Greg Cochran argues that it is highly likely that exclusive male homosexuality is caused by an infectious agent, likely a virus. As he explains, there are several good reasons to suspect that this is the case, including:
- the low heritability of male same-sex attraction (0.22)
- the absence of homosexuality in hunter-gatherer populations
- the relatively high frequency of homosexuality (~4% in the West)
- the lack of any sort of plausible evolutionary explanation
As Cochran notes, a complete male disinterest in sex with females is always evolutionary maladaptive. Even if homosexuals do reproduce (which they do), the reduced reproductive fitness they incur would have selected the trait out long ago. As well, male homosexuality is too common (~4%) to be the result of deleterious mutations.
So we’re faced with a pathogenic agent as the likely culprit. There are clear examples of infectious agents which produce changes in behavior, including toxoplasma, influenza, and the virus involved in narcolepsy. Cochran suspects that the pathogen is agricultural in origin (which many are) perhaps being acquired from sheep.
Discussion on the issue is on-going over at West Hunter. However, even if we find an explanation for homosexuality, there is one other thing we need to explain: homo phobia. Homophobia (which is poorly named) – aversion and hatred of gays – is heritable (like all things) – indeed, significantly so (50%, as with most behavioral traits). Interestingly, and ironically, it appears to be far more heritable than homosexuality itself!
If homophobia is heritable, what purpose does it serve? Particularly, what purpose does it serve if homosexuality is caused by an infection? While homophobia is hardly limited to male homosexuals (there may be a reason for that as well, as I’ll soon discuss), it is particularly targeted at them. Studies on the nature of homophobia itself offers a clue.
Psychologist Jesse Bering blogged about studies done by Gordon Gallup on homophobia. Gallup found that homophobic reactions seemed strongest with regard to homosexuals’ contact with children:
In his first of four studies, Gallup administered a survey to 167 self-identified straight undergraduate students—males and females—a survey designed to gauge the student’s “degree of discomfort” in interacting with homosexuals who held different jobs. Importantly, these occupations varied along one dimension: the extent to which the job entailed interaction with children. Included were nine sample occupations—three that afforded a high degree of contact with kids (teacher, school bus driver, medical doctor) and six that provided moderate to low contact (lawyer, construction worker, bank teller, pilot, mechanic, sales clerk). As predicted, the degree of discomfort was significantly correlated with the likelihood that persons in these categories would come into contact with children.
Intriguingly, hypothetical gay medical doctors elicited the most discomfort among the participants, an unexpected finding that Gallup sought to better understand in his second study. “There are at least two ways to interpret the greater discomfort expressed by respondents concerning homosexual doctors,” he writes:
One possibility is that medical doctors have privileged access to children’s genitals in the context of conducting routine medical examinations, and therefore might be perceived as posing a more serious threat to a child’s developing sexuality. An interesting alternative interpretation concerns the prospect of contracting [HIV] from a homosexual doctor through nonsexual modes of transmission (e.g., blood, hypodermic needles).
In the second study, all of the characters were doctors of various kinds, physicians varying in the extent to which they would have intimate contact with children (pediatrician, child psychiatrist, general practitioner, cardiologist, brain surgeon, gerontologist). When left uninformed about the doctor’s sexual orientation, participants expressed the most discomfort about the prospect of interacting with those who had “invasive” techniques, such as the brain surgeon. But the picture changed dramatically when they were told the doctor was gay. Contrary to the HIV-exposure hypothesis, which should have produced little to no differences in attitudes toward the different gay doctors, it was the opportunity for intimate contact with children that correlated with discomfort. The participants were significantly less comfortable about the idea of interacting with gay pediatricians and general physicians than they were for the other types of gay doctors. In fact, gay brain surgeons, associated readily with infectious material, elicited the least aversion.
Gallup’s third study was even more revealing. Imagine, undergraduate participants were told, that you had a son or a daughter, either an 8-year-old or a 21-year-old, who was invited to spend the night at a friend’s house. On a scale of 1 (“not at all upset”) to 4 (“very upset”), how upset you would be, as a parent of this hypothetical child, to learn that the friend’s mother or father was gay? The participants expressed most concern when their imaginary younger child was exposed to same-sex homosexual parents (young sons being around the friend’s gay father; young daughters being around the friend’s gay mother). This was especially pronounced (mean concern = 3.3) for male participants thinking about their imaginary eight-year-old son (compared to 2.3 at the thought of him being around a lesbian). These very same male participants didn’t seem to mind the prospect of their 21-year-old son being exposed to their friend’s lesbian mother (1.6), or even for this older imaginary son spending the night around their friend’s gay dad (2.3). So, the participants’ homophobia didn’t seem to be moralistically generalized to the “gay lifestyle” but instead it emerged specifically in terms of their folk beliefs about children’s sexual impressionability.
Gallup’s final study replicated his basic findings with a broader sample. Nearly two hundred people from the Albany area, varying along a wide range of demographics (age, sex, religiosity, education, number of gay friends) were polled on a “Homosexual Reproductive Threat Scale.” Participants responded to statements such as, “I would feel uncomfortable if I learned that my daughter’s teacher was a lesbian,” “I would feel uncomfortable if I learned that my neighbor was a homosexual,” and so on. As you might expect, variables such as sex (males being more negative) and religiosity predicted homophobia. But parental status was independently correlated with negative attitudes to gays and lesbians, too; and this effect was especially salient for the males in the survey. Fathers with young children were the most homophobic.
This jives with common experience with regard to homophobia, explaining the particular resistance to things such as gays being Boy Scout masters or allowing them to adopt.
Indeed, the behavioral genetic study by Verweij et al., which I’ve cited above, found results consistent with this: respondents were more averse to having homosexuals as teachers, ministers, or doctors (all professions where they’d come in contact with children) and less averse to gays being government officials.
Gallup claims that the results of his studies have been replicated in Taiwan, indicating that this phenomenon is not confined to Western societies.
(I will note that it seems that there is one potential confound in Gallup’s studies: conservatives – who tend to hold more anti-gay attitudes – are also more likely to be parents, particularly at younger ages. I haven’t read his studies, but perhaps this is influencing his results.)
It seems then that homophobia is aimed at preventing children, particularly younger children, from being exposed to homosexuals.
Gallup hypothesizes that this may be due to “sexual imprinting” stemming from sexual contact between gays and young children. He proposes that sexual molestation of young boys by gay pedophiles “imprints” on the boys, making it more likely that these boys become homosexual themselves.
However, I doubt this idea. Indeed, I doubt the existence of sexual “imprinting” in humans, for which I’ve seen little solid evidence.
Rather, what if homophobia is aimed at preventing the spread of the pathogen that causes homosexuality?
Cochran asserts that it’s not likely that the pathogen is spread by homosexual sex. How the putative pathogen is spread is not clear at this time. Even less clear is whether there is a “critical period” for this infection to affect sexual orientation. It’s also not clear how prevalent the pathogen is in the population, or what percentage of infected individuals become homosexual.
Regardless of how the pathogen is spread, it likely that extended periods of fairly close contact with an infected individual is more likely to result in transmission of the infectious agent. If there is a critical period of time, say some time in childhood, for an infection to result in sexual orientation being altered, the evolutionary purpose of homophobia starts to become more apparent.
Indeed, as Jesse Bering points out, people aren’t most homophobic as adults, but as children:
if it’s all social learning, it’s curious, is it not, that children all over the globe must be explicitly taught not to be homophobic, not the other way around; antigay attitudes in sixth-grade boys seem as naturally emerging as language acquisition in infants. Exceptions are rare; so rare, in fact, that they make national headlines.
The “It Gets Better” Project is a testament to the homophobic attitudes that exist among children.
The aversion of gays may have evolved as a defense mechanism to protect oneself (or one’s children) from infection, and its apparently highly deleterious (evolutionarily speaking) results.
Indeed, the existence of homophobia may stand as pretty good evidence in support of Greg Cochran’s pathogenic hypothesis for homosexuality. Indeed, for as many have pointed out, homosexuals are otherwise harmless and indeed perhaps beneficial to other males in the group (reduced competition for females, for example). That gays are nonetheless hated seems hard to explain otherwise.
One possible way to test Cochran’s hypothesis is to observe if there is a higher incidence of homosexuality among the adopted children of homosexuals. Using adoptees controls for heredity, and presumably, sharing a household should give plenty of opportunity for the pathogen to be passed on to the adopted child. Ideally, the study should look only at children adopted very young, from strangers (to minimize selection bias among the adopted children). If higher rates of homosexuality were observed among these adopted children, it would point to some environmental factor – the most likely being infection.
The low, but non-zero heritability of male homosexuality may be indicative of some sort of genetic susceptibility to the pathogen, perhaps through weakened defenses or a vulnerable neural architecture.
(In the same vein as Greg Cochran’s infection hypothesis, Peter Frost has recently discussed a bacterial agent that may reduce mate-guarding behavior among men [i.e., sexual jealously], and incidentally lead to female bisexuality.)
If homosexuality is indeed caused by an infectious agent, it would have broad implications for society, particularly the prospect of being able to prevent homosexuality (perhaps through a vaccine).