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Biology and Homosexuality 9 June 2006

Posted by Todd in Biology, Democratic Theory, Gay Rights, Homosexuality, Inequality & Stratification, Sexuality.

[This is a response to a comment made my Allen Lambert on another post (edited intro 6/30/07).]

Mr. Lambert is partially correct. There is no gay gene (at least none has been found so far) and hormones are not to blame (gay and straight people have indistinguishable hormone loads; although gay men recover much more slowly from a female hormone overload than do hetero men). However, biology is vastly more complex than this would imply. Genes act in cascades, more like a recipe than a blueprint; and they act in response to environmental influences, most notably here, the environment of the womb. Genes, cell growth and mutation, hormones, enzymes, proteins, aging, development, etc., all act in concert to create the phenotypical diversity of the human population.Any one study on the origins of homosexuality or one line of thinking alone is not sufficient to indicate a biological etiology. However, taken together, the evidence is overwhelming that the homosexual phenotype is biological in origin (if expressed in vastly diverse ways among human populations).

Here’s a brief rundown of the high-points:

1-Social scientific data: all societies ever studied have a minority population that is same-sex oriented (although they have different roles for such individuals and different meanings for such a sexuality). See the work of Stephen O. Murray for a run-down.

2-Zoological data: indicates that nearly all bird and mammal species have individuals in their population with preferences for sex with members of their own sex. See the work of Bruce Bagemihl for a summary of this data.

3-The Gay Gene: Dean Hamer and his colleagues found an area on gay men’s x-chromosome that appeared to be passed on through the mother’s line. However this line of research has not been able to be verified and appears to be a dead end for the moment.

4-Maternal pattern: However, the statistical relationship between the maternal line and gay sons conducted by Hamer has been verified numerous times. That is, homosexuality is not evenly distributed in the population, but is actually found to be more dominant in some families, and seems to follow the mother’s line, indicating heritability.

5-Twin Studies: Early studies were faulty methodologically, but more recent studies, most notably those conducted by Michael Bailey and Richard Pillard, found that when one identical twin is gay, there is a 52% chance they other is also gay; one one fraternal twin is gay, there is a 22% chance; and one separate-birth sibiling is gay, only a 6-10% chance (i.e., the general population). This has been validated in over 14 different studies, and has been shown to hold true for both gay men and gay women. This indicates both heritability and that something environmental is at play (most likely developmental, that is, part of the process of fetal development). There has been more recent studies that have indicated that whether or not the twins share an amniotic sack basically clenches the deal. That is, when identical twins share an amniotic sack, they nearly always have the same orientation, gay or straight (I’ll have to look up the authors of that study.)

6-Fraternal Birth Order: Dr. Ray Blanchard and colleagues discovered accidentally that with each subsequent male birth to a given women, the chance that the boy will be gay increases by about 30%. Older sisters do not affect the probability, only older brothers. Later studies found that whereas normally subsequent male births have higher birth weights, gay male births have lower birthweights. These studies have been reproduced and verified in numerous populations. They indicate again a heritability and a connection between the mother and the gay son. (This particular pattern does not hold true for lesbians.) Dr. Blanchard argues that this seems to indicate an immuno response in the mother (a genetic process) to a male birth. The most likely hypothesis from this data as it now stands and as we understand fetal development now is that when a child with a genetically possible phenotype of homosexual is in the womb of a woman whose genetic phenotype has an auto-immune response to a male fetus, the fetus will be homosexual.

7. Brain morphology: In the late 1980s, the first clues that gay men’s brains me be morphologically similar to straight women’s in certain key areas of the hypothalmus and pituitary first emerged (Simon LeVay). These human studies are problematic because they used cadavers for the experiments and its unethical to cut open live humans and measure their brains. However, recent work at Oregon State University has found that a small percentage of rams shows an exclusive preference for mounting other rams. Numerous experiments led these researchers to conclude that among sheep, there are indeed homosexuals. Part of their studies included researching their brain morphologies. The homosexual rams’ brains were identical to the ‘normal’ rams’ except in those key structures of the brain regulating sexual desire and response. Although these aren’t human experiments, they support the older data gathered from human cadavers. Among biologists, similarities among mammals, although not conclusive, is highly suggestive; the OSU research adds weight to the highly controversial studies of Le Vay.

8. Fingers: In the late 1990s, a group of scientists (Terrance Williams, et al) found that the ratio of the finger length of the ring finger to the index finger was the same between straight men and gay women; and between gay men and straight women. The significance of this study is that we know very much about how finger lengths develop (the gene cascades that stop and start finger development in utero), and so given the corresponding ratios across sexual orientations, this indicates again a developmental component to homosexuality. These results have been verified and reproduced.

9. Pheromones: The pheromonal studies are quite recent, within the last 18 months, and were simultaneously conducted at a the Karolinska Institute in Sweden and another in the United States at the Monell center. They have repeated the experiments this past year, and are so far withstanding verification processes. Basically, gay mens brains respond to men’s pheromones like straight womens; and gay women’s brains respond to female hormones like straight men’s. The U.S. study also found (accidentally) that gay men respond more strongly to other gay men; and that straight men respond the least to pheromones from gay men (i.e., the respond more to the pheromones of other straight men). [The weakness in these studies is that human pheromonal studies is tricky and its hotly debated whether or not humans have pheromonal receptors at all. The receptor in our nose was thought to be dormant for many years; but it looks like those were conclusions drawn without study and probably emerging from the old view that humans are “special” or “separate” from other mammals.]

These are just the high points and I haven’t expounded all the arguments and data interpretation (this is, after all, a blog). Again, the point is that taken separately, none of these is sufficient to warrant the claim that homosexuality has a biological etiology; but taken together, they indicate both a heritability and a developmental component to sexual orientation development (in much the same way that height is determined by genetic predisposition in interaction with developmental factors): i.e., homosexual orientation is biological


And so I return to my original point, which is that for those of us in favor of full equality for gay and lesbian citizens, the argument over biology is merely academic and is useless in the public sphere. If we take the stance that it’s biological, opponents of gay rights say “No it isn’t, it’s cultural.” If we say, sexuality is is cultural, the opponents respond, “It’s immoral.”

And so it really comes down to a question of democracy. In a good democracy, the curtailment of rights must be backed by reasons, that is, arguments about the harm caused by allowing a particular behavior, belief or practice. These arguments about harm must withstand rigorous scrutiny, before anyone’s civil rights may be abridged. For 55 years, the best argument that anti-gay forces have been able to mount is that it’s offensive to them, that is, that it’s different from the way they think things ought to be. That is simply not an acceptable democratic argument, inasmuch as one of the main purposes of democracy is to maximize individual freedom.

[posted with ecto]



1. Hellmut - 9 June 2006

You are very cautious, Todd. The fact that homosexuality occurs across a wide variety of species ranging from primates to birds indicates that homosexuality is a natural rather than a societal phenomenon.

The dichotomy between natural and societal is, of course, clumsy. But you know what I mean in the context of the debate over the causes of homosexuality.

2. Capt Jack - 9 June 2006

Interesting piece, Todd.

3. Lunar Quaker - 11 June 2006

Thanks for posting this, Todd. Your insights and your information are always helpful to me.

4. belaja - 12 June 2006

I second what Hellmut said. I understand your points, but I do think that the fact that it is a natural phenomenon shouldn’t just be passed over. It is, it’s true not entirely useful in certain arenas of debate, but I think there are strong reasons to insist publically that it is natural rather than a superficially chosen thing–or worse, some kind of disease. All kinds of pernicious mischief can be got up to if you don’t insist on that, in my opinion.

But really, excellent, lluminating piece, Todd. As always.

5. belaja - 12 June 2006

Hmm. Maybe I meant to post on the other entry. Ah, well. I’ve said my peace ;^)

6. J. Todd Ormsbee - 12 June 2006

I understand what you and Helmutt are saying, and trust me, I never let that bullshit pass (it hasn’t been proved, blah blah blah). It is even more irritating when my colleagues in the humanities and social sciences make that argument. It’s like this particular issue makes them shut off their brains.

Now I need to get back to blogging about other stuff. I”ve been reading about Kuhn lately…maybe I’ll say something about scientific revolutions next… 🙂

7. Tom - 15 June 2006

NIcely done. Thank you.

8. nicolaepadigone - 16 June 2006


as per your request, I’ve moved over from that thread, so you can remain on subject.

“Nic, the fundamental question that you still have not answered is WHY SHOULD a gay person try to conform to hetero norms? There are no compelling reasons whatsoever. Whether it’s a choice or biological, there are simply no good reasons why I should not love and have sex with men. It harms no one and it’s between consenting adults.”

Physiologically speaking, what is the purpose of a penis? What is the purpose of a vagina? What is the purpose of an anus? These questions need a clear anwer it seems.

You make a big fuss about “harm.” Tell me this, if a man gets sexually active with another man, just what does that entail sexually? There is no vagina involved, so where does a man go? Into the anus. Tell me, naturally speaking, without any protection, just how harmful is this to either of the two men? If it is natural, i.e. God created it to be as thus, is there really any harm to either individual? What is the level of “harm” that could happen between two sexually active men in comparison to a heterosexual couple? (controlling for outside sexual activity, let’s say both couples were monogamous all their lives). What is the proportion of other STDs in comparison between gay men and heterosexual couples?

I specifically asked about monogamous relationships because you can more easily control for other factors. If you take a heterosexual couple that has been sexually active before their union, they will probably be at a higher risk of STDs, just like homosexual couples. The point here is to show that naturally speaking, one has a far greater preponderance of diseases than the other.

The reason I bring this up is because nature is great at getting things right most of the time. God designed this world of ours to work, and to work right. When things do not work right, whether out of a flaw in the biology, or out of choice, there is a higher showing of negative consequences, such as disease and death. This seems to show that it really is more of an aberration, even biologically, and not the actual creation God made.

9. ECP - 14 February 2007

Since the “enlightenment” we live in a world where science seemingly rules and popular culture is dominated by notions of “empiricism” and fact. While difficult to retrieve, the powerful mystery of same sex attraction is one of the most compelling parts of ancient culture. Perhaps we are attracted to other men for wondrous, magical reasons that make our lives more complex, and yet more illuminated. However, the most difficult thing for the post-Enlightment crowd to accept is touching and joining for pleasure and joy instead of procreation, even as we live amidst the modern day versions of temple prostitution and public orgy.

10. Biology of Homosexuality, revisited: In humans, it’s a spandrel « Todd’s Hammer - 20 June 2007

[…] are actually mounting the more we study these things, and the evidence is just piling on that homosexuality is biological. Of course, in my own experience, I already knew this, as I don’t remember ever not being gay […]

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