Field of Science

Homosexuality is not a choice

ResearchBlogging.orgWhat are the causes of homosexual behavior in animals? Contrary to what most people probably think, homosexual behavior is not just common in animals, it is catholic.

A new paper in TREE has gotten a lot of press (most papers on sex do, I suspect): Same-sex sexual behavior and evolution, by Bailey and Zuk at UC Riverside.

In their table 2 (email me for copy of PDF) they list a wealth of hypotheses about the nature of homosexual behavior, but I find it very incomplete:

Adaptive explanations: Social glue, Intrasexual conflict, Practice, Kin selection, Indirect insemination, Overdominance, Sexually antagonistic selection
Non-adaptive explanations: Mistaken identity, Prison effect, Evolutionary byproduct, Maladaptation, Infection

I do very much appreciate this list, because so many people insist - consciously or not - that there must be an adaptive reason for homosexuality. There need not be. My own personal, unfounded, suspicion is that homosexuality in humans can best be described as a by-product; hormonal balances in utero that sometimes (say, about 10 percent of the time) shift slightly, changing the preference for sexual partners. But notice that whether an adaptive or non-adaptive hypothesis is supported, they all imply that the animal does not choose to be sexually attracted to one sex or the other. It would be rather hard to argue that fruit flies and penguins choose it (I dare you to try), and if so, it makes me wonder what basis there is left to suppose that humans do.

I said I find the list incomplete, so what missing? This:

The Christian explanation: Choice

It's more than a common idea among American Christian homophobes that homosexual people choose their own sexual desires. For example, one person commented on my post about Safeway posters that "Homosexuals choose a lifestyle, they are not born that way." Which is completely unfounded. There are many Christian prayer groups that try to help homosexuals change their ways (e.g. Exodus International). Their stupid prayer groups does nothing but suppress the nature of homosexuals. Why do I believe that? Because that's what the evidence tells us. The evidence from animals, and the fact that no heterosexual would ever admit that they chose to be heterosexuals, which leaves no argument left that anyone ever chose to be homosexual either.

Nathan W. Bailey, Marlene Zuk (2009). Same-sex sexual behavior and evolution Trends in Ecology & Evolution


  1. Hmmm....still having problems with the Name/URL option. No matter.

    It's like fundamentalists and...well, I guess pretty much anything sex-related, but I'm thinking here about their apparent firm conviction that if you don't teach kids about sex, they won't do it. Because Humans Are Not Just Animals, and don't have instincts, so the fact that nowhere else (that I'm aware of, anyway!) in the animal kingdom do the critters fail to breed due to a lack of education on the particulars, isn't relevant to humans in any way. Flip side: if the kiddies find out about sex, they'll do nothing else---especially if they find out about (dun dun DUN!) contraception!

    So, you see, all that data about homosexed animals is completely beside the point. Apples and anvils, really.


  2. A hormonal (im)balance in utero? So you think that even though homosexuality is common in all kinds of animals, including insects and birds it has a different cause in mammals than in the others?
    Well, I guess it's not clear at this point, so you could be right, but I find that hard to believe.

  3. Why do you find it hard to believe?

    Hormonal imbalance here or there. In the uterus, in the egg, in the pupa. I think it's a fair hypothesis, is what I'd say to be rigorous.

  4. A hormonal (im)balance in utero?

    Without picking too many nits I must say that I have a problem with the implications in the use of the term "imbalance". This is not a defect we're discussing. As Bjørn said, we're talking about a shift, simply a part of the hormonal balance spectrum and not an "imbalance". Interpreting this as an imbalance is just fueling the We-can-fix-it fires.

  5. Without picking too many nits I must say that I have a problem with the implications in the use of the term "imbalance". This is not a defect we're discussing

    While I understand you are trying to avoid giving the wackos a toehold, this is a bit too much sensitivity. firstly it's you that went from the relatively neutral 'imbalance' to 'defect' and took offense at it. What exactly is a defect? nearsightedness? in that case I have it in spades. Am I offended by consideing this a defect? no, not at all. some people refuse to use any word that suggests that deafness is in the slightest bit negative. Evolutionarily I don't think that can be justified.

    Homosexuality is benign and harmless, but it does reduce reproductive success, just as something that alters fertility does. Is a survivial disadvantage a defect? Does it really matter which words you choose?

  6. Ah, would you be offended if someone referred to the sick heterosexual lifestyle? Isn't it defective? They beat each other, sell their children into slavery, kill their children, kick them out if they're queer. Heterosexuals are busily OVERPOPULATING the planet that does not have the resources to sustain all these people. Thus, couldn't one argue that the defect is heterosexuality?

    Gosh. Honestly, some of my best friends are heterosexual. It's the sin I hate, not their peculiar and disgusting behavior that they choose.

    (If this isn't snarky enough for you, do let me know!! ;)

  7. While I agree that
    a)The evidence backs it up
    b)It helps the gay rights movement in the short term

    I don't like the idea of pursuing the "homosexuality is not a choice" line politically (I'm talking about politics here, not science) - because it prevents people from asking the question "so what if it were a choice?". The following quote sums it up I think:

    Inherent in the "we can't help it" response to homophobia is the implication that if we could help it, we would. Even when that isn't what we mean, it's what a fair number of straight people hear, including some of our allies. It's easier for some of them to pity us as bearers of a genetic flaw than to respect us as equals. Not challenging them might gain us some votes, but in the long run it means that we're subtly putting the word out that it's O.K. to regard us as sexually defective.
    —Lindsy Van Gelder, "The 'Born That Way' Trap," Ms., Vol. 1 No. 6, May/June 1991

  8. Anon, I didn't actually think about it like that. However, I still think everyone understanding that sexual desire really isn't a choice will help also in the long run. But of course, if it were true that we could choose one way or the other, and our instincts would follow, then that really should be okay, too. I don't, however, think that the inference that if it's not a choice then it's a genetic flaw is valid. Besides, as an evolutionary biologist, I don't accept anything as a genetic flaw.

  9. Well, I should have said that I don't agree on the "genetic flaw" phrase in the quote either, but the majority of people who are either not very knowledgeable on biology or who are not interested in thinking about the matter too seriously will interpret it to mean some kind of "biological flaw". Lindsy Van Gelder herself seems to have fallen into that trap.

    But I agree with Gelder that a lot of straights can pursue this line of thinking and end up pitying gays without being aware of it themselves.

  10. More education seems to be the way forward (isn't it always). Shame that parents choose to homeschool their kids exactly because they are afraid what they might hear in sex-ed.
    (Previous post on homeschooling.)

  11. Terms like "imbalance" and "defect" indicate that it is negative and if it could be changed it should.

    Whether or not it's good for natural evolution we humans need to consider our own needs, which are different from other species. With the new technology we aren't bound by natural selection. Soon we will be able to choose genes in utero. And we can already reproduce through in-vitro insemination. Even without the technology we're smart enough to figure out that if you're gay and you want to reproduce just have sex with the opposite sex not for pleasure but for the sake of having kids. This isn't necessary because of technology, but we're smart enough to figure it out anyways.

    Also if its to be considered a defect shouldn't we call the defect "aheterosexuality", because it's not the homosexual behavior that is a disadvantage to reproduction, it's the abstinence from the heterosexual behavior, and so asexuals would be considered to have this defect but not bisexuals? A person who has sex with a certain number of fertile members of the opposite sex still has the same chance of reproduction no matter how many times they have sex with the same sex.

  12. I'll just add...

    Since with technology nothing is really a hindrance to reproduction labelling something as "disease", "defect", "disability", "flaw", or what ever should be based on its inherent effect on quality of life and ability. Homosexuality does not have an inherent effect on quality of life. As for ability it can be argued that it's disabling because they aren't attracted to the opposite sex, but by that logic it's as disabling as heterosexuality and only bisexuals are truly healthy.

  13. With the new technology we aren't bound by natural selection.

    Oh yes we are. Unless we can, and do, choose the exact genetic makeup of all humans born, we are still very much under selection. It's a pervasive process, and while you may shift the fitness landscape in a significant way, you will not be able to negate selection. Saying so just makes it clear that one hasn't really understood how natural selection works (Steve Jones comes to mind)

  14. Sexual desire is never a choice, whether it is hetero, homo, pedophile, or bestial. Sexual behavior is _always_ a choice. Gay advocates are unwilling to distinguish between the two because they believe that the right of those with homosexual desires to act on those desires is absolute. In reality, society always has made and continues to make somewhat arbitrary decisions as to what sexual behavior is allowed. Why, for example, should society allow gay marriage but forbid polygamy?

  15. Loren, that's a very good point, the distinction between desire and behavior. I agree that behavior is a choice, of course. However, to say that homosexuals are unwilling to make the distinction is a disingenuous and unfair generalization. What homosexuals will probably for the most part argue is that they, or anyone, should be allowed to do what they please with consenting adults behind closed doors.

    You then move the discussion from sexual behavior to marriage - two things are are not the same at all.

    There can be no doubt that homosexual couples who wish to marry both consent to it as much as heterosexual couples. Additionally, as for all the benefits that comes with marriage, nothing has to be redefined except that they should also apply to couples of the same sex.

    Polygamy is quite a different story in both cases. Should three men who are all married to the four same women file tax jointly, all get the same benefits from the state and AAA, and should they be allowed to divorce from each other in any combination possible (e.g. all seven are married, but can one woman divorce one of the women and two of the men only?). More importantly, though, is that there is some evidence (put forward without references, I admit) that some people in polygamous marriages are part of it against their will.

    Also, we must all admit that there is a huge demand for changing the law to allow same-sex marriages. This much is undeniable. But I wonder if that's the for polygamy. I suspect/hypothesize that same-sex marriage will be no more used to deceive the partner than heterosexual marriage is, but that polygamous marriage will be taken advantage of for personal gain. I would like this clarified before (or soon after) polygamous marriage is allowed.

    That being said, I don't have any deep aversion against polygamy, if all problems mentioned here can be solved satisfactorily. For me, marriage is not holy, but rather just a requirement from society to file tax jointly, to live with my spouse (we are both foreigners), and to make sure we both are legal guardians of our children, etc.


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