Homosexuality: Is There a Gay Gene?
Genetic Explanations For Homosexuality
Much recent attention has been focused upon the work of geneticists in search of a gene causing homosexuality; an endeavor littered with papers illustrating little beyond authorial bias. While proving or disproving the existence of a gay gene would constitute a grail-like quest for such writers, the roots of homosexuality are, in all probability, far too complex to be explained by a single gene.
Psychological research and collective experience indicate that the terms “gay” and “straight” by no means represent the continuum of sexuality. Thus, the question becomes whether one or several genes can account for such a diverse spectrum of gender preference. If so, are these genes more active in some than in others? As always, this type of discussion spawns the nature Vs nurture debate: the extent of interaction between heredity and environment, and to what degree homosexuals have a choice as to their orientation.
Beyond the search for a gay gene, biologists are presented with the dilemma of whether one should exist in the first place. Homosexuals are less likely than heterosexuals to pass on their genetic material through reproduction, meaning any predisposition for homosexuality should have long since disappeared from the human genome through natural selection. Indeed, this article will have a twofold function of summarizing the evidence for and against gay genes, and showing why this evidence is relevant to an evolutionary explanation for homosexuality.
Is There A Gay Gene?
According to a study conducted by Bailey and Pillard, when one identical twin is homosexual, there is a 52% chance that the other twin will be as well. The figures drop for reduced genetic linkages, with 22% of fraternal twins and 9.2% of non-twin brothers both being homosexual. Some theorists have suggested this study is proof for a gay gene, whereas others have pointed out that identical twins should have shown 100% agreement.
Bailey and Pillard’s work discounts the concept of a genetic "on/off switch” for homosexuality, while suggesting some level of genetic involvement. However, as the siblings were not separated at birth, the results could be explained in terms of environmental factors. The tendency of twins to mimic the behavior of each other leads to the expectation that this type of mirroring is more prevalent in siblings who share greater similarity. Indeed, Bailey and Pillard’s study fails to explain why fraternal twins and non-twin brothers, who have the same level of genetic similarity, produced such different results. Furthermore, twins may experience similar family environments to a greater degree than that of non-twin brothers, allowing a greater possibility for sexual correlation due to environmental factors.
Nevertheless, Dean Hamer has since offered evidence of genetic consistencies in gay men by demonstrating that they have more homosexual male relatives through maternal than paternal lineage. Notably, his genetic analysis of gay male siblings found increased sharing of Xq28 genetic markers. These findings were disputed by George Rice who found no such sharing. It is noteworthy that Hamer utilized no control group, and did not test his subjects’ heterosexual brothers for the same linkage. While Hamer’s study was criticised for this oversight, Rice’s study was branded biased because he had previously professed the belief that a gay gene could not exist. Indeed, further evidence has arisen (discussed below) that helps to confirm a genetic basis for homosexuality in the maternally inherited X-chromosome (Xq28).
Most biologists concede that genetic factors only contribute about 30-45% of the variation in male sexuality. The remainder likely stems from their interaction with environmental factors. Indeed, genetic differences between men and women are reflected in our psychology. For example, women’s emotional responses to stimuli are more immediate and heightened than those of men.
An over-abundance of non-physical female attributes in men, and male attributes in women, at the genetic level, may increase one’s susceptibility to becoming gay as a result of internal and external pressures to establish a personal identity. Genetic factors may dispose a male child to be more compassionate, gentler, less competitive, compliant towards bullies, or sociable with members of the opposite sex. One thirtyish gay male professional, interviewed for this article by Colleen Swan, said his happiest childhood memories were of making tinfoil figures and stringing beads with a female cousin. Consequently, he experienced ridicule and rejection from peers, and was labelled as homosexual with demeaning epithets. These social pressures could conceivably lead an individual to resolve a genetically primed identity crisis by accepting the conclusion of peers.
During the mid to late teenage years, nearly everyone experiences an identity crisis. According to Erik Erikson, during this crisis we strive to understand ourselves by searching for, and strengthening our attributes to create the basis for our adult selves. Grey-areas in our thoughts become black and white: discontent with a deity might expand into full blown atheism, or a mild political view may evolve into a radical mindset. Arguably, grey-areas in sexuality similarly crystallize into black and white, and this reinforcement of identity is often a time during which gay individuals “out” themselves. This position is bolstered by the work of Richard Green in his discussion of the “Sissy-Boy Syndrome”. Green followed the development of seventy-eight male children, forty-four of whom were identified as exhibiting feminine behaviours. Two-thirds of these boys became homosexual, as opposed to only one of the non-feminine boys.
Can Homosexuality Be Naturally Selected?
The existence of a gay gene would present a dilemma for evolutionary biologists: if gay sex doesn't produce children, why haven't gay genes died out? One potential solution is kin selection. Without children of their own, gay individuals will be able to provide assistance and protection to the offspring of their brothers and sisters, ensuring those offspring stand a greater chance of survival. By sharing some of the same genetic material, gay genes will survive in these offspring. For example, feminine male Samoans, or fa'afafine, are known for their laborious dedication to family.
However, most Westerners do not live in familial units, and this has led to an absence of evidence for kin selection (see Jim McKnight's book). It may be that homosexuality was naturally selected in the West due to kin selection, but it is no longer relevant to the way Westerners live their lives. If this is true, then homosexuality should be in decline, although this could be offset by increased rates of homosexuals becoming parents through sperm donors or surrogate mothers.
An alternative position was proposed by E. J. Miller in 2000. He argued that a moderate amount of genetic homosexual traits can make males more attractive to the opposite sex (less aggressive, empathic, committed, etc). Conversely, highly heterosexual males are more aggressive and less committal, making them unattractive mates. If some male offspring are homosexual, then it is likely that their straight brothers will have a number of genetic homosexual traits that make them more attractive mates (allowing gay genes to be naturally selected). However, a 2009 study by Pekka Santtila found that heterosexual men with homosexual brothers had no statistically significant reproductive advantage over heterosexual men with heterosexual brothers, suggesting Miller’s polymorphism theory is unlikely.
A third alternative, called sexually antagonistic selection, may be more agreeable. Rather than the brothers of homosexual males enjoying a reproductive advantage, it is possible that sisters do instead. If gay genes increase one's attraction for the same sex, then siblings of the opposite sex who share this genetic material will enjoy greater heterosexual attraction. This would mean that sisters of gay men (or brothers of gay women) will have more children, leading to the propagation of gay genes. Studies conducted in Britain and Italy have confirmed that women with gay male relatives have significantly more children, and this occurs even if the relative was from a different generation (discounting kin selection as an explanation). This effect is seen in the maternal pedigree line, implying that gay genes exist in the X-chromosome. This supports the earlier research that found the Xq28 genetic marker to be important for causing homosexuality.
The sexually antagonistic selection theory for homosexuality allows gay genes to propagate through natural selection because of the benefits they bestow on siblings of the opposite sex. This opens the door for researchers to ask if homosexuality is genetic. While current scientific and psychological research indicates the existence of genetic causes for homosexuality, there is no basis for the belief in one controlling “gay gene”. Homosexuality appears to be the result of a cluster of genetic factors that are influential only when particular psychological and social factors are present. As we cannot control the genetics we are dealt, or the environment we grow up in, it is highly unlikely that homosexuality is a life-style choice for the vast majority of gay individuals.