The evolutionary puzzle of homosexuality

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In the last two decades, dozens of scientific papers have been published on the biological origins of homosexuality – another announcement was made last week. It's becoming scientific orthodoxy. But how does it fit with Darwin's theory of evolution?

Macklemore and Ryan Lewis's hit song Same Love, which has become an unofficial anthem of the pro-gay marriage campaign in the US, reflects how many gay people feel about their sexuality.

It mocks those who "think it's a decision, and you can be cured with some treatment and religion – man-made rewiring of a predisposition". A minority of gay people disagree, maintaining that sexuality is a social construct, and they have made a conscious, proud choice to take same-sex partners.

But scientific opinion is with Macklemore. Since the early 1990s, researchers have shown that homosexuality is more common in brothers and relatives on the same maternal line, and a genetic factor is taken to be the cause. Also relevant – although in no way proof – is research identifying physical differences in the brains of adult straight and gay people, and a dizzying array of homosexual behaviour in animals.

But since gay and lesbian people have fewer children than straight people, a problem arises.

Written By: William Kremer
continue to source article at bbc.co.uk

40 COMMENTS

  1. How can a trait like male homosexuality, which has a genetic component, persist over evolutionary time if the individuals that carry the genes associated with that trait are not reproducing?

    Interesting. Although why anybody would want to look into that, escapes me. You might just as well look into what makes people short or tall or left-handed. So what? Mind you, I imagine that a trait like male homosexuality, which has a genetic component,* can *persist over evolutionary time if the individuals who carry the genes associated with that trait are not reproducing, could be due to the fact that now, as in the past, many homosexual men married and had children. Places like Saudi Arabia must be teeming with homosexuals who are married, as would have largely been the case in the West until the 60 and 70s of the last century.

    • In reply to #1 by Net:

      Interesting. Although why anybody would want to look into that, escapes me.

      Well I guess we are even because how anyone wouldn’t find this interesting escapes me.

      You might just as well look into what makes people short or tall or left-handed. So what?

      Yes, and people do look into those things as well and I think they are also interesting but there is something extra interesting about homosexuality. The evidence from twin research indicates there is very likely a genetic influence. Twins raised apart usually have the same sexual preferences. But at first look it’s counter intuitive from the standpoint of evolution, why should there be a gene that encourages humans to waste reproductive energy on encounters that can’t lead to actual reproduction. It seems at first that a gay gene shouldn’t make sense. It’s similar to the problems of altruism, when we see something like that it’s a clue that there may be some interesting aspect of behavior that we can better understand and that understanding it may not just be an answer to the specific question but it may lead to a more general theory that explains lots of additional stuff as well.

      • In reply to #3 by Red Dog:

        In reply to #1 by Net:

        Interesting. Although why anybody would want to look into that, escapes me.

        Well I guess we are even because how anyone wouldn’t find this interesting escapes me.

        You might just as well look into what makes people short or tall or left-handed. So what?

        Yes, and people do l…

        No, I did say it was interesting – by way of concession, I guess. But what you mean by* being even* escapes me. Perhaps at some level you see posts and replies as competition: I’m more evolved and aware than you … If people find bringing a magnifying glass to trivial and irrelevant differences between people, then perhaps it’s because at some level they see themselves as superior. Far more interesting, and useful to delve into the physical causes of things which make people’s lives miserable.

  2. I was reading something by Dawkins recently where he mentioned a point that had never occurred to me before on this. I’m paraphrasing but he said something like “looking at modern humans and wondering about the evolutionary origins for their behavior makes as much sense as looking at circus animals doing tricks and wondering about the evolutionary benefit of jumping through flaming hoops” His point in both cases isn’t that we should never consider the evolutionary explanations but that the behavior that we exhibit as modern humans is influenced by many factors, with evolution being an important one but not the only one by far. In the case of homosexuality he made the point that it could be that the traits associated with a “gay gene” (assuming one exists) seldom if ever caused homosexual behavior in our hunter gatherer ancestors and such behavior is only exhibited in the modern world where the various influences on behavior are much different.

    That’s only one possible explanation of course, another would be that gay behavior turns out to be evolutionarily effective due to secondary effects on raising kin. BTW, none of this discussion IMO has any impact on whether homosexuality is moral or should be legal. How “natural” a behavior is does not impact how moral it is if it did rape would be moral.

  3. Would the gay allele or genes dictate the levels of the two hormones…Testosterone and Oestrogen…?
    Men and Women are made up of different amounts of both of these…
    Those men with high T and low O are macho males….those men with equalling levels of T and O might be gay or effeminate hetero men – Females with equalling levels of T and O will be gay or tomboy hetero girls and finally the women with high O and Low T as the girly girls….? is this kinda how it works ?

    • In reply to #4 by Light Wave:

      Would the gay allele or genes dictate the levels of the two hormones…Testosterone and Oestrogen…?
      Men and Women are made up of different amounts of both of these…
      Those men with high T and low O are macho males….those men with equalling levels of T and O might be gay or effeminate hetero men…

      If it were that easy, we’d already have an answer.

      • In reply to #13 by QuestioningKat:

        In reply to #4 by Light Wave:

        “If it were that easy, we’d already have an answer”

        I’m assuming that by ‘we’ you mean – you are gay …..or you just mean the world in general ? – Why do you assume hormonal causes are an ‘Easy’ answer ? What’s your answer to the question ?

  4. I’d love to read Richards take on this. As a rank amateur in genetics, I seem to recall that certain nucleatides like guarine (sorry if I’m butchering these spellings- it’s been a while) can in some sequences be substituted for another without affecting the survival-beneficial main trait or phenotype. But could such substitutions have unintended consequences?

  5. I am surprised people are questioning the worth of studying this. Consider the mental damage some “gay cure” homophobe religions do, especially to young people who may be unsure of their sexuality anyway. Plus the number of states that will happily gaol or kill gays and lesbians. This will not change things overnight and the battle against prejudice will take a long time but if we have positive evidence that homosexulaity is a natural genetic occurence we have something more positive to fight back with.

    • In reply to #6 by Stephen Mynett:

      I am surprised people are questioning the worth of studying this. Consider the mental damage some “gay cure” homophobe religions do, especially to young people who may be unsure of their sexuality anyway. Plus the number of states that will happily gaol or kill gays and lesbians. This will not change things overnight and the battle against prejudice will take a long time but if we have positive evidence that homosexulaity is a natural genetic occurence we have something more positive to fight back with.

      I know a lot of people, all of my gay friends probably, would agree with you but I vehemently disagree for two reasons.

      First, because what you are essentially doing is saying we should decide what research to do and what conclusions we want based on a political agenda. And I don’t care how much I agree with any political agenda (and I strongly support gay rights and equality) I think it’s always a bad idea to do research for political or other motives. Doing that inevitably leads to bias and bias means bad science. We should always go where the theories and the data take us and never have preconceptions about what we expect or hope to find. Of course being human few if any of us can ever completely live up to that ideal goal, there will always be some bias but starting out to do research with an explicit bias in mind is never a good idea.

      And second, and I think this is the most important point you are conceding far too much to the bigots in the way you frame the problem. Saying “if we have positive evidence that homosexulaity is a natural genetic occurence we have something more positive to fight back with.” implies that being gay is something that has to be explained and apologized for. I know you don’t mean it that way but if you think about it that is really what is behind these kinds of arguments:

      “it’s wrong to discriminate against me because I’m gay, it’s just genetics and I can’t help being gay”

      No one should ever have to explain or justify being gay. If we believe in personal freedom then one of the most essential freedoms is being free to chose who you make love with. Whether being gay is totally determined by the environment or heredity (I doubt it’s either one exclusively but for the sake of argument I”m saying IF) it still doesn’t matter.

      It’s why I hate the phrase “being gay is not a choice”. I agree it’s not a choice, if it were I would choose to be bisexual, I would have a much easier time finding someone to have sex with, but we shouldn’t even be defending it that way because even if it WAS a choice it should still be a legitimate choice for a human being to make in a society that values freedom and personal liberty.

      • In reply to #18 by Red Dog:

        >

        First, because what you are essentially doing is saying we should decide what research to do and what conclusions we want based on a political agenda.

        Not at all, what I am saying is a useful piece of research has come along and we should use it to our advantage.

        And second, and I think this is the most important point you are conceding far too much to the bigots in the way you frame the problem. Saying “if we have positive evidence that homosexulaity is a natural genetic occurence we have something more positive to fight back with.” implies that being gay is something that has to be explained and apologized for. I know you don’t mean it that way but if you think about it that is really what is behind these kinds of arguments:

        No again. I do not think it has to be explained but the bigots are making false statements about being gay being a disease and these should be refuted.

        All I have suggested is a bit of opportunism to use some research that can be helpful in a fight against bigotry, I think you are looking for some sort of hidden agenda that does not exist. I will fight prejudice any way I can but the best way is with solid evidence.

  6. Doesn’t this seem like a likely solution to this dilemma

    Another way a “gay allele” might be able to compensate for a reproductive deficit is by having the converse effect in the opposite sex. For example, an allele which makes the bearer attracted to men has an obvious reproductive advantage to women. If it appears in a man’s genetic code it will code for same-sex attraction, but so long as this happens rarely the allele still has a net evolutionary benefit.

    There is some evidence for this second theory.

    Plus the fact that so many gay men until the recent past would have married and had children.

    Michael

    • In reply to #11 by mmurray:

      Doesn’t this seem like a likely solution to this dilemma

      Plus the fact that so many gay men until the recent past would have married and had children.

      But what about before this time, when homosexuality wasn’t even in the minds of very early humans?

      • In reply to #17 by veggiemanuk:
        >
        >

        But what about before this time, when homosexuality wasn’t even in the minds of very early humans?

        I’m not sure I fully understand what you mean here, but how do you know what early humans did or did not think about homosexuality? Let alone whether they practiced it? Do we have any direct evidence?

        • In reply to #24 by BanJoIvie:

          In reply to #17 by veggiemanuk:

          But what about before this time, when homosexuality wasn’t even in the minds of very early humans?

          I’m not sure I fully understand what you mean here, but how do you know what early humans did or did not think about homosexuality? Let alone whether they practiced it…

          This confused me as well. There is certainly evidence of homosexuality a long way back. I’m not sure what evidence there is in hunter gatherer societies.

          Michael

          • In reply to #25 by mmurray:

            In reply to #24 by BanJoIvie:

            In reply to #17 by veggiemanuk:

            But what about before this time, when homosexuality wasn’t even in the minds of very early humans?

            I’m not sure I fully understand what you mean here, but how do you know what early humans did or did not think about homosexuality? Let…

            This confused me as well. There is certainly evidence of homosexuality a long way back. I’m not sure what evidence there is in hunter gatherer societies.

            To clarify, what I meant to say is, What about a time when being gay wasn’t an issue? This time must have existed at some point in the distant past.

            Could it be that before the advent of Human societies, homosexuality was just part of the norm like it is in other animals and only with the advent of structured societies were people made to conform to some sort of standard?

          • In reply to #26 by veggiemanuk:

            Ah OK I see what you mean. So instead of assuming that up until a few decades ago gay men were secretly marrying and passing on genes there would have been a long period of evolution when they weren’t. Which impacts the argument about how the genes spread.

            Thanks for the clarification.

            Michael

          • In reply to #27 by mmurray:

            In reply to #26 by veggiemanuk:

            Ah OK I see what you mean. So instead of assuming that up until a few decades ago gay men were secretly marrying and passing on genes there would have been a long period of evolution when they weren’t. Which impacts the argument about how the genes spread.

            If we ignore the distant past for the time being and assuming that the spread of the gene was indeed helped by (Closeted) homosexuals marrying and having children, what then might the impact be on this gene in the next few generations, especially in the west where the need to ‘Blend in’ and have children has and continues to diminish?

            Could we see (I’d rather hope not) see a genuine decline in homosexual numbers as the gene is selected out?

          • In reply to #26 by veggiemanuk:

            “Could we see (I’d rather hope not) see a genuine decline in homosexual numbers as the gene is selected out?”

            I wondered that same thing, but at the same time it wouldn’t surprise me if more people start taking more advantage of surrogate mothers, or if it became more common for gay and lesbian couples to have children together, or if people hit on some other solution. I wouldn’t try to predict it.

            I also wonder how much more likely a gay person is to have a gay child. There’s surely a more accurate way to put this, but my understanding is that everyone has some “potential” to have gay children. Mothers who have already had sons have higher potential. Do gay people have much higher potential as well, or do epigenetic factors, or hormonal factors in the womb play a dominant role?

            The most surprising fact for me was that there’s only a 20% likelihood for the identical twin brother of a gay man to be gay himself. That would seem to rule out all sorts of theories that I’d heard before. If anyone can explain how or why identical twins wouldn’t be subject to the same epigenetic factors, I’d be very interested to learn.

    • In reply to #11 by mmurray:

      Doesn’t this seem like a likely solution to this dilemma

      Another way a “gay allele” might be able to compensate for a reproductive deficit is by having the converse effect in the opposite sex. For example, an allele which makes the bearer attracted to men has an obvious reproductive advantage to w…

      This seems the most likely to me. Consider that each of us (especially males) actually hold a complete human genome in our DNA, and somewhere in there, whether it’s switched on or off, are the genes for developing both same-sex and opposite sex attractions. That they can be switched around in a (statistically consistent) minority of cases, regardless of whether it’s directly inherited or due to hormonal influences during development, isn’t at all surprising.

  7. Both Peter and his brother Modest Ilyich Tchaikovsky were gay, which fits in with the research findings that homosexuality is more common among brothers and relatives on the same maternal line.

    • In reply to #12 by Stafford Gordon:

      Both Peter and his brother Modest Ilyich Tchaikovsky were gay, which fits in with the research findings that homosexuality is more common among brothers and relatives on the same maternal line.

      Notice how women, once again, are absent from research.

      • In reply to #14 by QuestioningKat:

        Notice how women, once again, are absent from research.

        It’s not nearly as much of an evolutionary puzzle for women as it is for human males. Keep in mind all I’m going to say here is about our primitive hunter gatherer ancestors not about how I think it is or should be in the modern world.

        For women whether to procreate again isn’t such an obvious choice. Women get stuck with most of the child rearing in primitive tribes. So if a woman gets pregnant again she is taking considerable resources away from her existing children. It’s not always the best choice from the standpoint of maximizing reproductive success. It may make more sense to just stick with the existing children and maximize their reproductive success rather than investing in another child and bringing the reproductive success of all of them down.

        Also, the benefits of lesbianism — at least intuitively — are more obvious. And again it comes down to women getting stuck raising the children. It makes a lot of sense to me that women could procreate a few times and then decide to stick together with each other and raise those kids and that would be a very effective reproductive strategy.

        I’m not saying it’s all figured out for the women, not by a long shot, just that at a surface level it seems more intuitively understandable from an evolutionary standpoint than for the men because for the men the best reproductive strategy is to just procreate as often and with as many women as possible.

    • In reply to #12 by Stafford Gordon:

      Both Peter and his brother Modest Ilyich Tchaikovsky were gay, which fits in with the research findings that homosexuality is more common among brothers and relatives on the same maternal line.

      It’s funny, when I first read about the great composers (this was back when they still called the piano the pianoforte, well not quite that far back but a long time ago) many of the most well read authors on music history were still tip toeing around the issue of whether Peter was gay. “Well he never married but maybe he just never found the right woman” Well no one said anything that outrageous but it wasn’t just considered an obvious truth the way it is now.

      But I don’t think the fact that Peter and his brother were gay supports either theory all that much. If you believe in alternate theories such as “domineering mother and weak father leads to gayness” (which I think are total rubbish) you could defend your rubbish against the evidence that Peter and Modest were gay by pointing out that they were both raised in virtually identical environments and hence had the same behavioral cues and influences as children.

      That is why of course the twins raised apart studies are so useful, and from what I’ve read they show a very strong tendency for such twins to have the same sexual preference.

    • In reply to #12 by Stafford Gordon:

      Both Peter and his brother Modest Ilyich Tchaikovsky were gay

      Interesting about Modest, meaning, I rarely hear about composer’s siblings.

      Purportedly, Pyotr was forced to drink some sort of deadly cocktail, for being homosexual. Really hope this is just urban myth, but then, look at Alan Turing. Ach :(

      • In reply to #31 by bluebird:

        In reply to #12 by Stafford Gordon:

        Both Peter and his brother Modest Ilyich Tchaikovsky were gay

        Interesting about Modest, meaning, I rarely hear about composer’s siblings.

        Purportedly, Pyotr was forced to drink some sort of deadly cocktail, for being homosexual. Really hope this is just urba…

        Robert Winston, Professor of Science and Society, has an occasional programmes on BBC radio 4, which delves into the medical reasons for the demise of historical figures, and which of necessity deals with their milieu, and apparently Russian society in Tchaikovsky’s time was not at all hung up about homosexuality, so the idea that the composer took his own life looses much of its persuasiveness.

        However, his letters reveal his passionate love for one of his servants, so perhaps his affections went unrequited and that led to his suicide; but if I wield Ockham’s razor here, I’m led to think that the most likely cause of his death was drinking unboiled water contaminated with Cholera.

  8. You might just as well look into what makes people short or tall or left-handed. So what?

    Has anyone taken a survey of gay people to see if they care? I think many do. I know many do. With religious wingnuts slamming your life and complete existence on earth, it seems as if any information that can be stuck in their face would be equivalent to giving them the finger and exhaling a bit. Any facts that run contrary to the Bible thumpers is a win. I find it interesting that whenever there is news or positive outcomes on a debate with Creationists people comment positively. Some here even like to stick it to Creationists who visit this site and probably feel a little proud of themselves afterward. Yet, some here see no benefit of this type of research. Gays have been beaten, murdered, bullied, discriminated against and even kicked out of their own biological families. Why? It boils down to either the “ick” factor or a belief that they have chosen an evil sinful path in life. Any bit of info that shows that the religious are wrong and perpetuating evil is a good thing. I say keep the research coming – step it up and stick it in the face of the mother fuckers.

  9. I found the book with the paper from Dawkins where he talks about homosexuality. Here is the exact text I was paraphrasing last night:

    Civilized human behavior has about as much connection with natural selection as does the behavior of a circus bear on a unicycle. And if that sounds unduly negative it’s not intended in that spirit. The analogy is rather apt. The tricks of circus animals usually tend to be based on the natural behavioral repertory of the species.But we still have to be cautious about interpreting such antics in a simple Darwinian way. Similarly, there probably is a connection to be found between civilized human behavior and natural selection but it is unlikely to be obvious on the surface.

    From The Natural Selection of Altruism by Ridley and Dawkins in Altruism and Helping Behavior edited by Rushton and Sorrentino

    The paper is mostly an overview about biology and altruism. It’s an excellent overview, I knew most of what they said but it’s one of the clearest expositions of the basic ideas I’ve seen, there was just a bit about homosexuality at the end because that behavior was used as another example of something that like altruism at first seems to be a puzzle. Also, some of the same models proposed for altruism have been proposed for homosexuality.

  10. Another puzzle about homosexuality is: why do men get so bent out of shape about other gay men? This is something that really has puzzled me. And as gay rights become more accepted by most of the population the way a few men just go insane over it still puzzles me. I remember a long time ago when one of my gay friends introduced the word homophobia to me at the time I thought it was just PC BS driven by pop psychology but the more I look at it the more I think he was right.

    And just now I came across a really interesting bit of research, not pop psychology but actual science, in one of Trivers papers on self deception that supports the idea. They found that there was a strong correlation between men who were actually aroused by homosexual pictures but denied having any homosexual urges and men who answered questions with an anti-gay bias. Essentially the tension from self deception may be what causes the men to be homophobic. Now this is an example of some research I think we should put in the faces of the anti-gay rights people. Speaking of things in faces ever notice how men opposed to gay rights often talk about having it “shoved down their throats”?

    The Trivers paper is The Elements of a Scientific Theory of Self Deception.

  11. It’s worth clicking on that first link “sexuality is a social construct” just to remember that even people on the side of all that’s good and right in the world can also be unbearable jackasses. “Science tells us X is true. No it isn’t. Science tells us Y is true. No it isn’t. Did you know Nazis were scientists? Science tells us Z is true but it’s not. Quack quack quack.”

  12. Interesting to see how they use the word “theory” all over the place.

    “…but one theory is that with each male pregnancy, a woman’s body forms an immune reaction…”
    “…then the helper in the nest theory may partly explain how…”
    “… is shared with nieces and nephews and so, the theory goes, the genes which code for sexual …”
    “…There is some evidence for this second theory. Andrea Camperio-Ciani, at the University of Padova in Italy…”
    “…Therefore, the theory goes, a low “dose” of these alleles enhances the carrier’s chances of reproductive success. …”

    I believe these are all “hypotheses”, and not “theories”.

  13. I wasn’t really listening, but today I think I heard a news item saying that Putin and his fellow thugs would reconsider their anti gay legislation if science could prove homosexuality was genetically derived.

    Big of them!

    Personally, I’ve always had my suspicions about Vladimir; methinks the gentleman protests too much.

    And the way he puts himself about: riding bears, bear back horse riding, gallivanting about topless; could it be that he’s secretly one of the Village People?

    • I think you’re on to something, SG! I remember an old Bobcat Goldwaithe routine where he portrays a homophobic bully who has found a target to torment. He then starts pantomiming pummeling the target while firing off a litany of insults to support the pummeling:

      I hate you because you’re gay, and you’re a faggot, and I hate you because you talk funny and dress funny, I hate you because you’re different…and I hate you [punches getting weaker] …because…you’re kind of cute…

      In reply to #34 by Stafford Gordon:

      I wasn’t really listening, but today I think I heard a news item saying that Putin and his fellow thugs would reconsider their anti gay legislation if science could prove homosexuality was genetically derived.

      Big of them!

      Personally, I’ve always had my suspicions about Vladimir; methinks the gent…

    • In reply to #34 by Stafford Gordon:

      today I think I heard a news item

      Was it Uganda’s president signing a convoluted anti-gay bill today, that you heard, perhaps?

      I say convoluted: a quick scan of other articles suggest he personally may not be hard core anti-gay, but rather it was officials, citizens, etc who “forced” him to sign. Also, the bill may have been watered down by the time he signed, due to politics.

      Conversely, a take-no-prisoners anti-gay bill in Arizona was just shoved to Gov. Brewer.

      I don’t understand the downright abhorrence that leads to drafting laws against homosexuality for consenting adults. Even in practical terms, how would it be policed?

      • In reply to #36 by bluebird:

        I don’t understand the downright abhorrence that leads to drafting laws against homosexuality for consenting adults. Even in practical terms, how would it be policed?

        Surely the same way it used to be 50 years ago. Raid all the gay bars and bath houses, arrest anyone in them, make sure they accidentally trip up going into the cells. Two men check into a hotel, call the local police, arrest them. Take them to the local station. Beat them up because they resisted arrest. etc. etc.

        Michael

  14. Another possibility is that gays tend to have skills or competences that straights tend not to, for instance to understand how both women and men think better than straights would the other (*). This would benefit their relations, and thus their genes: not those in their own bodies, but those of their relatives. If families with gays did better than families without, that would seem to alleviate the paradox. This is kin selection, and I think Richard has spoken about it as the “gay uncle” hypothesis. It’s not sufficient by itself, but it may point to lines of investigation.

    (*) note this is a significant simplification– sexuality seems to have many more dimensions than one might expect. I’m using gays as short hand for atypical configuration of sexuality that leads to reproduction not occurring. That would include celibates, for instance.

  15. In reply to #1 by Net:

    why anybody would want to look into that, escapes me. You might just as well look into what makes people short or tall or left-handed. So what?

    Height and handedness are both studied. Science! Seriously, it’s all part of understanding how humans work. Surely you can see how that’s useful?

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