    This distinction is lost on the general public, who read the word "environment" and automatically think about how a child is raised, etc. I see this word used in many scientific articles with no further explanation, which I think is very misleading for the untrained reader, and potentially harmful.

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  3. Sam Papillo

    Landscaper

    How do researchers differentiate between environmental effects and genetic effects in studies of closely related people?

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    1. Sam Papillo

      Landscaper

      In reply to Sam Papillo

      Answer to my own question:
      Being in the same family somewhat controls environmental effects, and analyses of individuals' DNA delineates genetic differences.

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    2. Nick Heidl

      logged in via Facebook

      In reply to Sam Papillo

      I wonder if bi-sexuals have a really serious issue with the male loving alleles fighting the female loving alelles? If ever a test was made to instantly determine you are gay wouldn't be a great thing in an anti gay society, particularly pro Sharia Law countries or northern tribal lands of India. Thank the lord we are not still still in the dark ages, I would hate to think witches or renouncers of God wouldn't be the only sinners to be given the death sentence. Next thing you know babies tested positive for gayness would be given a death sentence. At what point of the grey scale of gayness is the cut off point? Please don't make a gayness testing machine, it would be the end of humanity, worst than the now available "death to pre-born girls in China" scan.

      Personal view is that it is 100% genetic, nothing to do with lifestyle preference.

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    3. Michael Shand

      Software Tester

      In reply to Nick Heidl

      "Personal view is that it is 100% genetic" - you should aportion belief to evidence rather than work on personal bias

      to state 100% genetic rules out any other effect including environmental, you yourself said there is a grey-scale and that hetero's in certain situations may indulge in homosexuality....so you contradict yourself - it's 100% genetic, except for the otehr factors

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    4. Nick Heidl

      logged in via Facebook

      In reply to Michael Shand

      "and that hetero's in certain situations may indulge in homosexuality."

      No I didn't, you said it :)

      Personal bias? Bias is a strong adjective, seriously, it points an evil finger at me. If anyone had absolute evidence I wouldn't need to have a personal view, now would i?

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    5. Michael Shand

      Software Tester

      In reply to Sam Papillo

      The fact that some people will indulge in homosexual practices in certain social environments suggest that it is 100% genetic or not whether environmental factors will affect their sexuality

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    6. Michael Shand

      Software Tester

      In reply to Nick Heidl

      So you think that your either gay or straight regardless of what social situation you find yourself in, I think you are mistaken

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    7. Sam Papillo

      Landscaper

      In reply to Michael Shand

      Yes, I'm just being a bit particular because you unfairly criticised Nick's comment as contradictory.
      E.g., a genetically bisexual man who goes through life without kissing a man remains essentially bisexual.

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    8. Michael Shand

      Software Tester

      In reply to Sam Papillo

      I think the problem lies in your understanding of homosexuality as if it is a thing

      it's a spectrum, there is no need to label people as either genetically gay or straight or bi, that doesn't make sense

      As an example, if a girl is comfortable making out with another girl, in your world you have to be like "No she is straight, just doing it for attention, or maybe she is bi, or lesbian and just afraid of being honest or maybe she is lesbian and the guys she hooks up with are just for show, let me…

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    9. Sam Papillo

      Landscaper

      In reply to Michael Shand

      Fair enough.
      You've erroneously extrapolated my comments by conforming them to your preconceptions: you don't know what's in my head.
      Genetics is interesting. Personally, I found the article's elucidation of "male-loving genes" useful.
      Nonetheless, your opinion is valid, perhaps it's a waste of time exploring genetics re allelic determination of sexuality, but I disagree.

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    10. Michael Shand

      Software Tester

      In reply to Sam Papillo

      I have no problem with the research being done, I just think societal and cultural constraints are a bigger factor than your genes in the level of homosexuality in society

      There are hundreds of millions of more chinese men that chinese women for instance, I expect homosexual encounters to rise in china as this demographic becomes more pronounced

      The question of whether these people are TRUELY gay or just wanting human contact is a trivial distinction to me - my guess is you will find everyone will have different combinations of these genes and scientists will have to try tell a straight or gay man that no, your not actually gay, you just think your gay and act gay and have sex with men..,...but you don't have the genes

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    11. Josh Godda

      logged in via Facebook

      In reply to Sam Papillo

      Right, but why is this suddenly valid? When these tools and qualifications are applied to IQ (intelligence), they suddenly become invalid. I take your point, but it's very interesting that no one here challenged you on your comment.

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  4. David Rennie

    IT Contractor

    It is tragic when when we prefer a stereotype to an individual.
    I have always enjoyed the view that 'G/L is normal not common'. I'm common and heterosexual but all the evidence shows that sexual orientation is not always aligned with physical status. It is the people who are afraid of G/L that are abnormal, but unfortunately they are common.

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    1. Nick Heidl

      logged in via Facebook

      In reply to David Rennie

      The only reason anyone is afraid are those who are not sure of their own sexuality; what is there to fear? It won't rub off onto you LOL

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    2. David Rennie

      IT Contractor

      In reply to Nick Heidl

      Every gay man reduces the competition for heterosexual women!
      What's not to like about gay men!
      Unless you think, they think, you are gay and you are not strong enough to resist them.
      So the only men who should be afraid of gay men are those who think they might like a bit on the side!!

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  5. Susan Nolan

    retired

    Fascinating - particularly that what we are possibly dealing with is male-loving alleles in both females and males and female-loving alleles in both females and males - rather than "gayness" as such.

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    1. Michael Shand

      Software Tester

      In reply to Susan Nolan

      ". Combined with environmental influences, it will be hard to detect individual genes.

      It’s a bit like height, which is influenced by variants in thousands of genes, as well as the environment, and produces a “continuous distribution” of people of different heights"

      The author is talking nonsense in a very round about way, if the "Gay-gene" is like the "Height gene" then they don't really know what they are talking about

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    2. Nick Heidl

      logged in via Facebook

      In reply to Michael Shand

      I think you need to re-read the article, will help you in your thought processes. Often it is said that people with the inability to understand scientific terminologies need to be told in layman's terms. Clearly not enough in layman's terms for some ;)

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    3. Michael Shand

      Software Tester

      In reply to Nick Heidl

      I will have to disagree with you and agree with Jenny Graves here mate

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  6. Paul Prociv

    ex medical academic; botanical engineer at University of Queensland

    Given that human sexuality is so incredibly complex, it only stands to reason that numerous genes must be involved, and that normally heterosexual individuals might indulge in homosexual behaviour under particular circumstances. I doubt that an underlying specific gene complex will ever be fully defined, but it's good to see a studious effort being made. As for the evolutionary advantages of homosexuality, if we accept that the evolutionary unit for Homo sapiens is the extended family (rather than the individual, as is often mistakenly assumed), could it be that having a gay member in your clan is somehow advantageous to the group? One example might include contributing to child upbringing, without the destructive distraction of competing for reproductive partners. Of course, once religion inserts its irrational prejudices, survival benefits can be seriously distorted.

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    1. Nick Heidl

      logged in via Facebook

      In reply to Paul Prociv

      "As for the evolutionary advantages of homosexuality, if we accept that the evolutionary unit for Homo sapiens is the extended family (rather than the individual, as is often mistakenly assumed), could it be that having a gay member in your clan is somehow advantageous to the group? One example might include contributing to child upbringing, without the destructive distraction of competing for reproductive partners"

      Clever thinking, I like it.

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    2. Gary Luke
      Gary Luke is a Friend of The Conversation.

      IT services

      In reply to Nick Heidl

      But that's been proposed as the evolutionary role of grandparents. And is there any evidence of gay siblings taking on that role rather than heading out for a party? It's clever thinking maybe, but could also be a hypothesis with only rare real world examples.

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    3. Nick Heidl

      logged in via Facebook

      In reply to Gary Luke

      For sure but world famous philosophers wouldn't be reliant just on real world examples; meaning there is nothing wrong with unique or unusual ideas to create others, this is why I liked the comment

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    4. Jenny Graves

      Distinguished Professor of Genetics at La Trobe University

      In reply to Paul Prociv

      The “super-uncle” hypothesis (Kin Selection), holds that gay men provide more benefit than straight men to their family members, who are supported to have more children. However, there’s no evidence for this - the few trials I have seen don’t show that gay men are any more generous to their siblings, nephews and nieces than straight men. (http://www.fed.cuhk.edu.hk/~lchang/material/Evolutionary/Test%20of%20homosexual%20hypothesis.pdf).

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    5. Robert Davidson

      logged in via Facebook

      In reply to Jenny Graves

      What matters, of course, is how these super-uncles behaved in the ancestral environment over thousands of generations, and how they behave now in a very complex, different culture from the one in which the selection took place is not necessarily going to shed that much light

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    6. Michael Leonard Furtado

      Doctor at University of Queensland

      In reply to Paul Prociv

      Well, there's nothing like a generalisation to prove an irrational prejudice! Catholic celibates, including especially nuns, brothers and priests, have contributed more than most to child upbringing over the last two thousand years, and my suspicion is that, like me, most of them carry a homosexual or lesbian gene of one sort or another.

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  7. Michael Shand

    Software Tester

    I'm calling BS, you didn't find a gay gene in the same way you didn't find a height gene, you said at the end it's multiple gene's fighting it out all having an influence

    ie. your talking nonsense, your making claims to knowledge you either do not know or could not possibly know

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    1. Jenny Graves

      Distinguished Professor of Genetics at La Trobe University

      In reply to Michael Shand

      It’s tough to find individual genes when there are many with small additive effects. But there are techniques now, called Genome-Wide Association studies (GWAS) to track even height genes down; have a look at http://www.well.ox.ac.uk/sep-10-genetic-link-to-height-variation. With a very large sample (180,000 people) and lots of molecular markers that are now available, they could identify 180 genes, variants of which contribute to being taller or shorter. Some of these genes regulate cell growth, bone elongation, bone density, growth hormone. These genes explain only about a quarter of height variation, so there are probably another 500 genes out there that influence height. I expect that the genetics of mating preference is similar, but even harder to study because height is a lot easier to measure than sexual orientation.

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    2. Peter Campbell

      Scientist (researcherid B-7232-2008)

      In reply to Michael Shand

      Michael, speaking as a biochemist, someone with expertise in a field far closer to Professor Graves' genetics than your software testing is, I say she is making far more sense than you are.

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    3. Nick Heidl

      logged in via Facebook

      In reply to Michael Shand

      This isn't a chat show, it's a think tank, it's what we can work on at the moment. I got my thinking cap on, have you?

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    4. Nick Heidl

      logged in via Facebook

      In reply to Jenny Graves

      Nice write up and we are honoured by your presence:) By the way, a clear indicator of multiple gene influence for a physical attribute like height would explain the differences in every bone or, what I call locality (legs, torso, head and neck, arms and tactile bits - feet and hands) Otherwise if only one gene is involved then we would be proportionately the same between all humans, but we are not.,

      For those who need that in layman's terms, as an example our legs would be say 40% of our overall height no matter what height you were.

      How is that for an observation? ;)

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    5. Nick Heidl

      logged in via Facebook

      In reply to Nick Heidl

      oh, that above example was as if there was only 1 gene, by the way ;)

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    6. Michael Shand

      Software Tester

      In reply to Nick Heidl

      Chat show? Think Tank? it's neither mate it's a news forum, have you got your thinking cap on?

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    7. Nick Heidl

      logged in via Facebook

      In reply to Michael Shand

      Sorry these days I am so use to opinion news being the main content like in the The Australian and The Daily Telegraph; just goes to show that I haven't a clue what news is these days.

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    8. Peter Campbell

      Scientist (researcherid B-7232-2008)

      In reply to Michael Shand

      "I will have to disagree with you and agree with Jenny Graves here mate" Huh? I was agreeing with Jenny Graves. Her description of how many genes, each of small effect, can lead to a continuum is standard textbook stuff. She explains why we don't have just tall or short people but a distribution with most towards the middle of the range. It seems quite plausible, and apparently supported by some evidence, that sexual preferences might have analogous genetic influences.
      I recall chatting with a male…

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    9. Jenny Graves

      Distinguished Professor of Genetics at La Trobe University

      In reply to Nick Heidl

      Interesting thought Nick. There must be both kinds of genes. Some have general effects on all growth in the body (for instance, genes that regulate cell growth directly or through the action of hormones). Others affect only certain bones (for instance, a variant of a growth gene that causes achondroplastic dwarfism affects only limb bones), or maybe only bones that grow at particular times in pregnancy.

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    10. Michael Shand

      Software Tester

      In reply to Peter Campbell

      What I got from the article was that the whole Hieght Gene Gay Gene Chocalate Gene stuff is nonsense, it's a variety of different genes all having some effect, which is exactly what I would expect.

      The only part I thought that was BS was the framing of gay genes, I very much doubt that the sexual preferences we see in today's society are ruled by genes. My guess is people's sexual preference is based more on sociatal constrainst than anything else

      When we look back through history and cultures…

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    11. Peter Campbell

      Scientist (researcherid B-7232-2008)

      In reply to Michael Shand

      Perhaps we are in agreement. I was not subscribing to a view that there is a singular 'gay gene'. It is conceivable but I think the polygenic effect described in the article is more probable. If it were a single gene effect it would have been rather more obvious. Perhaps you think that scientists think that genetics is utterly determining? For some traits it is. If an individual lacks the ability to make some particular protein that is absolutely required to have some particular effect, no amount…

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    12. Nick Heidl

      logged in via Facebook

      In reply to Jenny Graves

      Do you think there is a connection between the primary genes that determine the sex you are and the sexual preference you have? My thought that there is, but, either there is a third primary influencer which is a scalable "inhibitor". Each of the three primaries have sub-genes that also have an influence their own primary gene and or crossover between the three primary influencers.

      If you like my theory on this let me know, I think I will start a new career in genetics ;) LOL

      I have a 40x microscope, so, am ready to start!! ;)

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    13. Nick Heidl

      logged in via Facebook

      In reply to Michael Shand

      the only constraint would be social norm (conventions) but doesn't stop people eventually knowing exactly what they are. Some G/L will practise straight sex either because of religion or young and confused. But I would say categorically rarely will a straight have gay or lesbian sex when they do know they are straight. It would be a perverted act of course unless it was for money ;)

      I knew of guy when he was in his early twenties struggling to know which sex he felt sexual to,. If I understood then what I know now, I would have spoken to him about it with some solidarity.

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    14. Nick Heidl

      logged in via Facebook

      In reply to Peter Campbell

      same here, I was agreeing with her too, especially as Jenny is the Guru ;)

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    15. Jenny Graves

      Distinguished Professor of Genetics at La Trobe University

      In reply to Nick Heidl

      We don’t know of any direct genetic link between sex determination and sexual preference. We know that maleness is determined in a human embryo about 12 weeks after conception by a gene (called SRY) on the Y chromosome, that kick-starts a genetic pathway that turns a ridge of cells in the embryo into a testis. The embryonic testis makes hormones, and the hormones make the baby male. However, SRY is active in tissues other than the gonads, and there is some evidence that it is active in the mouse brain, so it might have some direct effect. So if you become a geneticist, there’s lot more exciting work to do on sex!

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    16. Richard Mansour

      Molecular biologist and spatial analyst

      In reply to Michael Shand

      When opining on these matters it is important to be clear whether you are talking about prevalence of homosexual behaviour or homosexual orientation (i.e. the extent to which a person feels instinctive sexual attraction to one sex or the other).

      Of course the prevalence of homosexual behaviour varies from time to time and culture to culture. But I don't think any one knows whether the prevalence of homosexual orientation varies over time and between cultures. Its hard enough to derive an accurate estimate of the prevalence of homosexual orientation in contemporary Western nations, due to the residual stigma associated with male homosexuality, never mind other cultures and and times.

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    17. Michael Shand

      Software Tester

      In reply to Richard Mansour

      You are right, my guess is that we are all much queerer and straighter than we have lead ourselves to believe

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    18. Michael Shand

      Software Tester

      In reply to Nick Heidl

      I think this idea about knowing what one you are is misguided and I think you are looking at sexuality too ridgidly as if you are either gay or straight, that it couldn't change over time

      That if you were a gay women like Greta Christina and later in life you have sex with a man....what? have you been lying to yourself the whole time thinking your gay when your bi? or is she straight? Whats the TRUTH, you can't handle the truth...

      THat's not true, you can handle the truth and the truth is sexuality is fluid and will change over time, hence genetics can have some effect but not the only effect and you can't label people as straight, gay, bi

      I say label everyone Queer because they are

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    19. Michael Shand

      Software Tester

      In reply to Peter Campbell

      Because sexuality is fluid and changes across the course of your life, hence why genetics can have some influence but to state it is the only or the major influence I think is mistaken

      You might think your straight right now, if I talk to you in 40 years taht might change

      were you mistaken before? were you denying your genetics? have you been living a lie your whole life and didn't actual enjoy that sex that you thought you were enjoying

      No, it's fluid man, genetics impact on behaviour is limited by the fact that we have reasoning brains, maybe limited is the wrong word but it is not the final be all and end all.

      Also, I take issue with the way these articles are written, it could be a lot more boring and a lot easier to understand but that doesn't get clicks

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    20. Stephen Ralph

      carer at n/a

      In reply to Michael Shand

      Michael I think there is fluidity amongst a certain % of men and women - more men I surmise, b/c for males sex is often a casual need.

      But that % is far less than those who are either hetero or homosexual entirely - in my opinion.

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    21. Michael Shand

      Software Tester

      In reply to Stephen Ralph

      Get rid of the "Entirely hetero" Concept and you are right

      no one is entirely hetero, I can concieve of conditions under which they would be gobbling some man jewls

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  8. Comment removed by moderator.

    1. Stephen Ralph

      carer at n/a

      In reply to susan morrow

      Susan

      you opinion is your own, of course.

      God didn't say that at all.

      God doesn't exist.

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    2. Conor King

      Executive Director, IRU at La Trobe University

      In reply to susan morrow

      More the question is why you care what God thinks and says? You dont care what I think or say, why do you fuss about the God beast?

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    3. Peter Campbell

      Scientist (researcherid B-7232-2008)

      In reply to susan morrow

      So, you say "GOD says 'gay sexuality' is abhorrent to HIM", and
      presumably you also say god made people as they are,
      and we have evidence of an intrinsic genetic component to being gay,
      So, what can we reasonably conclude about the character of your god?

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    4. Nick Heidl

      logged in via Facebook

      In reply to Nick Heidl

      It's okay, I reported her for "Discredited research" LMAO

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    5. Deborah Cowell

      Teacher

      In reply to susan morrow

      Susan, this is a discussion about genetics, and established research. It allows people of differing sexualities to be treated with tolerance and understanding.
      Views like yours promote only intolerance, and misunderstanding. I do not think you really wish to give your religion a bad name with posts like this, but you have achieved it anyway.

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    6. Nick Heidl

      logged in via Facebook

      In reply to Alice Kelly

      Can I suggest to people not to reply to any of her coments, click on her name and you can see she just trollsw; she doesn't even follow the comments once she writes about her imaginary friend.

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    7. Robert Davidson

      logged in via Facebook

      In reply to Nick Heidl

      It would be great if you didn't ridicule theism by talking about such silly ideas as "imaginary friend", and keep in mind that theists include the majority of the world's leading thinkers throughout history. We are not dummies, and we are not all alike.

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    8. Robert Davidson

      logged in via Facebook

      In reply to Stephen Ralph

      Well that is certainly debatable. Odd that you make the claim like it's just a fact.

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  9. Conor King

    Executive Director, IRU at La Trobe University

    can anyone point to any harm in genetics or evolution from gay people ? Many gay people have children, this would be the greater in pre contraception times. so what else? nothing I would think.

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    1. Jenny Graves

      Distinguished Professor of Genetics at La Trobe University

      In reply to Conor King

      It’s not a question of any kind of harm done either by or to gay men. Rather the puzzle is why is homosexuality is so common. Since gay men have, on average, fewer children than straight men, you might expect the gay alleles to die out. My suggestion is that the high frequency of gay allele(s) is because they propagate themselves through the female relatives of gay males, who share (and pass on) their genetic variants at higher-than-average frequency.

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    2. Richard Mansour

      Molecular biologist and spatial analyst

      In reply to Jenny Graves

      My view about why homosexual orientation continues to exist is based on ideas in quantitative evolutionary biology. The shape of the frequency distribution of many personality traits is different in females compared to males. For almost any given trait, males show a wider, shallower bell curve than females. Another way of thinking of this is that you get more extremes of various sorts among men than in women. This is logical for humans because of the more diverse roles that males adopt compared to…

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  10. Gregory Thomas Hargreaves

    farmer/vet

    Good article. I was at Melbourne University in the 70's when I think it was Hans Eysenck was going to give a lecture and there was a lot of protest and discussion about Nature versus Nurture. As a farmer you can breed for intelligence in sheep dogs and temperament in dairy cows. P=G+E and it just seems common sense to me that there is a genetic component in all things biological including behaviour and sexual orientation. I was in a college on campus at the time and it was my first experience with trying to argue with intelligent people who were ignorant about science and wasting my breath.

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    1. Alison Moore

      logged in via Facebook

      In reply to Gregory Thomas Hargreaves

      I really enjoyed this article too. I hope we hear from more from Professor Graves.

      I am hopeful the forms of ignorance Gregory describes are actually dwindling. There are a few pear-shaped responses in this comments field, but actually not nearly as much of the kind I might have expected.

      Late twentieth-century thought was so haunted by that yoking to dichotomies and many people are still not prepared to accept that either/or reasoning misses the point of the subtle interactions between genes and environment.

      Admittedly too, for many years, certainly geneticists did talk as if there might be a 1-1 gene-phenotype relation, and even as the mapping of the human genome debunked that myth, the habit of thought still lingers in popular understandings of what genetics is about.

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  11. Mark Maughan

    Builder

    Fantastic article! Another explanation for the prevalence of non-heterosexuality amongst humans is our "odd" sexuality, that is, sex for recreation not just procreation. This is further supported by models of "group selection" as proposed by E. O. Wilson, whereby traits (such as altruism) are selected at the group level, rather than the individual level. Given "gayness" is most likely to be a spectrum trait, then could it not benefit us at the group level?

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  12. Michael Leonard Furtado

    Doctor at University of Queensland

    A wonderful article, Jenny, offering new hope for the millions of homosexuals and heterosexuals with a desire to contribute equally and without prejudice to an appreciation of human sexuality without having two-bob each way about sex and gender being two separate and clashing constructs.

    Genetic predisposition, like the colour of one's eyes and skin, goes a long way towards settling the out-of-date moralties that impose one standard for straight people and another for gays.

    That said, my view is that people who comment one way or another on your article should for ethical reasons announce their sexual orientation as I have done before posting so as to uphold the presumed high ethical standards of this site, as proselytism has no place where scientific fact is under discussion.

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    1. Jena Zelezny

      research for second PhD in Humanities and Social Sciences (Performance Studies/Theatre & Drama/Dramatic Literature/Visual Arts) at La Trobe University

      In reply to Michael Leonard Furtado

      Yes it's an easy solution Michael, but is it as simple as that?

      I'm more inclined toward Butler's theory of performativity.

      I feel there is more to gain by investigating the ways in which hetero-centicism has become a hegemony. After all just making a pre-disposition toward same-sex-desire a normative concept does not alter dominant social hierarchies.

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  13. Peter Hannan

    Teacher

    A few years ago while teaching biology in Mexico this question came up, and I ended up writing an article about it for students and others. Here are the references I found useful (some cited in the article above):

    Paul L. Vasey and Doug P. VanderLaan, Birth order and male androphilia in Samoan fa’afafine, Proceedings of the Royal Society B, 2007, 274, 1437 – 1442 http://rspb.royalsocietypublishing.org/content/274/1616/1437.long

    David A. Puts, Cynthia L. Jordan, and S. Marc Breedlove, O brother…

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  14. Josh Godda

    logged in via Facebook

    LOL!

    When scientist applied twin studies and GWAS tools to determine the genetic contribution to intelligence, the usual crop of excuses were trotted out as to why these tools were invalid. BUT when these tools are used to show that homosexuality has a genetic component, the tools suddenly become valid!

    This is funny stuff. Really funny stuff. I applaud "the conversation" for making me laugh tonight.

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    1. Peter Wilkin

      Australian Realist

      In reply to Josh Godda

      I can't think of any examples where an actual scientist hasn't been very clear about how much their results suggest one sort of influence or another. Science acknowledges the grey areas that many of us can't be bothered seeing.

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  15. Walter Roberts

    retired typesetter

    Anything that does not have some type of genetic selective advantage would have presumably been selected out during the evolution of any species.

    So…the immense number of homosexuals found in hundreds of animal species – including humans – would simply not exist if they did not naturally assist in the evolution of these species.

    And, for those of you who do not understand or believe in evolution, we might posit the question: Why exactly would an all-knowing and supposedly competent Creator produce…

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    1. Jena Zelezny

      research for second PhD in Humanities and Social Sciences (Performance Studies/Theatre & Drama/Dramatic Literature/Visual Arts) at La Trobe University

      In reply to Walter Roberts

      I find your argument warped particularly the genetic disposition of pedophiles. I do not feel it is valid to assume that a pedophile is/was necessarily a "strong male member of the species" nor do I see the logic in asserting that this male member's intention was to "guard the offspring".

      Pedophiles exploit(ed) the young - they do not/did not guard. Pedophiles are not/were not sexuallly motivated to guard. This is a false conclusion/conflation of intentions.

      One cannot "certainly imagine" that pedophiles "could have been a critical part of the natural survival of our species". The guarding of the offspring is/was a task undertaken by females not males.

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