Edit 28 July 2015: This post argues that strong social pressures are the primary reason homosexuality occurs with such high frequency (vs. ~0%). Though I do not rescind the claim of social pressure affecting rates of homosexuality, I do now believe that the intrinsic noisiness involved in differentiating the androphilic brain from the gynephilic brain in the developing human is probably the greater causal factor in the high rates of homosexuality. A better treatment can be found here.
I hang out at Lion/halfsigma’s blog occasionally, and something he posted yesterday caught my eye. You can read it yourself, but the post was about Obama’s recent call to end conversion therapies for LBGT youth. I won’t comment on that topic itself, other than to note I don’t see anything wrong with governments banning unproven/disproven/known deleterious medical interventions, particularly in youth where consent is squishy. Instead, I want to comment on the responses to his post, in particular JayMan’s comment and hyperlinked post about the topic of the causes of homosexuality. I wrote a reply there, but I want to make a post for my own blog on the topic.
The first thing I want to very forcefully clarify on this topic is that sexuality is patently and obviously genetic. Whether or not you have a Y-chromosome predicts with around 93~98% accuracy whether you find women or men sexually attractive. Almost all the people that have the specifically genetic entity known as the Y-chromosome are sexually attracted to women, and almost all the people that do not have that genetic entity are sexually attracted to men.
Now, I understand that there are potential readers that may have concerns along the lines of “maybe men and women are socialized into a sexual orientation?” This is also known as blank-slatism, and if you hold that perspective it means you are some shade of either ignorant or stupid, so please don’t contribute to the conversation until you have disabused yourself of your suboptimality.
So here we are. We’re all HBD-aware adults, so we’re not scared about talking about natural selection, genotypes and phenotypes, etc., in the context of Homo sapiens. So now let’s talk about homosexuality. A common trope is that homosexuality can’t be genetic because it would be selected out of the population. This perspective certainly has merit, but it’s rather sloppily stated. First, homosexuality is not a sexuality phenotype. Androphilia and gynephilia are the phenotypes. Androphilia is the sexual [primarily, but also romantic] attraction to men, and gynephilia is the attraction to women. The genotype that includes the sex-determining region of the Y-chromosome is highly correlated with the gynephilic phenotype. So we can all agree that androphilia and gynephilia are genetic. This is where the conversation must start if it’s going to get anywhere pointful. It’s obvious that the neurological mechanisms that make men attracted to men (a form of homosexuality) are akin to those that make women attracted men (a form of heterosexuality) and are relatively unrelated to those that make women attracted to women (another form of homosexuality)
We can further point out that since essentialism is false and thus <man> and <woman> are merely statistical invariances, only correlations between some variable and the man/woman variable need to be explained and not the noncorrelations. Gynephilia is correlated with <man> and androphilia is correlated with <woman>. If they weren’t correlated, 50% of men would be androphiles, 50% gynephiles, and similarly with women, so 50% of the population would be heterosexual, and 50% of the population would be homosexual. We find that the population is not evenly divided between homosexuals and heterosexuals, so we need an explanation. Note that, given the existence of androphilia, gynephilia, men, and women, the existence of homosexuality [unqualified] does not need an explanation. What needs an explanation is that, given the existence of androphilia, gynephilia, men, and women, why is heterosexuality so much more common, and why is the percentage its specific value (e.g. 96%)?
People with male genitals that want to put them close to other male genitals don’t have as many children as people with male genitals that want to put them close to female genitals. Similarly, people with female genitals that want to put them close to other female genitals don’t have as many children as people with female genitals that want to put them close to male genitals. Natural selection takes over, and the population is quickly driven so as to have correlations between the androphilia/gynephilia variable and the woman/man variable. It is supremely important to recognize that the only reason this is so is that an individual’s sexual orientation is causally implicated in the exploits of their genitals.
Now the question: are there other variables that are causally implicated in genital exploits? Are there forces in the world that direct men and women to have heterosexual sex, at least sometimes regardless or in the face of their orientation? Yes, plainly, homosexuality is stigmatized the world over, and individuals receive a tremendous amount of pressure (often from extended family) to have biological children. Natural selection and social forces compete to make everyone have heterosexual sex. The extent to which social forces are responsible for that is inversely related to the extent that natural selection is responsible.
So why is around 4% of the population homosexual, rather than, say, 0.004%? Because there are social forces that have existed for a very long time that encourage heterosexual sex. It is a supreme irony that the widespread tolerance of homosexuality is likely to select it out of the population within several generations. As anecdata, it’s not a secret that I’m no prude, and it’s my experience that homosexuality is significantly more rare in certain populations, in particular among Indians. Perhaps it’s no coincidence that at least one form of biological maleness+social female attributes has been tolerated on the subcontinent for thousands of years. My hypothesis is very testable: there should be correlations between a society’s history of stigmatizing male deviance and the prevalence of homosexuality within that society.
But what is the mechanism behind the genetic causation of sexuality? I think an analogy will help. In the sexually undifferentiated human embryo, there are two genital duct systems, known as the Wolffian and Müllerian ducts. With differentiation, one withers away, and the other grows and matures, turning into the baby’s genitalia. I strongly suspect there are two analogous systems of neurons in the brain, the selective maturation of which leads to either androphilia or gynephilia. The maturation of both might lead to bisexuality, and the maturation of neither to asexuality. Also, please note the rank stupidity of positing maturable heterosexual and homosexual neural systems in the undifferentiated human brain.
I’ll conclude with a couple caveats. It’s likely that, without the selective pressure towards a heterosexual orientation, we would not evolve to a balance of homosexuality and heterosexuality. Instead, asexuality would probably become more common, as well as the desire to have biological children. Furthermore, the tolerance of homosexuality only leads to its demise if homosexual couples aren’t allowed reproductive technologies. This is not the case in America.