Based on comments following my last post, it seems that the conversation has shifted from a broad discussion about whether or not human sexuality at large is innate to a specific analysis about the nature vs. nurture of LGBT orientation, attitude, and lifestyle. So, let's talk about this.
I acknowledge that it is both arrogant and naïve to assume that this is purely a scientific problem. It is multidimensional. It must be discussed in terms of biological, evolutionary, psychological, environmental, and socio-cultural correlates. Science is not an island. It does not exist in a vacuum. Even though the outcomes of scientific studies should be unimpressed upon by societal or even moral influence, the discussion of results gained are not. Science is done by scientists. Scientists are people. People have biases. Scientists try not to, but they aren't robots. Along the same vein, scientists must fund their work, which basically means begging for grant money any place it is available. Often times to get that money you have to please the right people. And those people, not being scientists, likely have an agenda. They aren't likely interested in learning about something purely for the sake of curiosity. Curiosity can be very expensive. This is not a perfect scenario by any stretch of the imagination.
Anyway, today's discussion was inspired by this comment:
Well, Sapphire, I don't know how to tell you this, but you are wrong. Scientists have found mountains of evidence to support the theory (yes, I said theory) that homosexuality is innate. Let's look at a small sliver of this evidence from a biological (anatomical/physiological and genetic) perspective.
As far back as 1992, a study by Allen and Gorski showed significant differences in the size of the anterior commissure in gay men, straight men, and straight women. The anterior commissure is a bundle of fibers (significantly smaller than the corpus callosum) that connects neurons in one hemisphere to the other. It specifically connects the temporal lobes, including the two amygdala, and it carries olfactory (smell) information and pain signals. The amygdala, if you recall from my Science of Fear post, is the region where frightening and other highly emotional memories are encoded. This will be important in a moment when we discuss another study. But back to Allen and Gorski's investigation, they found that the midsagittal plane of the anterior commissure was 18% larger in homosexual men than it was in heterosexual women and a full 34% larger in gay men than in straight men. This structure is not known to have any role in reproductive functioning, so the authors posit that factors involved in early development are producing a sexual orientation dimorphism (anatomical difference) in human brains.
The latter study only focused on the brains of gay men. What about lesbian brains? More recently, a study by Swedish researcher Ivanka Savik revealed that brain structures differ in areas involved in emotion, mood, anxiety, and aggressiveness in gay and straight individuals of both sexes. In fact, lesbian brains look more like those of straight men in these regions, and gay men's brains look more like those of straight women. One major difference seen is that of a slight asymmetry in the brains of straight men and gay women, wherein the right hemisphere is larger. In the brains of straight women and gay men, the cortices are largely symmetrical. Looking back at the amygdala, Savik demonstrated that in straight women and gay men, the amygdala had stronger connections to regions involved in fear and anxiety processing, whereas in straight men and gay women, the amygdala fed mostly into fight-or-flight areas. This is an important distinction because many published studies have shown that rates of depression are significantly higher in women than men, and new research is showing trends in that direction for gay men. We should be cautious about determining the causal factors involved however, because as we know, gay men are often the targets of bullying and experience alienation especially in adolescence.
In general, it is unknown if differences in brain anatomy and physiology between homosexual and heterosexual individuals are inherited or are related to hormonal changes in utero. The available evidence does point to the fact that genes seem to be a player in whether or not we grow up to be gay.
In 1993, Dean Hamer found that a patch of DNA called Xq28, which is inherited through the maternal line (on the X chromosome), appeared to be a genetic marker for homosexuality. In 1999, George Rice published research that refuted Hamer's finding. The search for the gay gene continues, but many researchers agree that homosexuality does appear to have a genetic foundation, even if it cannot be precisely pinpointed. This is because many published studies have shown higher concordance rates in monozygotic (MZ) twins than in dizygotic (DZ) twins. MZ twins are identical twins. They share the same DNA. DZ twins are fraternal twins. They are only as genetically similar as any two siblings; they just happened to be gestated and born at the same time. Although concordance rates of homosexuality are significantly higher in MZ twins, they are not 100%. Why is this? Identical twins may have the exact same DNA, but gene expression and activity may vary among them due to environmental and epigenetic factors. Lastly, a researcher named William Reiner looked at a group of boys who were underwent gender reassignment surgery in infancy because they had gender malformations. At the time, reassignment to female genitalia was an easier surgery, so that's what was done. Psychological influences didn't seem to factor into the surgeons' decisions for some reason. Anyway, all of the study participants grew up to be attracted to women, even though they were raised as girls and most had no idea that the surgery had taken place. If societal influence can "turn you gay," as so many commenters have claimed, shouldn't it have turned these gender-reassigned girls straight?
Obviously, the nature-nurture question involving sexual orientation is an extremely complicated topic with varying lines of available evidence. Even though biologists have yet to discover a gay gene, from a scientific perspective, genetic, hormonal, and structural-anatomical data show that homosexuality is definitely rooted in our biology. But what does this mean from an evolutionary perspective? Let me know what you think so that we can talk nerdy about that next.