It is admittedly odd to think that a progressive, humanitarian shift in attitudes toward gays and lesbians might lead, ironically, to a noticeable decline in the homosexual population. Yet this is precisely what I predict will happen over the very long course of natural selection should the societal-level normalization of adult homosexual relationships, such as is happening currently with the triumphant legalization of gay marriage in my new home state of New York, continues happily on its way. (I add these emotive terms, “triumphant” and “happily,” to highlight the obvious and inherent goodness of a legal acknowledgment of human sexual diversity, and to make it clear that what I’m exploring in this brief, speculative essay are only the non-politic, genetic consequences of these accomplishments, and nothing more.)  

Not so very long ago, the concept of “gay marriage” was so far from being a legal possibility in its literal sense that most listeners would have probably interpreted this phrase to mean a closeted gay man married to a woman, or a lesbian to a man. From all accounts, such “mixed-orientation marriages” have been around since the very institutionalization of marriage itself and are so common as to be banal. In one extensive study in 1978, for example, researchers Alan Bell and Martin Weinberg, factoring in ethnic differences, found that 35 percent of gay white males, and 13 percent of gay black males, reported having been married to a woman. By contrast, 47 percent of black lesbians and 20 percent of white lesbians had been married to a man.  

And Bell and Weinberg’s figures almost certainly underreport the actual frequency of such relationships, too, since their data come from surveys of sexual orientation collected during an unapologetically homophobic era. In other words, these statistics only take into account those individuals previously or currently in a mixed-orientation marriage willing to acknowledge their primary homosexual leanings. Those gay respondents still in the closet of conventional suburban matrimony would have been rather difficult to get an empirical grip on. (Just think of the tortured character of Colonel Frank Fitts in the film American Beauty.)  

Still, many studies have since examined the psychological experiences of those who acknowledge being in mixed-orientation marriages—including motivations to enter into such a marriage to begin with, internalized homophobia, self-awareness and acceptance, religious ideology, experimenting with open relationships, and so on—from the perspective of the homosexual as well as from that of the heterosexual spouse. The particular dynamics between such couples vary dramatically, of course, but the data reveal unequivocally that mixed-orientation marriages have an extraordinarily low rate of success, with one or both partners inevitably leaving due to sexual incompatibility. One interesting sex difference , reported in 1985 by University of Minnesota psychologist Eli Coleman, is that lesbians tended to marry men at younger ages (mean age of 21) than did gay men marrying women (mean age of 24). Lesbians also reported being less aware than gay men of their own homosexual orientation upon entering such ill-fitting marriages and a slower realization of their same-sex attractions. Personally, I don’t think I would ever have signed on to deceiving a marital partner as a cover. But I do remember scheming briefly, at the very closeted age of 17, about finding myself a nice, repressed lesbian who would be game for a lifelong sham marriage; alas, I’d no idea where such pitiable creatures congregated. (The Chinese seized on this ridiculous idea years later, however.)  

Yet mixed-orientation marriages, which, in the mid-1980s when the most recent data were collected, lasted on average 8.5 years for lesbians and 13.1 years for gay men, are often fruitful, even if they do involve undesirable sexual activity for at least one of the individuals in the relationship. And for our purposes, the most relevant findings for the question we started off with—which is whether the increasing public support for gay marriage will lead, ironically, to the eventual decline of the homosexual population—is the fact that most homosexuals in mixed-orientation marriages have had at least one child with their spouse. In fact, Coleman found that gay men married to women sired an average of 2 children with their wives, whereas lesbians bore an average of 1.2 children with their husbands.  

Perhaps you’re beginning to see where I’m heading with all of this. Although the precise genetic mechanisms underlying homosexuality are still relatively unknown, we do know that, however these mechanisms actually work, there are indeed clear, contributing genetic factors underlying homosexual orientation. The best evidence that homosexuality runs in families as a heritable biological trait comes from 1990s-era twin studies, which revealed that the concordance rate (the rate by which twin members overlap on anything from schizophrenia to creativity to sexual orientation) for homosexuality is significantly greater in monozygotic twins (identical) than in dizygotic twins (who share only half of their genes, just like non-twin siblings). The more rigorously controlled twin studies adjust for possible shared environmental influences by taking into account, for instance, the sexual orientation of non-twin siblings or twins separated at birth, and yet all reveal that homosexuality is at least partially heritable.  

Homosexuality is often presented as an evolutionary “mystery” because of the obvious reproductive disadvantages, and thus for decades researchers have sought some adaptive function for the culturally recurrent percentage (anywhere from 1 to 10 percent of the population, depending on the measures used) of the human population that is aroused more by the same than it is by the opposite sex. Yet if we consider the historical, and perhaps even the ancestral, percentage of the homosexual population that did in fact reproduce because of societal proscriptions against adult relations with the same sex, the mystery becomes considerably less profound.  

Even in societies where homosexuality was tolerated , such as in Ancient Greece, men tended to engage in pederasty with adolescent boys while maintaining wives and families at home—romantic relationships with fellow adults were by contrast considered reprehensible. Offspring resulting from such forced adult heterosexuality would require no effort on the part of lesbians, since sexual arousal is not a prerequisite for conception. For gay men, a healthy imagination ( what I’ve discussed before in this column in terms of erotic mental representation) would be all that is needed to transform in one’s mind a female vagina into one’s favorite male anus or mouth. If zoophiles can ejaculate into their wives only by imagining that their spouse’s vagina is actually a horse’s vulva, a man’s anus must certainly be within mind’s reach of the average married homosexual.  

Whatever alleles are associated with homosexual orientation are transmitted by these faux heterosexual means, and this is an age-old reproductive cycle that has been occurring for as long as adult homosexuality has been proscribed by human societies—and by all accounts, such proscription has been the species’ norm. But now, through our collective intelligence and our common sense, we’re breaking from that norm, and exclusive homosexual relationships are becoming not only tolerated, but legalized. These cultural developments are significant for the homosexual population, not only for the obvious sake of gaining equality and protection against persecution for an unalterable phenotypic trait, but because it means that the age-old reproductive cycle that has been so central to mixed-orientation marriages is slowly but surely breaking. This is not to say that lesbians and gay men who are now free to marry the same sex will no longer reproduce—many do, and this trend will continue with the advent of new reproductive technologies and increasing societal support (such as surrogacy) for those who desire their own biological children. But with the societal expectation for men and women to bear children under the roofs of traditional opposite-sex relationships obviously lessening, combined with the hefty financial costs of reproductive technologies, as well as the costly interpersonal complexities of arrangements such as surrogacy, not to mention the fact that homosexual activity among same-sex married couples cannot possibly lead to unplanned pregnancies, homosexual reproduction will clearly decline as same-sex marriages continue to rise.  

In an evolving culture of tolerance and with the available option of gay marriage, “coming out the closet” will occur at younger and younger ages, and fewer young people will therefore feel strong-armed by shame and obligation to enter into mixed-orientation marriages to begin with. As the direct result of an increasing understanding and acceptance of sexual diversity in human societies, fewer children in subsequent generations will be born in the wedlock of sexual-identity confusion. Even those who score more along the “bisexual” scale, but with a stronger arousal pattern for the same sex, will opt for their primary erotic target as a marriage partner rather than conform to cruelly imposed social scripts. And—if you’ll follow this through—over an exhaustive span of time, fewer heritable components associated with homosexuality will come to penetrate our species’ genome. Additionally, with this increasing societal acceptance of homosexuality, and as a way to circumvent the often insurmountable costs associated with alternative reproductive technologies (at least for gay men) I suspect that gay married couples will begin adopting children with increasing frequency through the support of state-sponsored equality initiatives , effectively putting a full stop to the transmission of their genes.  

In fact, these prosocial cultural developments may have consequences not only for the reproductive rates of homosexuals, but also for their heterosexual relatives who carry homosexual alleles. For example, findings from a 2008 study by Brendan Zietsch and his colleagues of the Queensland Institute of Medical Research revealed that the biological relatives of homosexuals (and therefore those that possess alleles linked to homosexuality, but who are themselves heterosexual) are at a reproductive advantage over those without homosexual relatives . According to the authors:  

    The genes influencing homosexuality have two effects. First, and most obviously, these genes increase the risk for homosexuality, which ostensibly has decreased Darwinian fitness. Countervailing this, however, these same genes appear to increase sex-atypical gender identity, which … increase(s) mating success in heterosexuals.  

Zietsch and his colleagues argue, essentially, that while too many or too potent homosexual alleles may result in full-blown homosexuality—which, all else being equal—is disadvantageous to reproductive success, these same alleles in a heterosexual relative tend to lead to that person having more lifetime sexual partners and thus greater reproductive success. The logic here is that sex-atypical traits (for example, men who score more like females in kindness, empathy, and sensitivity, or women who, like men, are more willing to engage in uncommitted sexual relations) are good but not perfect indices of homosexual orientation , and when they do occur in heterosexual individuals, they make these people more attractive and or interpersonally appealing to the opposite sex. What I’d wager is that even this effect—which the authors believe is evidence of antagonistic pleitropy, a sort of cost-benefit heuristic in which the maladaptiveness of certain genetic expressions in one phenotype is offset by these same genes’ adaptiveness in another—will be compromised by same-sex marriage trends. After all, if nothing else, alleles linked to sex-atypicality will decrease in frequency as fewer homosexuals reproduce.  

Again, these are just my, admittedly, entirely speculative predictions for the decline of homosexuality as a direct result of the increasing legalization of gay marriage and the domestication of exclusively same-sex relationships. If only religious fundamentalists were brighter—which, by contrast, I see absolutely no sign of change—they might begin to see gay marriage as an answer to their homophobic prayers after all.  

Biology is infinite irony.


About The Author: Want more Bering in Mind? Follow Jesse on Twitter @JesseBering, visit, or friend Jesse on Facebook. Jesse is the author of newly released book, The Belief Instinct: The Psychology of Souls, Destiny and the Meaning of Life (W. W. Norton).

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