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Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Tuesday, July 11, 2006

On the biological basis of homosexuality

A study published in the prestigious Proceedings of the National Academy of Sciences by Ivanka Savic and colleagues indicates that the brains of lesbian women react differently to sexual stimuli when compared to those of heterosexual women. The researchers found that lesbians respond to both AND, a progesterone derivative, and EST, an estrogen-like substance – both hormones involved in sexual responses in humans. The interesting finding was that lesbians process these hormones in a way similar to heterosexual men, and distinct from heterosexual women.

The same group of scientists had previously found that the anterior hypothalamus is activated in response to AND (which is found in sweat) in both homosexual men and heterosexual women, while the same brain region responded to EST in heterosexual men.

All of this strongly hints at some biological basis for human gender preferences, which implies that so-called “re-education” programs – strongly advocated by Christian conservatives – may not work because the “problem” (such as it is) is not a matter of individual choice, but rather of biological preference.

Two caveats, as usual. First, “biological” here doesn't (necessarily) mean genetic. Savic's research shows that the brains of her subjects reacted differently, but it doesn't imply a genetic basis for such differences. Brain structure is known to be strongly affected by environmental influences, particularly by exposure to various hormones while in utero. Still, the same is true for, say, natural propensities for music or math, and nobody in his right mind would suggest that an individual that shows such propensities should be “re-educated” out of them.

Second, one can always argue that biological tendencies, as strong as they may be, can be resisted by cultural conditioning or will power. For example, I have a strong natural tendency to eat fat and sugar, but I fight it (mostly) successfully every day of my life. Then again, the assumption here is that homosexuality is bad for the individual or for society. While I can see the argument when it comes to the dangers of obesity, I fail to grasp why societies should care about the sexual preferences of individuals.


  1. This is something that's in the odd position of both being news and NOT being news, inasmuch as it is just one more confirmational tidbit indicating a biological basis for homosexuality. A number of studies coming at the issue from a wide range of approaches, have all had results consistent with that theory. The legitimate studies, at least.

    Of course, this latest study will quite readily be dismissed by irrational rightists and religionists who continue to insist that sexual orientation is a choice. On what basis can these people claim that it's a choice? They never say. (It usually comes down to something biblical.)

    However, I do want to point out that I agree with you that a distinction must be made between orientation being biologically derived and being genetically derived. The evidence for the former is extensive and growing; the evidence for the latter is still skimpy and preliminary, at best.

    What that means is that sexual orientation, within the realm of human qualities, is better compared with handedness rather than eye-color. In other words, left-handedness, like gayness, is a naturally occuring minority variation, which can, theoretically, be overcome through reconditioning and traing. But it's unnecessary to do so, since both characteristics are not innately harmful, to the self or to others.

    But then, don't bother irrational homophobes with facts--they know what they know, end of story.


  2. Many on the Christian Right have already found a way around a biological cause for homosexuality.

    Some now claim (including Jerry Falwell) that if homosexuality is biological, that's just the way Satan has tempted homosexuals. It is still up to the homosexual to overcome their biology and, thus, Satan.

    So I wouldn't get my hopes up about Christians changing their minds just because science proves them wrong. They usually just rationalize after the fact.


  3. While I can see the argument when it comes to the dangers of obesity, I fail to grasp why societies should care about the sexual preferences of individuals.
    I fail to grasp it, too. And I think this failure on the part of sensible folk like us doesn't bode well for the prospect of actually convincing people to stop caring about others' sexual preferences.

  4. Fundamentalist religionists of all flavors will forever find ways to stick their snouts into, and to attempt to control other peoples lives - of that we can be sure!

  5. in response to anonymous: Homosexuality IF it results in no procreation is clearly a more complex trait to explain than being left handed or having blue eyes. One has very limited evolutionary implications, the other very big ones.

    The real legitimate concern I have heard from some is that increasing acceptance of homosexuality is that it will result in increasing kids raised in homosexual households. Some argue that these are kids who would have no families otherwise. Good point, but do we really want to say gay people only get to raise the unwanted children of the world? As far as I know the implications of having homosexual parents is an open empirical question..although also a moral question for most.

  6. Anyone who claims sexual preference is a choice would logically be bisexual - equally attracted to both sexes and choosing only one through an act of conscious will. If they are not equally attracted to both sexes then they cannot justify a claim that sexual preference is a choice.

    And only they are in a position to know if they find both sexes arousing...

  7. in response to dtae:

    There's a misconception about evolution that you're falling prey to: that only traits that somehow benefit a species' survival are passed on, with all others being weeded out over time. Not necessarily so. Traits can be passed down through the evolutionary process that are species survival neutral. So long as a particular trait does not inherently inhibit a species' survival, it could be passed down in perpetuity. And given that homosexuality as a trait seems to occur with similar frequency in a (very) wide range of species, is an argument that homosexuality is, at worst, evolutionarily neutral, if not in some way evolutionarily beneficial.

  8. For more on what gld is saying:

    This post by Pharyngula blogger PZ Meyers examines
    the question of homosexuality and evolution.

    It discusses whether homosexuality is adaptive or selectively neutral; specifically whether it exists because of group selection, is tied to other selectable advantages or is a developmental byproduct.

    The article is interesting as it illuminates a lot about evolution science and could be talking about any given trait(s). Its interesting to see how complex the nature / nurture thing can be for any trait.

    The post is here....


  9. But wouldn't exposure to hormones in utero still possibly be genetic (thought genetically expressed by the mother and not the embryo)? Some phenotypes really are expressed in offspring but are genetic expressions of parents (one of the first example was about some snail coil curvature).

  10. Exposure to hormones in utero could be an indirect result of the genotype of the mother, but it can also happen because of medical procedures, or simply because of the mother's response to stress caused by external factors.

  11. You can't win this argument. Religious folks would then make the argument that traits ( genetic or environmental ) might make someone more prone to criminal behavior, but we still expect them to follow the laws.

    I, personally, feel that this whole things falls under the whole "freedom and justice for all" category in so far as the government has little to no compelling state interest in differentiating between heterosexual and homosexual relationships. The government can't be hypocritical and turn a blind eye to non-procreating heterosexual marriages yet claim that homosexual marriages do not create children.

  12. When a religious right-winger tries to make a connection between biologically innate sexual orientation and tendencies toward criminal behavior, one has to counter with challenging the rightist's definitions of what is and is not harmful behavior. Clearly, criminal behavior is harmful to other individuals and/or society (depending, of course, on the rationality of the law being broken), which explains why criminal behavior (innate or not) should be repressed.

    Now, religious right-wingers would make a similar claim of harmfulness inherent in homosexuality. They say it threatens families, chilren or, more vaguely, society at large. Of course, when asked HOW homosexuality threatens anyone, they either retreat post-haste, or rely on unproven or disproven tropes, almost inevitably religiously derived.

    So, I suppose the argument CAN be won, if winning can consist of forcing the other side to rely on lies and emotional appeals to a "higher power." But I understand your point. How often does reason actually convince anyone that far out in right field?

  13. I have a friend through work that is homosexual. Several years ago a group of us went drinking in the A.M. after work(worked nights), after several drinks (and other) we managed to get into the philisophical talk and the conversation turned to the subject of his homosexuality. I eventually asked the question of choice to him. I will never forget his reply. With almost tears in his eyes he said "why would anyone choose this lifestyle". He was about as sincere as anyone could be.
    The reason I tell the story is because I could be considered somewhat of a religious conservative, and my point is not to debate the question of choice or not. I honestly believe there is obviously some predisposition for homosexual behavior. My point is, just what does this study actually prove? Massimo states that brain structure can be strongly affected by enviormental influences. So what's to say that the enviorment brought on by a choice to be homosexual isn't soley responsible for the differences witnessed between homo and heterosexual individuals. How do we actual know that prolonged homosexual behavior can't cause the differences measured. Keep in mind I dont actually believe this, so don't eveyone get in an uproar. My point is just that the study doesn't actually prove the root cause for homosexuality is biological in nature.
    In order for the study to prove biological root cause. It would first have to find these chemical differences in people prior to their own discovery of homosexuality. Then use that information to predict who will become homosexual and who won't. so basically the study would have to be done on children and then make the predictions and follow them into adulthood. Then if the predictions used have overwhelming statistical evidence, we can say that homosexuality or at least the desire to be homosexual is biological in root cause.

  14. Jim,

    there is neither evidence nor a proposed mechanism for how engaging in homosexual behavior can actually change someone's brain structure (besides, brain structure doesn't change much in the adult individual). When I mentioned environmental effects I was referring largely to in utero exposure to hormones. All of which is perfectly consistent with your friend's denial that homosexuaity is a matter of choice. Of course, if you ask me, even if it were a choice I would see absolutely nothing wrong with it, but that's another story...

  15. I really think that the earlier comment by "me" puts the issue of choice in the proper perspective. At least it is an interesting thought experiment. And it jibes well with the personal testimonies of numerous homosexuals, who speak of discovering their sexuality, rather than choosing it. On CNN there was a debate in which Jerry Falwell was asked whether he remembered his first interest in girls, whether it was a choice, etc. Of course he remembered his puberty very well, and frankly admitted that there was no choice involved, in any ordinary sense of the word.

    Of course, even if this is true, it does not necessarily mean there is a single cause of omosexuality, which is a complex behaviour, and not just a simple trait. The whole discussion reminds me a lot of discussions of alcoholism, where genetic (familial) factors are posited by some, while others at the opposite extreme cite broadly sociological or cultural factors, pointing out low alcoholism rates in certain cultures, etc.

  16. The real question in my mind regarding this question is first of all - who gives a shit? Biological choice or not, it would be absurd to posit that it is a conscious choice. And should I as an individual really be held responsible by society for an unconscious choice I made as an infant/teenager?

    That said, I have no problem with religious people claiming they feel the lifestyle is wrong. There should be no thought police, and most people feel that way without imposing the view on others. I can also understand the hostility to gay marriage by pastors who under the current discrimination laws would be forced to marry gay couples. How about we just delegalize marriage all together and let people who want to get married in a church do that if they can find one. Problem solved.

  17. As with all desires, there is some biological basis but also a psychological component. Depending on the person and the particular desire, the balance of causation will differ. In general, the more the desire relates to bodily functions, the more the influence stems from biological causes. The more the desire has a biological origin, the harder it is to dismiss or reject. Probably only essential functions like breathing and sleeping are impossible to defeat.

    One could of course, decide to engage or to not engage in homosexual (or hetero) acts without regard to one's desires. You can choose your actions. But you cannot choose your desires. You can only have an influence on your desires, with effectiveness related closely to whether the desire is more biological or psychological in origin.

    Desires are not directly beneficial or harmful, except as the actions they inspire. And there is nothing inherently more beneficial or harmful about homosexual acts as compared to heterosexual ones.

  18. Many Christian groups present themselves quite overzealously, and for that I apologize. I am a Christian myself, and let me assert that the reason we (or society, for that matter) care so much about the sexual orientation of people is because, quite simply, we believe in a right and a wrong. What kind of people would we be if we forwent our convictions for the sake of dodging political/social bullets? I admit, for many of you out there, my faith drives you insane. But trust me when I say that I oppose homosexuality in the most loving and civilized way. The assertion in the above article, that homosexuality may very well be "biologically permissible" does not justify it. In fact, I consider the presence of homosexuality in our world as evidence of the Fall of man, just as my seemingly natural desires to hate, steal, lust, etc., are consequences of this same fall.

    I know a friend who went to Bible school, and he actually met a homosexual student studying to become a pastor. Not only was this guy an amazing person to be around, my friend told me that as a believer in Christianity, he considered his homosexuality to be a result of sinful nature and he had committed himself to a life of celibacy. Let this be a testimony to us all, that there is more than meets the eye when it comes to the "right wing" stance on this subject.


    1. You oppose homosexuality in the most loving and civilized way. Well, what if I were to say I opposed small children in the most civilized and loving way ? Or that I opposed blacks in the most loving manner possible ? You don't need science to understand that homosexuality or heterosexuality is something people pick up when they hit their teen years. Or worse as I've been told by fundamenatalists, that homosexuality occurs as a result of deviant thoughts or behaviors in early adolescence.

      People who are homosexual don't need you to justify it. It is a biological and social fact regardless if science hasn't sorted out it's underpinnings. The world we live in will be a much better place when we all realize that our sexual natures and how we express them as mature adults, between and with other consenting adults, is nobody's business and affects nobody but the individuals involved. Loving in ignorance is just ignorance with a sweet frosty coating on top.


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