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 

OKCupid Blog: Gay Vs. Straight Sex

I’m of the mindset that gay men and women are pretty much just like straight men and women, the real difference being their preference for which gender they find attractive, which is why the following presentation struck me as interesting:

Their sample size was 3.2 million, which is pretty fucking impressive. The thought of having access to the data set they do is sexually thrilling for me (perhaps we could tack another letter onto the end of LBGT for people with my proclivities), so I decided to do another edition of Pop Psychology to take a closer look at what our Okcupid blogger decided to present from that data set and raise some questions that will remain unanswered, but serve as practice (for me, anyway) for critical evaluation. After all, having access to something so amazing demands that it not be squandered or misused.

The first question I’d pose is about that impressive sample size itself: what percentage of it represents straight/ gay men and women? You’d think, this being an article about straight vs. gay sex, that would be the first thing they’d mention. If we assume population level frequencies, that would mean that sample is about 1.6 million men and women total, about 80,000 of which will be gay men (5%, published range from 3-10%) and about 40,000 of which will be lesbian women (2.5%, published range from 1 – 3%). That is assuming we can assume population levels; there is no data presented concerning the the percentage of Okcupid users who identify as straight or gay in the first place. I’m sure the Okcupid people have this data available, but it’s not shown here for whatever reason. Since it’s not shown, there’s no way of inferring whether this population is representative or not, which could throw a possible wrench into its interpretation. I’m not saying it does, just that it might.

Let’s start by looking at the first point raised by the article:

Gay people are not sexually interested in straights.    

Match Search Returns

  • only 0.6% of gay men have ever searched for straight matches.
  • only 0.1% of lesbians have ever searched for straight matches.

What that tells us is that most gay and lesbian people do not go looking explicitly for straight people on the website, which is pretty expected, especially when people’s sexual orientations are readily visible. What that does not tell us is is that gay people are not sexually interested in straight people; I assume most of them are, and I assume that for the same reason that most heterosexual men are sexually interested in lesbians, even though they’ll probably never sleep with them (but more on that in a bit). I have found that knowing a woman’s sexual orientation has not made me any more or less attracted to them, though it does affect my judgments of whether or not I’m likely to have sex with them. I imagine other people don’t need to know someone’s sexual orientation before they feel any sexual attraction, nor do I feel that knowledge would do much to change that attraction. The website just allows for screening based on sexual orientation, skipping what would be an in-person trial and error process, since not everyone has their sexual orientation tattooed on their forehead.

Those absolute percentages are very small, granted, but they also tell us something else: relatively, gay men are six-times as likely to have ever searched for straight men than lesbians are to have searched for straight women; an interesting finding to be sure. Bear in mind those numbers refer to people who have ever searched for a straight match, not how frequently they do it. My guess is that gay men also search for straight matches more frequently, but without the data available I can’t say with any certainty. Moving on:

Gay people aren’t promiscuous.

Median Reported Sex Partners

  • straight men: 6
  • gay men: 6
  • straight women: 6
  • gay women: 6

This stuck out to me above everything else in the article because it stands in stark contrast to everything I’ve ever read in the published literature. Simply put, men and women (straight ones) don’t report identical numbers of sexual partners, generally speaking, and men and women (gay ones) don’t report identical numbers of sexual partners. Has Okcupid, with its huge data set just blown all those other results out of the water? I don’t think so; consider the following number sets to understand why:

(1) 0, 0, 1, 3, 5, 6, 10, 30, 100
(2) 3, 3, 3, 3, 5, 7, 7, 7, 7

If we assume those numbers represent number of sexual partners, then in both samples, the median (the middle) number of partners is 5; the mean (the average) number of partners is still 5 for sample (2), but in (1) it’s 17.22. See the very big difference? Most every study I recall reading reports the mean, and if they report the median at all, it’s in conjunction with the mean. That the Okcupid post only reports the median at best doesn’t allow them to make the statement they did, and at the worst reeks of spin to attempt to make groups look  more similar than they actually are.

There are two other problems: the first is that those numbers refer to number of partners, not number of same/opposite sex partners. It’s not uncommon for lesbians to have several male partners (in some cases, more male partners than female ones), and that can matter a lot (especially because the same isn’t true of gay men).
The second problem, again, returns to the sample itself: the age of these people are not reported. Older people tend to have more sexual partners than younger ones, simply because they’ve had more time to rack up the numbers. Gay men tend to report establishing a clear sense of their orientation before lesbians, which could mean our lesbian sample is substantially older. Perhaps they controlled for this, but if they did, they make no mention of it (they do mention controlling for things in other blog posts, so I can only assume they did not here).

  • 45% of gay people have had 5 or fewer partners (vs. 44% for straights)
  • 98% of gay people have had 20 or fewer partners (vs. 99% for straights)

What is curious about this is that the previous stats had broken down the data by gender and sexual orientation; here, we see it recombined to just sexual orientation. I can’t think of any good reason to do that from a strictly informative point of view, which implies to me there’s probably something else going on (namely, controlling the light in which these findings are presented).
While those differences in percentages appear small absolutely, as was the case previously, they can also be read to say something else: gay people are twice as likely to have more than 20 partners, relative to straight people. I also assume that effect is largely being carried by the male portion of the gay side, which could potentially mean that gay men are up to four-times as likely to have over 20 partners, depending on what percentage of that gay 2% and straight 1% are men. So gay men could be somewhere between 2-4 times as likely to have over 20 partners, relative to their straight counterparts, which strikes me as more promiscuous.On that note:

we found that just 2% of gay people have had 23% of the total reported gay sex, which is pretty crazy.

An interesting finding to sure, but the same probably holds for straight people. Male numbers of sexual partners (straight) are distributed differently from female numbers; there are a small number of men with a large number of sexual partners along with many men that have low numbers to no number at all. On the other hand, women are less likely to have the peaks that men do in the high end, but they’re also less likely to be shut out of the game entirely (fewer women with no numbers). Accordingly, if this was broken down by gender, I’d predict that most of that effect was being carried by gay men, not lesbians.

However, since we are dealing with a single gender in the case of gay men or women, the distribution curves would have to look different from their heterosexual counterparts: either the peaks of the gay community would have to be smaller than those of the straight community and the distribution more even, or larger numbers of gay men and women would not have (m)any sexual partners. Since we already know from the previously reported data that, at the upper end of 20+ partners, gays outnumber straights 2-to-1, that would require more gays not having, relative to straight people. That would mean, cutting off the top end of the distribution, the gay community should be even less promiscuous than the straight community, on average.

Then again, perhaps gay men are more promiscuous all around (which would simply shift the graph up), while lesbians are less so (shifting the graph down), but that article seems to imply that’s an unfair stereotype.

So there are good reasons to doubt the statement that promiscuity is equal across the four combinations of straight/gay men/women; it’s very expected, and established, the that groups are not the same sexually (men are not women, and women are not men). However, there are two more possibilities that the article doesn’t touch on that I think could underestimate the extent of gay promiscuity.

The first is the social risks openly gay people may face, which could result in them being less willing to try to hit on people they otherwise would like to. In that sense, it’s not that homosexuals are less promiscuous then they’d prefer by choice.

The second is the size of the dating/mating pool that gay men and women have to deal with; were only 2.5% of the population potentially sex-able to me (50% aren’t men, and of that 50% that are men, only about 5% are gay, and of that 5%, not all will be attractive), I’d either have to know many, many more people than average to reach the average number of sexual partners, or be particularly more motivated to make it happen, provided that 2.5% was no more promiscuous than the roughly 50% I have potentially available now. Since I don’t think gay people know substantially more people than straight ones, that raises the possibility of motivation and/or promiscuity.

Of course, none of this says anything about judging the worth of a person by their number or choice of sexual partners. I can’t help but wonder if the people at Okcupid were trying to present the data selectively to make the case that gay people are really just like straight people, which means they’re OK. If they were, they went wrong on two major fronts. The first is that the gay community does not need to be the same as straight people to be OK. They’re already OK; always have been. The second big issue is that for gay men and women to be similar to straight men and women, gay men are going to be different from lesbians along the same lines that straight men differ from straight women. The real differences in behavior emerge because when a man is pairing with other men, their sexual interests tend to converge more than the interests of men with women; that same goes for women pairing with other women. There’s no need for everyone to be identical for everyone to be equal, and trying to present select bits of the data to make them look more the same isn’t helping.