Bryan Caplan  

Born Gay?

Theories of the Recession... Nature, Nurture, and Orientati...
Ryan Sorba, author of The "Born Gay" Hoax, was recently booed at the CPAC convention.  Since I recently read all of the main twin and adoption studies of sexual orientation, I wondered what he had to say.  He focuses on Bailey and Pillard's 1991 twin study, which he correctly reports, "found that 52% of the identical twin brothers of gay men were gay, as were 22% of fraternal twin brothers, and 11% of genetically unrelated brothers."  Sorba's critique:
[I]n order to show that "homosexuality" is genetic using identical twins, one must demonstrate that when one twin is "gay" the other will also be "gay" 100% of the time. The results of this twins study however, fell a long way short of the mark.
If the claim is that 100% of the variance in orientation is genetic, then Sorba's right.  But by this standard, no complex human trait is genetic!  Identical twins are not 100% identical in height, IQ, personality, or criminality, either.  In each of these cases, however, identical twins are much more similar than fraternal twins, indicating that these traits have strong genetic components.  We are not "born gay" any more than we are "born tall," but our genes definitely push us in these directions.  Sorba's just attacking a straw man.

His other complaint is better: "[T]his study shows that unrelated stepā€brothers are both 'gay' more often than genetically related brothers."  This is indeed a piece of evidence against the genetic hypothesis.  If Sorba had merely observed that the results of this study were "inconsistent" and then turned to the broader literature (which confirms a strong genetic component, a mild family environment component, and a lot of randomness), I'd commend him.  But instead, he bizarrely picks one hole in one study, then claims complete vindication for environmentalism.

HT: David Boaz

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COMMENTS (21 to date)
RL writes:

Sorba may argue that gayness itself is not genetic, but he also argues that gays are intrinsically evil and necessarily opposed to a small government agenda. So it seems he believes that while there is no gay gene, there is nonetheless a strong genetic link between gayness and a preference for big government...

David R. Henderson writes:

Alexander McCobin, in the link above, did a nice job. I liked his tone and attitude and I liked the fact that he used the term "advocate freedom," rather than the much more common (and incorrect) "advocate for freedom."
Didn't like the fact that people kept booing Sorba though. One short "boo" is enough to let him know where you stand and then let him speak uninterrupted.

Rachel writes:

In fact, there's a huge environmental component of homosexual behavior. In Ancient Athens, most men engaged in homosexual behavior at times. In modern America, relative few men do. The key is big variation in the potential environments.

Adam writes:

It's exactly as you say--genetics doesn't work the way he seems to think that it does.

Moreover, even if you could demonstrate that genetics plays a very very weak role in the whole thing, it still wouldn't be enough to demonstrate that homosexuality isn't biological--because it could be a trait that emerges as much developmentally (due to conditions in the womb and whatnot) as it does from some specific gene(s).

PrometheeFeu writes:

I think a big issue with this topic is the fact that it has become so politicized. I believe that the environment is an important factor. I also believe that most likely, some personal decisions about how one lives their life probably affects one's sexual orientation to some degree. When exposing my view of the topic to some gay friends/acquaintances, I was instantly told that if I believed that, I believed that gays choose to be gay and therefore I want to kill them all. (This is barely a hyperbole)

Now as it turns out, I have absolutely no preference whatsoever as to people's sexual orientation. I think who should be allowed to marry and under what conditions is definitely not something that should be limited by the government and I think that gay people are just as likely as non-gay to be able to provide a healthy nurturing environment for a child.

But the debate has gotten so polarized and politicized that you are either in the "people are born gay and being gay is fine" camp, or you are in the "people choose to be gay and want to kill gay people" camp. I am quite resentful I must say of being typecast in either camp and I think that there are probably a lot of moderates out there who recognize that the issue is complex and that you can believe the environment has an effect AND that gay people are allowed to marry. It's also possible to believe that gay people should have the same rights as others and that having gay parents does present unique challenges that need to be addressed.

That's my rant.

Carter writes:

Greg Cochran explains it's not genes, it's germs.

tim writes:


Straw man. There is a big difference between homosexual "behavior" as you put it (sex I can only assume) and homosexuality. Just because someone may engage in sex with someone of the same sex doesn't mean they are gay. As it has already pointed out - its a complex issue.

Another note - why are people like Sorba (and Rachel apparently) so obsessed with the sex lives of gay male men? What is always left out of the discussion is gay women. But I guess openly discussion the sex lives of women doesn't conjure up the same fear and loathing among the wingnuts.

agnostic writes:

We have to be careful about what heritable means. It refers to the amount of variation in phenotype (an observable trait like sexual orientation) that is associated with variation in genetic makeup. So it's defined at the level of a population.

It does not mean what role if any genes play in mechanistically producing the phenotype. That refers to the building process within an individual, not the process that distinguishes on individual from another within a population.

The mechanistic process producing the phenotype could be only the function of genes and have no environmental or chance inputs, but if everyone in the population has the same genetic variants or if everyone has the same phenotype, the trait has a heritability of 0.

Conversely, we could have a phenotype that had no mechanistic influence of genes at all, but that was still perfectly associated with genetic differences across the population. This trait would be 100%. Suppose that instead of Social Security numbers, we had a number -- a really long number -- that identified us by what values we had across our genome. Obviously this is a social convention that genes don't mechanistically produce, but differences in genes perfectly predict differences in the phenotype.

Strictly speaking, heritability doesn't tell us that genes are involved in causing the particular phenotype to show up or not. They might if there's a mechanism, like finding genes that code for proteins related to bone growth would make us suspect that the heritability of height was picking up on the mechanistic action of genes.

But there's not going to be such a mechanism for genes causing a male to be preferentially homosexual because these will get weeded out by natural selection. (Google "cochran gay germ" for the basic logic and arithmetic.) To make it more intuitive to folks here: why would a firm not only refuse to seek out customers but also actively turn away any customers that did show up? Obviously that firm will get driven out of business.

Random mutations don't happen at a high enough frequency to produce about 3% of the male population that's gay. And inclusive fitness arguments don't work because the cost they incur by nearly not reproducing would have to be compensated for by raising scores of nieces and nephews, not just acting warmer than a straight male toward his siblings.

Incuhed writes:

@ Rachel - I rearranged your assertion a tad to

"In fact, there's a huge environmental component of homosexual behavior. In prison, men engaged in homosexual behavior at times. In modern America prison....well...The key is big variation in the potential environments."

I don't think any one in prison goes in straight and comes out like John Waters. Don't know what the Greeks were up to, but I'm guessing it was not based on "modern" gay inclinations.

guthrie writes:

@ Tim,

You forget that women aren't supposed to enjoy sex in the first place! :)

Dave writes:

Who cares? As long as no one bothers me or does anything illegal I don't care what they do.

Is this issue ever going to end?

On another note, what incentives are there to keep this issue going ad infinitum? Is there a Gay Inc? like Breast Cancer Inc. Racism Inc. Domestic Violence Inc.

Who's making the money off of this issue?

Jim Ancona writes:

There's also evidence that fraternal birth order (the number of older male siblings a male has) influences the likelihood that he will be gay, and that this effect seems to exist even in sons not raised by their birth-mother, implicating some in-utero cause. See this article for an overview.

Blackadder writes:

There is a big difference between homosexual "behavior" as you put it (sex I can only assume) and homosexuality. Just because someone may engage in sex with someone of the same sex doesn't mean they are gay.

I think most people would look very skeptically on a person who claimed having gay sex didn't mean he was gay (think Ted Haggard).

Another note - why are people like Sorba (and Rachel apparently) so obsessed with the sex lives of gay male men? What is always left out of the discussion is gay women.

The twin study at issue here was about gay men, not lesbians. Also, concluding that someone is obsessed with something based on a single blog comment is both rude and irrational.

Troy Camplin writes:

I've read a few months ago that there seem s to be a connection between pheromone receptors and homosexuality. Specifically, gay men have male pheromone receptors, making them sensitive to male pheromones, and lesbians have female pheromone receptors, making them sensitive to female pheromones.

I have also read that male homosexuality seems to be linked genetically to their mothers.

Add these two together, and you get a connection between sexual orientation and the sex chromosomes themselves -- something we should perhaps not be all that surprised about.

My wife has a gay friend whose brother is also gay, who has a gay uncle on his mother's side, and many gay and lesbian cousins -- again, on his mother's side. This seems to argue in favor of the genetic linkage to the mother. This got me thinking about the possible genetics behind this.

It seems likely that male pheromone receptors are on the X chromosome, and female pheromone receptors are on the Y chromosome. I'm guessing that Y chromosome also has a way of blocking the production of male pheromone receptors. We can make sense of the cause of same-sex sexual orientation with a simple phenomenon: a chromosomal recombination that placed a female pheromone receptor on the X chromosome.

How does this make sense? Through the fact that sometimes, when you add another gene to a chromosome, instead of making more of the gene, it shuts the genes off. As a consequence, the presence of the female pheromone receptor on the X would turn off the gene on the Y, meaning only male pheromone receptors would be made. This would explain the sexual orientation of gay men. It would then suggest that having an X chromosomes having this gene would make a woman a lesbian, since one of the X chromosomes would be acting like a Y.

If true, this should be fairly easy to prove.

fundamentalist writes:

agnostic: "Random mutations don't happen at a high enough frequency to produce about 3% of the male population that's gay."

Good point! If it was genetic, it would have to be caused by random mutations or else it would have died out.

Caplan: "Identical twins are not 100% identical in height, IQ, personality, or criminality, either."

But the differences are quite small, small enough that most people can't tell identical twins apart. If only "52% of the identical twin brothers of gay men were gay", then that is a huge difference. Comparing the tiny differences in the physical features of identical twins with the enormous difference in sexuality is odd. Besides, one could explain the more frequent instances of homosexuality among identical twins who had homosexual twins by the fact that identical twins think more alike (like the same things) to a greater degree than do fraternal twins or brothers/sisters that aren't twins. It doesn't have to be genetic at all.

I think Dr. James Dobson has the best explanation of homosexuality. He has written that the sexuality of boys when they hit puberty is vulnerable to a lot of different influences for a few years. Experiences during that vulnerable period will affect sexual preferences to a high degree. Most of Dr. Dobson's work has been on the dangerous effects of pornography at that vulnerable age, which leads to a large number of deviant behavior. But he applies it to homosexuality as well. If a young boy has sufficient number of same-sex experiences at that age, it will strongly affect sexual orientation for life.

Dr. Dobson has a different explanation for lebsians. Lesbian behavior is much more complex and related to sexual abuse and a greater capacity for intimacy on the part of females. But he doesn't think that a lesbian lifestyle is permanent as is homosexuality with males. Women can drift in and out of lesbian behavior.

Neverfox writes:

It might be interesting to know if a genetic basis exists, but since the ultimate purpose of this discussion is to ground moral norms, both sides - to the degree that they count on the result - failed before they began by attempting to infer a moral norm from genetic fact. Even if a theory of naturalist moral normativity is brought in, one would still need to argue why our raw genetics are more fundamentally explanatory than, say, our ability to reason and form cooperative bonds. After all, what our genes "want" is for us to engage not only in reproductive sex (to the exclusion of all other kinds) but to engage in it at every conceivable moment. Sorba, like the rest of us undoubtedly, does not hold this up as the "good life."

Zubon writes:

I don't know why you chose to be so short, but it's time people finally accepted that height is a learned behavior. I totally know this one guy who is taller than either of his parents.

ad nauseum writes:

Interesting post, it helps to show that the argument in and of itself is more complicated than many people make it out to be.

Also, as a guy who is taller than both of my parents, I'd like to thank my parents for both their genes and what they fed me. I totally know this first generation American who's taller than either of his parents, who emigrated here from a much poorer country, and they were able to feed him much better quality food in higher quantities than they had.

cdrealist writes:

I see lots of references here to genetics but not to epigenetics. Congenital characteristics need not be genetic. The relative positions of twin fetuses in the uterus can affect the amount of testosterone each receives, which has been implicated in the development of homosexuality.

Troy Cmaplin writes:

Those who argue for abuse as a major source of homosexual behavior have to also explain why non-human animals also express homosexual behaviors (bighorn sheep, dolphins, and especially bonobos). Most notably, our closest genetic relatives, bonobos, exhibit homosexual behavior as a way of social bonding. Bonobos are basically bisexual. It may be that humans are basically bisexual, but our awareness of the relation between reproduction and sex pushed us culturally toward more heterosexual behavior (and the wide taboo on homosexual behavior in many cultures).

Courtney writes:

Gayness is not genetic. There is no excuse for being gay. People are gay because they want to be gay. You are not "born gay." Being a twin and being gay does not have any correlation to the other twin being gay. If your brother is gay, this doe not increase or decrease your chances of becoming or ending up homosexual. Maybe homosexuality is learned? So much is our in the open now that people are curious, they wonder what it is like. Experimentation plays a big part in this subject I believe. I do not think we will ever be 100% sure of what causes homosexuality.

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