Darwin Day 2015 Questions: #4 How does evolution explain homosexuality?

Mar 24, 2015

Richard Dawkins answers your questions about evolution in honor of Darwin Day 2015.

“For things such as homosexuality, which people who argue against evolution ceaselessly will insist, there appears to be no linear Darwinian reason to possess this trait”

Edited by Stephanie Renee Guttormson

Copyright 2015 Richard Dawkins Foundation for Reason & Science

164 comments on “Darwin Day 2015 Questions: #4 How does evolution explain homosexuality?

  • While it is good that Richard introduced the idea of interaction between genetic predisposition and environment, I think in general he should stay away from questions like this, which presuppose that sexual orientation is a clear cut behavioral phenomenon, like being tall or athletic. Sexuality, like personality in general, is way more complex than that. His example of identical twins is misleading because there are many cases in which only one of the twins is homosexual, so the question is not answered. Ironically, I think we have more to learn from the old Kinsey square in which sexuality existed on a continuum, with a wide variety of factors all contributing. I speak as a lesbian who in my years of political activism, have come in contact with literally thousands of other lesbians, and have found every conceivable combination: from women who were genuinely happily (heterosexually) married and found lesbian love late in life (sorry for all the Ls) to women who knew from earliest childhood they loved only their own sex. I cannot speak with such authority about men, but wonder why they would be different.

    I might add here that rigidly sexually segregated societies have enormous amounts of pre-marriage male homosexuality before the young man is married off for the purpose of founding a family. That puts homosexual behavior into a far higher percentage of the population, to the point it is almost normalized. And should we count public school lads who have crushes, or who masturbate together as homosexual? When you consider that, it becomes much harder to define who is homosexual and who is not.

    My point is that it is not a good question. It is like asking “how does Darwinism explain heroes or novelists?



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  • Forgive me if I’m talking about things that I know not-well-enough to talk about. I’m open to any thoughts that will help me understand this subject more.

    Genetic drift within a group (i.e. in this case the passing along of genes that promote homosexuality) would only be selected against if it presented an obstacle for the group. If the appearance of this phenotype was rare enough, which seems to be the case with homosexuality, I don’t think that it would present an obstacle for the genotype of the group and thus could remain in the gene pool. Sexuality seems to be comprised of a great many factors as well, and mutations that encourage homosexual attraction could wax and wane in a number of ways throughout time.



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  • Of course sexuality is complex and is not completely determined by genetics. I’m sure Prof. Dawkins would agree. But what makes you think that athleticism or even height are completely determined either? The evidence is clear that they are not. If you took Michael Jordan and raised him in a culture that looked down on athletics as only for the “lower classes” most likely he would have grown up to be an investment banker or anything but a great athlete. Why do you think so many great athletes in the US are african american? There may be some genetic aspect to it but for the most part it is because for many poor blacks athletics were highly valued and one of the few ways out of poverty. And while height is certainly genetic it is actually a myth that the increase in height over the last centuries is primarily genetic. Steven Pinker talks about this in one of his books, the main reasons are better nutrition, pre-natal care, etc.

    Or consider language. There is overwhelming evidence that humans have a genetic predisposition to learn language (again read Pinker, this time The Language Instinct and The Blank Slate) but that of course doesn’t mean that language is completely determined by genetics, if it were we would all speak the same language.

    The fact is that for just about ANY behavior (and not just human behavior) the causes are complex and some combination of genetics and environment/learning.



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  • I’m not sure what you mean by genetic drift there or how it is supposed to relevant but there clearly IS a very strong selection pressure against a “gay gene”. Human males that have a preference for homosexual behavior will not have as much reproductive success as males that only are attracted to females. There are all kinds of examples in biology where genetic changes that yield relatively minor increases or decreases in reproductive success are selected for or against, far less than what seems would be the result of a “gay gene”.

    I’m not saying that there can’t be a genetic component to homosexuality, actually I haven’t even listened to what Prof. Dawkins says here but even before watching that I think the science isn’t conclusive either way yet but if there is a “gay gene” it is a bit of an evolutionary puzzle. Which doesn’t mean it can’t exist, indeed it is why it is such an interesting topic to study because puzzles, things that seem to conflict with the current paradigm often are a way to make interesting breakthroughs and discoveries.



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  • I’m given to understand that Bonobos enjoy a whole range of homosexual behaviors and they aren’t going extinct -because of that: they have their cousins Sapiens to help them off existence.

    So I wonder: before we were able to override biologically defined strategies with cultural based idiosyncrasies, would homosexual behaviors really be a significative disadvantage?
    Because, if you think about it, you don’t need a lifelong commitment to heterosexual intercourse in order to have a considerable offspring.



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  • but there clearly IS a very strong selection pressure against a “gay gene”.

    There’s a caveat to that: only if that “gay gene” would prevent you to have offspring. In other words, only if you have individuals that are heterosexuals XOR homosexuals.
    Questions:
    1) Is this the case?
    2) If it is the case, is that genetically encoded or is it a cultural artifact?



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  • Lorenzo Mar 24, 2015 at 6:42 pm

    So I wonder: before we were able to override biologically defined strategies with cultural based idiosyncrasies, would homosexual behaviors really be a significative disadvantage?

    I think we have been over some of these issues before, but in extended families, non-breeding siblings, support the offspring and social group, led by the alpha male(s) and/or female(s) who are their parents:- improving the survival and reproductive chances of close relatives.



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  • No, that is wrong. It doesn’t require that a particular gene has to completely prohibit you from reproducing in order for that gene to have evolutionary pressure to be replaced by an alternative. In fact very few changes to the genotype of any organism are caused by such radical effects on reproductive success.

    Consider the “arms race” among species like Peacocks to have ever brighter feathers to better attract mates. It isn’t the case that the Peacocks with less bright feathers can’t get mates at all only that the ones with brighter are slightly more likely to get them. In fact the differences in reproductive success can be very small and still one gene (e.g. the straight gene) can quickly replace another (e.g., the gay gene).

    I forget where I read it, I think it was the beginning of his book Social Evolution but in something by Trivers he showed a hypothetical example of two alternatives for a gene, call them the A version and the B version. Even if A only had a very small percentage decrease in reproductive success compared to B (all other things being equal) he showed through a simple mathematical model that the B version would quickly replace A in only a few generations.

    Of course it is the “all other things being equal” that is the caveat. It could be that while the “gay gene” makes it less likely for males to mate with females it encourages their selfish genes through nephews, etc. Although I find that doubtful, for one thing those models work much better for Haplodiploid insects who share much more DNA with cousins, etc. than with mammals. I think the second argument Dawkins gives here, that the “gay gene” may only be expressed as gay behavior in modern (modern being at least back a few thousand years) societies is the most likely although as I said in an earlier comment from what I know it is still very much an open question.



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  • I would like to posit here an idea I have, or should I say an observation regarding how people look at evolution and how it might be better explained regarding homosexuality as well as other traits.
    I am only a layman with regards to evolution but I often see that people almost invariable look at evolution as a process that takes place in individuals. What I mean by that… well, let me propose another possible explanation for homosexuality as an evolved trait in a community.
    Consider the possibility of random mutation in any given individual. This mutation may not always be active and may not even be expressed in the individual with the mutation. If however that individual is able to reproduce, that genetic mutation can be dispersed among a community or family. Now consider two or more such communities one of which expresses this mutation in a small percentage of its population. During times of food shortage, the community which expresses homosexuality could have a better chance of survival as it could naturally regulate its own population. If I am not mistaken, there is a clear increase in homosexual tendencies in high population environments. This would be consistent with my hypothesis.
    Given that as a living organism like every other organism, reproduction lies at the very heart and nature of our existence, it seems particularly likely, or should I say efficient, to switch the proverbial track rather than completely stop the train. Diminishing our sexual drives would reduce our chances of survival but introducing homosexuality into a community when it gets too large actually would improve the survivability of the community as a whole. If the genetic trait is only expressed under certain conditions, it becomes a distinct advantage to the species.
    Please let me know if you think what you think of this hypothesis or if you have ever heard anyone ever express a similar notion.



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  • 11
    Lorenzo says:

    Dawkin’s over that in his video response as well but that was not my point, actually.
    What I meant is in the paragraph next to the one you quoted: it is assumed that homosexual behaviors are inherently a disadvantage from the perspective of natural selection; this requires evidence, it cannot be assumed.



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  • 12
    Lorenzo says:

    No, that is wrong.

    No, you got it wrong (and I didn’t help because I forgot a “significant” in front of offspring, apologies). My point is: it’s being assumed that a) homosexuality is a disadvantage in reproduction because b) it tends to be exclusive. Those two points have to be substantiated with evidence and cultural idiosyncrasies have to be dealt out -since culture is too recent an innovation to have had a significant pull on sexual strategies, I suppose.
    If you will, if you don’t count modern technologies, all you need to do to have N children is to have heterosexual intercourse N + M times, where the M is the number of “misses”. This hardly requires a lifelong commitment to heterosexuality.

    the second argument Dawkins gives here

    Is fascinating and, I think, more likely to be true than the “safe when left with the ladies” argument. But, still, it implies that homosexuality is, on average, on the rise (for those few thousands years) and that, again, needs substantiation.
    Also, it’s tailored to humans, but humans are not the only life forms engaging in homosexual behavior: that aspect should be taken in account, too, I think: I don’t see any reason to consider homosexuality among H.S.Sapiens separately from that of the rest of the other species’.



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  • Prof Dawkins never raised the hypothesis that homosexuality is a product of defective development in utero and so it is not genetic. Basically, through incorrect dosage and timing of hormones, a male XY embryo ends up with an anatomically female brain. The brain is the location of sexual orientation, not the genitals or the XY or XX genes. If a hypothesis can answer observed data it gains weight.

    (BTW, this explanation has some supporting evidence but is not yet definitive.)

    It explains why homosexuality persists over history in not only human populations, but animal populations over time, where if it were genetic, it would be selected against and disappear. A genetic explanation cannot explain persistence.
    It explains why anatomically female brains are found during autopsy in male homosexuals. And visa versa. A genetic explanation fails this entirely.
    It explains the spectrum of sexuality depending on the erroneous dosage, not genetics. Someone above mentioned the Kinsey square. I’ve also heard it referred to as a dumbbell curve. Human sexuality is smeared across a continuum.
    It provides an explanation that can explain the homosexual manifestations of observed behaviour.
    It explains the identical twin effect, which may have been due to differential hormonal bathing of each embryo during gestation.
    It disposes of the choice argument proposed by conservative religious bigots. It portrays the homophobic as people equivalent to racists enacting prohibitions on the basis of difference. You don’t ban cerebral palsied people from being able to marry.

    When tested against Ockham’s Razor, this hypothesis scores more highly than competing theories I’ve looked at.

    Prof Dawkins or any other contributor. If you are monitoring this discussion, do you have any views on the above. Where does this hypothesis fail.

    Experiment. Monitor a population of pregnancies testing for ratio’s and timings of hormones. Follow the children long term to 25 years old. If there is a correlation between homosexuality and in utero hormone levels and timings that vary from the mean, it may test this hypothesis. An excess of female hormones or a failure of the male hormones to arise at the three month point in embryonic development results in a miss-orientation of brain and body genitals.



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  • This is in response to your reply to me above. Now I see what you mean. It took me a while to get it because it just seemed so obvious to me that a male who is bisexual will spend less time mating with females than one who is completely straight and so clearly there is a reproductive disadvantage.

    But now I think I get your point and it’s an interesting take that I hadn’t considered before. It isn’t how many times you have sex that matter its how many times you have sex that results in pregnancy and it is at least conceivable that being bisexual wouldn’t decrease the males number of successful sexual encounters. Although I still think it is doubtful but I agree it is an empirical question that we shouldn’t assume an answer to based on intuition. I could even see how perhaps homosexual relations (e.g., with powerful members of the tribe) would increase the males status so that while having less female encounters the male has more chances for encounters with high status women, with women who aren’t already pregnant, etc.

    Of course that is really only viable for a “bisexual gene” rather than a “gay gene”. But I could see some combination of your idea with Dawkins idea. In pre-modern cultures the gay gene resulted in bisexual behavior where as in modern cultures it results in purely gay behavior.



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  • 15
    mistermack says:

    The post about hormones is an attractive comment, but the fact still remains that the identical twin effect shows a genetic component. It may be genetics that causes the hormone phenomenon.
    The genes that lead to homosexuality might not have a wholly negative effect though, in the overall chances of successful reproduction.
    While in some individuals their result might be negative, in others, it might be positive.
    They might produce a less aggressive, less violent, but sexually straight male, who is more attractive to females than a male who got a bigger dose of male hormones. So the success of these non-gay males could produce a higher percentage of gay males as a by-product of their success.
    I’m not claiming that as the answer, I’m just trying to show that genes can have a complicated result, and their persistence in the population may be due to a more subtle advantage than the black and white view of sexuality as either gay or straight.



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  • I’m just trying to show that genes can have a complicated result, and their persistence in the population may be due to a more subtle advantage than the black and white view of sexuality as either gay or straight.

    There may be a genetic component buried deep without our genome. It may be that the twin effect, where the “Gene” is present, leaves them more susceptible to the effects of non mean hormonal floods.

    And there is nothing black and white about human sexuality. Human sexuality is smeared across of a whole spectrum of tendencies. This factor alone should make it obvious to the blindly religious that males and females are not immutable templates. Straight. Gay. Lesbian. Bisexual. Transgender. With percentages and combinations of all of the above. If this is the best that god can design then he either doesn’t exist or there needs to a class action law suit by all of humanity.

    What incenses me is that anyone could discriminate against anyone on the basis of a different sexual preference. Non of your business.



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  • If the hormonal effect in utero theory applies, I would strongly object to the term “erroneous dosage’. There is no “correct” dosage. Sexual inclination, like temperament and personality, spreads across a wide spectrum and a male fetus who emerges as a (potentially) homosexual male is not defective or an ‘error’. This argument comes dangerously close to the ‘homosexuality is a sickness’ assertion, and I think most of us are past that.



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  • An after thought Justine. If this science is correct, distasteful though it is to you, it defeats immediately the religious bigots argument of “choice”. It moves the political campaign for equal rights out of the morality morass, and into science. It removes all arguments from the prejudiced religious bigots. The science doesn’t care what you think. Any thoughts.



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  • 20
    Lorenzo says:

    That’s exactly my point. It also took me a while to word it in a comprehensible manner, I’m afraid. Anyhow: we’re on it.

    Of course that is really only viable for a “bisexual gene” rather than a “gay gene”.

    I’m given to understand that there has been some search for the “gay gene”, and nothing has been found. I admit I’m really not aware of any papers on the matter or whatever, it’s just a notion.
    If I were to research the matter, and if it were actually true that a “gay gene” hasn’t been found, I’d start over by considering homosexual behaviors as a variation of a biological strategy -thus likely in correlation with a number of genes, which in turn will have also other effects, which in turn would result in a more complex picture when it comes to natural selection.

    In pre-modern cultures the gay gene resulted in bisexual behavior where as in modern cultures it results in purely gay behavior.

    Yes, and here’s what I was talking about when I mentioned cultural idiosyncrasies: they may result in a polarization of sexual orientation or a smoothing of said polarization. I doubt culture has had time to exert a significant pull on the genotype, but it surely exerts a pull on behavior.
    If I don’t remember incorrectly, a situation not too dissimilar to the one you hypothesized in your comment was present in ancient Greece, as far as male homosexuality was concerned: it was tolerated and, in some instances, even praised. On the other hand, female homosexuality was despised -perhaps even more strongly than “today”.



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  • Basically, through incorrect dosage and timing of hormones, a male XY embryo ends up with an anatomically female brain. The brain is the location of sexual orientation, not the genitals or the XY or XX genes.

    What are some papers, or at least the best one that proposes this and supports it with evidence? The idea that gay men have “female brains” sounds to me like the kind of bad science that was around when the DSM listed homosexuality as a psychological disorder but has since been discredited. I could be wrong, I haven’t read much in this area but this sounds very much like pseudo science to me.



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  • The population control hypothesis would be supported more if the current “proliferation” of homosexuality were accompanied today with a decrease in resources, not just a higher population. Instead, we have an increase in resources as well as a higher population, so scarce resources would appear not to be the trigger.



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  • I have read in Richard’s book A Devil’s Chaplain that difference between hetero and homosexuality is one piece at the top of X chromosome. The X chromosome can be inherited from the mother side. Therefore males are not “guilty” for transferring homosexuality. Males will, without knowing, copulate with females that also carry genes for homosexuality and on that way transfer this sexual orientation on the next generation. I think this is good explanation.



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  • No, the problem is with language, homosexuality does not exist, it is a sociological construct, also problem with labels and categories, a false dichotomy. The Greco-Roman world would not have recognized it as such. Many men and women can respond to their own sex anatomically and physiologically, however, many chose not to do so, it is choice, many do not identify themselves as “gay”, also a cultural/sociological label. Don’t believe me, go to a site such as Sean Cody.com, where heterosexual men (very muscular and “masculine”) respond sexually to other men, but, that does not mean that they regard themselves as “gay”. They do it for money, as do incarcerated men with other men when those of the opposite sex are not available. In other words they are capable of responding sexually to those of their own sex. it is on a continuum, as Kinsey demonstrated, some are bi-sexual, some are same-sex oriented for part of their life, heterosexual later, some never respond sexually to their own sex, but can. And of course, may “gay” men produce children. What did they say about Julius Caesar? Every woman’s husband, every man’s wife! Go figure, human behavior is very variable. Language, labels can be a snare and a delusion.



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  • I think David R Allen has come up with a most interesting explanation of the origin of homosexuality. The fact that we all start as females, and that hormones changes 50% of us into males opens for all sorts of intermediates from variations in hormone levels. To me this seems like a plausible explanation of the wide range of sexual behaviors and expressed personalities, in man as in animals, and it leaves out the need for complicated explanations from natural selection, which Mr. Dawkins clearly has a difficult time to find. I don’t know why female homosexuality is left out, but lesbianism is also well covered in David’s theory. There is also a range of physical intermediates between male and female, persons with both male and female sexual characteristics, again being well covered by David’s theory.

    To-day, as in the past, homosexuals are just as fond of children as heterosexuals, and there is no hocus-pocus if they wish to have children of their own. Trusted homosexual males staying home to protect women and cousins and thus taking the opportunity to fertilize someone else’s woman seems somewhat far fetched and unnecessary to me.

    I do not think that scientific explanations of homosexuality / bisexuality will ever remove religious people’s fear of sexuality and their clinging to stupid texts in the Bible and Khoran. Fear is a basic component of all religions. For the rest of us who do not fancy Bronze Age Desert Gods and the Laws written by mentally disturbed men, should really appreciate and enjoy the wide specter of sexual and personal varieties and acknowledge that the treatment of our fellow humans must be based on love, empathy, compassion, tolerance and respect.

    I will advice Mr. Dawkins to spend some money on educating his photographer / editor. Picture composition is really bad, and Dawkins suddenly, and with no motivation, looking somewhere else while talking to us, indicates he is talking to another person in the room. This is clearly not the case which is revealed when cutting to the other camera and there is no one else there but Dawkins. Most irritating, takes your concentration away and gives a very amateur look and feel. Nice advertising for buying tulips, however.



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  • 26
    Michael Paul says:

    Might it be possible that the homosexual tendency in humans and other animals is a preventative gesture against over population. I’m a musician and certainly no scientist but I’m surprised that no-one seems to have posited this as a reasonable explanation.

    I await to be enlightened 🙂

    Good wishes to you all.



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  • As I understand it, male pattern baldness (no genetic advantage that I can discern) is genetically carried by the mother (only) and manifested in sons (only). Is the reason known? I agree with someone else on the chain who said that this is a question that is out of the expertise of Richard. If homosexuality is heritable as Richard states, the manner of transmission and reason there has been no natural de-selection should be a topic for genetic research, not an item of intellectual speculation. Until there is better science, non-geneticists need to leave it as “not yet understood” rather than falling into the trap of inventing a Golden Chariot Flying Across the Sky to Create Daylight story. It is OK if we don’t know yet.



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  • That is sort of what I was getting at, William. I dislike any brow-furrowing “study” of homosexuality as if it were a problem that must be done away with. In my first remark, I mentioned adolescent boys in societies that rigidly separate the sexes, and in public schools, who form intense emotional and often sexual connections with other boys — and later marry. Is that homosexuality? Should we be examining their genes to determine what caused that? The penis, as I understand it (not having one) can respond to a wide variety of stimuli, not just naked women. Freud suggested that humans are ‘polymorphically perverse’ and while I don’t care for the term ‘perverse’ I like the idea that all healthy humans, i.e. who have sexual urges, at least start off having them indiscriminately and that social (and economic) necessity directs us in one direction or another.



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  • bocaj Mar 25, 2015 at 11:50 am

    I think David R Allen has come up with a most interesting explanation of the origin of homosexuality. The fact that we all start as females, and that hormones changes 50% of us into males opens for all sorts of intermediates from variations in hormone levels.

    As with many variations, throwbacks and abnormalities, there is still a range of sexual diversity in humans.

    http://www.dailymail.co.uk/health/article-2107085/Caroline-Kinsey-lived-man-41-years-parents-didnt-tell-shes-hermaphrodite.html

    .Caroline Kinsey, 42, was born with both male and female sex organs but was raised as a boy.
    She didn’t find out she had Disorder of Sex Development until she was 19

    She began dressing as a woman two years ago and now plans gender surgery



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  • The discussion as you presented it was about ‘erroneous’ amounts of maternal hormones having a deleterious effect on the development of the male fetus. That is not science; it is your proposal and has no more validity than the proposal that homosexuality is a form of mental illness.



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  • MIchael Paul: I proposed this to my high school biology professor back in the 1950s, when the subject itself was taboo. He asked (a classroom full of 16 year olds) what were some natural checks on population and when I piped up with the word ‘homosexuality’ it was as if I’d said ‘fucking your mother.’ He said ‘nonsense’ and changed the subject quickly to plagues and droughts.



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  • I don’t think you know what you are talking about. The Greeks absolutely knew what homosexuality was. Plato had Socrates talk about it in several of the dialogs and a play that mocked Socrates called “The Clouds” by Aristophenes was full of lewd jokes about homosexuality. Its a long time since I read the play but I remember one line in particular where Socrates showed that essentially all the men of influence in Athens were gay and the person he was debating with exclaimed “beaten by the buggers!”

    I may have the context a bit wrong, like I said it was decades ago that I read it but that line stuck in my head.

    This idea that sex is completely “a sociological construct” is just pseudoscience from liberal arts who have to write papers about something. Of course there is a very huge sociological aspect to sex but there is also the fact that some men like to have sex with women and some prefer men.



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  • I don’t think it is possible. The idea of a genetic trait to work “against over population” is essentially a group selection argument. It isn’t for the good of the individual, since by definition it reduces the individual’s reproductive success. It is for the good of the species and genetic traits for the good of the species at the expense of the individual don’t exist. This was one of the key points of Dawkins’ first book The Selfish Gene.



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  • 36
    tom.cantwell.908 says:

    If reality deniers are questioning why evolution would produce homosexuality perhaps they should stick with their reasoning as to why god produced it.



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  • Red Dog Mar 25, 2015 at 12:41 pm

    It is for the good of the species and genetic traits for the good of the species at the expense of the individual don’t exist.

    But for the good of the close relatives at the expense of the individual does.

    This was one of the key points of Dawkins’ first book The Selfish Gene.

    Kin Selection P 88 to 107 in “The Selfish Gene”.



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  • 38
    markap11 says:

    Couldn’t an even simpler explanation be that even in primary societies in many cases homosexuals were demonstrating bisexual behaviour having occasional heterosexual relations and so they carried the relevant gene from generation to generation?



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  • 39
    Josealb says:

    I have something that i might not understand very well, and im hoping someone here can clear it up. Homosexuality is present in other mammal species as well, other than humans. If its present today, its safe to assume that it has been present for a long time, or at least enough time for natural selection to enforce its filter. My question is this: If a homosexual individual of a species, throughout its history, does not mate during its lifetime, then how does the gene keep surviving generation after generation, when that particular line of a species ends with its homosexual member not passing on its genes? Im talking about other animals, since humans are complex animals, and we pass them on regardless of homosexuality or not (like Dawkins said most sexual orientations are blurred lines where bisexuality prevails). If the homosexual lines in the animal kingdom continue to pop up, when they are not mating, then isnt this an indicative that the gene is not hereditary? Cant it just be a random, harmless womb development anomaly, that has no impact in survival, so natural selection turns its blind eye to it?



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  • tom.cantwell.908 Mar 25, 2015 at 1:09 pm

    If reality deniers are questioning why evolution would produce homosexuality

    In our close relatives Bonobos, sex in general is a group bonding thing!

    In evolution sex changes are not at all unusual.

    Quite a few vertebrate species can easily change sex, but this is usually to enhance reproduction.

    http://evolutionfaq.com/articles/sex-change-nature-coral-reef-fish

    In nature, some animals have the ability to change sex if the population size gets too biased toward any one gender. In this article, we discuss the mechanisms which perform this feat.

    There are also the effects of hormones or hormone-like chemicals.

    http://news.bbc.co.uk/1/hi/uk/3882159.stm
    Pollution ‘changes sex of fish’

    A third of male fish in British rivers are in the process of changing sex due to pollution in human sewage, research by the Environment Agency suggests.

    A survey of 1,500 fish at 50 river sites found more than a third of males displayed female characteristics.

    Hormones in the sewage, including those produced by the female contraceptive pill, are thought to be the main cause.



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  • I agree with Dawkins assumption that “homosexual” gene becomes active only in right environment. It is silly to call it homosexual gene but in order to explain… . It is not some especial gene, but it is only triggered in right environment. Psychologist have the same theory. A human being is actually androgynous. If a child is raised in environment where there is no verbal input from parents that determine their sex they are going to choose who to love. And if girl loves girl, or boy loves boys we call them homosexual.

    If girl infants are told for example “Do not do that,you are not boy; girls do not behave in this way”, or “You have to wear skirt, not trousers like boys”, they suppress their masculine part of identity and when they grow up they look for that suppressed part, they fall in love with man. When boy infants are told for example: “Do not cry, only girls cry”, or “Be a strong man, not delicate as girls”, when they grow up they seek that suppress part of them, they seek girls. Only children that are raised free of all this stereotypes choose who to fall in love, they are not victims of stereotypes and false mental maps, those people are free to choose and they choose person regardless of gender. They choose person, not social role or wrapping material so to speak. So, perhaps, bisexual people are the healthiest one regarding sexuality.

    We, as human beings, learn our social behavior, and our sexuality is one of those learned behaviors. As Dawkins suspects, it is environment that decides.



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  • It seems clear to me that sexuality runs along a continuum, which may even vary throughout a person’s life. It also seems clear that male and female homosexuality are fundamentally different. At a different time, when society was less accepting or there were fewer people in the world or in the tribe, more men who might have otherwise lived gay were pressed into the service of propagating the species, thereby passing along their genes. My guess is, as Dawkins says, that gay men are to a more or less degree, bisexual, ie, reproducing. The real test will be whether, given the freedom to not mate with women, over time, homosexuality will endure. If not pressed into the service of reproduction, gay genes, should be self limiting.



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  • I agree. To be honest I think it’s less to do with evolution than chemistry in the brain. Sexuality is a scale from 100% heterosexual to 100% homosexual. All of us are somewhere along that scale.



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  • I forgot to write that I think there is no gene for sexuality. We have genes regarding our gender, but I don’t think there is gene for sexuality. I think that sexuality is a social term, not determined by genes. It is about behavior, and we learn behaviors.



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  • Josealb Mar 25, 2015 at 1:22 pm

    I have something that i might not understand very well, and im hoping someone here can clear it up. Homosexuality is present in other mammal species as well, other than humans. If its present today, its safe to assume that it has been present for a long time, or at least enough time for natural selection to enforce its filter. My question is this: If a homosexual individual of a species, throughout its history, does not mate during its lifetime, then how does the gene keep surviving generation after generation, when that particular line of a species ends with its homosexual member not passing on its genes?

    Identical copies of the genes are passed on in close relatives (whose lives may be helped by non-breeding brothers, sisters, aunts and uncles) or by recessive genes which are not expressed in all the individuals who carry them.

    (Eg. – Thousands of worker bees and soldier ants, have no offspring, but support their mother queens, who have identical copies of their genes, and produce thousands, including some breeding new queens and some males.)



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  • I dislike any brow-furrowing “study” of homosexuality as if it were a problem that must be done away with.

    Are you saying this is what Dawkins is doing because I don’t think that is true at all. No one is saying we should study homosexuality because we want to get rid of it. Certainly not Prof. Dawkins, not me, and not anyone I’ve ever read (Pinker, Trivers) who have written about the topic, or the other people like me making speculations in these comments.

    The reason it is interesting is because on the surface it is an evolutionary puzzle. It would seem a “gay gene” would clearly reduce a man’s reproductive success so it shouldn’t exist but there is good evidence that there is some genetic component to homosexual behavior. As Chomsky has said the start of good science is at the boundaries of our understanding. Not trying to tackle problems that we have no clue about but finding puzzles that seem to be hard to explain with what we currently know about the existing science, in this case evolution and behavior. Homosexuality is such a minor puzzle and as a result it is an interesting area to study.

    An analogy is in the minor perturbation in Mercury’s orbit that couldn’t be explained by Newtonian physics. Solving that puzzle provided some of the most compelling ealry evidence for curved space time.



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  • It is possible to argue that homosexuality is not genetically based and not be some drooling God warrior. There are plenty of intelligent people who would make the case such as the commenter who argued that “homosexuality is purely a social construction”. I think he was wrong and I gave my reasons in my reply but he didn’t seem to be making a theist argument and I’ve read others who make similar arguments to his.

    It’s funny how so many people on this site who claim to believe in the scientific method quickly abandon that method and turn to the same techniques the theists use (labeling, mocking) rather than engaging in intelligent discussion.



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  • I think the greater reason we’re seeing more homosexuality is not because of a greater incidence in the population, but a greater acceptance in modern society. People are not as afraid to come out of the closet today than they were a decade or more ago.



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  • I did read of a study a good many years ago that was testing for overcrowding and its effects on sexuality.
    Sorry it was too long ago to remember all details, but they used rats, and when the population became unbearably, for the rats, overcrowded, the study claimed many of them became homosexual.

    I expect there are statistics for the world populations which may have a bearing on this.



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  • Richard Dawkins (and many other thoughtful people) has wrestled with the difficult question of homosexual causation. It seems to be an unsettled and touchy subject.

    In this video (it would be great to have a text version), Dawkins mulls over the implications of homosexuality on evolution. Assuming, as he and many others do, that this behaviour has a genetic basis, then according to the usual simplistic Darwinian interpretation, homosexuality should have negative survival value, due to a lesser tendency to reproduce. According to this argument, it should have died out. He then tries to answer this objection, sometimes voiced by opponents of evolution.

    I do not pretend to be an authority on evolution, religion, or homosexuality, but here are my thoughts, offered with all due respect.

    Evolution is a way of understanding development and change. It is much broader than biological evolution. Once human cognition appeared, then our own social and cultural evolution far outpaced biological evolution. In recorded history, there has been little change in human physiognomy, but great social and cultural changes.

    Dawkins uses the example of identical twins to explain why he thinks homosexuality has a genetic (biological) origin. The co-occurrence of homosexuality is said to be statistically higher in such twins. Since identical twins are often used in studies that suggest a genetic origin of some trait, Dawkins feels this applies to homosexuality.

    Showing a genetic basis for a physical trait like eye, hair, and skin pigmentation, or susceptibility to some disease, is much easier than showing a genetic basis for behaviour. For it is behaviour, not physiognomy, that we are dealing with. In spite of popular caricatures, homosexuals appear no different than heterosexuals.

    To say that homosexuaity runs in the family, is like saying Protestantism runs in the family. It is much more plausible that behavioural traits (incidentally including political and religious beliefs) are passed socially rather than by genetic mechanisms. Identical twins are famous for identical behaviour, due to their physical association and shared milieu. The same would be true of other siblings to a certain extent.

    This is not to say that physical traits play no part in behaviour. For instance, although it would be ridiculous to claim basketball ability is genetic, the predisposition to play basketball well might well be connected to height, which few would disagree is at least partially genetically determined. Possibly, there is some as yet undiscovered genetic predisposition to homosexuality. However, autopsies of homosexuals show no difference in physiognomy from those conducted on heterosexuals. The difference would only be perceptible when they had been alive and interacting with others – i.e. their behaviour.

    There have been attempts to prove a genetic basis for homosexuality. Dean Hamer, an NIH AIDS researcher, famously claimed to have done so in 1993, but his work has been criticized for lack of proper controls, misinterpretation of data, and bias (Hamer is a pro-gay activiist). Hamer later also hypothesized a “God gene”, an intellectual excursion that should interest Dr. Dawkins.



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  • The hormonal theory of sexuality holds that, just as exposure to certain hormones plays a role in fetal sex differentiation, such exposure also influences the sexual orientation that emerges later in the adult. Prenatal hormones may be seen as the primary determinant of adult sexual orientation, or a co-factor with genes, biological factors and/or environmental and social conditions.

    Garcia-Falgueras A, Swaab DF. Sexual hormones and the brain: an
    essential alliance for sexual identity and sexual orientation. Endocr
    Dev. 2010;17:22-35. PMID 19955753

    Justine. It’s actually good science. The power of this science is that it solves almost all of the political problems associated with the GLBT community. Homosexuality is as normal as blue eyes, blond hair or left handedness. Would you say to blue eyed people that they cannot marry. Would you prohibit blonde haired people from adoption. Would you enact laws that prevent left handed people from inheriting their partners assets. This is the stupidity of current laws in relation to homosexuality. Homosexuality is not a disease or a mental illness, it is one of the available norms produced during gestation.

    If you would like to read more of the science, it is summarized here in the Wikipedia article with references back to the actual research.

    http://en.wikipedia.org/wiki/Prenatal_hormones_and_sexual_orientation#cite_note-Garcia-1



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  • What exactly is the driving force behind reproduction? If it is just physical attraction then why dont animals who are identicle, regardless of sex, just shack up randomly? At what point did those prehistoric fish, the first to copulate, work it out?



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  • 56
    Stephen says:

    When considering the idea of the “selfish gene” it is worth remembering that many of the species we might have had have been winnowed out by genetic traits that lead to self-destruction. Therefore we have to ask not only why do we have the species we have, but also why do we NOT have some species which, on the basis of a simple “selfish gene” argument. should exist.

    Consider honeybees: in a hive all the workers effectively give up propagating their own genes and act as protectors and providers to the offspring of their sister, the queen. Note that a queen only exists because she was fed a special diet as a larva, otherwise she would have hatched as a worker. So it is possible for a population to sacrifice individual genetic propagation and achieve a species benefit from doing so.

    Consider Ebola: whether or not it is a successful virus. It is extremely contagious but also very likely to kill its host in short order. Therefore Ebola populations rise and crash quickly as all the hosts in an area are killed off and the virus dies with them. I think that Ebola is not as successful a virus as eg the common cold which is far more prevalent.

    It seems therefore that the reproductive success of a species can be influenced by factors that are not directly linked to the fate of each individual. Species with poor self-control (like Ebola) are very likely to have died out completely leaving those with control mechanisms, such as homosexuals being protectors and providers for offspring without their own offspring consuming scarce resources, to succeed over a long period of time. Genes that result in such self-moderating behaviour would therefore tend to persist.



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  • 57
    Lorenzo says:

    I think David got confused up there: a brain with a gender different to that of the rest of body is the characterization of transgenderism -and, to support that, there are some papers that locate brain’s structures characteristic of the gender opposite to the “physical” one.

    As far as homosexuality is concerned, I’m not aware of any difference detected so far. And this was not for lack of trying.



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  • Sexulaity may exist on a continum but I suggest you review statistics. This continuum is normally distributed with a mean of sexual behavior and almost 70% of people are within one standard deviation of this mean.



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  • Red Dog. Lorenzo. Wikipedia as always gives a good summary of the science in support of my position. I’ve actually read more in depth stuff but the Wikipedia stuff will give you the science behind my position, and a few references if you want to delve further.

    As I said above, it does better in the Ockham’s Razor test than competing theories, so I think it deserves some respect and nees to be on the table for discussion.

    http://en.wikipedia.org/wiki/Prenatal_hormones_and_sexual_orientation



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  • There is a lot of great stuff on Wikipedia. I’ve written some things myself. But there ie some very weak and incoherent stuff as well. Especially on topics like this you hae articles primarily with a biological cognitive psych background. But you might also have articles written from the perspective of Freud or gender studies or any endless number of humanities pseudoscience. Wikipedia has a process to identify what they call fringe theories what most of us would call pseudoscience. But they are a lot more open minded than most of us would be.

    Of course it is fairly easy to tell by the refs, look forward to seeing them



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  • Sorry I must have misunderstood what you meant. In your first comment you said

    If reality deniers are questioning why evolution would produce homosexuality perhaps they should stick with their reasoning as to why god produced it.

    To me that meant anyone who questioned why evolution would produce homosexuality was a reality denier and theist, neither of which I think are true.

    If you didn’t mean that what did you mean?



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  • Agree. Wikipedia is not a bad starting point but it is not definitive. I’m a bit out of my depth with making assessments of the research links but from my amateur skeptic position, it seems to have some level of responsible scientific support.

    The explanation appeals to my commonsense gene in that it can provide a potentially evidence based explanation. I also think that homosexuality will be one of those issues with nature, nurture, science, psychology and mystery and various combinations of all of the above. I don’t think there will ever be a definitive “That’s the Answer” moment. But there is enough rational explanations out there to defeat any of the religious choice arguments. When someone starts to argue sin and prohibition of homosexuality based on an argument that it is choice with a sprinkle of theology, the red mist descends. No discrimination. Not ever. Full citizenship. End of story.



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  • Dr. Dawkins cautiously approaches evolutionary questions impinging on homosexuality from a “Big Tent” frame of reference that includes environmental factors and diverse social and cultural practices rooted in time and place. A tentative biological approach might recommend investigation into epigenetic factors driven by specific genes as yet undiscovered or poorly understood. If I hear Dawkins correctly, he acknowledges underlying genetic configurations as potential causes that only produce actualized homosexual orientation when the “genes’ are triggered (expressed) by effective environmental and/or epigenetic pressures.

    We pragmatists favor such open tentative approaches to understanding how phenomena work. We call these approaches holistic in the sense of not being limited to one point of view, description or narrative and seeking relational, interactive qualities over foundational explanations.

    One useful narrative considers the “normal” biological process of sexual development in human males and females without in any way implying exclusion of other viewpoints or inputs. Unfortunately I have to use the term “normal” to indicate a distribution of a trait among the vast majority of the population. Only 3.5% of Americans identify as LGBT. Even if the share were doubled to 7%, the vast majority (93%) would still follow the statistically “normal” path to sexual maturity and lifelong heterosexual orientation while taking into account all variations.

    The “normal” story goes like this: Until reaching the age of around 12 to 13, most boys and girls prefer same sex social interactions. Many feel more or less incompatible with the opposite sex. Around 13, a strong often mystifying attraction for the opposite sex brought on by hormonal and physiological changes takes boys and girls by surprise, tormenting their being with frustrating desires and obsessions driven by compelling sexual appetite.

    Most boys and girls grow from adolescence into adulthood with “normal” sexual orientation fully internalized and expressed -sexual orientation that is holistically rooted in biology, physiology, dimorphic anatomy and socio-cultural conditioning.

    Is the story too simplistic? By a country mile. A ten year old boy or girl may develop a same-sex crush and cuddle affectionately in bed during a sleepover with little or no no sexual motivation. Curious adolescent kids at an all-boys boarding school may “beat-off” other boys with pleasure while biologically grounded in heterosexuality. Yes, a tiny share of the LGBT community practice bi-sexual behavior (excluding “straights” who experiment) over prolonged periods. A share of the bi-sexual population probably represent an attenuated class where the self-identified bi-sexual actually prefers homosexual orientation and intercourse.

    And so, is homosexuality like heterosexuality genetic? Probably yes, but only in the sense that we need a word that sounds as if we know more than we actually know. Holistically with respect to sexual orientation, we evolved largely to be sexually attracted to the opposite sex for obvious reasons. But whatever the sexual orientation, we are what we are.



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  • It was philosophy from Kant, who with the “categorical imperative” that behavior could become beneficial or harmful to a human group, whatever this was. Through reason he used the universalization of such conduct, to observe the outcome. For example: What if all members of that group, conduct their vehicles, regardless red traffic lights. Surely that such conduct would cause a lot of accidents to members of that group. In the same vein, we might also get to ask, what if all members of that group were homosexsuales? Human group that is probably extinct in one or at most two generations. In my view the question arises in these terms



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  • Before asking how one can explain homesexuality, one must ask whether homosexuality exists in primitive human societies. To the best of my knowledge, it does not. Neither does heterosexuality, but rather different forms of bisexuality. Truth may be that sexuality is a normal distribution and not a binary one.



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  • So what about the notion that humans are not the only animal to have homosexual traits? Where does that leave homosexuality on an evolutionary scale? Maybe it’s an effect of a sizable population telling the genetic markers that procreation is no longer the ONLY directive but help provide resources to help child rearing or running of society? Each GLBT person still serves their purpose in society while still being available to the gene pool but not readily and actively populating (or overpopulating in our case!)



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  • The non-heritability of Protestantism would show up when comparing its incidence in identical twins versus non-identical twins.

    Prof Dawkins made it very clear in his video that there would be no selection “problem” to explain if homosexuality were a result of an environmental factor. My understanding is that the evidence for a significant genetic component of homosexuality is now generally accepted. Dawkins’ speculative reasons for the trait’s persistence are just that – speculative. If the assumption of heritability is false, the speculations are moot, but still interesting.



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  • Michael G Mar 26, 2015 at 5:55 am

    A sizeable population telling the genetic markers something? How does that work?

    That would only work in terms of selection in competition between competing populations, with tendencies for different percentages of those genetic traits to be expressed.

    Genes are not about each person serving their purpose.

    They can be in the context of the survival of multiple copies of genes in a social group. (Such as social insects)



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  • I think Prof Dawkins addressed and explained the debunking of community- or group-based theories of evolution in a previous video.

    Evolution works at the level of genes, and the mutations happen at the individual level, not within a group. If the individuals carrying a particular gene are less reproductively successful than the average, the gene will eventually be eliminated, no matter how beneficial it is to the community as a whole. Unless one can demonstrate that the holders of a homosexual gene have a comparative advantage (or at least no disadvantage) over the other members of the same community, one can’t explain how the gene can survive in the long term.

    It can’t arise, for example, that a species of herd animals would have a few individuals who would selflessly sacrifice themselves to predators to keep the majority of the herd safe. Those individuals, along with the gene that led to that behaviour, would sooner or later be wiped out, no matter how much better off the herd was. (Of course, if the gene, or the role, came with compensatory benefits that improved that individual’s reproductive success, then it wouldn’t be selfless, and would be perfectly possible).



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  • Let’s not forget that evolution only selects traits where they are disadvantageous to survival. One could argue that homosexuals are less likely to breed and would therefore be selected out over time. However, we must remember that even up to the present day there is social pressure for people to conform to the norm. It is only for a few 10’s of years that people have been able to be openly gay without fear of jail or even death. In many countries that is still a problem! Homosexuals will have conformed to marriage and having babies for all of time and continue to do so. I would argue that the 50 years or so where homosexuality has not been a legal offence, in some developed countries, is nothing on an evolutionary scale so there has been no chance for Darwinian selection to occur.
    As far as homosexuality goes in animals, it is well documented that homosexual activity occurs in many many species. However, I’m not aware of any animal being documented as leading a purely homosexual life and so again, there is no reason to suspect that those tendencies would be selected out by Darwinian evolution.



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  • I think it would be fair to call what you are describing a “defect”, in the sense that it is not only well outside the bell curve, but it contrary to what the rest of the genome is optimised for. One can call Down Syndrome a defect without making any moral judgement.

    But it does raise an interesting point – aren’t non-heritable defects also subject to genetic correction? The defects have a cause, either a deep-rooted genetic one, or an environmental one. Either way, some “immunity” or defence against the defects are just as likely to arise genetically in the long term, as defence against other dangers, surely?



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  • @Stephen

    However, I’m not aware of any animal being documented as leading a purely homosexual life

    This is one example that I am well acquainted with. When an Australian Merino Ram is sold, the contract of sale has an out clause because there is a persistent but small percentage that are exclusively homosexual. You get your money back along with a big BBQ pack.

    Sheep may display homosexuality, which occurs in about eight percent of rams.[2] Its occurrence does not seem to be related to flock hierarchy (as some homosexual behavior is in mammals), rather the ram’s typical motor pattern for intercourse is directed at rams instead of ewes.[2]

    It is common in animal species to display homosexuality. Around 1000 species recorded so far. That sexuality may change over time and spreads across the entire spectrum of possible tendencies. A bit like us really, given we’re just another animal.

    Wikipedia as always, gives a beginners look at the issue here.

    http://en.wikipedia.org/wiki/Homosexual_behavior_in_animals

    If it was genetic, then evolution would dispose of gay rams millions of years ago, so there must be something else in play. The in utero hormone flood hypothesis explains the persistence of homosexuality when evolution should delete it. (I wrote about it somewhere above if you want to read the theory. )



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  • Michael G Mar 26, 2015 at 6:20 am

    I think Prof Dawkins addressed and explained the debunking of community- or group-based theories of evolution in a previous video.

    The debunked “group selection”, should not be confused with the valid “kin selection” in groups of closely related relatives.

    Evolution works at the level of genes, and the mutations happen at the individual level, not within a group. If the individuals carrying a particular gene are less reproductively successful than the average, the gene will eventually be eliminated, no matter how beneficial it is to the community as a whole.

    Unless it leads to improved survival of identical copies of that gene present in the closely related group.

    http://brembs.net/hamilton/



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  • Somewhere in the last month or two I read that a small dose of the genes that make you gay, makes you sexy, both more appealing to others and more eager for sex. In a full dose you are gay. So the partial dose effect causes more babies than the full dose prevents, so the genes prevail.

    One of the key things to explain is why gay people nearly always come from nominally heterosexual parents. I am gay and there is nobody in the extended family who is. There is one possibility, my maternal grandfather, who delayed marriage until late in life.

    My own hypothesis is are many different kinds of homosexuality. We foolishly lump them all together even though to the untrained eye they are totally different. It is sort of like lumping all coughing diseases as the same thing, not that I mean to imply being gay is a disease.

    I am very impressed by the patience straight males exhibit in seeking sex, even the most bigoted of them. It is quite rare for a gay person to invest more than 24 hours in getting laid.

    I have known bisexual people who preferred females who had more male sex partners than most nominally gay males. They basically would not turn down any opportunity for sex.

    I also read somewhere recently that many genetic defects actually help prevent serious disease, for example sickle-cell anemia partly protects against malaria. Cystic fibrosis protects against something … This is why these conditions did not disappear.

    I am going to have to come up with a scheme to track sources and their reliability.



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  • But the problem with kin selection as an explanation is that the advantage to kin must be additional. Assuming that an average heterosexual individual in a given community has, say, two surviving children of average “fitness”, then having a homosexual uncle must confer an additional advantage to his nephews, equivalent to his brother having a total of four average fitness children. If his brother was likely to have achieved this and and have had four average fitness children even without the assistance of the homosexual uncle, then the uncle would have been evolutionarily better off heterosexual and having two of his own.

    In other words, the kin selection argument implicitly posits that a homosexual uncle will be twice as successful with his brother’s children, than the brother himself would be (or than he himself would be with his own children). This seems possible for an occasional outlandish set of circumstances, but unlikely in general. (Perhaps, of course, the gene might be switched on by an environmental indicator of outlandish circumstances, but surely that has been explored?)

    The non-competition idea that I’ve seen floated doesn’t count either, if it advantages all or most other males in the community, rather than being restricted entirely to kin only.



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  • Male pattern baldness, doesn’t on the face of it, confer a disadvantage, so I am not sure one needs to understand it in the same way as homosexuality. Evolutionary theory is falsified by the continued propagation of a heritable trait that confers a disadvantage to the holders. Speculating about an explanation leads to hypotheses for scientific investigation.

    Furthermore, if a logically consistent explanation can be posited, evolution isn’t falsified, even if that explanation isn’t verified.



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  • I agree, Red Dog. I think tom.cantwell either expressed himself badly in the first place, or is back-tracking rather disingenuously now… His reply to you, below, makes me think the latter.



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  • But the question is, if the phenotype confers a significant disadvantage, even just some of the time, how does the genotype get propagated in the long term? Why would we have evolved behaviour that, if we “are raised free”, allows us to choose same-sex partners, when that behaviour impairs our reproductive possibilities? Environmental triggers may well be involved, but one still needs to explain the kind of circumstances where homosexuality would be advantageous (or at the every least, not significantly disadvantageous), if it is not to invalidate our understanding of natural selection.



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  • @Alan4Discussion
    I think you make too much of kin selection in humans.

    Firstly, it’s not the same as in the colony insects you give as examples. On those, the worker bees, soldier ants, etc., are not “individuals” in the genetic sense. They are much more phenotypes – constructions of the breeding pair -, much the same as a beaver’s dam isn’t an individual, but does contribute to the success of the breeding pair of beavers.

    Secondly, kin selection requires that holder of the gene in question, must confer twice the advantage to his closest kin, than he would to his own offspring. I wouldn’t die for my brother, but I would for two brothers or four nephews. In practice, that means that small sacrifices to one’s self and one’s own children can be made when they result in large additional benefits to one’s brother or one’s nephews etc.

    But maintaining the ratio gets increasingly difficult. Sacrificing your own child completely, means expecting at least a two-nephew compensation, over and above what your brother would manage on his own. In fact you have to raise two nephews over and above any contribution from their own father (your brother), at least as successfully as you would manage to raise one child of your own. How likely is that? And how likely is that to be the basis of an evolutionary “strategy”?



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  • 85
    maria melo says:

    Somewhere in the last month or two I read that a small dose of the
    genes that make you gay, makes you sexy, both more appealing to others
    and more eager for sex.

    Funny reply, and I agree.
    i went to a concert of Ney Mato Grosso some years ago, I never thought he could be so sexy atrractive to me, these ambigous traits seem sexy to me indeed.



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  • Similar to some insects that produce virgin birth females during the summer but return to sexual generation in the fall to ensure male and female offspring to overwinter. I’ve always thought that the overpopulation idea was correct.



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  • 89
    Malessa says:

    Animals in nature pair up in much the same way as humans – males and females join to copulate and reproduce.

    Animals, arguably, don’t have the same sterotypes/behaviours forced onto them (as you seem to suggest) yet they still make hetrosexual couplings. Homosexual unions are rare.

    So I think you assumption that humans are somehow pressured into heterosexual behaviour is ridiculous.

    We already know that from a reproduction point of view, male/female sex is the only combination that will create new human life. So that is the ideal coupling. “Falling in love” is insignificant from an evolutionary point of view – it does not effect species chance of survival. You are just adding a narrative that simply isn’t there.



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  • Not all forms of sexuality fit in between heterosexual and homosexual – that kind of leads to the idea that people can only be one or the other or in the middle (bisexual), and that is not the case at all.

    You have folks who are pansexuals, demisexuals, asexuals, there are even people who are attracted to objects like cars or buildings and there are so many others out there.

    I guess it goes without saying that this is the reason the LGBTQ community uses a rainbow rather than a grayscale to represent that sexuality is not just black and white with a lot of gray in the middle, but really an entire spectrum of various orientations that go beyond just straight or homosexual.



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  • MisterMack: Thank you .. I was becoming concerned with these dogmatic replies (many are ‘experts’, apparently..!) … From the studying I’ve done (so there.!!) and, I believe, in the revised edition of The Selfish Gene, there is no one gene that controls any phenotype, let alone behaviour. However, it is normal to speak of genes for this and that but this is wrong as it leads to such ideas as ‘gay Gene’ or ‘God Gene’ or whatever – sounds like someone wishes to cut it out like a bad bit of an apple.!! and that, IMHO, is the problem with the terminology. Also, IF, when born, females have a different brain from men (and I doubt it) … then, is it not social and environmental considerations that cause the differences perceived by scientists measuring adult brains to detect these differences – who go on to announce ‘the female brain’, the ‘male brain.’ To start with an identical blue-print (in this case I mean the brain) and then alter it’s aspect, attributes, due to hormonal differences etc., btwn males and females sounds more likely to me. Creating a separate male and female brain doesn’t sound anything like the beauty of ‘genetic creation’ as I’ve understood it – sounds more like the problems of a ‘discontuous mind’. The difference btwn a chimp and us is a few % – why create a separate female brain … madness!!? I like your bit about less violent males as I am hetero but not knuckle-dragging .. a rather misunderstood specie (especially by the ‘knuckle-draggers’).



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  • Couldn’t agree more. We tend to be anthropocentric and elitist this can distort our view of genes and their function. It is easy to use terms that imply that genes ‘do things’ for the betterment of the individual, close relative etc., and this is their wish – as opposed to the idea that genes don’t think at all and evolution/genetic change is a matter of luck (environment etc.,). For those wishing to debate this, consider that there are far more extinct specie than extant – mostly from luck on the part of the extant and bad luck on the part of the extinct (ask any dinosaur – with SUPERB genes … err.. hetero – or homo sexual or not). These driving forces and mutations don’t mean a lot when you get hit by an earthquake, tsunami or the odd rock or two – and these events happen frequently. The Greatest Gene in the Whole World …. could been created and died out in one animal millenia ago .. (so what?). I appreciate that the more thoughtful MUST base their thoughts upon ‘steady state conditions’ etc., (which I am used to) but those I lecture ‘Believe’ it all inc., ‘Gay Genes’ .. One Gene sitting there looking at you … doesn’t happen … doesn’t exist.



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  • There is no darwinian reason for homosexuality, nor is it in the DNA, although Matt Ridley argues that a mutation occurs during the copying proces of the endocrine system (Hormones); effectively setting the stage for homosexualty in the womb already. Also, it is not limited to humans; birds and penguins have a high occurence rate of preferring social bonding over sexual reproduction. Homosexuality is as old as humanity, just not as expressed as today. And as homo’s do not reproduce, there cannot be heredarity of “Homo genes”.



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  • I must counter what I believe are unhelpful misconceptions about the role that natural selection or DNA (specific genes) play in the persistence of homosexual orientation and separate thoughts on current politicized conceptions of human sexuality.

    Homosexuality does not threaten population growth. The current consensus is that the LGBT share of the population is 3.5%. Suppose subsequent findings boosted this figure to 10%. Neither finding is statistically significant for human reproduction which is solely dependent on the fertility and fecundity of women.
    Historically and still extant in countries today a modest lifetime fertility rate of 3 children per woman on average would increase the initial base by 50% in one generation and more than double the population in two generations. Most homosexuals are men and the small lesbian cohort may also reproduce through bisexual intercourse, a factor which is also statistically insignificant.

    Homosexuality is almost certainly not caused exclusively by a determinant gene or set of genes. Hormonal activity in the mother’s womb and other poorly understood epigenetic factors interacting with postnatal treatment of the infant, occur frequently enough to keep homosexuality persistent yet rare in our species.
    If every living LGBT person disappeared in an instant, 3% to 4% of new live births, majority male, would still display the trait. Although Dawkins coherently cites inherited genetic configurations modified by variant pressures for gene expression, other studies of identical twins contradict the premise that homosexuality is decisively inherited. Dawkins wisely emphasizes in effect that we just don’t know (yet).

    While sexual identity, behavior, and attraction lie along a continuum, sexual orientation in human populations is less malleable than argued on this thread. The popular misconception is that bisexual orientation is rampant among large segments of the population ambivalent about their desires for same-sex or opposite sex interaction. The fad developed from ingesting anecdotes about famous eccentric painters, poets, film stars, etc., reliably recorded in biographies or unreliably in urban legend who were besotted with strange sexual appetites to shag anything that moved -women, men, little boys and girls, old ladies, sheep and so on. None of this is to deny the varieties of sexual behavior expressed under certain conditions and historically in certain societies including but not limited to, all-boys/girls secondary schools, prisons, the military, some primitive societies, Ancient Greece, etc. As we all know from critiques of ancient religious scripture, homosexual “deviance” was a moral transgression, a taboo, an abomination in the sight of God and man calling for harsh punishment including execution. Until science enlightened humankind to celebrate homosexual relationships as expressions of love integral to a minority born with a “different” sexual orientation, the prevailing view of world societies consigned homosexuality to some combination of foul perversity, mental illness and mortal sin.

    Allowing for limited exceptions and qualifications, most people are not “confused” about their sexual orientation. I wish that the current hysteria of “gender studies” will subside enough to bring folks back to common sense.



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  • 95
    Ardo Ci says:

    Firstly – happy birthday, Richard!

    I loved this thought-provoking consideration of homosexuality, brilliantly delivered as always.

    Is homosexuality to be considered an abnormality of nature or a desire, a fashion, a result of upbringing and surroundings and even then, if it be so, is it occasioned more often by an aberrant gene or an individual’s decision whatever the situation he finds himself in? In my view, nature has designed two sexes as the extreme complement of one another in accordance with the grand determination of duality but it also allows for an area, a middle ground, for the merging of these opposites to be obscured and where anything can happen.

    Nothing in nature is sharply divided.

    Everything is, and should be, acceptable but man has yet to emerge from the cave. Perhaps, we may get there in another 1,000 years but I doubt it.

    I should add I am not homosexual and I have no desires such as some of the men of the Roman legions who were desperate for a toga-hoisting and ‘felt’ anything would do.



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  • @Alan4Discussion

    Unless it leads to improved survival of identical copies of that gene present in the closely related group.

    As I have discussed in more detail in other replies to your posts here, the kin selection proposition is a bit thin for exclusive homosexuality. It’s not just a case of “improved survival of identical copies of that gene present in the closely related group”. The degree of improved survival must be a multiple inverse to the degree of relatedness. So a trait that precluded offspring would need to add massive advantage even to very direct relatives (and furthermore, none of that advantage being conferred on non-kin. So non-competition for potential mates doesn’t count).



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  • 99
    fadeordraw says:

    Two of the first three RD videos honouring Darwin Day 2015 deal with homosexuality. This one generated lots of discussion, though, for me, not too much in the context of evolutionary theory. I would appreciate it if his next videos force this context to be present in the subsequent discussion.



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  • I’ve always thought that the overpopulation idea was correct.

    Humans are not insects. Rearing a child is a life-threatening, 15-year commitment of significant resources. To raise a sterile child is a disaster from a genetic point of view. This is not like a queen-bee laying extra eggs to create non-breeding workers, who will confer advantage on the whole colony, all of whom are siblings.

    What possible model could apply that allows a sterility gene to survive at all, much less if it results in a community benefit? Presumably, overpopulation means “too few resources – let’s say food – for everyone to survive”. How does raising a sterile child help the parents or siblings of that child, even if, in the long term, the community were better off? Even if, somehow, the random-sterile-child gene was initially prevalent, the few people without it would eventually out-breed those with it.

    The survival of heritable exclusive homosexuality is tricky enough to explain in terms of sufficient plausible individual (or close kin) benefit, without having to explain how it could possibly survive as a community benefit!



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  • The power of this science is that it solves almost all of the
    political problems associated with the GLBT community.

    Let’s not tie the morality of discrimination or bigotry, to some scientific explanation of why someone might be gay. As you say, the science isn’t affected by the moral outcome. By your reasoning – that this would be a “good news” discovery – it might be “bad news” if something else was discovered to be the cause of homosexuality.

    How we treat people shouldn’t be dependent on why they are what they are. If being gay were a choice, (imagine if science demonstrated that it is!) why would that justify any bigotry?

    Similarly, arguments against sexism should never revolve around whether there are differences between men and women. That’s a scientific question. The moral question is about whether any human should be denied the opportunity to pursue their aspirations on the basis of their gender. That’s a question that survives any scientific discoveries.



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  • Michael. I’ve read your replies. You seem, on the face of it to have some expertise in evolutionary theory. Do you think there is an evolutionary component to homosexuality? What do you think is the cause?

    I posit the in utero / hormone answer, but I suspect it is a combination of a number of factors, including some randomness. I can’t see how a non breeding, or limited breeding section of homo sapiens can pass on enough of their genes, to maintain a constant presence over time. While earlier stats on percentages of homosexuals in a population may not be that reliable, it has been a constant in the years with reliable data. So if it is a constant, and evolution fails Ockham’s Razor, then what maintains this consistent production of homosexuals.

    Any thoughts.



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  • Given that successfully raising a human to maturity is a 15-year, life-threatening, massively resource-consuming enterprise, to have one turn out to be exclusively homosexual is a disastrous by-product, from a genetic point of view. I like the thinking behind your explanation, but how much comparative advantage could the nearly-gay males have, that they outweigh losses made by the overdosed ones? And wouldn’t such a genetically expensive error be corrected in short order? Mis-calibrations are usually fairly quickly corrected, I would think.



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  • Other species don’t reproduce as humans do, so the meanings of “individual” and “self-sacrifice” and “species benefit” are very different.

    In your honeybee example, there is no mechanism for a mutated gene of a particular worker, to be propagated. His genes are irrelevant, evolutionarily speaking. If he does his job better or worse as a result of his mutation, it makes no difference to anyone, they won’t be passed on either way.

    The colony consists of literally thousands of siblings, all carrying genes from a single queen and a single drone. Since only a tiny proportion of them will ever reproduce, once again, their individual characteristics matter far less in evolutionary terms than in mammals, for example. As the colony consists almost entirely of siblings, any trait that is to the benefit of the colony is very likely to propagate the gene that caused it, even if the “individual” dies as a result of the trait.



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  • It seems to be an unsettled and touchy subject.

    It is an unsettled topic. I said that in several of my comments. As for it being “touchy” I don’t know what that means except perhaps that people who don’t really understand science and have a political agenda want to put their politics ahead of science which is always a mistake. It doesn’t matter if there is or isn’t a genetic component to it, there probably is, but either way to assume that it matters is to commit the naturalistic fallacy in ethics. If we say that something is right or moral because it is in nature then we should say that rape, cannibalism, murdering one’s half children, just to name a few are all “right” because they are natural.

    Assuming, as he and many others do, that this behaviour has a genetic basis, then according to the usual simplistic Darwinian interpretation, homosexuality should have negative survival value, due to a lesser tendency to reproduce. According to this argument, it should have died out. He then tries to answer this objection, sometimes voiced by opponents of evolution.

    As I’ve said elsewhere it’s a puzzle. You even said so yourself in your first comment: “it is an unsettled subject”. It is interesting because the simplistic (Dawkins and I admit its simplistic) argument about reproductive success must be wrong if there is a genetic component to it. Either that or we are going to have to rethink our whole models of altruism and behavior, which is unlikely but would certainly be cool.

    But there are plenty of precedents for this. The behavior of termites and other haplodiploid insects was a complete puzzle for Darwin. Here you have animals laying down their lives for their brothers and sisters and often not even reproducing. It seems to conflict with the most basic concepts of evolution until you understand DNA, selfish genes, and how haplodiploid insects share much more DNA with their cousins and siblings than other animals.

    Showing a genetic basis for a physical trait like eye, hair, and skin pigmentation, or susceptibility to some disease, is much easier than showing a genetic basis for behaviour.

    It is probably easier but that doesn’t mean it is necessarily any less likely. Look at the waggle dance that bees do, very complex behavior, no biologist in their right mind would think it wasn’t virtually completely genetically determined. Or the nests of birds or language acquisition in humans. Read Steven Pinker’s book The Blank Slate for many more examples and supporting data. Pinker clearly shows that the idea that physical traits are genetic but behavioral traits aren’t is clearly wrong.



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  • Lorenzo said above:

    If I don’t remember incorrectly, a situation not too dissimilar to the one you hypothesized in your comment was present in ancient Greece,

    Yes, actually ancient Greece was exactly what I had in mind. Actually the Romans might be a good example as well, Caesar was rumored to be bisexual and if that is true from what I’ve read about Caesar pretty much everything he did was calculated to advance his position. I wouldn’t surprise me at all if he and other Romans often used gay liaisons as a way to curry favor with those in power and to gain status.

    Just wanted to say thanks for correcting my completely wrong first impression of your comment, once I understood what you meant it is one of the most interesting ideas I’ve read here.



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  • 108
    Lorenzo says:

    Well, I took a look at the page (not at its sources, yet) and… those kind of correlations aren’t all that compelling: they found some features which seem to be correlated to homosexual behaviors and to some other feature that is known to be correlated to parental hormones (?). I’d like to see a bit more math but… I’ll categorize it as circumstantial evidence, for now.

    Anyhow, it seems a plausible explanation of the “how it happens”, but I don’t really see how this would explain how homosexual behaviors are still very much present in H.S.Sapiens -and many more species: it changes the subject of the alleged selection, from the offspring to the parent. But the question stays.

    Once again, I’d like the assumption that homosexuality is a selective disadvantage checked. On a semi-humorous note: if you’re a giant cuttlefish, cross dressing is the best thing you can do to get a girl. By a huge margin.



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  • 109
    maria melo says:

    As usual, people that don´t accept Darwin are social darwinists (remember the famous Marx´s sentence “I am not marxist”.
    Taking into account “ideals” rather than “facts” doesn´t help either.



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  • David,

    If Prof Dawkins is correct that there is a greater correlation with identical twins than non-identical, then it would seem very likely that there must be a genetic component. Of course there might be non-genetic components too, and your suggestions about in-utero / hormonal influences could well be at least part of the answer.

    A possible explanation for the survival of the trait is that perhaps in our ancestors’ societies, it was very seldom expressed as exclusive homosexuality. Perhaps culturally, even those men or women who much preferred their own gender, were encouraged or forced to establish and maintain a family unit? There may even have been some additional advantage in being gay, in the sense of “best of both worlds”, with strong, even if clandestine, ties to the significant other, who would be like a third parent in some respects. Pure speculation, of course!

    There is an interesting implication that arises out of this: I wonder if, somewhat ironically, the homosexuality phenotype is more likely to thrive in a repressive society that demands conventional relationships, versus societies where people can live more freely in accordance with their desires?

    Another point about heritability to consider: Aren’t all traits, heritable or not, ultimately subject to evolutionary selection? Let’s imagine that homosexuality had a entirely non-genetic cause. Let’s also imagine that the trait was always entirely exclusive, so was tantamount to sterility, and that there was a significantly high incidence in the population. Surely, in the long run, humans would develop a “defence”? In short order, the trait would have a genetic component, because other characteristics which are genetic, and which happened to mitigate (or aggravate) the individual’s susceptibility to environmental homosexuality, would be selected for (or against).

    With that in mind, perhaps it shouldn’t surprise us that the trait does actually show up in twin studies as being heritable. It could well be that it is not heritable itself, but its incidence is affected by some other heritable factor.

    I confess I’ve not thought that through very carefully, so I particularly welcome any critical or supporting thoughts.



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  • If you were a female looking for a male to be a good father to your children, which would you pick, a stolid marine with an over-testosteroned face (built like a tank) or someone with a fey sense of humour who loved imaginative play and singing silly songs? Who would be the better dad?



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  • A cogent and interesting post.

    I have only skimmed through some reading on the research into the heritability of homosexuality, and on the face of it, it seems clear that there is a decisive, although only partial, genetic component to it.

    If the trait resulted in exclusively same-gender sex, (i.e. if it precluded reproduction entirely) , then I would think that a 3.5% incidence would make it hugely significant, genetically. The risk and cost of successfully raising a human child who then doesn’t reproduce, is astronomical from the point of view of the genes!

    My suspicion is that the answer is probably that, for our ancestors, exclusive homosexuality may have been vanishingly rare, for cultural reasons, and regardless of the inclinations and preferences of the individual.



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  • A straw poll of female preferences would tell us little. Especially as we need to be asking that question in the context of our ancestors. If anything, I would imagine that a fey sense of humour and an inclination to sing silly songs might well have been qualities low down on the list of priorities!

    But the principle is good – there may indeed have been qualities that went along with homosexuality, that were favoured by females. You’re presumably hypothesising that the sexual selection of “mildly-homosexual” men might have offset any reproductive deficit that occurred at the exclusively-homosexual end of the spectrum?



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  • 114
    maria melo says:

    forgot to wish

    HAPPY BIRTHDAY !

    (live long)

    Thanks for the initiative to honour Darwin (no matter how silly the questions may be, and the answers I guess, including mine).



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  • Yes, but even that requires an explanation because on the surface (Lorenzo makes an interesting argument that this might not be true) even being bisexual would decrease your reproductive success compared to 100% straight.



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  • Was just reading an interesting bit in Trivers book Social Evolution pp. 184-198 in birds and other animals there are “helper” animals usually one child who is old enough to breed but for some reason sticks around and helps raise a new brood of newly hatched birds.

    One of the reasons I find this so interesting, is that there is a family or Red Tail hawks that lives near my home in San Francisco. Often I see them circling above the sky. I love just about all of nature (except mole rats and most humans) but there is just something amazing about watching a hawk fly overhead. Not sure why. Anyway it always really puzzled me that often it wasn’t two hawks circling overhead and declaring their territory but 3. I could never figure out why don’t they chase that third hawk away? Now I think I know the third one is probably a helper hawk, hawks are one of the species that do this.

    This may be similar to what is going on with homosexuality. Actually it IS similar in the sense that on the surface it is also an evolutionary puzzle. It is clear why the parents would want one child to stick around and “help with the chores” but not why it wouldn’t decrease the RS for the child.

    It looks like the best explanation (from what I’ve read so far this is similar to the homosexual case… there isn’t a clear and compelling explanation yet) but the best explanation is that the phenomenon occurs in areas where food is scarce and successful breeding is difficult (which would definitely be true here where most of the ground is pavement except for the little park which these guys essentially “own”). So the child would have better chance to breed sucessfully anyway when he/she has grown completely (they are capable of procreating but not yet completely grown I think) and rB > C applies, C is low since they don’t have a great chance for breeding their first year out of puberty anyway and r is high since they are helping to raise siblings and B is also high (that is something they can measure and the helper makes a big difference.

    Whatever is going on with homosexuality isn’t a direct analogy to helpers but there might be similar types of logic, people mentioned “population control” which I find doubtful because it sounds like group selection but as Allen has said these kinds of scenarios where one animal temporarily sacrifices RS for siblings or cousins definitely occur and homosexuality may be similar.



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  • Michael G Mar 26, 2015 at 9:25 am

    Secondly, kin selection requires that holder of the gene in question, must confer twice the advantage to his closest kin, than he would to his own offspring. I wouldn’t die for my brother, but I would for two brothers or four nephews. In practice, that means that small sacrifices to one’s self and one’s own children can be made when they result in large additional benefits to one’s brother or one’s nephews etc.

    I think you cover these points well.
    It very much comes down to the numbers involved. We should remember that for much of human history, families were much larger than in the developed world today.
    Also from an evolutionary point of view, there are polygamous societies and related tribal situations.

    When we look at troupes of Chimps and Bonobos, the situation is very different to present day monogamous human families.



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  • 119
    maria melo says:

    Don´t be sorry for me (I read Kant from my youth, and was an A level student in philosophy and I was invited to attend to philosophy classes whenever I want to.
    Don´t you blame Kant for such a ridiculous, childish and stupid ideas of yours.



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  • 120
    Dustin says:

    I don’t quite know if this has been brought up yet, and I’m no scientist so this may sound ‘dull’ of me to ask, but there are organisms that self-reproduce or have self-reproduced in the past but now require partners. Are there arguments for humans having once had a similar system or be heading in a direction of such a thing?



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  • The understandable confusion of sexual behavior with sexual orientation leads to many skewed misconceptions about the expression of human homosexuality in societies both currently and historically. Because Greek culture apparently sanctioned the practice of man-boy “love,” and Roman aristocrats and commoners romped in homosexual dalliance during bath time, the stereotype emerged of classic cultures pervaded disproportionately by men biologically grounded in homosexual orientation. We forget that traditional social structures have separated and still separates the sexes on religious, moral and sexist ethical grounds. Ancient Greece and Rome were authoritarian patriarchies where women played little role in public life confined to domestic settings in order to “protect” their virginity and reputations from “improper,” especially unchaperoned, associations with men outside their families. Reinforcing male dominance was the consensus that women were not only the physically weaker sex but also weaker in intellect and morality. Of course prostitutes, “loose women” and rape victims provided heterosexual outlets for pent-up tensions. But men often found themselves isolated from female companionship for prolonged periods of time mandated by social values and institutions. “Naturally” they turned to same-sex interactions to relieve sexual tensions whatever their sexual preference -their biologically grounded sexual orientation.

    Another more recent stereotype of disproportionate homosexual orientation affecting a population derives from misconceptions of the single-sex schooling system in England where boys are falsely believed to engage in rampant “buggering.”

    In another comment I hope to present some statistics about the current composition of LGBT populations and possible implications of those statistics.



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  • 122
    Lorenzo says:

    No, really not.
    You have to go up the family tree hundreds of millions of years before finding a common ancestor we share with asexual reproducers.
    Also, I’m not aware of anybody who has been born from a mother alone without any technological help.



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  • If there is a genetic component, could it be dormant, unless certain circumstances come together, one of which would be a non mean hormonal situation in utero. Nothing happens with this gene in normal gestation. But if for some random reason, the hormone balance is not right, it has a propensity keep a feminized brain in a male body.

    Looking at reliable stats across the world, the population of exclusively homosexuals runs around 3%. That’s a lot of homo sapiens. And it persists over time.

    In researching the hormonal cause, I have found that experiments are not possible because it would not be ethical to artificially alter the in utero hormone levels. I need some help here from more scientifically literate people. If the homosexual population base line in a given population is 3%, this would be 30 people in a 1000. So if you followed a thousand random pregnancies, took readings of hormonal levels every 2 weeks, then followed the 1000 children to adulthood, if there was a correlation between raised hormone levels and homosexuality, it would provide evidentiary support for this hypothesis. It would also be ethical, because the scientist would not be taking any action to alter the baseline, just observing. Would this experiment work.



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  • 125
    Donald says:

    The epigenetic answer that professor Dawkins promotes is a good one, but he stops short of the full implications. Currently it would not be politically correct, but it may e good science to match the observation with common categories. A birth defect can be described as “Birth defects are health conditions that are present at birth. They change the shape or function of one or more parts of the body. Birth defects can cause problems in overall health, how the body develops or how the body works.” So if there is an environmental effect that “causes” homosexuality, and we’d agree that homosexuality is not the normal function or workings of the human species, then homosexaulity may be called a birth defect in the cases where it is “present at birth” as some adherents to this stance claim. Hormone levels in utero may change the normal development of the sexual orientation.
    But we also know that some homosexual people are not born homosexual but move into that direction as a result of traumatic experiences in life. Look at Melissa Etheridge as a prime example of this. Abused by a sibling and unloved by her mother. Psychotherapists will acknowledge many cases such as this. Whether by abuse or confusion of experiences during adolescence, sexual orientation can be manipulated on that bisexual continuum that others commented on.
    This makes for a simple explanation and gives no cause for prejudice against homosexual people. The various genetic mutations or epigenetic causes would have been present throughout all periods of human existence. The rate of other birth defects is much higher than that of homosexuality so it isn’t beyond statistical possibility either. This explanation passes Occam’s Razor test.



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  • I never had much respect for Kant. I tried reading his works several times and either it seemed to me he was just stating truisms dressed up in huge German words, truisms based on an assumption that God exists whIch he never provided any compelling evidence for, or things that if you dig into them really deeply you would 1) get a headache and 2) realize they were essentially incoherent.

    I like some of the things he says about human rights but you don’t need all the big words and convoluted logic to support them. In fact I think those things get in the way and make it seem like you have to have a PhD to understand them when in reality they can be described much more powerfully with simple arguments and lots of examples the way Chomsky does.



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  • Leaving questions open, I cite statistics from Pew Research on LGBT populations in the United States and make some observations. While reasonable estimates range from 3.5% to 5% of total population, a 7% stipulated base will be assumed here to avoid under-counting. (A UK consensus recognizes 6% of the British population) About 93% of the U.S. population may be considered heterosexual. (Note: The 5% Transgender share of the LGBT community is not treated in these assessments.)

    Composition of LGBT Populations : Male homosexuals -(Gays = 36%) -constitute almost twice the number of female homosexuals -(Lesbians = 19%). Self-identified homosexuals weighted with a ratio of 2 males for every female calculated on the robustly stipulated 7% LGBT base yields a homosexual population of 3.85% of the total population.

    40% of the LGBT community self-identify as Bisexual. By definition the category represents degrees of ambiguity and ambivalence, but further breakdowns reveal anomalies that are surprising and difficult to explain. Contrary to the 2 to 1 ratio favoring male homosexuals over female homosexuals, the tables are turned excessively in this category with 29% of women reporting Bisexual orientations compared to only 11% of men, a ratio weighted in favor of women 2.64 to 1.

    The conclusion I draw is that both homosexuality and heterosexuality are driven predominately (not exclusively) by stronger male sexuality. Twice as many boys “know” that they are homosexual as girls. Only 11% of men self-identify as Bisexual suggesting that a significant share of these men really “know” they are homosexual but because of fathering children, marriage to women, “straight” sexual encounters, and other factors not integral to biological sexual orientation, they feel qualified to position themselves in this ambiguous category. Similarly, women experiencing on average less urgent, less frequent, and attenuated sex drives decoupled from obsession with opposite sex anatomy, are significantly more likely to experiment with same-sex interactions while “knowing” that the “Lesbian” label is not a good match for their basic orientation.



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  • Male homosexuals -(Gays = 36%) -constitute almost twice the number of female homosexuals -(Lesbians = 19%).

    I knew there was something else I’d forgotten. The differing rates of male to female homosexuals. Remember, your brain determines your sexual orientation, not your genitals.

    The brain in a fetus starts out in default female configuration, and must be forced by hormones to become male configured. They are more to likely to fail in conversion from female brain to male brain in XY males bodies, than with female to male conversions in an XX female body. The latter is far more difficult. A female XX fetus, in a female mother, is less likely to produce enough male hormone to create a male brain. But a male XY fetus, that starts out with a female brain, has to get the right doses for conversion, or it stays female.

    Another small notch in Ockham’s Razor, that hormones play a role in gender identity.



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  • Given how rude females are to males who approach them, I find it hard to believe they would persist in taking such abuse. I know other species are not in the least discouraged by being rebuffed. I hate it myself, and would spend quite a bit of time estimating my odds of acceptance before approaching anyone.

    Further, when females dump males, they are often incredibly cruel, trying their best to utterly destroy the ex. Males are not usually anywhere near that nasty. Back in the 1970s one of the hypothesised causes of homosexuality was traumatic early experiences with females. In my own case I tend to distrust females. This goes way back to when I was two years old. A little girl roughly my own age tricked me into putting my thumb into a gate mechanism, then slammed the gate and burst into giggles. The distrust was amplified when another girl snuck up behind be and pushed me into the ocean from a dock. In the process I lost a swim mask and a flipper. She was not in the least apologetic.

    It is more common for women who have been burned by a heterosexual relations to become lesbian than it is for men.



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  • You say: “I cannot speak with such authority about men, but wonder why they would be different.”

    I have heard the following posited. A man is most likely to have gene reproduction where he impregnates as many women as possible, particularly where he can get another man to help raise his biological children to the age oaf sexual maturity. Therefore men are perhaps genetically advantaged to be promiscuous.

    Women on the other hand, are best genetically advantaged to have the optimum number of healthy children which requires 20 years of devoted food provision and protection, which is most efficiently achieved by having a devoted food provisioner and a partner. Women are therefore genetically advantaged by having a sexuality that is less promiscuous and grows in reinforcement to an attachment figure.

    Some women therefore could be lesbians all their life, but others may grow an attachment to a particular woman later in life, or more generally ‘learn’ the capacity for sexual pleasure with women through a series of later life relationships.

    Men rarely report ‘going gay’ later in life by developing a relationship with one particular man, but rather tend to come out with a ‘bang’ having numerous same-sex sexual partners.



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  • I note Lorenzo’s reply to your answer. Sexual reproduction by gay men is perhaps best illustrated in countries that have strong social sanction against homosexuality. Where there is no age pension, almost all individuals in a society seek to reproduce (and create a religious obligation to care for parents, and an unbreakable marriage vow), simply to provide for a time when economic production becomes impossible. In those countries gay men simply need to get married and produce the optimum number of children likely to survive to adulthood. Gays may be more easily aroused by the same sex, but for millennia have been able to reproduce the optimum number of children for survival in old age.

    Noting that the best chance of gene reproduction for women is to have an optimum number of children that grow to adulthood supported by a devoted male rather than one that spreads his devotion to other women and their children, it may well be in their gene’s best interests to have gay man as a permanent partner rather than a heterosexual one.



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  • I received this today in correspondence for a campaign I am supporting in Australia on the rights of gay marriage. I think it carries some weight.

    If you have to make laws to hurt a group of people just to prove your morals and faith, then you have no true morals of faith to prove.



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  • I will try to tie in the Pew Research findings on the composition of the LGBT population in the United States with possible hereditary factors without resorting to impersonating a biologist. Reasonable estimates calculate the LGBT share of the total U.S. population at between 3.5% and 5%. I inflated these estimations to a stipulated 7% of the total population in order to eliminate any bias of under-counting.

    Of respondents who self-identify unambiguously as Homosexual 36% are Gaystrong text men and 19% are Lesbian women, a ratio of about 2 males for every female. Therefore:
    .36 X .07 = .0252 or 2.52% Gay of total U.S. population
    .19 X .07 = .0133 or 1.33% Lesbian of total U.S. population. 3.85% of the total population are homosexual but…
    Gays represent (.0252 / .0385 = .655) or 65.5% of the LG homosexual population
    while Lesbians represent only (.0133 / .0385 = .345) or 34.5% of the **LG ** homosexual population.
    Clearly epigenetic processes interacting with genetic inputs and specific post-natal influences, which are poorly understood, favor males over females almost 2 to 1 for homosexual orientation.

    The 40% Bisexual category of LGBT populations poses challenges for interpretation. The class choosing to identify as Bisexual certainly consists of persons consciously aware of a stronger sexual attraction or preference for one sex over the other. Those so choosing must obfuscate weighted preference to claim self-identify in an ostensibly balanced-sexual-orientation category where attraction for same sex and opposite sex are roughly equal.

    The fact that men comprise only 11% of the Bisexual category suggests that men are far more unlikely than women who comprise a disproportionate 29% share to succumb to ambivalence about their sexual orientation. The dilemma pits biology against semantics. Male sexuality embodies stronger biological drives, urgency, frequency than female sexuality on average; biologically facilitated by involuntary ejaculation and automatic orgasm providing relief for sexual tension, and by a compulsive focus on the sexualized anatomy of the partner.

    Of the small 11% of Bisexual ** men, I suspect a hefty share are firmly rooted in biological homosexual orientation. These men tend to report **Bisexual orientation because of extraneous contingencies: children, marriage, social reputation, etc. circumstances which disadvantage inclinations to report accurately.

    Conversely, the large 29% of Bisexual women are more likely than men to value “technique” in sexual interactions over the sexualized physical body of their partner; and therefore are willing to experiment more in same-sex relations. At the same time they are far less likely to identify themselves with firm homosexual orientation (Lesbian) contrasted with men (Gay)

    It seems reasonable to speculate that natural selection for predominately male homosexuality within tiny LGBT sub-categories in our species would advantage the reproductive role integral to female heterosexuality. If homosexuality were the other way around -predominately affecting females who avoided sexual intercourse with males- fertility rates throughout our 200,000 year species history might have dropped to extinction-levels especially during famines, epidemics, natural disasters and climate change.



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  • What of traits inherited from only one parent? As in mitochondrial DNA from females. Or of traits expressed differentially in males and females i.e. expressed as unusually strong heterosexuality in females and homosexuality in males? Such traits are absolutely certain to pass on to the next generation via the female side of the equation.

    GL



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  • Self-identifying gays are still a minority of gays. Most are still in the closet, at least those over 50.
    Kinsey used to grill people till they “confessed”. But just gets you false high numbers.



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  • I thought Dr. Dawkins made a great comment about genes not being expressed now the way they were back when we live in isolation in small groups. I think that may be the key to understanding alot of behavior that we see now days. We didn’t evolve to live like we do.



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  • Self-identifying gays are still a minority of gays. Most are still in the closet, at least those over 50.
    Kinsey [65 years ago] used to grill people till they “confessed”. But just gets you false high numbers.

    While responsible polling emphasizes the caveat that data collected from self-reporting of homosexual, bisexual, and heterosexual orientation contain errors in methodology, substantively reflecting subjects who misreport or refuse to participate, the response rate trends impressively high. No one knows the exact share of LGB persons in the population but a synthesis of the best studies suggest a reliable range of 3.5% to 5%. I doubled the 3.5% figure to 7% to assure an estimate significantly higher than the consensus. The doubling probably “overcounts” the LGB population by at least 1% to 2%, and as much as 3% to 4%. Note that contemporary gays seem forthcoming and eager to self-identify thereby boosting their numbers in the socio-political arena shaped by a sea change in cultural consciousness shifting towards promoting gay rights and celebrating gay pride.

    I thought Dr. Dawkins made a great comment about genes not being expressed now the way they were back when we live in isolation in small groups. I think that may be the key to understanding alot of behavior that we see now days. We didn’t evolve to live like we do

    If there is such a thing, “genes [per se]” that express homosexual orientation in behavior enjoy far more “freedom of expression” today than in our distant and more recent past before 1970. Harsh legal, moral, cultural and religious sanctions have been imposed on homosexuals, oppressed, terrorized and tormented for most of human history. Currently we may be witnessing the unfolding of authentic homosexuality whose liberated expression has been welcomed by progressive majorities in straight developed societies for the first time in history.



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  • Well that depends on the timescale you are looking at. For the bulk of human history the growth in the number of human adults was minuscule (especially compared to modern growth rates). By definition this means that on average two adults raised an average of just over two children to sexual maturity,



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  • you might be confusing deviant behaviour from natural homosexual behaviour.

    David, thanks for pointing out this commonly confused view of sexual orientation. It is an important distinction which many Xians don’t appreciate. A number of family and acquaintances have shown this confusion to me when discussing the Catholic clerical problem. They believe the perpetrators are gay because the raped children were mostly boys.

    I always school them about the spectrum of normal orientations and such perverted deviant behaviour. Harking back to your anecdote about the sale of prized bulls – gay bulls (or other species) aren’t interested in engaging a calf. Juveniles aren’t sexually attractive, normally. That seems to occur only in primates who were subjected to regressive or perverted religious sex ed.



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  • Surely the first question should be…. how are heterosexuals attracted to each other?. Not an evolutionary explanation which is well known, but an biological one. I.e how and by what actual biological and biochemical processes do opposite sexes attract? . As far as I know that has not been scientifically adequately explained, and until it is we cannot hope to answer the related gay question. If we cannot adequately biologically or biochemically explain how one individual is attracted sexually to another, irrespective of orientation, it seems pointless to single out gay attractions as if they needed some “special” or “different” explanation.

    Ignoring my own stricture it would seem fairly obvious , as other people have pointed out,that it cannot be primarily genetic . Which leaves the possibility that it is epigenetic or developmental, or both.



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  • 142
    vsherren1 says:

    I’ve heard that, for the purpose of breeding, the animals (like the T-Rex for instance) can change their sex – that isn’t homosexuality in the human sense – that’s evolution ensuring the survival of the species (including mankind)? Is this why a number of humans feel they’re in the “wrong body”?



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  • 143
    vsherren1 says:

    I’m pleasantly surprised that my little comment was actually included. The comments of the other people looked quite daunting for someone like me (I’m fascinated by science but not scientifically experienced).



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  • Surely the first question should be…. how are heterosexuals attracted to each other?. Not an evolutionary explanation which is well known, but an biological one.

    If as a male, I see an attractive healthy female, my brain gives me a hit of hormones. It makes me feel warm and fuzzy. Probably oxytocin but may include a cocktail of chemicals. These chemicals make me attracted to the female and want to mate. NOW. Hollywood, and teens confuse this feeling. They call it love at first sight, but it is actually a desire to mate with a good set of genetics. To put it bluntly, lust at first sight. Many a marriage has been based on lust, but usually fails, because lust only lasts long enough to impregnate, then your off. If you marry in lust, after the glow goes, you find that you don’t actually like the underlying human being. Divorce. You actually have to like the human being behind the body.

    Every feeling you feel is a chemical reaction in the brain. Fear – adrenaline. etc. That’s how the brain works. Chemicals / receptors. The biological process that attracts opposite sexes is chemical / hormonal. In homosexuals, it is identical, but because of brain misalignment, those very same chemical floods cause the attraction to the same sex.

    Ever been to a great rock concert. Know all the words. Sung our heart out. You leave all warm and glowing. The same feeling that the drug Ecstasy gives as it hits the same brain receptors that oxytocin hits. All warm and glowing. The happy clapper christian revivalists know this feeling with the rock concert style religious services. The clergy tell their sheeple that this is the spirit of god moving withing them. No. It’s just hormones.



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  • Welcome aboard vsherren1. Every player wins a prize here. There are some brilliant people inhabiting these places. Ask questions. Say what you think. People will provide references, guidance, evidence and arguments in support of their positions. Great fun and enlightening.



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  • David R Allen Mar 30, 2015 at 5:18 pm

    It makes me feel warm and fuzzy. Probably oxytocin but may include a cocktail of chemicals.

    ….. . . . …..

    The same feeling that the drug Ecstasy gives as it hits the same brain receptors that oxytocin hits. All warm and glowing. The happy clapper christian revivalists know this feeling with the rock concert style religious services. The clergy tell their sheeple that this is the spirit of god moving withing them.
    No. It’s just hormones.

    I might as well add the link to the science of the mechanism:

    http://faculty.washington.edu/chudler/synapse.html

    Many psychoactive drugs and neurotoxins can change the properties of neurotransmitter release, neurotransmitter reuptake and the availability of receptor binding sites.



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  • 147
    vsherren1 says:

    I’ve watched a number of documentaries about nature, and there seem to be an unexpectedly high presence of same-sex relationships with animals from monkeys to penguins. I’ve also heard that creatures such as a T-Rex can change sexes to ensure that breeding can occur, which gives the species a chance of survival. There are many types of organisms that are hermaphrodites, which I think is another evolutionary mutation to give the organism a better chance to live. These ancient evolutionary codes can be very deep-seated in our genetic make-up and may actually connect the different species (such as human beings) on a much primal level than we think. One query I have is whether, given all the technological advances (such as IVF or surrogacy) whether homosexuality, bisexuality and other sexual types will matter any more – it can all be done chemically without all that nasty touching – all that is needed are sperm banks and do-it-yourself impregnation.



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  • 148
    vsherren1 says:

    Thank you, David for your welcoming words. Having read a large number of the posts, I felt I had a few views of my own – but that is what learning is all about
    we exchange ideas & thoughts and, hopefully, we learn from each other



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  • If we cannot adequately biologically or biochemically explain how one individual is attracted sexually to another, irrespective of orientation, it seems pointless to single out gay attractions as if they needed some “special” or “different” explanation.

    Steve, the point is that we can adequately explain human sexuality. David R Allen and Alan 4 discussion, both scientifically literate laymen, do more than a fair job of filling in some blanks above. There are many sources available through Google on the internet authored by scientific experts in academia or research fields. Youtube almost certainly provides many lively and comprehensive video lectures delivered by qualified, sometimes eminent, biologists, physiologists, neurologists, and science educators speaking on the subject.

    On the other hand you may be asking about the “magic spell” a young man falls under when cast by the “goddess” he falls in love with. It’s harder to Google that one. Beats me.

    it seems pointless to single out gay attractions as if they needed some “special” or “different” explanation.

    Gay attractions require “variant” explanations and are “special’ only in the sense that homosexual orientation is relatively rare in the human species. No moral disapprobation is intended or relevant.



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  • I did not put my point clearly, and fully accept your explanation of what attraction, once it has risen, is in terms of hormones etc.

    My point was more , Why does person X, or Set of persons X, trigger these feelings rather than person Y or Set of persons Y

    I understand the explanation of the feelings AFTER they have been triggered, my question was what biologically speaking causes the trigger to trig?(sic)

    You cannot explain it in terms of the physiology after the trigger is activated and, as the triggered feelings are the same irrespective of orientation, the explanation must lie in how the trigger is activated by X but not by Y.

    T



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  • I did not put my point clearly, and fully accept your explanation of what attraction, once it has risen, is in terms of hormones etc.

    My point was more , Why does person X, or Set of persons X, trigger these feelings rather than person Y or Set of persons Y

    I understand the explanation of the feelings AFTER they have been triggered, my question was what biologically speaking causes the trigger to trig?(sic)

    You cannot explain it in terms of the physiology after the trigger is activated and, as the triggered feelings are the same irrespective of orientation, the explanation must lie in how the trigger is activated by X but not by Y.

    T



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  • *it seems pointless to single out gay attractions as if they needed some “special” or “different” explanation.

    Gay attractions require “variant” explanations and are “special’ only in the sense that homosexual orientation is relatively rare in the human species. No moral disapprobation is intended or relevant.

    **

    My point was not moral. Everybody of whatever orientation has a certain “type” to which they are most attracted e.g blondes, muscular, slim, young etc . If we ignore the gender of the persons having the attraction, and then break down and categorise the objects of desire, would we then be able to even recognise something called homosexuality? Homosexuals desire the same types as heterosexuals, there is no “variant” homosexual desire to be found. Where is the homosexual variance we need to explain? If we cannot recognise homosexuality so to speak “blind” then the whole debate hinges on us presupposing, as a biological “norm” ,a gender split in sexual desire based on gender, somewhat circular reasoning.



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  • Humans are part of natural world, we are not on a seperate plane, so surely our interaction with other animals is as much “natural” selection as any other predators relationship with its prey.



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  • Steve Mar 31, 2015 at 1:18 pm

    Humans are part of natural world, we are not on a seperate plane, so surely our interaction with other animals is as much “natural” selection as any other predators relationship with its prey.

    . . . . . . A good point to remember when considering the environment:- . . . . . . . but “artificial”, can be a convenient label, to distinguish deliberate human managed changes, from other non-managed changes, when dealing with topics like breeding domestic animals.



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  • In these days is not self identification as much political proposition as a biological one.

    “Homosexuality” seems rather vague. No problems in definition with people who are 100% gay(sic), but what about someone who has the occasional gay thought or experience, and how many of these do they have to have before being considered homosexual and exhibiting “variant” behaviour in need of genetic explanation?

    Does the fact that a male felt a “stirring” on seeing say, David Beckham, need a different genetic explanation than if he felt a stirring on seeing Beyonce?

    If you say sexuality is a continuum then again, why does one part of that spectrum require a different genetic explanation than the rest?



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  • Forgive my ignorance but I always wonder when I hear discussions on this. Why must there be a “homosexual” gene rather than an “attracted to men” gene passed down from the mother or an “attracted to women” gene passed down from the father which sometimes get passed to offspring of the opposite gender?



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  • Genes get passed on to girls as well. A male homosexuality gene may manifest in them in the obvious way, but might just remain silent unless in a male.

    So if a homosexual male has 4 siblings who each have at least 3 kids each instead of the usual 2, the gene has broken even. Extra brothers are better, because they can “play the field” and leave more offspring (not necessarily care for them).

    Suppose a gene manifested itself as follows: play it straight if you’re the eldest, or have fewer than 4 brothers. If you have 4+ brothers, and none are gay yet, then be gay. [4 is an arbitrary choice.]

    In generations or genders where the gene doesn’t manifest, it gets passed on silently and does no better and no worse than average. When conditions are ripe (loads of brothers), it yields a small pay off.



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  • 158
    mistermack says:

    Instead of asking, why are there homosexuals, maybe we should consider what it would take to produce a population with no homosexuals.

    If you think that any reproductively negative trait should have died out long ago, you will be constantly proved wrong by the facts. Why should some men and women be infertile? Why should some have Down’s syndrome? Why should some people be born deaf or blind? Or any of the other genetic occurrences that produce an individual that was less likely to reproduce in the wild state of our ancestors? There are lots of genes that persist in the general population, that would eliminate any chance of successful reproduction of the individual, in our wild ancestral state. Genes that might increase the chances of a human becoming homosexual are just one example.

    One major reason why such genes still exist, is that they don’t cause a problem in every case. They are successful genes, except when they are combined with certain others.
    The population can withstand some failures, it always produces an excess of young, and some wastage is no problem at all. That’s how evolution works.

    To produce a perfect population of heterosexuals only would be difficult to achieve, in a system {evolution} that thrives because of variety.

    Humans are sexually attracted by mostly visual and audible signals. To achieve perfection, evolution would have to make the signals unmistakeable and the brains perfect in the reading of the signals.

    In today’s society, we exaggerate the signals, with clothes, makeup, grooming and plastic surgery. Our wild ancestors didn’t have any of that. The visual difference between the sexes was much less striking. And some women have quite quite deep voices, and some men have quite high voices. Some women have tiny breasts. Some men have quite pronounced ones. Some men have big prominent penises. Some have small ones. The same goes for any characteristic that is attractive to one or other sex.

    So any individual that responded only to the clearest sexual signals would be missing out.
    So being less than binary sexually increases the chances overall of successful mating.



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  • Global distribution of our “out of Africa” ancestors would create great spaces between groups (as it did). Different languages would develop because of environmental and spacial differences regardless how much language determination is genetic. To say we would all speak the same language is ridiculous.



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  • 160
    Weverton says:

    Is it not easier to understand that for genetic reasons he or she developed homosexual tendencies rather than blaming religion, parents care, childhood, etc.?



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  • I believe it is environmental and how we are disciplined, watch our parents interact, gravitate to or away from same sex influences due to social atmospheres determines the outcome of how we experience sexuality by the same or another gender. As a female who discovered my anatomy late in life to the extent in which the full desires became very much made aware of, had I been taken by the same gender to the fullness I now know I am capable of it would have most definitely had a psychological effect upon my self image and the graces of an ideology that accepts that lifestyle would make it more comfortable for me had it happened that way. I am glad I experienced my full sexuality with a male however the genders we are surrounded by do affect our visual, mental and behavior outcomes. The shaming that religious rhetoric does to people who has not been educated regarding anatomy sexual responses and the confusion in understanding human behavior it causes is a psychological crime speaking from a females standpoint.



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  • I would also like to add I experienced the fullness of my sexuality with MY HUSBAND. We were involved in church and a split occurred due to divisions regarding a leaders background in which few knew about. I sat back and watched people act terrible wondering why. Now I know to what extend lust must be controlled by a female.



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  • Researchers in Australia have discovered that mourning cuttlefish (Sepia plangon) have the unique property of being able to change the coloring on one side of their body to mimic the coloring of a female to fool rivals.

    Remind me to song played in mrs. Doubtfire movie. Dude looks like A Lady!


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