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Homosexuality: Is There a Gay Gene?

Dr. Thomas Swan studied cognition and culture at Queen's University Belfast. He's researched a range of psychological traits and disorders.

Could being gay be determined by our genetic makeup?

Could being gay be determined by our genetic makeup?

Genetic Explanations for Being Gay

Much recent attention has been focused upon the work of geneticists in search of a gene that might cause a gay orientation; 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 this sexual orientation 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 gay people 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. Gay people are less likely than straight people to pass on their genetic material through reproduction, meaning any predisposition for being gay 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 this orientation.

Twin studies show a partial genetic influence on the manifestation of a gay orientation.

Twin studies show a partial genetic influence on the manifestation of a gay orientation.

Is There a Gay Gene?

According to a study conducted by Bailey and Pillard, when one identical twin is gay, 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 gay. 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 being gay, 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 gay 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 a gay orientation in the maternally inherited X-chromosome (Xq28).

The "Sissy Boy Experiment" showed that boys displaying feminine characteristics often become gay.

The "Sissy Boy Experiment" showed that boys displaying feminine characteristics often become gay.

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Environmental Factors

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 gay 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 78 male children, 44 of whom were identified as exhibiting feminine behaviours. Two-thirds of these boys became gay, as opposed to only one of the non-feminine boys.

Can Being Gay 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?

Kin Selection

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 being gay 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 the gay orientation should be in decline, although this could be offset by increased rates of gay people becoming parents through sperm donors or surrogate mothers.

Polymorphism Theory

An alternative position, called the polymorphism theory, was proposed by E. J. Miller in 2000. He argued that a moderate amount of gay genetic 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 gay, then it is likely that their straight brothers will have a number of gay genetic traits that make them more attractive mates (allowing gay genes to be naturally selected). However, a 2009 study by Pekka Santtila found that straight men with gay brothers had no statistically significant reproductive advantage over straight men with straight brothers, suggesting Miller’s polymorphism theory is unlikely.

Sexually Antagonistic Selection

A third alternative, called sexually antagonistic selection, may be more agreeable. Rather than the brothers of gay 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 a gay orientation.


The sexually antagonistic selection theory for the gay orientation 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 being gay is genetic. While current scientific and psychological research indicates the existence of genetic causes for being gay, there is no basis for the belief in one controlling “gay gene”. Being gay 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 being gay is a lifestyle choice for the vast majority of gay individuals.

Further Reading

This content reflects the personal opinions of the author. It is accurate and true to the best of the author’s knowledge and should not be substituted for impartial fact or advice in legal, political, or personal matters.

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