More Evidence Regarding The Causes Of Homosexuality

Many years ago, the initial inspiration for beginning my blog was a critique I had written of the logic underlying a Lady Gaga song, “Born This Way,” which I felt committed itself firmly to the naturalistic fallacy (it’s also where the namesake of the site came from: Pop Psychology, or the psychological theory found within a pop song). Specifically, I felt that many aspects of the development of homosexuality (both the male and female varieties) were not as well understood as they should be in order to make some of the claims that many people felt confident in expressing. Today, however, I’m pleased to report on some new – and very interesting – research that might pave the way for furthering that understanding. Many important questions still remain regarding how to interpret the results of this research, but I believe that they are certainly looking in the right places for useful leads. 

“Ur-u-guay, huh? Sounds like as good as place to start as any…”

There’s a lot to discuss regarding the results of the paper (Skorska et al, 2016), so I wanted to jump right into it. The researchers were examining the possibility that a maternal immune response might play a key role in the developmental of a homosexual orientation in males. This effect is said to be the result of the mother’s immune system having a maladaptive reaction to the male-specific proteins associated with the Y-chromosome during pregnancy. Effectively, then, the mother’s immune system would (sometimes) treat certain male proteins produced by the fetus as a foreign pathogen and attempt to attack it, resulting in a few quirks of development, such as a homosexual orientation or even fetal loss if the reaction was strong enough (i.e. miscarriages). Already there is a lot to like about this hypothesis on a theoretical level, as it doesn’t posit any hidden adaptive benefits for a homosexual orientation (as such proposed benefits have not received sound empirical support historically). The question remains as to how to test for this kind of an effect, however. The method that the authors use is a rather simple one: examining maternal reports of fetal loss and birth weights. The logic here is that higher rates of fetal loss and lower birth weights both index perturbations in development. As such, they could provide indirect evidence for some kind of maternal immune response doing the causing.

The researchers recruited approximately 130 mothers and classified them on the basis of what kind of children they had: those who had at least 1 gay son (n = 54), and those who only had heterosexual sons (n = 72). These mothers were asked about their age, pregnancy history (numbers of miscarriages, stillbirths, and live births), the duration of their pregnancies, and the sex and sexual orientation of their offspring. These mothers were then classified further into one of five groups: those with gay male only-children (n = 8), those with gay male offspring that had no older brothers (n = 23), those with gay male offspring with older brothers (n = 23), those with heterosexual male only-children (n = 11), and those with heterosexual male offspring with siblings (n = 61). 

First, the authors compared the history of fetal loss between these groups of mothers. In total, 62 instances of fetal loss were reported (60 miscarriages, 1 still birth, and 1 unreported). As predicted, the average number of fetal losses were higher in the first group (mothers of gay male only-children; M = 1.25), relative to all the other groups (d = 0.76), which did not significantly differ from each other (respective Ms = 0.43, 0.74, 0.09, and 0.39). When considered in terms of the ratio of miscarriages to live to births, a similar picture emerged: mothers of gay male only-children reported more miscarriages to live births (M = 1.25) than the other groups (d = 1.55), which did not differ from each other (respective Ms = 0.14, 0.24, 0.09, and 0.17).  

Next, the authors sought to compare birth weight between the former groups. As birth weight tends to increase over successive pregnancies, the comparisons were limited to first live-born sons only (n = 63); this left 4 gay male only-children, 7 gay males with no older brothers, 14 heterosexual males with gay younger brothers, 10 heterosexual male only-children, and 28 heterosexual males with siblings. The results mirrored those of the fetal-loss data: mothers of gay male only-children tended to give birth to infants that weighed significantly less (M = 2970 grams), than all other groups (d = 1.21), which did not differ (respective Ms = 3713, 3489, 3506, and 3633). This was the case despite the duration of pregnancies not differing between any of the groups.

“Please just get out of me”

In sum, then, mothers of gay male only-children tended to have a greater number of miscarriages and give birth to significantly lighter offspring than mothers of other kinds. While it’s important to not get carried away with this finding given the relatively small sample size (I wouldn’t put too much stock in an N of 8), there is some suggestive evidence here worth pursuing further that something might be going awry with fetal development in the case of gay male offspring. That said, I’m going to assume for a moment that these results are indicative of more general patterns in order to speculate about what they could mean.

In general, these results present us with more questions than answers concerning both what might be going on, as well as why it is happening. The first question that comes to mind is why this effect seemed to be specific to gay male only-children, rather than gay male children with siblings? Skorska et al (2016) posit that this might have something to do with some mothers showing a greater immune response against male offspring, resulting in more fetal loss, the net result being that such mothers are both less likely to have any children at all and more likely to have gay male children in particular. While that might have some degree of plausibility to it, it seems that such an effect should be male-specific, and not expected to impact the number of live female births a mother has. In other words, mothers with gay male offspring should be expected to have proportionately more female children owing to a greater male fetal loss. I don’t know of any data bearing on that point, but it seems easy enough to obtain. If mothers of gay men do not tend to have a greater ratio of female-to-male offspring, this would cast some doubt on the explanation (and, since the only data I’ve heard reports that gay men tend to have more older brothers, it seems they would have noticed the sister point by now if it existed). On the other hand, if this is a more general immune reaction against fetal bodies, regardless of their sex, we would not expect such a pattern (it might also predict that mothers taking immunosuppressants would be less likely to have gay offspring/miscarry, but things are unlikely to be that simple owing to the fact that other effects would result too).

Another piece worth considering is the twin data on homosexuality. Identical male twins – those who share both their genetics and maternal fetal environment – only show a concordance rate of homosexuality of approximately 30%. The extent to which this complicates the maternal immune hypothesis is hard to say: it could be possible that one twin tends to get exposed to the brunt of these maternal antibodies despite both being approximately as vulnerable to them, but that remains to be seen.  

On a broader, theoretical level, however, the maternal immune response hypothesis raises an important question. As far as I’m aware, homosexual preferences (not the occasional behavior) do not appear to be well documented in nonhuman species; the only exception I’m aware of is Rams. If it is truly the case that maternal immune responses are the drivers of homosexual development in humans, if would be very curious that similar outcomes don’t appear to obtain across at least other mammalian species. I suppose it’s possible that these outcomes do occur in other species and it’s just the case that no one has really noticed it yet, but I doubt that’s very likely. So the matter of why humans seem rather unique in that regard is a question that needs answering. Has evolution managed to “figure out” a solution to this problem in other species (metaphorically speaking)? If it has, why hasn’t a similar solution arisen in humans and sheep?

It just ran out of square-shaped blocks?

This brings me to the final idea; one that I’ve discussed before. It is indeed possible that looking for something immune-related is in the right ballpark, but maybe in the wrong area. Perhaps what we’re seeing isn’t necessarily the result of a maternal immune response against male fetuses, but rather the result of an immune response against an actual infectious agent (or the result of that agent’s behavior itself). Admittedly, I’m no expert in the realm of immune system functioning or infectious agents, but two possibilities come to mind: first, perhaps mothers infected with a particular pathogen during fetal development might ramp up their immune response temporarily, a byproduct of which being that fetal bodies get fewer resources from the mother or caught up in the immune response themselves, both of which could plausibly affect development. Mothers more-chronically affected might have fewer children in general and more gay male children in particular, potentially explaining the current pattern of results. Alternatively, it is possible that some infectious agent itself affects the development of the fetus (such as how pathogens can render people blind or deaf). As a byproduct of that infection, if acquired during a particular critical developmental window, the child comes to develop a homosexual orientation (or is miscarried by the mother). At present, I am not aware of any evidence that speaks to this possibility, but it certainly accords with the known data.

References: Skorska, M., Blanchard, R., VanderLaan, D., Zucker, K., & Bogaert, A. (2016). Gay male only-children: Evidence for low birth weight and high maternal miscarriage rates. Archives of Sexual Behavior, DOI: 10.1007/s10508-016-0829-9

Homophobia Isn’t Repressed Homosexuality

In the wake of the Orlando shooting at the Pulse nightclub, there were quite a number of speculations floating around my social media that the shooter himself had been harboring homosexual urges that he had been trying to repress. Repression – being the odd thing that it apparently is – in this case involved his visiting gay nightclubs and using gay dating apps to communicate – and presumably have sex – with other gay men; he might have even been doing all those things while telling himself he had no interest in such activities, that they were morally wrong, or at the very least while trying to keep it secret from other people in his life. The shooting resulted, then, at least in part from this unsuccessful repression of his homosexual urges; an inward loathing directed outwards at others. Or so the story went, anyway. Subsequent official investigations into Omar Mateen’s life revealed no evidence of such behavior: no gay dating apps, no credible homosexual partners, and no gay pornography. Perhaps he was just very good at covering his tracks, but a more parsimonious explanation jumps out at me: he probably wasn’t grappling with homosexual urges.

“Keep grappling with those urges! Don’t stop! You’re almost there…”

The underlying idea in that case – that some degree of homophobia is actually explained by the homophobes in question trying to deny their own homosexual urges – remains a somewhat popular speculation. It has roots as far back as Freud, and I’ve already discussed one piece of more modern research on the idea from the mid-90s. This homosexuality repression hypothesis is also even a subplot in one of my favorite movies, American Beauty. For an idea with such a long history, it does seem rather peculiar that more empirical research on the topic doesn’t seem to exist. Perhaps the most obvious guess as to why such research doesn’t exist is that its not exactly the easiest thing in the world to measure someone’s implicit sexual attraction (provided such a thing can even be said to exist at all). If the subjects themselves aren’t even aware of it, a failure to uncover any evidence of its existence might not mean it’s not there; it might just mean that you don’t know how to uncover it. Designing the proper experiments and accurately interpreting the data resulting from them thus becomes troublesome.

Before considering some new research on the hypothesis, then, I wanted to take a step back and consider why, on a theoretical level, we shouldn’t expect implicit or repressed homosexual urges to predict homophobic attitudes particularly well. The first starting point is to note that explicit homosexuality is rare in humans (about 1-3%). This should be expected, as homosexuality does not appear to be adaptive; same-sex attraction just isn’t a good way to reproduce ones’ genes directly or indirectly (whether through kin or alliance formation). Further, open homosexuals don’t tend to be particularly homophobic; at least not as far as I know. Given that rarity, then, if something around even 20% of the population is homophobic, then there is either a lot of homophobia unrelated to homosexuality, or repressed homosexuality is very, very common. In other words, one of two statements follow, neither of which bode well for the homophobia-as-repressed-attraction hypothesis: (a) lots of people who are homophobic harbor no homosexual urges or (b) many of those who are homophobic harbor such urges.

If the first idea is true, then very little homophobia could even be explained in principle by homosexual urges. Most people who were homophobic just wouldn’t have homosexual urges, and an absent variable can’t explain a present trait.

If the second idea is true, however, then repression-via-homophobia strategy would be fairly ineffective. In order to understand why, we need to start with the following point: people are only repressing homosexual urges to convince others that they are not gay. From an adaptive point of view, an organism does not need to deceive itself about its desires. False beliefs, in that sense, just don’t do anything functionally useful, and there is no “self” to be deceived in the first place, given the modular nature of the mind. Taking that as a given for the moment, if you’re trying to convince others that you don’t have a desire, you will only be successful to the extent you engage in behaviors that someone with that desire would usually not. Placed into a simple example, if you’re trying to convince others that you’re not hungry, you turn down food. Eating a lot isn’t a particularly good way to do that, as people who aren’t hungry don’t normally eat a lot. So, if lots of people who do have homosexual urges were homophobic, then adopting a homophobic stance should actually be expected to positively signal that one is a homosexual, as being homophobic is something lots of (closeted) homosexual people actually do.

Thus the dilemma of the homophobia-as-repression hypothesis is highlighted: if only few homophobes are meaningful homosexual, then homosexuality can’t explain much; if many homophobes actually are homosexual, then homophobia will be ineffective at persuading others one is straight.

“They’re trying to signal they’re gay so much that they must be straight!”

As such, it should come as little surprise that some recent research finds no evidence for this homophobia-as-repressed-homosexuality hypothesis. MacInnis & Hodson (2013) sought to examine whether any link exists between a measure of implicit sexual attraction and explicit homophobia in heterosexuals. In order to do this, the authors used an implicit association task (IAT) adapted to sexual attraction: a task in which participants have to categorize pictures as male/female and words as sexually attractive/unattractive, and the speed at which they do so should tell you something about the cognitive association between the two. I’m wary of the interpretations of IATs for a number of reasons, but I’ll assume for the time being that such a test does indeed kind of measure what they hope. Participants were also asked about their explicit sexual attractions to men and women, and their attitudes towards gay/lesbian and heterosexual populations. In total, their sample represented 237 Canadian undergraduates (85 men).

As I would expect, the IAT results only correlated modestly with explicit measures of sexual attraction (r = .37 for men, r = .15 for women). The correlations between those IAT measures and negative, explicit evaluations of homosexuals for men was r = -.06, and for women, r = -.24. In other words, not only were such correlations quite small, but they nominally went in the opposite direction of the repression account: as people showed more implicit attraction to the same sex, they also showed less explicit negativity. On a similar note, men’s explicit attractions to the same sex negatively correlated with their homophobia as well (r = -.31), meaning that as men reported more conscious attraction to other men, they were also more positive towards homosexuals. People tend to be more positive towards those that resemble them – for good reason – so this isn’t terribly shocking.

The researchers tried additional analyses as well to address other interpretations of the repression-to-attraction account. First, they divided the data such that those who showed positive homosexual implicit attraction were compared to those who on the negative side. The male sample, it’s worth noting, could not be analyzed here as only 4 of the 85 men had such a score (perhaps there’s just not much implicit attraction floating around?); for women, the same finding as before emerged: those showing more implicit attraction were less negative towards homosexuals. Next, the authors tried to examine only those in the upper-half of homophobia score, and then those in the more extreme ends. However, the implicit attraction scores did not differ between those high and low in prejudice for men or women. The repression hypothesis wasn’t even supported when the authors tried to isolate those participants whose explicit and implicit attraction scores were maximally different from one another (the authors frame this as participants overstating their heterosexuality on an explicit level, but I suspect the actual interpretation is that the IAT isn’t too great of a tool).

Directions for future research: invasive mind-reading technology

With all the dividing of their sample, MacInnis & Hodson (2013) gave their data every possible advantage to find somethingeven some spurious relationship – but essentially nothing arose. They broke the data down by men and women; attitudes towards gays, lesbians, and homosexuals in general; those high or low in prejudice; those whose implicit and explicit attractions diverged. No matter how it was sliced, support was not found for the repression idea. When relationships did exist between implicit attraction and explicit attitudes, it usually ran in the opposite direction of the repression hypothesis: those who showed implicit attraction were less negative towards homosexuals (albeit quite modestly). I don’t suspect this will stop those who fancy the repression hypothesis to abandon it – likely because they value it for reasons beyond its established truth value, which is currently dubious at best –  but it is a possible starting point for that journey.   

References: MacInnis, C. & Hodson, G. (2013). Is homophobia associated with an implicit same-sex attraction? Journal of Sex Research, 50, 777-785.

Examining Arousal And Homophobia

In my last post, I mentioned that the idea of people misplacing or misinterpreting their arousal as being a silly one (as I also did previously here). Today, I wanted to talk about that arousal issue again. In the wake of the supreme court’s legalization of same-sex marriage here in the US, let’s consider arousal in the context straight men’s penises reacting to gay, straight, and lesbian pornography. Specifically, I wanted to discuss a rather strange instance where some people have interpreted men’s physiological arousal as sexual arousal, despite the protests of those men themselves, in the apparent interests of making a political point about homophobia. The political point in question happens to be that a disproportionate number of homophobes are actually latent homosexual themselves who, in true Freudian fashion, are trying to deny and suppress their gay urges in the form of their homophobic attitudes  (see here and here for some examples).

Homosexual individuals, on the other hand, are only repressing a latent homophobia

The paper in question I wanted to examine today is a 1996 piece by Adams, Wright, & Lohr. The paper was designed to test a Freudian idea about homophobia: namely, as mentioned above, that individuals might express homophobic attitudes as a result of their own internal struggle regarding some unresolved homosexual desires. As an initial note, this idea seems rather on the insane side of things, as many Freudian ideas tend to seem. I won’t get too mired in the reasons the idea is crazy, but it should be sufficient to note that the underlying idea appears to be that people develop maladaptive sexual desires in early childhood (long before puberty, when they’d be relevant) which then need to be suppressed by different mechanisms that don’t actually do that job very well. In other words, the idea seems to be positing that we have cognitive mechanisms whose function is generate maladaptive sexual behavior, only to develop different mechanisms later that (poorly and inconsistently) suppress the maladaptive ones. If that isn’t torturous logic, I don’t know what would be.

In any case, the researchers recruited 64 men from their college’s subject pool who had all previously self-identified as 100% straight. These men were then given the internalized homophobia scale (IHP), which, though I can’t access the original paper with the questions, appears to contain 25 questions aimed at assessing people’s emotional reactions to homosexuals, largely focused on their level of comfort/dread being around them. The men were divided into two groups: those who scored above the midpoint on the scale (the men labeled as homophobes) and those who scored below the midpoint (the non-homophobes). Each subject was provided with a stain gauge to attach to their penis which functioned to measure changes in penile diameter; basically how erect the men were getting. Each subject then watched three, four-minute long pornographic scenes: one depicting heterosexual intercourse, another gay intercourse, and another for lesbian intercourse. After each clip, they were asked how sexually aroused they were and how erect their penis was, before being given a change to return to flaccid before the next clip was shown.

In terms of the arousal to the heterosexual and lesbian pornography, there was no difference between the homophobic and non-homophobic groups with respect to how erect the men got and how aroused they reported being. However, in the gay porn condition, the homophobic men became more erect. Framed in terms of the degree of tumescence (engorgement), the non-homophobic men displayed no tumescence 66% of the time, modest tumescence 10% of the time, and definite tumescence 24% of the time in response to the gay porn; the corresponding numbers for the homophobic group were 20%, 26%, and 55%, respectively, while there was no difference between the homophobic and non-homophobic groups with respect how aroused they reported being, the physiological arousal did seem to differ. So what’s going on here? Does homophobia have its roots in some latent homosexual desires being denied?

And does ignoring those desires place you in the perfect position for penetration?

I happen to think that such an idea is highly implausible. There are a few reasons I feel that way, but let’s start with the statistical arguments for why that interpretation probably isn’t right. In terms of the number of men who identify as homosexual or bisexual at a population level, we’re only looking about 1-3%. Given that rough estimate, with a sample size of 60 individuals, you should expect about 1.5 gay people if you were sampling randomly. However, this sampling was anything but random: the subjects were selected specifically because they identified as straight. This should bias the number of gay or bisexual participants in the study downward. Simply put, this sample size is not large enough to expect that any gay or bisexual male participants were in it at all, let alone in large enough numbers to detect any kind of noticeable effect. That problem gets even worse in that they’re looking to find participants that are both bisexual/gay and homophobic, which cuts the probability down even further.

The second statistical reason to be wary of these results is that bisexual men tend to be less common that gay men by a ratio of approximately 1:2. However, the pattern of results observed in the paper from the homophobic group could better be described as bisexual than gay: each group reported the same degree of subjective and physiological arousal to the straight and lesbian porn; there was only the erection difference observed during the homosexual porn. This means that the sample would have been needed to have been compromised of many bisexual homophobes who publicly identified as straight, which seems outlandishly unlikely.

Moreover, the sheer number of the participants displaying “definite tumescence” requires some deeper consideration. If we assume that the physiological arousal translates directly into some kind of sexual desire, then about 25% of non-homophobic men and 55% of homophobic men are sexually interested in homosexual intercourse despite, as I mentioned before, only about 1-3% of the population saying they are gay or bisexual. Perhaps that rather strange state of affairs holds, but a much likelier explanation is that something has gone wrong in the realm of interpretation somewhere. Adams et al (1996) note in their discussion that another interpretation of their results involves the genital swelling being the result of other arousing emotions, such as anxiety, rather than sexual arousal per se. While I can’t say whether such an explanation is true, I can say that it certainly sounds a hell of a lot more plausible than the idea that most homophobes (and about 1-in-4 non-homophobes) are secretly harboring same-sex desires. At least the anxiety-arousal explanation could, in principle, explain why 25% of non-homophobic men’s penises wiggled a little when viewing guy-on-guy action; they’re actually uncomfortable.

Maybe they’re not as comfortable with gay people as they like to say they are…

Now don’t get me wrong: to the extent that one perceives there to be social costs associated with a particular sexual orientation (or social attitude), we should expect people to try and send the the message that they do not possess such things to others. Likewise, if I’ve stolen something, there might be a good reason for me to lie about having stolen it publicly if I don’t want to suffer the costs of moral condemnation for having done so. I’m not saying that everyone will be accurate or truthful about themselves at all times to others; far from it. However, we should also expect that others will not be accurate or truthful about others either, at least to the extent they are trying to persuade people about things. In this case, I think people are misinterpreting data on physiological arousal to imply a non-existent sexual arousal for the purposes of making some kind of social progress. After all, if homophobes are secretly gay, you don’t need to take their points into consideration to quite the same degree you might have otherwise (since once we reach a greater level of societal acceptance, they’ll just come out anyway and probably thank you for it, or something along those lines). I’m all for social acceptance; just not at the expense of accurately understanding reality.

References: Adams, H., Wright L., & Lohr, B. (1996). Is homophobia associated with homosexual arousal? Journal of Abnormal Psychology, 105, 440-445.

Bonding (Physically) With Same-Sex Individuals

Humans face the adaptive problem of forming and maintaining social bonds with others. Our ability to bond is rather extraordinary. As one example of our capacity to bond, like many people, I am a (habitual) pet owner. My personal preference – though I like most mammals – is towards cats, and I’ve had at least one cat for about as long as I can remember. Also, like many pet owners, I have a habit of holding, hugging, and kissing my cats. Though I can’t say for certain, my intuition is that this affiliation is mutually pleasurable: when I return home after some time out, my cat will greet me with a series of meows, purrs, and rubs; she will even crawl into my lap while I’m sitting at my computer. The relationship between pets and owners often appears to resemble the relationship parents have towards children in a number of respects and it should come as no surprise, then, that we often also observe parents touching, hugging and kissing their children. While people don’t need to bond with animals socially, we often can as a byproduct of our ability to bond with other people (in this case, probably offspring).

And since one won’t need college, the superior bonding choice is clear

Now perhaps all this kissing and touching parents do with children and people do with pets reflects our bonds with them. That is to say that this behavior is a signal of our love and affection, rather than it’s cause. Then again, maybe kissing children and pets deepens those bonds. Let’s assume for the present discussion that it’s actually the latter. Why might it do this? According to a recent paper by Fleischman, Fessler, & Cholakians (2014), the why might have something to do with some parts of the cognitive mechanisms that evolved for sexual pair bonding being co-opted. The basic logic in their paper, I think, is that there exist cognitive mechanisms that find erotic (i.e., arousing) acts typically rewarding (pleasurable). As social bonds are often centered around pleasurable interactions, acts associated with erotic or sexual behavior – like kissing or genital touching – can be used to strengthen bonds between people as it leads to additional pleasurable interactions, reinforcing a relationship. It’s worth noting that their paper isn’t focused on explaining kissing per se, but rather homosexual/homoerotic behavior: the argument is that homoerotic behavior functions to build social bonds between same-sex others. By that train of thought, I imagine, those who engage in more “erotic” behavior with each other should be more socially bonded because of it.

I find several facets of that explanation for homoerotic behavior to be a bit strange. One of those facets is that parents and offspring (or pets, for that matter) need to avoid engaging in sexual intercourse, as intercourse with genetically-close others, other species, and those too young to reproduce, tends to carry some reproductive consequences (or fails to carry any benefits). Accordingly, those who found kissing their close kin, animals, or pre-reproductive others erotic should be at a fitness disadvantage, relative to those who did not. In other words, as kin need to bond with one another socially, they also need to avoid engaging in sexual intercourse; any system that blurred the lines between sexual arousal and social bonding in that context might end up with poor fitness outcomes, relative to a system that did not blur that line. So, as one might expect, people who kiss their children, siblings, or pets rarely experience the behavior as erotic.

Similarly, one might expect that the cognitive system designed for governing sexual arousal should be relatively autonomous from systems designed to bond socially with same-sex others, as homosexual behavior is a bit of a reproductive dead-end. Most kin and social bonding appears to be successfully navigated without any erotic behavior taking place (Kirkpatrick, 2000), so we can safely say that homoerotic behavior is in no way a requirement of bonding for humans. That’s not to say that many people don’t engage in some kind of same-sex behavior at some point in their life with an individual or two (sometimes girls kiss girls and they might even like it, though if they’re young it might not have any erotic or sexual overtones), but to say that such behaviors do not appear to be a hallmark of forming social bonds.

Foregoing those issues, though, the affiliation hypothesis for homoerotic behavior would not necessarily tell us much about the existence of homosexual orientations. It’s one thing to say that my providing erotic experiences to others of my sex could increase the degree of concern they might have in my welfare; it’s quite another to say that I should not only prefer to engage in erotic behavior with them over opposite sex individuals if I had to choose, but that I would actively avoid engaging in heterosexual intercourse when presented with the opportunity if I didn’t. After all, having same-sex allies would only be selected for insomuch as they afford additional opportunities for heterosexual opportunities. Indeed,  Fleischman, Fessler, & Cholakians (2014) reported that men primed with sexual words saw no increase in their homoerotic motivation, though there was a slight increase in the affiliation primed group. It seems, by their own logic, we should not predict homoerotic motivations to stop heterosexual ones (they predict the opposite, in fact).

This makes the apparent distaste for heterosexual erotic behavior in homosexual populations appear rather curious. Perhaps that point could be skirted if one posits that there exists some variance in people’s preferences for bonding with same/opposite sex individuals (in the same way people vary in their height), that the two desires trade off against each other for some reason (such that being aroused by men means you couldn’t also be aroused by women), and that this explains the variance in sexual preferences.

Figure 1: Not what the distribution of sexual orientation looks like

This would predict that sexual orientation follows something of a normal distribution – with most people being bisexual – which it clearly doesn’t. Instead, sexual orientation is heavily skewed towards heterosexual (as one should expect from a fitness standpoint), with around 97-99% of people identifying as such. The distribution problem is even worse when considering male sexual orientation, which finds most men reporting a heterosexual orientation, homosexual being second most common, and very few indicating being bisexual. This is not the kind of variation you see in many other adaptations (like height, which is much more normally distributed, like the above graph). It is possible, I suppose, that there exist many more male bisexuals out there than the surveys typically find; Fleischman, Fessler, & Cholakians (2014) suggest that many (male) bisexuals don’t want to admit to their bisexuality owing to some social stigma against it. While that’s possible, I don’t think we want to venture into the realm of question begging in the interests of making the available evidence fit the theory.

On the topic of social stigma, though, if the function of homoerotic behavior is to bond with others socially, it seems peculiar that so many moral injunctions against homosexual behavior exist in many cultures worldwide. Yes, the tolerance of such behavior does vary across time and place, but that people condemn it at all seems rather strange if the function is social bonding; surely everyone wants to be able to make friends. It’s even stranger because people don’t seem to be condemning other acts of social bonding, like doing favors or exchanging gifts; they seem to condemn the sexual thoughts and behaviors associated with same-sex erotic behavior. Even if it’s the case that homoerotic behaviors might have only become condemned in relatively recent times (I don’t know if that’s true or not), that would still leave us with the matter of why there was an uptick in homoerotic condemnation.

Even more peculiar is that same-sex behavior appears to be quite rare if it functions as an affiliation-building mechanism. By that I don’t mean that many people haven’t engaged in something resembling homoerotic behavior (like a man kissing a man on the lips) at any point in their life, but rather that I feel we should see otherwise-straight male friends (especially good friends) kissing each other goodbye (erotically) every day, or male businessmen engaging in some light genital petting after a meeting to keep up the impression of being a friendly, valuable asset to one another. If homoerotic behavior helped cement social bonds, it seems like it should be as common as handshakes or hugs. Perhaps such practices are more common elsewhere in the world that I am unaware of, but that they are not much more common than they appear to be, at least here in the US, seems out of place if the bonding explanation is true.

I say that because if we were talking about another adaptation – like vision – we might be curious if we found that one-in-four males had the ability to see (at some point in their life), whereas the remaining 80% of men were blind. Adaptions – because of their reproductive benefits – tend to be common (generally universal) in populations. This is why pretty much everyone has two hands and a functioning liver, barring some environmental insult. Yet homoerotic behavior is anything but ubiquitous. Kirkpatrick (2000) cites a number of studies finding that around 20% of men (and women, but let’s stick to the men for now) report having homosexual intercourse at some point in their lives (though most of this behavior – about two thirds of it – seems to take place before the age of 19). Assuming these numbers are representative, that people found all of those encounters erotic even when they were younger children, and that the behavior wasn’t coerced by others, we would still be looking at around 4 out of 5 males who have never engaged in homosexual intercourse at any point in their life. For a purported adaptation with social benefits, this seems strange; why would 80% (or 93% if we’re talking about 19+ year olds) of the male population be foregoing the social-bonding benefits of a bit of buggery?

That’s what I’ve been saying; you just have to convince my good buddies.

We could, as Fleischman, Fessler, & Cholakians (2014) do, expand the definition away from just homoerotic intercourse to behavior that doesn’t include the genitals, but this (a) runs us back into the problem that most men don’t seem to be kissing their good friends good-bye erotically and (b) that we should expect behavior that resulted in orgasm to be more rewarding – and thus bonding – than non-orgasmic results, if I follow the logic here correctly. No matter how I try to slice it, I keep ending up at the idea that, if homoerotic behavior functions to cement social bonds – that we should be seeing a lot more of it in terms of prevalence, frequency, and intensity. As it stands, it’s as if most of the male population doesn’t seem to want to improve their social bonds, which would be odd.

The only way I see to side-step that issue is to suggest homoerotic bonding is a facultative adaptation: one which responds to specific environment contexts. While such an explanation is not out of the question, it would need to identify some feature of the environment that encourages same-sex bonding via erotic behaviors for some individuals but not (most) others. As far as know, no such context is currently on offer, so there’s not much more to say about it.

In the interests of adding some testable suggestions to hopefully move the debate forward, one analysis that would be relevant to the current functional explanation would be to examine what factors make same-sex partners erotic. If these erotic relationships function to help build productive friendships, we might expect the criteria for a same-sex erotic friend to look a bit different from, say, a heterosexual erotic partner. As a for instance, when seeking mates, heterosexual men tend to value youth in women, as youth tends to correlate well with reproductive potential. When seeking friends, however, I don’t get the sense that youth is perceived to be as desirable of a trait. A question of interest, then, would be whether, when seeking erotic encounters with other men, do gay men value youth or not? Presumably, these homoerotic encounters should be driven by friendship-relevant, rather than mating-relevant variables, if the function is friendship building. Another interesting avenue would be to examine mating and friendships in a short-term versus long-term contexts. Admittedly, it sounds a bit strange to talk about short-term, casual, no-strings attached friendship, which is why I happen to think that men aren’t using Grindr to meet one-night friends and people at glory holes aren’t looking for help moving; I could be wrong about that, though.

Separating the variables into more distinctly mate-selection and friend-selection driven might be difficult – as many of the qualities that make one a good mate, like kindness, might also make one a good friend – but I’m sure that analysis could be taken in a number of interesting directions.

References: Fleischman, D., Fessler, D., & Cholakians, A. (2014). Testing the affiliation hypothesis of homoerotic motivation in humans: The effects of progesterone and priming. Archives of Sexual Behavior, DOI: 10.1007/s10508-014-0436-6

Kirkpatrick, R. (2000). The evolution of human homosexual behavior. Current Anthropology, 41, 385-413.

Mothers And Others (With Benefits)

Understanding the existence and persistence of homosexuality in the face of its apparently reproductive fitness costs has left many evolutionary researchers scratching their heads. Though research into homosexuality has not been left wanting for hypotheses, every known hypothesis to date but one has had several major problems when it comes to accounting for the available data (and making conceptual sense). Some of them lack a developmental story; some fail to account for the twin studies; others posit benefits that just don’t seem to be there. What most of the aforementioned research shares in common, however, is its focus: male homosexuality. Female homosexuality has inspired considerably less hypothesizing, perhaps owing to the assumption, valid or not, that female sexual preferences played less of a role in determining fitness outcomes, relative to men’s. More precisely, physical arousal is required for men in order for their to engage in intercourse, whereas it is not necessarily required for women.

Not that lack of female arousal has ever been an issue for this fine specimen.

A new paper out in Evolutionary Psychology by Kuhle & Radtke (2013) takes a functional stab at attempting to explain some female homosexual behavior. Not the homosexual orientations, mind you; just some of the same-sex behavior. On this point, I would like to note that homosexual behavior isn’t what poses an evolutionary mystery anymore than other, likely nonadaptive behaviors, such as masturbation. The mystery is why an individual would be actively averse to intercourse with members of the opposite sex; their only path to reproduction. Nevertheless, the suggestion that Kuhle & Radtke (2013) put forth is that some female homosexual sexual behavior evolved in order to recruit female alloparent support. An alloparent is an individual who provided support for an infant but is not one of that infant’s parents. A grandmother helping to raise a grandchild, then, would represent a case of alloparenting. On the subject of grandmothers, some have suggested that the reason human females reach menopause so early in their lifespan – relative to other species who go on with the potential to reproduce until right around the point they die – is that grandmother alloparenting, specifically maternal grandmother, was a more valuable resource at the point, relative to direct reproduction. On the whole, alloparenting seems pretty important, so getting a hold of good resources for the task would be adaptive.

The suggestion that women might use same-sex sexual behavior to recruit female alloparental support is good, conceptually, on at least three fronts: first, it pays some mind to what is at least a potential function for a behavior. Most psychological research fails to think about function at all, much less plausible functions, and is all the worse because of it. The second positive part of this hypothesis is that it has some developmental story to go with it, making predictions about what specific events are likely to trigger the proposed adaptation and, to some extent, anyway, why they might. Finally, it is consistent with – or at least not outright falsified by – the existing data, which is more than you can say for almost all the current theories purporting to explain male homosexuality. On these conceptual grounds, I would praise the lesbian-sex-for-alloparenting model. On other grounds, both conceptual and empirical, however, I have very serious reservations.

The first of these reservations comes in form of the source of alloparental investment. While, admittedly, I have no hard data to bear on this point (as my search for information didn’t turn up any results), I would wager it’s a good guess that a substantial share of the world’s alloparental resources come from the mother’s kin: grandparents, cousins, aunts, uncles, siblings, or even other older children. As mentioned previously, some have hypothesized that grandmothers stop reproducing, at least in part, for that end. When alloparenting is coming from the female’s relatives, it’s unlikely that much, if any, sexual behavior, same-sex or otherwise, is involved or required. Genetic relatedness is likely providing a good deal of the motivation for the altruism in these cases, so sex would be fairly unnecessary. That thought brings me neatly to my next point, and it’s one raised briefly by the authors themselves: why would the lesbian sex even be necessary in the first place?

“I’ll help mother your child so hard…”

It’s unclear to me what the same-sex behavior adds to the alloparenting equation here. This concern comes in a number of forms. The first is that it seems adaptations designed for reciprocal altruism would work here just fine: you watch my kids and I’ll watch yours. There are plenty of such relationships between same-sex individuals, regardless of whether they involve childcare or not, and those relationships seem to get on just fine without sex being involved. Sure, sexual encounters might deepen that commitment in some cases, but that’s a fact that needs explaining; not the explanation itself. How we explain it will likely have a bearing on further theoretical analysis. Sex between men and women might deepen that commitment on account of it possibly resulting in conception and all the shared responsibilities that brings. Homosexual intercourse, however, does not carry that conception risk. This means that any deepening of the social connections homosexual intercourse might bring would most likely be a byproduct of the heterosexual counterpart. In much the same way, masturbation probably feels good because the stimulation sexual intercourse provides can be successfully mimicked by one’s hand (or whatever other device the more creative among us make use of). Alternatively, it could be possible that the deepening of an emotional bond between two women as the result of a sexual encounter was directly selected for because of it’s role in recruiting alloparent support, but I don’t find the notion particularly likely.

A quick example should make it clear why: for a woman who currently does not have dependent children, the same-sex encounters don’t seem to offer her any real benefit. Despite this, there are many women who continue to engage in frequent to semi-frequent same-sex sexual behaviors and form deep relationships with other women (who are themselves frequently childless as well). If the deepening of the bond between two women was directly selected for in the case of homosexual sexual behavior due to the benefits that alloparents can bring, such facts would seem to be indicative of very poor design. That is to say we should predict that women without children would be relatively uninterested in homosexual intercourse, and the experience would not deepen their social commitment to their partner. So sure, homosexual intercourse might deepen emotional bonds between the people engaging in it, which might in turn effect how the pair behave towards one another in a number of ways. That effect, however, is likely a byproduct of mechanisms designed for heterosexual intercourse; not something that was directly selected for itself. Kuhle & Radtke (2013) do say that they’re only attempting to explain some homosexual behavior, so perhaps they might grant that some increases in emotional closeness are the byproduct of mechanisms designed for heterosexual intercourse while other increases in closeness are due to selection for alloparental concerns. While possible, such a line of reasoning can set up a scenario where the hits for the theory can be counted as supportive and the misses (such as childless women engaging in same-sex sexual behaviors) dismissed as being the product of some other factor.

On top of that concern, the entire analysis rests on the assumption that women who have engaged in sexual behavior with the mother in question ought to be more likely to provide substantially better alloparental care than women who did not. This seems to be an absolutely vital prediction of the model. Curiously, that prediction is not represented in any of the 14 predictions listed in the paper. The paper also offers no empirical data bearing on this point, so whether homosexual behavior actually causes an increase in alloparental investment is in doubt. Even if we assume this point was confirmed however, it raises another pressing question: if same-sex intercourse raises the probability or quality of alloparental investment, why would we expect, as the authors predict, that women should only adopt this homosexual behavior as a secondary strategy? More precisely, I don’t see any particularly large fitness costs to women when it comes to engaging in same-sex sexual behavior but, under this model, there would be substantial benefits. If the costs to same-sex behavior are low and the benefits high, we should see it all the time, not just when a woman is having trouble finding male investment.

“It’s been real, but men are here now so…we can still be friends?”

On the topic of male investment, the model would also seem to predict that women should be relatively inclined to abandon their female partners for male ones (as, in this theory, women’s sexual interest in other women is triggered by lack of male interest). This is anecdotal, of course, but a fairly-frequent complaint I’ve heard from lesbians or bisexual women currently involved in a relationship with a woman is that men won’t leave them alone. They don’t seem to be wanting for male romantic attention. Now maybe these women are, more or less, universally assessing these men as being unlikely or unable to invest on some level, but I have my doubts as to whether this is the case.

Finally, given these sizable hypothesized benefits and negligible costs, we ought to expect to see women competing with other women frequently in the realm of attracting same-sex sexual interest. Same-sex sexual behavior should be expected to not only be cross-cultural universals, but fairly common as well, in much the same way that same-sex friendship is (as they’re hypothesized to serve much the same function, really). Why same-sex sexual interest would be relatively confined to a minority of the population is entirely unclear to me in terms of what is outlined in the paper. This model also doesn’t deal why any women, let alone the vast majority of them, would appear to feel averse to homosexual intercourse. Such aversions would only cause a woman to lose out the hypothesized alloparental benefits which, if the model is true, ought to have been substantial. Women who were not averse would have had more consistent alloparental support historically, leading to whatever genes made such attractions more likely to spread at the expense of women who eschewed it. Again, such aversions would appear to be evidence of remarkably poor design; if the lesbian-alloparents-with-benefits idea is true, that is…

References: Kuhle BX, & Radtke S (2013). Born both ways: The alloparenting hypothesis for sexual fluidity in women. Evolutionary psychology : an international journal of evolutionary approaches to psychology and behavior, 11 (2), 304-23 PMID: 23563096

A New Theory For Homosexuality: A Lot Like The Old Ones

Homosexuality – male homosexuality in particular – poses a real evolutionary mystery that researchers have been trying to solve for at least the past two decades without much success. Though many explanations have been put forth to try and find the hidden fitness benefits that might allow male homosexuality to persist in the substantial minority of the population that it does despite the substantial fitness costs to the sexual preference, all the adaptive explanations have been left wanting. Decades of failed research has not seemed to have deterred new hypothesizing, though. For better or worse, I find the tenacity of the adaptive hypotheses for homosexuality to be fascinating: it is as if people cannot accept, or even consider the possibility, that homosexuality might not carry any reproductive benefits, hidden, indirectly, or otherwise. Were other key adaptations (that are not sexual orientation) to fail to develop in an adaptive fashion early in life – such as vision or hearing – I don’t think many people would be trying to find the hidden reproductive benefits or functions to being blind or deaf. The causes, certainly, but not the benefits.

“But what if being blind caused him to invest more in kin…?”

On the subject, there’s a new paper out in Evolution and Human Behavior (Barthes, Godelle, & Raymond, 2013: H/T to Dan) that, again, asks whether there might be some hidden fitness benefit associated with male homosexuality. In this case, the focus of the benefits are the female sisters of male homosexuals. The theory goes like this: after the advent of agriculture, social classes began to take root as large quantities of resources could now be generated and defended. Women could thus gain some reproductive advantage were they able to pair with men of higher social status who had these resources; a preference for doing so is known as hypergyny. However, only a small proportion of these pairings occur across social classes: women of higher social classes tended to marry men of higher social classes, and likewise for the lower classes. Accordingly, any trait that could help women mate upwards in the social ladder would have been selected for, even if it came at some expense to male reproductive fitness.

So, in this theory, male homosexual preference is a byproduct of females being able to better pursue their hypergynous inclinations. The male reproductive disadvantage from developing a homosexual preference would be more than offset by the presumed increases to female fertility and/or attractiveness to higher-status males. One distinct advantage that the authors feel this theory has is its ability to explain why male homosexual preference seems to be exclusively human (the one notable exception might be rams, a species with a history of co-residence with humans). Since male homosexuality only came to be after the advent of agriculture, long-term pair bonds, and the establishment of social classes, which other species tend to not have, this helps explain why we don’t see sexually-antagonistic male homosexuality in other species. It’s a neat idea, but neatness alone doesn’t win the day in the world of science, so let’s move on to consider what data they bring to bear on this hypothesis.

The first piece of “evidence” they present in support of this hypothesis is a mathematical model attempting to demonstrate the conditions under which such a genotype could come to exist. I’ve previously made my stance on the usefulness of such models rather explicit, but I’ll restate it here in a sentence: these models are philosophical intuitions written in the form of math, rather than English (or the language of your choice), and can be used to demonstrate literally anything. Since the models are only as good as their match to reality, my concern is, justifiably, on the extent of that match rather than the model itself. The evidence presented in terms of said match is an examination of the anthropological record of 48 societies to find out where the presence of homosexuality has been recorded, where it seems to be absent, and where it might exist. Further, these societies were also assessed in terms of how socially stratified they were, and these results were compared to the presence of male homosexual preference. The results showed that increasing social stratification was correlated with a increases in finding the presence of male homosexual preference.

Does the income disparity in America see a little…gay…to you?

When it comes to the social stratification hypothesis, should you not believe the hype, or does it bring the noise? We can begin by noting that the empirical support here is extremely weak. The paper doesn’t test to see whether more social stratification leads to more homosexuality; it merely examines whether societies that are socially stratified are more likely to have homosexual preference present or absent. Such a correlation is unlikely to be very informative, much less establish any kind of causation. Second, the paper didn’t bother to examine whether the female relatives of male homosexuals tended to actually be any more likely to marry up, or be more fertile, or be more attractive, which seems like necessary components of this model. Positing design features in a trait and then not bothering to see if those design features are present seems like poor research design. Those two points are, however, only the two things the authors talked about and didn’t test: there are also points the authors fail to mention, which I think have a strong bearing on their hypothesis.

The first of these points is that the paper makes no mention of the genetic data showing that monozygotic male twins are only concordant for a homosexual orientation around 30% of the time. This means that though the authors suggest some genes might make it more likely that a male develops a homosexual orientation, they fail to specify precisely which factors are important for developing one and why some twins fail to end up with the same orientation. So that leaves no mention of the genetic data, no mention of a developmental story, and no good test of the paper’s main contentions. I’m not sure to what extent this lack of any good empirical tests is the result of the paper’s reliance on a mathematical model, but I will note that, in my personal experience, there seems to a correlation between generating these models and poorly supporting them empirically.

There is, however, one final point I would like to mention that the authors don’t seem to really make any mention of. Part of their model requires that females have a preference for hypergyny but, in order for this preference to exist, it requires differences in social status to exist. After all, you can’t select mates on a non-existent criteria. If the authors are postulating, which they seem to be, that such a mate criteria didn’t exist in force before the advent of agriculture, it begs the question as to where this female mate preference for higher status men came from in the first place. This would require one of two things for the model: first, either that agriculture arose, followed by the female mate preference, followed by male homosexual preference, which is an awful lot to ask of 10,000 years.

Alternatively, one could argue, that differences in male status and its effect on female fitness likely predated agriculture and, further, that this preference might have been exaggerated to some degree and in some places in relative recent time periods. This would imply, in terms of the social stratification model, that the selection pressures responsible for generating the conditions for homosexuality were already in existence beforehand, so homosexuality is likely older than agriculture. If that is the case, then evolution would have had much more time to strip out the deleterious effects of any sexually antagonism. So, really, neither answer to this last concern bodes well for the model.

At least they had a mathematical model, which really saved things…

As I initially stated, I find the emphasis that people place on finding an adaptive explanation for homosexuality to be a bit curious. I would like to add that I also find the emphasis that some people are willing to place on mathematical models curious as well. There are a not insignificant percentage of academics who seem to find mathematical models to be impressive despite many cases, like this one, where they don’t seem to add much to the discussion. I get the impression that if these models were written in English, rather than math, people would be far less swayed by them, as it would make clear precisely how much many of them appear to just assume or ignore. Once the assumptions are stripped away, all this paper seems to add is a correlation between social stratification and the mere existence of homosexuality. Then again, it seems to persuade the reviewers to publish it, so maybe there’s something I’m missing…

References: Barthes, J., Godelle, B., & Raymond, M. (2013). Human social stratification and hypergyny: toward an understanding of male homosexual preference Evolution and Human Behavior DOI: 10.1016/j.evolhumbehav.2013.01.001

5 Weak Ideas About The Origin Of Homosexuality: A Reply

Back at the end of last month, Mark Van Vugt presented what he considered to be five candidate selection pressures which might explain how homosexuality as an orientation – the exlcusive preference for same-sex sexual partners – came to both (a) exist in human populations in the first place, and (b) have its existence was maintained in the face of, what appear to be, obvious reproductive disadvantages. In each of these five cases I find the arguments lacking for either theoretical or empirical reasons, and, in most cases, both. Before I get to the science, however, I would like to deal with a troubling claim that Mark makes at the beginning of his post:

“The converging findings suggest that exclusive homosexuality is not a “life style choice” but a perfectly natural sexual orientation….Although these findings make a reasonably strong claim that homosexuality is part of someone’s genotype, there is still much speculation as to how it got there.”

There are three problems I have with those two above statements (admittedly, juxtapositioned for effect) that are worth pointing out. The first is the language used: while I’m in no way about to tell you that being gay is a choice (I happen to think it isn’t one), I will point out that the opposite of “choice” is not “genetic” or “natural”. If it was discovered tomorrow that homosexuality was determined by some environmental variable, say, a specific pathogen affecting development, (Cochran, Ewald, & Cochran, 2000) that would make homosexuality no more or less of a “choice”. The second issue is that all biological traits are equally and entirely codetermined both by environmental and genetic factors. Accordingly, saying homosexuality (or any single other trait) is “part of someone’s genotype” is both trivially and true as well as potentially misleading for those who are not well-versed in genetics.

Finally, the third issue is a cautionary point I made about a year-and-a-half ago: presumably, all the talk about choice, genes, and “being natural” has little to do with statements of fact, but are rather about the moral status of homosexuality. While I fully support the moral acceptance of homosexuality, I would be very wary of basing that support on the notion that homosexuality is a “genetic” trait that people “don’t choose”. Not only do I think homosexuality should be accepted regardless of whether it’s a choice or caused by some environmental factor, but I further would hate to see the arguments for acceptance slip away on the basis of the concordance data not panning out (which we’ll see in a moment, it does not).

Politics and science make awkward bedfellows, not unlike gay men and women…

Now that the political-stuff is out of the way, we can start dealing with some of Mark’s claims. The first thing I’ll take issue with there is the prevalence data. The stable 8% figure that Mark mentions is one that exceeds most every published estimate of homosexuality I’ve seen; those have typically hovered about 1-3%. Bear in mind, one isn’t simply trying to estimate the percentage of people who have had a homosexual experience before; it’s preferences which are of primarily interest. Further, there is little reason to think that such a figure is stable, as Mark implies it is, across time, place, or history. It well might have been, but one would have an awful hard time demonstrating that it is if one wishes to go beyond pure assertion.

As for his next point, yes; there is indeed evidence that twins tend to share a sexual orientation, as they do many other things. However, the concordance rates for a homosexual orientation among identical twins (that is, given that one twin has a homosexual orientation, how often does their co-twin have a similar orientation)  is only about 30%, and about 8.3% for non-identical twin pairs (Kendler et al, 2000). To make matters even more complicated, it’s worth noting that these concordance rates only tells us that some amount of what these twins share – genes, prenatal, and postnatal environments – makes it more likely that both will eventually develop a homosexual orientation, but it doesn’t tell us what that something is. Twin pairs, for instance, are similarly concordant for patterns of infectious disease (Cochran, Ewald, & Cochran, 2000), but it doesn’t mean they inherent genes that function to make them sick.

Finally, before getting to the selection pressures, it’s also worth countering the claim that homosexuality is well-documented in non-human species. Sure, there are some species that will, occasionally, engage in brief interactions more typical of mixed-sex pairs, be those interactions sexual or non-sexual in nature. What needs to be explained when it comes to homosexuality is not homosexual behaviors, but rather heterosexual avoidance. This more-or-less exclusive sexual preference for same-sex conspecifics has only been documented in rams, to my knowledge, and in no other non-human species, much less many or most of them.

Selection Pressures: Kin Selection
The first of the five selection pressures that Mark mentions is kin selection: helping others who share your genes reproduce. As Mark correctly points out, there’s little evidence for his hypothesis being correct, but the issues are much larger than that. For starters, the relationship coefficients don’t work well here: for each offspring a homosexual individual doesn’t produce, they would need to ensure that a full sibling produced an additional two that they otherwise wouldn’t have had for them to just break even and for this hypothesis to work. This would require an intense level investment that, if it existed, would be plainly obvious to any observer. It’s not enough that a homosexual individual is occasionally or even often nice to their relatives; they would need to be utterly devoted around the clock.

More to the point, though, is the seemingly apparent point that having a same-sex sexual attraction does nothing to help you invest in kin. Sure, maybe an asexual preference would work, if you wanted to save the time otherwise spent pursuing sex; a facultative heterosexual preference would probably do just as well, if not better. A homosexual orientation, on the other hand, is a complete waste of time; it would be a pointless distraction from the investment issue. Unless seeking out same-sex sexual relations was somehow functional in terms of increasing investment (or a rather odd byproduct), this explanation makes little sense.

Ants are very helpful, yet not very gay…

Selection Pressures: Group Selection
Group selection – the idea that a trait can spread if it offers group-wide advantages despite being individually detrimental – is a conceptual nonstarter, running counter to everything we know about how evolution works. Since I’ve written about this matter before on several occasions, there’s little need to continue beating this theoretical horse which has been dead since the 1960s. As Mark, again, points out, he knows of no evidence in favor of this hypothesis either, so there’s little less to say about it, other than that it doesn’t sound like a very “big” idea.

Selection Pressures: Sexual Attraction
This one, I admit, is probably the strangest of the selection pressures Mark posits. The idea here seems to be that because women might find homosexual men sexually attractive, this could give homosexual men a reproductive advantage. Now, perhaps I’m misunderstanding the basic idea in some fundamental way, but if an individual with a homosexual preference is found to be attractive by opposite sex individuals, it would seem to not matter much, as it’s quite unlikely that the two will ever end up having sex at all, let alone frequently. Provided these increased opportunities for sexual encounters even exist(Mark says there’s no evidence available that they do), they wouldn’t seem to do much good if the urge to take them is all but absent.

In case the problems aren’t plainly apparent at this point, imagine a hypothetical species of bird, like a peacock. In this species, males grow elaborate ornaments that females find to be attractive, generally speaking. Growing these ornaments, however, carries a cost: it makes the males sterile. In this case, no matter how attractive a male is to the females, his genes will never be benefited because of it. Attractiveness only matters so much as it leads to reproduction. No reproduction, no selection.

Selection Pressures: Balanced Selection
This argument at least poits that homosexuality is reproductively detrimental. These detriments are made up elsewhere, though, in the form of benefits to other carries of the genes. In essence, this argument says homosexuality is a lot like sickle-cell: harmful in some cases, but beneficial in others. There’s nothing theoreticall wrong with this possibility, but there are some serious practical hurdles. Specifically, if homosexual orientations ensured that 1-8% of the population was, effectively, sterile, there would need to be tremendous compensating benefits. Sickle-cell, for instance, is only common in areas that have a ton of malaria – which can kill huge minorities of populations and leave even more severely harmed – and pretty much the only known byproduct of its kind with a fitness hit as great as homosexuality (Cochran, Ewald, & Cochran, 2000). It also doesn’t fit well with the concordance rate data. So, while this explanation is theoretically possible, it’s highly improbable. At the risk of sounding like a broken record, there’s also no known evidence for this being the case.

Selection Pressures: Sexually Antagonistic Selection
This brings us to the final selection pressure. Here, the idea is that a gene is detrimental when it’s inherited by one sex, but beneficial in the other. This is another theoretically plausible suggestions with some consistent evidence behind it (but the account isn’t anywhere near complete, and only considers male homosexuality). Unfortunately for this suggestion, like the above hypothesis, it also suffers from the concordance rate data. It would also require that females consistently more than make up for the detriment to the male offspring, reproductively. Remember, this isn’t just a matter of slight disadvantages; this is a matter of effective sterility. Further, such sexually antagonistic issues tend to be weeded out over time, as any new modifications that can avoid the costs associated with expression in males will be selected for. Even if this was a viable account, then, it would still be far from a complete one, as it would not be able to explain why some of the twin pairs turn out concordant, but most don’t, why these reproductive costs have yet to be eliminated, and it’s missing an account of female homosexuality.

“Would you care for a sixth cup of weak tea?”

Out of the five “big” ideas, then, four seem to be basically dead in the water and the fifth, while potentially plausible, is by no means conclusive or complete. In my experience, poor outcomes like these can be seen frequently when people attempt to use scientific research to justify some political or moral opinion: any available evidence that can be potentially interpreted in a favorable light is seized upon, no matter how weak or nonsensical the underlying connection between the two is. The goal, after all, doesn’t appear to be accuracy, but rather persuasion; to the extent that the former helps with the latter, all the better for the persuader, but their need not be any necessary connection between the two goals.

References: Cochran, G., Ewald, P., & Cochran, K. (2000). Infectious Causation of Disease: An Evolutionary Perspective. Perspectives in Biology and Medicine, 43 (3), 406-448 DOI: 10.1353/pbm.2000.0016

Iemmola F. & Ciana, A. (2009). New evidence of genetic factors influencing sexual orientation in men: Female fecundity increases in the maternal line. Archives of Sexual Behavior, 38, 393-399.

Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (2000). Sexual orientation in a U.S. national sample of twins and nontwin sibling pairs. American Journal of Psychiatry, 157, 1843-1846

Is The Exotic Erotic? Probably Not…

Last time I wrote about the likely determinants of homosexuality, I ended up favoring the pathogen hypothesis that was put forth by Cochran, Ewald, and Cochran (2000) as the theory that had the most currently going for it. What is particularly interesting about my conclusion is how much empirical evidence directly confirms the theory: none. Don’t get me wrong; the pathogen hypothesis is certainly consistent with the known findings about homosexuality – such as the widely-varying reported concordance rates and the large fitness costs associated with the orientation – but being consistent with certain findings is not the same as being demonstrated by that evidence. If the currently most plausible theory for explaining homosexuality has, in essence, no direct evidence in its favor, that clearly must not be saying a lot about the alternative prospects. The two theories I covered last time – kin selection and sexually antagonistic selection – can’t even seem to account well for the existing evidence, so a neutral point with regard to the evidence is actually preferable. There was one theory that I neglected to mention last time, however, and this is a theory that purports to be able to explain both how heterosexual and homosexual orientations come to develop, and in both sexes, no less. If such a theory proved to have anything to it, then, it would be a highly valuable perspective indeed, so it deserves careful inspection.

“Nope; still not finding any indication of plausibility yet. Get the bigger microscope”

The theory, known as “Exotic Becomes Erotic” (EBE) was proposed by Daryl Bem (1996). If that name sounds familiar, it’s because this is the same Daryl Bem who also thought he found evidence for “extra-sensory porn-ception” in 2011, so we’re already not off to a good start. Pressing ahead despite that association, EBE puts the causal emphasis of developing a preferential attraction towards one sex or another on an individual’s perceptions of feeling different from other members of one sex: for instance, if a boy happens to not like sports, he will feel different from the majority of the other boys who do seem to like sports; if he does like sports, he’d feel different from the girls who did not. Following this perception of one sex as exotic, EBE posits that individuals will come to experience “non-specific, autonomic arousal” to the exotic group in question and, subsequently, that arousal will be transformed into an erotic preference for members of the initially exotic group. So, if you feel different from the boys or the girls, regardless of whether you’re a boy or a girl, you’ll come to be vaguely aroused by that sex – either by apprehension, anger, fear, curiosity, or really anything works, so long as it’s physiologically arousing – and then your body will, at some point, automatically turn that arousal into lasting sexual preferences.

Like most of the theories regarding homosexuality I discussed previously, this one also have very little actual evidence to support it. What it does have is a correlation between retrospective reports of childhood gender nonconformity and current sexual orientation. In fact, that single, underwhelming correlation is about all that EBE has going for it; everything else in the model is an assumption that’s largely built off that correlation. While a retrospective correlation is slightly better than having no evidence at all, it’s not better by a whole lot (in much the same way that 53% accuracy at guessing where some stimuli will show up between two options isn’t much better than 50%, yet apparently both are publishable). So, now that we’ve covered what the theory has going for it, let’s consider some of the things that EBE does not have going for it. You might want to take a break now to use the bathroom or get a snack, because this is a long list.

Let’s begin with the matter of this “non-specific physiological arousal”: at a bare minimum, EBE would require that the sex an individual perceived to be the least exotic ought to be consistently less physiologically arousing, on average, than the gender that individual did identify with. Without that arousal, there would be nothing to eventually convert into later sexual preference. So what does Bem have to say about the presence or absence of this arousal?

“To my knowledge, there is no direct evidence for the first step in this sequence beyond the well-documented observation that novel (“exotic”) stimuli produce heightened physiological arousal in many species, including our own”

So, in other words, there is no empirical evidence for this suggestion whatsoever. The problems, however, do not stop there: EBE is also massively under-specified in regards to how this hypothetical “non-specific arousal” is turned into eroticism in some cases but not others. While Bem (1996) proposes three possible mechanisms through which that transition might take place – sexual imprinting, the opponent process, and the extrinsic arousal effect – there are clearly non-human stimuli that produce a great deal of arousal (such as spiders, luxury cars, or, if we are talking about children, new toys) that does not get translated into later sexual attraction. Further, there are also many contexts in which gender-conforming children of the same sex will be around other while highly physiologically aroused (such as when boys are playing sports and competing against a rival team), but EBE would seem to posit that these high-aroused children would not develop any short- or long-term eroticism towards each other.

Nope; nothing even potentially erotic about that…

Bem might object that this kind of physiological arousal is somehow different, or missing a key variable. Perhaps, he might say, that in addition to this yet-to-be-demonstrated arousal, one also needs to feel different from the target of that arousal. Without being both exotic and arousing, there will be no lasting sexual preference developed. While such a clarification might seem to rescue EBE conceptually in this regard, the theory again falters by being massively under-specified. As Bem (1996) writes:

“…[T]he assertion that exotic becomes erotic should be amended to exotic – but not too exotic – becomes erotic. Thus, an erotic or romantic preference for partners of a different sex, race, or ethnicity is relatively common, but a preference for lying with the beasts in the field is not.”

In addition to not figuring out whether the arousal required for the model to work is even present, in no treatment of the subject does Bem specify precisely how much arousal and/or exoticism ought to be required for eroticism to develop, or how these two variables might interact in ways that are either beneficial or detrimental to that process. While animals might be both “exotic” and “highly arousing” to children, very rarely does a persistent sexual preference towards them develop; the same can be said for feelings between rival groups of boys, though in this case the arousal is generated by fear or anger. EBE does not deal with this issue so much as it avoids it through definitional obscurity.

Continuing along this thread of under-specificity, the only definition of “exotic” that Bem offers involves a perception of being different. Unfortunately for EBE, there are a near incalculable number of potential ways that children might feel different from each other, and almost none of those potential representations are predicted to result in later eroticism. While Bem (1996) does note that feeling different about certain things – interest in sports seems to be important here – appears to be important for predicting later homosexual orientation, he does not attempt to explain why feeling different about gender-related variables ought to be the determining factor, relative to non-gender related variables (such as intelligence, social status, or hair color). While erotic feelings do typically develop along gendered lines, EBE gives no a priori reason for why this should be expected. One could imagine a hypothetical population of people who develop preferential sexual attractions to other individuals across any number of non-gendered grounds, and EBE would have little to say about why this outcome does not obtain in any known human population.

The problem with this loose definition of exotic does not even end there. According to the data presented by Bem, many men and women who later reported a homosexual attraction also reported having enjoyed gender-typical activities (37 and 37%, respectively), having been averse to gender-atypical activities (52 and 19%), and having most of their childhood friends be of their same sex (58 and 40%). While these percentages are clearly different between homosexual and heterosexual respondents – with homosexuals reporting enjoying typical activities less, atypical ones more, and being more likely to predominately have friends of the opposite sex – EBE would seem to be at loss when attempting to explain why roughly half of homosexual men and women do not seem to report differing from their heterosexual counterparts in these important regards. If many homosexuals apparently did not view their own sex to be particularly exotic during childhood, there could be no hypothetical arousal and, accordingly, no eroticism. This is, of course, provided these retrospective accounts are even accurate in the first place and do not retroactively inflate the perceptions of feeling different to accord with their current sexual orientation.

“In light of not being hired, I can now officially say I never wanted your stupid job”

On a conceptual level, however, EBE runs into an even more serious concern. Though Bem (1996) is less than explicit about this, it would seem his model suggests that homosexuality is a byproduct of an otherwise adaptive system designed for developing heterosexual mate preferences. While Bem (1996) is likely correct in suggesting that homosexuality is not adaptive itself, his postulated mechanism for developing mate preference would likely have been far too detrimental to have been selected for. Bem’s model would imply that the mechanism responsible for generating sexual attraction, when functioning properly, functions so poorly that it would, essentially, render a rather large minority of the population effectively sterile. This would generate an intense selection pressure either towards any modification of the mechanism that did not preclude its transfer from one generation to the next or decisive selection towards a much greater gender conformity. Neither outcome seems to have obtained, which poses a new set of questions regarding why.

Precisely how such a poorly-functioning mechanism would have even come to exist in human populations in the first place is a matter that Bem never addresses. A major issue with the EBE perspective, then, is that it more-or-less takes for granted the base rate existence of homosexuality in human populations without asking why it ought to be that prevalent for humans but almost no other known species. Though Bem does not discuss it, almost every other species appears to navigate the process of developing sexual attraction in ways that do not result in large numbers of males or females developing exclusive same-sex attractions. If this was any other key adaptation, such a vision, and significant minorities of the population consistently went blind at very young ages in a world where being able to see is adaptive, we would want a better explanation for that failure than the kind that EBE can provide. Now if only the creator of EBE has some kind of ability to see into the future – an extra-sensory ability, if you will – to help him predict that his theory would run into these problems, they might have been avoided or dealt with…

References:Bem, D. (1996). Exotic becomes erotic: A developmental theory of sexual orientation. Psychological Review, 103 (2), 320-335 DOI: 10.1037//0033-295X.103.2.320

Cochran, G., Ewald, P., & Cochran, K. (2000). Infectious Causation of Disease: An Evolutionary Perspective Perspectives in Biology and Medicine, 43 (3), 406-448 DOI: 10.1353/pbm.2000.0016

Making Your Business My Business

“The government has no right to do what it’s doing, unless it’s doing what I want it to do” – Pretty much everyone everywhere.

As most people know by now, North Carolina recently voted on and approved an amendment to the state’s constitution that legally barred gay marriage. Many supporters of extending marriage rights to the homosexual community understandably found this news upsetting, which led the predictable flood of opinions about how it’s none of the government’s business who wants to marry who. I found the whole matter to be interesting on two major fronts: first, why would people support/oppose gay marriage in general, and, secondly, why on earth would people try to justify their stance using a line of reasoning that is (almost definitely) inconsistent with other views they hold?

Especially when they aren’t even running for political office.

Let’s deal with these issues in reverse order. First, let’s tackle the matter of inconsistency. We all (or at least almost all) want sexual behavior legislated, and feel the government has the right to do that, despite many recent protests to the contrary. As this helpful map shows, there are, apparently, more states that allow for first cousin marriage than gay marriage (assuming the information there is accurate). That map has been posted several times, presumably in support of gay marriage. Unfortunately, the underlying message of that map would seem to be that, since some people find first cousin marriage gross, it should be shocking that it’s more legal that homosexuality. What I don’t think that map was suggesting is that it’s not right that first cousin marriage isn’t more legal, as the government has no right legislating sexuality. As Haidt’s research on moral dumbfounding shows, many people are convinced that incest is wrong even when they can’t find a compelling reason why, and many people likewise feel it should be made illegal.

On top of incest, there’s also the matter of age. Most people will agree that children below a certain age should not be having sex, and, typically, that agreement is followed with some justification about how children aren’t mature enough to understand the consequences of their actions. What’s odd about that justification is that people don’t go on to then say that people should be allowed to have sex at any age, just so long as they can demonstrate that they understand the consequences of their actions through some test. Conversely, they also don’t say that people above the age of consent should be forbade from having sex until they can pass such a test. There are two points to make about this: the first is that no such maturity test exists in the first place, so when people make the judgments about maturity they’re just assuming that some people aren’t mature enough to make those kinds of decisions; in other words, children shouldn’t be allowed to consent to sex because they don’t think children should be allowed to consent to sex. The second point is, more importantly, even if such a test existed, suggesting that people shouldn’t be allowed to have sex without passing it would still be legislating sexuality. It would still be the government saying who can and can’t have sex and under what circumstances.

Those are just two cases, and there are many more. Turns out people are pretty keen on legislating the sexual behavior of others after all. (We could have an argument about those not being cases of sexuality per se, but rather about harm, but it turns out people are pretty inconsistent about defining and legislating harm as well) The point here, to clarify, is not that legalizing gay marriage would start us on a slippery slope to legalizing other, currently unacceptable, forms of sexuality; the point is that people try to justify their stances on matters of sexuality with inconsistently applied principles. Not only are these justifications inconsistent, but they may also have little or nothing to do with the actual reasons you or I end up coming to whatever conclusions we do, despite what people may say. As it turns out, our powers of introspection aren’t all they’re cracked up to be.

Letting some light in might just help you introspect better; it is dark in there…

Nisbett and Wilson (1977) reviewed a number of examples concerning the doubtful validity of introspective accounts. One of these finding concerned a display of four identical nylon stockings. Subjects were asked about which of the four pairs was the best quality, and, after they had delivered their judgment, why they had picked the pair the did. The results showed that people, for whatever reason, tended to overwhelmingly prefer the garment on the right side of the display (they preferred it four-times as much, relative to the garment on the left side). When queried about their selection, unsurprisingly, zero of the 52 subjects made mention of the stocking’s position in the lineup. When subjects were asked directly about whether the position of the pair of stockings had any effect on their judgment, again, almost all the subjects denied that it did.

While I will not re-catalog every example that Nisbett and Wilson (1977) present, the unmistakable conclusion arose that people have, essentially, little to no actual conscious insight into the cognitive processes underlying their thoughts and behavior. They often were unable to report that an experimental manipulation had any effect (when it did), or reported that irrelevant manipulations actually had (or would have had) some effect. In some cases, they were unable to even report that there was any effect at all, when there had in fact been one. As the authors put it:

… [O]thers have argued persuasively that “we can know more than we can tell,” by which it is meant that people can perform skilled activities without being able to describe what they are doing and can make fine discriminations without being able to articulate their basis. The research described above suggest that that converse is also true – that we sometimes tell more than we can know. More formally, people sometimes makes assertions about mental events to which they may have no access and these assertions may bear little resemblance to the actual events.

This – coupled with the inconsistent use of principled justifications – casts serious doubts on the explicit reasons people often give for either supporting or opposing gay marriage. For instance, many people might support gay marriage because they think it would make gay people happier, on the whole. For the sake of argument, suppose that you discovered gay marriage actually made gay people unhappier, on the whole: would you then be in favor of keeping it illegal? Presumably, you would not be (if you were in favor of legalization to begin with, that is). While making people happy might seem like a plausible and justifiable reason for supporting something, it does not mean that it was the – or a – cause of your judgment.

Marriage: a known source of lasting happiness

If the typical justifications that people give for supporting or opposing gay marriage are not likely to reflect the actual cognitive process that led to their decisions, what cognitive mechanisms might actually be underlying them? Perhaps the most obvious class of mechanisms are those that involve an individual’s mating strategy. Weeden et al. (2008) note that the decision to pursue a more short or long-term mating strategy is a complicated matter, full of tradeoffs concerning local environmental, individual, and cultural factors. They put forth what they call the Reproductive Religiosity Model, which posits that a current function of religious participation is to help ensure the success of a certain type of mating strategy: a more monogamous, long-term, high-fertility mating style. Men pursuing this strategy tend to forgo extra-pair matings in exchange for an increase in paternity certainty, whereas women similarly tend to forgo extra-pair matings for better genes in exchange for increased levels of paternal investment.

As Chris Rock famously quipped, “A man is only as faithful as his options”, though the sentiment would apply equally well to women. It does the long-term mating strategy no good to have plenty of freely sexually available conspecifics hanging around. Thus, according to this model, participation in religious groups helps to curb the risks involved in this type of mating style. This is why certain religious communities might want to decrease the opportunities for promiscuity and increase the social costs for engaging in it.  In order to decrease sexual availability, then, you might find religious groups doing things like opposing and seeking to punish people for engaging in: divorce, birth control use, abortion, promiscuity, and, relevant to the current topic, sexual openness or novelty (like pornography, sexual experimentation, or homosexuality). In support of this model, Weeden et al (2008) found that, controlling for non-reproductive variables, sexual variables were not only predictive of religious attendance, but also that, controlling for sexual variables, the non-reproductive variables were no longer predictive of religious attendance.

While the evidence is not definitively causal in nature, and there is likely more to this connection than a unidirectional arrow, it seems highly likely that cognitive mechanisms responsible for determining one’s currently preferred mating strategy also play a role in determining one’s attitudes towards the acceptability of other’s behaviors. It is also highly likely that the reasons people tend to give for their attitudes will be inconsistent, given that they don’t often reflect the actual functioning of their mind. We all have an interest in making other people’s business our business, since other people’s behaviors tend to eventually have an effect on us – whether that effect is relatively distant or close in the causal chain, or whether it is relatively direct or indirect. We just tend to not consciously understand why.

References: Nisbett, R., & Wilson, T. (1977). Telling more than we can know: Verbal reports on mental processes. Psychological Review, 84 (3), 231-259 DOI: 10.1037//0033-295X.84.3.231

Weeden, J., Cohen, A., & Kenrick, D. (2008). Religious attendance as reproductive support Evolution and Human Behavior, 29 (5), 327-334 DOI: 10.1016/j.evolhumbehav.2008.03.004

What Causes (Male) Homosexuality?

My initial inspiration for starting this blog was a brief piece I had written about why Lady Gaga’s song, “Born This Way”, really got under my skin. The general premise of the song is, unless I’m badly mistaken, that homosexuality is genetic in nature, and, accordingly, should be socially accepted. The song is full of very selective logic and a poor grasp of the state of scientific knowledge, all of which is accepted in the service of furthering a political goal. For what it’s worth, I agree with that goal, but the means being used to achieve it in this case were misguided because:

“…I’m not so sure Lady Gaga – or any gay-rights supporter – wants to base their claims to equal rights on the supposition that homosexuality is a trait people are “born” with…If further research uncovers that people can come to develop a homosexual orientation for a number of reasons that have nothing to do with being “born like that”, I wouldn’t want to see the argument for equal rights slip away.”

Today, I’m going to be stepping back into that same political minefield that I did on the topic of race, and discuss a hypothesis regarding the cause of male homosexuality that some people may not like. People will not like this hypothesis for reasons extrinsic to the hypothesis itself, but do your best to contain any moral outrage you may be feeling. My first task in presenting this hypothesis will be to convince you that male homosexuality is not genetically determined – despite what an eccentric young pop-star might tell you – and is also not an adaptation.

Convincing critics is always such a pleasure.

For some, it might seem insulting that homosexuality requires an explanation, whereas heterosexuality does not. Aren’t both just different sides of a very bisexual coin? There’s a simple answer to that concern: heterosexual intercourse is the only means to achieve reproduction. An exclusive homosexual orientation is the evolutionary equivalent to sterility, and if three to five percent of the male population was consistently sterile – despite neither of anyone’s parents being sterile, by definition – that would raise some questions as to how sterility persists. There would be an intense selective pressure away from sterility, and any genes that actively promoted it would fail to reproduce themselves. That homosexuality seems to persist in the population, despite it being a reproductive dead-end, requires an explanation. Heterosexuality poses no such puzzle. 

The first candidate explanation for the persistence of homosexuality is that it’s part on an adaptation for assisting the reproduction of one’s kin. While homosexuals themselves may suffer a dramatic reduction in their lifetime reproduction, they activity assist other genetic relatives, delivering enough benefits to offset their lack of personal reproduction, similar to how ants or bees would assist the queen, forgoing reproduction themselves. This suggestion is implausible on three levels: first, it would require that homosexuals deliver enormous benefits to their relatives. For each one child a gay man wouldn’t have, they would need to ensure a brother or sister would have an additional two that they wouldn’t otherwise have without those benefits. This would require an intense amount of investment. Second, there’s no theoretical reason that’s ever been provided as to why homosexuals would develop a homosexual orientation, as opposed to, say, an asexual orientation. Seeking out intercourse with same-sex individuals doesn’t seem to add anything to the whole investment thing. Finally, this explanation doesn’t work because, as it turns out, homosexuals don’t invest anymore in their relatives than heterosexuals do (Rahman & Hull, 2005). So much for kin selection.

A second  potential explanation for homosexuality is that it’s the byproduct of sexually antagonist selection; a gene that damages the reproductive potential of males persists in the population because the same trait is beneficial when it’s expressed in female offspring (Ciani, Cermelli, & Zanzotto, 2008; Iemmola & Ciani, 2009). Another potential explanation is that a homosexual orientation is like sickle cell anemia: while it hurts the reproductive prospects of those who express it, it provides some unspecified benefit that outweighs that cost in some carriers, as sickle cell protects against malaria. Both explanations have a large issues to contend with but one of the most prominent shared issues is this: despite both hypotheses resting on rather strong genetic assumptions, half or more of the variance in male homosexual orientation can’t be attributed to genetic factors (Kirk et al., 2000; Kendler et al., 2000). Identical twins don’t seem to be concordant for their sexual orientation anymore than 30 to 50% of the time when one of the twins identifies as non-heterosexual. If homosexuality was determined solely by genes, there should be a near complete agreement. 

In fact, most of the variance appears to be due to our decadent Western lifestyle. Who knew, right?

Accordingly, any satisfying explanation for homosexuality needs to reference environmental factors, as all traits do; the picture is far from as crude as there being some genes “for” homosexuality. While there clearly are some genetically inherited components in the ontogeny of a homosexual orientation, it’s entirely unclear what those genetic factors are. It’s also far from clear how those genetic factors interact with their environment – or when, for that matter. They would seem to act sometime before puberty, but beyond that the door is open. What seems to have been established so far is that an exclusive homosexual orientation is detrimental to reproduction in a big way, and these costs are not known to be reliably offset.

There is one last hypothesis that may hold some potential, though, as I mentioned, I suspect many people won’t like it: the “gay germ” theory. The general idea is that some outside pathogen – be it a bacteria or a virus – manipulates development in some way, the end result being a homosexual orientation. This hypothesis seems to have potential for a number of reasons: first, it neatly deals with why homosexuality persists in the population, despite the massive reproductive costs. It could also account for why monozyogtic twins are often discordant for homosexual orientation, despite sharing genes and a prenatal environment. As of now, it remains an untested theory, but other lines of research suggest some preliminary success using the same basic idea to understand the persistence of disorders like schizophrenia and obsessive compulsive disorder, among many others. Of course, such a theory does come with some political baggage and questions.

Like: will two gay men ever be able to hold hands, post love-making, on top of an American flag, just like straight couples do?

The first set of questions concern the data speaking to the hypothesis: what pathogen(s) are responsible? When do they act in development? How do they alter development? Are those alterations an adaptation on the part of the pathogen or merely a byproduct? These are no simple questions to answer, especially because it won’t be clear which children will end up gay until they have matured. This makes narrowing the developmental window in which to be looking something of task. If concordance rates for monozyogtic twins are similar between adopted and reared together twins, that might point to something prenatal, depending on the age at which the twins were separated, but would not definitively rule out other possibilities. Further, this pathogen need not be specific to gay men; it could be a pathogen that much of the population carries, but, for whatever reason, only affects a sub-group of males in such a way that they end up developing a homosexual orientation.        

The second set of questions concern potential implications of this theory, were it to be confirmed. I’ll start by noting these concerns have zero, absolutely nothing, to do with whether or not the gay germ theory is true. That said, these concerns are probably where most of the resistance to the hypothesis would come from, as concerns for data (or lack thereof) are often secondary to debates. Yes, the hypothesis cries out for supporting data so it shouldn’t be accepted just yet, but I’m talking to those people who would reject it as a possibility out of hand because it sounds icky. In terms of gay rights and social acceptance, it shouldn’t matter whether homosexuality is 100% genetically determined, caused by a pathogen, or just a choice someone makes one day because they’re bored with all that vanilla heterosexual sex they’ve been having. That something may be, or is, caused by a pathogen should really have no bearing on it’s moral status. If we discovered tomorrow that it was a virus that caused men to have larger-than-average penises, I doubt many people would cheer for the potential to cure the “disease” of large-penis.         

References: Ciani, A.C., Cermilli, P., & Zanzotto, G. (2008). Sexually antagonistic selection in human male homosexuality. PLosone.org, 3, e,2282.

Iemmola, F. & Ciani, A.C. (2009). New evidence of genetic factors influencing sexual orientation in men: Female fecundity increase in the maternal line. Archives of Sexual Behavior, 38, 393-399

Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (2000). Sexual orientation in a U.S. national sample of twins and nontwin sibling pairs. American Journal of Psychiatry, 157, 1843-1846

Kirk, K.M., Bailey, J.M., Dunne, M.P., & Martin, N.G. (2000). Measurement models for sexual orientation in a community twin sample. Behavior Genetics, 30, 345-356

Rahman, Q. & Hull, M.S. (2005). An empirical test of the kin selection hypothesis for male homosexuality. Archives of Sexual Behavior, 234, 461-467