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Genetic Factors in Homosexuality

This article in Scientific American would seem to lend support to the theory that homosexuality is not entirely a choice, at least not always. The interesting thing about the genetic theory of homosexuality is, that if it’s correct, is going to imply quite a bit about the number of homosexuals within the population.

Much like the laws of thermodynamics, natural selection is a bitch. Genetic traits that interfere with reproduction don’t get passed on to future generations, and eventually work their way out of the gene pool. This would mean the number of homosexuals should be a good bit smaller than is often claimed (I’ve heard 10% bandied about). If they are high, there needs to be an explanation as to how the trait is continuing to propagate within the population. It’s quite possible it propagates because many homosexuals, because of social pressure, live heterosexual lives. If this is the case, increasing public acceptance of homosexuality should actually reduce their numbers (let’s see the Moral Majority types try to wrap their heads around that one). It’s also possible it propagates through the general population, but gets activated by other factors. I don’t think we really understand enough to make a certain conclusion, but a genetic root for homosexuality should mean the number of genetic homosexuals should be quite small.

Hat Tip to Instapundit for the link.

22 Responses to “Genetic Factors in Homosexuality”

  1. karrde says:

    Per the 10% number…from my vague memories, I believe Kinsey claimed to have gotten 10% of men as homosexual from his surveys.

    However, the same vague memories saw some more-recent (as in mid-1980’s) studies which claimed that something like 3-5% of males in the U.S. have ever had a sexual encounter with another man…

    But since both are hazy recollections, I don’t know how much credence can be given to them.

  2. Stacy says:

    Selection doesn’t operate on all genetic traits. In particular, as Malthus famously discovered, mean intelligence of a population remains the same from one generation to the next, even if only the smarter people reproduce.

  3. Matthew Carberry says:

    karrde’s memories aren’t that fuzzy. The 10% comes from Kinsey, there are multiple modern peer-reviewed and all that studies that put it consistently around 3-5%.

  4. Sebastian says:

    That’s interesting. If that were true how did we evolve from stupid apes to smart apes?

  5. Jake says:

    It’s quite possible it propagates because many homosexuals, because of social pressure, live heterosexual lives.

    I’d say it’s almost a certainty that that is one factor.

    It’s also possible it propagates through the general population, but gets activated by other factors.

    I know one theory I’ve read about is that there is a genetic factor that is activated (or not) by hormonal changes either during gestation or during pregnancy. This would also help account for transgender children, where there is some actual evidence of differences in brain structure.

    Interesting thing to consider: there are children born whose physical gender is the opposite of their genetic gender, often due to hormonal issues during gestation (genetic boys who for some reason did not get the testosterone surge that leads to male development, or genetic girls who did). Possibly homosexuality is something similar?

  6. Keep in mind, for most of our history (and even somewhat true today) most of society frowns on people not getting married and having children. This means that homosexuals often pass on the genetic trait before they come out of the closet.
    Also, with modern science, it is possible for homosexuals to reproduce without having intercourse.

  7. Sebastian says:

    True, but it seems to me that gay adoption is more common than artificial means of reproduction, and even that’s not all that common, AFAIK.

  8. Jake says:

    I believe Kinsey claimed to have gotten 10% of men as homosexual from his surveys.

    However, the same vague memories saw some more-recent (as in mid-1980′s) studies which claimed that something like 3-5% of males in the U.S. have ever had a sexual encounter with another man…

    Of course, the fun part is that pretty much any study requires self-reporting. IIRC, due to the appearance of AIDS, in the 1980s persecution of homosexuality became more publicly known, and somewhat more vicious, which would have had an impact on people’s willingness to admit to being gay, and even on gay men’s willingness to actually have a homosexual encounter in the first place. It’s no wonder Kinsey’s study in the 1950s got higher numbers.

  9. “It’s no wonder Kinsey’s study in the 1950s got higher numbers.”

    (1) Do you really think the 1950 and 50s were a less sexually repressed period than the 1980s? Really?

    (2) There is a fair amount of suspicion that Kinsey had deliberate selection bias within his own data set. Kinsey was very sexually adventurous especially for his time. He knew and used a lot of people living the same lifestyle within his research. There is some evidence that he may have skewed his data set to justify his on inclinations.

  10. Doh! 1940s and 50s.

  11. Drang says:

    If that were true how did we evolve from stupid apes to smart apes?
    I Am Not A Geneticist, but it seems to me that a recessive gene could be propagated generation to generation without influencing behavior, or influencing it minimally.

  12. karrde says:

    I will say that if I read something, I rarely forget it…though I do have to consider the validity of the source, and I don’t always remember the source in precise-enough detail.

    As an aside, there were (in the 1970’s) psychologists researching whether people could switch from homosexual orientation to heterosexual orientation. They studied a subset of people who had an apparent desire to seek the change, or at least attempt it. The success rate was not phenomenal, nor was it negligible.

    (This item I can cite my source on: Clayton Cramer has mentioned it several times in his discussions of the subject.)

    This suggests to me that homosexual orientation and behavior is caused by a mix of forces, even if there is a genetic component.

  13. My understanding is that in complex animals, evolution tends to select for diversity in survival strategies, so that the species can more quickly respond to changing environments.

    Given that humans are social animals that rely on community to survive, and often use physical affection to reinforce both reproductive and non-reproductive relationships, it doesn’t seem especially surprising that the evolutionary selection for varied preferences could regularly produce individuals who aren’t as good at passing on their genes.

    Add the fact that our society pressures many people with flexible preferences to choose one sex and stick with it, inflating counts both for gay and for straight people, and I’d say it isn’t surprising at all.

  14. Jake says:

    Do you really think the 1950 and 50s were a less sexually repressed period than the 1980s? Really?

    No, but I didn’t say that, either. I said:
    “in the 1980s persecution of homosexuality became more publicly known, and somewhat more vicious”

    Perhaps “more highly publicized” would have been a better way to say it. There was more awareness of it. I would also say that the rise of HIV/AIDS, the early lack of knowledge about how it is spread, and the way it was framed as “the gay plague” may have caused the actual incidence of violence against gays to increase. It definitely added to the pre-existing stigma attached to homosexuality.

  15. “It definitely added to the pre-existing stigma attached to homosexuality.”

    Just to clarify. Yes, you’re arguing that homosexuality was more stigmatized, repressed, and persecuted in the 80s than the 40s and 50s. Not all sexuality, but homosexuality. You can try to dress it up, but that’s really it, isn’t it?

    Can you name a 40s or 50s equivalent to Paul Lynde? Or Charles Nelson Reilly? Or Jim J. Bullock? Or Freddie Mercury? The 70s and 80s are dripping with prominent gay men in popular culture. In comparison Rock Hudson was gay, but fought hard to stay in the closet his whole life. Liberace sued a tabloid that alleged he was gay in ’56 and denied it until the day he died. I don’t have hard numbers on this, but I don’t really buy it.

    According to Wikipedia (big grain of salt!) Kinsey didn’t buy into the idea that gay/straight was boolean anyway and used a continuum scale to classify individuals. He thought that 10% number was at best a useful oversimplification.

  16. Jake says:

    “It definitely added to the pre-existing stigma attached to homosexuality.”
    Just to clarify. Yes, you’re arguing that homosexuality was more stigmatized, repressed, and persecuted in the 80s than the 40s and 50s. Not all sexuality, but homosexuality. You can try to dress it up, but that’s really it, isn’t it?

    Ugh. I seem to be suffering from a lack of clarity of expression today. Ignore that sentence – it was really comparing the ’80s to the ’70s more than anything. Poor writing on my part.

    I’ll clarify: I am not saying that homosexuality was more stigmatized, repressed, and persecuted in the 80s than the 40s and 50s. If I said or say anything here that implies that, please take it as me not expressing myself clearly.

    What I am saying is that the stigmatization, repression, and persecution was more widely known and acknowledged in the 80s than in the 40s and 50s (when the general attitude was that it wasn’t a suitable topic for discussion in polite society), and that violence against gays was more widely publicized as violence against gays, which may have caused a greater reluctance among gays to admit to homosexuality, even in an ostensibly confidential study. I’m also saying that AIDS contributed to that increased publicity, caused some gains made in the 60s and 70s to be lost, and may have caused increased violence against gays.

  17. ParatrooperJJ says:

    Hopefully a vaccine will become available.

  18. Sam says:

    I’ve seen a study (which I can’t remember the details of now) that suggested that some of the genes tied to homosexuality in men were tied to increased fertility in women. Genetics is a complicated science, with many genes having many unrelated effects, or having a variety of different effects when combined with the presence of other genes. It’s entirely possible for a gene that isn’t necessarily evolutionarily beneficial to still be passed on for generations and generations.

  19. Jim W says:

    It’s also possible that homosexuals serve a similar purpose to non-reproducing insects in a beehive. From a reproductive standpoint, males are mostly superfluous. We exist to provide genetic variety and our strength and risk-taking proclivities make us well suited for attacking cave bears and tigers which would otherwise be threatening reproductive females. But our usefulness, from a reproductive standpoint, consists of a few seconds of muscular contractions prior to conception. Getting to those seconds and dealing with their consequences consumes enormous amounts of energy.

    Homosexuals are basically just the male of the species minus all the reproductive baggage. Think about it- homosexuals tend to be highly successful because they aren’t burdened with families or children. This frees up their siblings to engage in child rearing behavior because their inability to bear children gives them a lot of excess resources.

  20. Alpheus says:

    “But our usefulness, from a reproductive standpoint, consists of a few seconds of muscular contractions prior to conception.”

    This assumes that the male’s only contribution to reproduction is genetic. Humans are much more complex: we teach our children, and it takes *years* for us to do so. Polygamy may confirm your statement somewhat–for a male can be a husband to several females, and can still be around to teach the children–but even still, the male has an important role.

    I’ve always been bothered by the “nature vs. nurture” debate: it assumes that we are either raised to behave a certain way, or have a genetic disposition to do so. It ignores a third aspect of our behavior, in that we also have free will, to either accept or reject whatever we are taught, or to alter how we are initially programmed (for better or worse).

  21. Matthew Carberry says:

    “That’s interesting. If that were true how did we evolve from stupid apes to smart apes?”

    There are several assumptions in that question. ;)

  22. Kinsey’s work never claimed that 10% of the population was homosexual; that’s a misrepresentation of his work done to create fear among politicians about voting against gay interests. Kinsey’s work had problems at least partly because his sample groups were hardly typical: disproportionately prison inmates, mental hospital inmates, and other socially marginalized populations. (Any guesses what sampling groups overly heavy in long-term, sex segregated institutions might do to sexual behavior results?)

    While Kinsey made a legitimate effort to adjust his raw data, he relied on four variables for making the corrections: race; sex; and two others that were not terribly useful. (Can’t remember: I read Kinsey’s works about fifteen years ago.) Getting raw data correctly adjusted for general population is a struggle under the best of conditions. It is also likely that in the 1950s, people prepared to honestly answer taboo subjects about sexuality were unlikely to be typical of the general population.

    When AIDS hit, a lot of energy was put into studying human sexuality, and pretty consistently, across multiple developed nations, they found that the percentage of those who had engaged in sex with a member of the same sex in the last five years was about 3-4.5% of men, and about 1-2% of women. The last five years matters quite a bit on this, because a significant fraction of those who do so move beyond it, into purely heterosexual relationships.

    Robert Spitzer, the psychiatry professor who led the effort to get homosexuality removed from DSM-III as a disorder, published a paper some years ago studying reparative therapy. A range of reparative therapies, both secular and religious, were represented, and seem to have been similarly effective.

    Of those who went through it (probably not a typical population of homosexuals, because they wanted to change), about half reported substantial change not just in behavior, but in sexual orientation. It was not a binary result. Some who had been exclusively homosexual were now attracted to heterosexuals; some bisexuals were now exclusively heterosexual in attraction. Of course, about half made no progress at all.

    There may well be a genetic aspect to homosexuality. But a number of longitudinal studies have found that victims of child sexual abuse are disproportionately adult homosexuals. That does not mean every homosexual was a victim, and certainly, many victims do not become homosexual. But does it really surprise anyone that premature sexualization might interfere with normal sexual orientation as an adult? It sure messes up a lot of other things.

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  1. SayUncle » Those genes look good on ya - [...] looks at genetic factors in homosexuality. The linked article is entitled Is your child a “prehomosexual”? Forecasting adult [...]
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