Dr. Thomas Swan studied cognition and culture at Queen's University Belfast. He's researched a range of psychological traits and disorders.
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.
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.
Thomas Swan (author) from New Zealand on October 03, 2017:
Thank you for the comment Paul. I believe this article was written before the newer studies. The conclusions have remained fairly consistent.
Paul Dirks on October 02, 2017:
Thomas, why are you using the oldest studies by Bailey on twin concordance, rather than newer and better ones, which find much lower concordance rates? A good overview is found in DOI: 10.1177/1529100616637616 (Bailey et al, 2016)
Cory on October 11, 2015:
I'm a ftm transgender and, according to my parents, I had a vanishing twin in the first trimester of my Mom's pregnancy. My Mom has an Rh positive blood type and so do I. I'm trying to get my Dad to find out his bloodtype. I'm a natural redhead and so is my Grandma on my Dad's side. I've heard that being ginger is a natural Rh negative trait. Also, it's possible for both parents to be Rh positive and each carry the Rh negative gene recessively. In the case of twins of such parents, what happens when the unborn twins have opposite Rh factors, one twin being Rh postive and the other being Rh negative? I'm disappointed to see no studies on parental blood type and Rh factors of gay, lesbian and transgender people. The question also needs to be asked if the parents if they had twins, do the twins have opposite Rh factors? Another good question.. was their child conceived shortly after the birth of an opposite sex sibling while the fetal DNA from the previous pregnancy was still fresh in the mother's womb and bloodstream? I think the focus needs to be on the parents of gay, lesbian, and transgender people, on their blood type/Rh factors as well as their child's blood type/Rh factor. See if a pattern can be found. If their child is not a twin, then the question needs to be asked if they thought they were having twins early on in the pregnancy (vanishing twin syndrome). I'd like to see more studies like this.
Cory on October 11, 2015:
Has anyone thought to check the Rh factor compatibility of the PARENTS of gay and lesbians? Maybe the answer is the parents having mixed Rh factors, an Rh positive mother and Rh negative father, and unborn twins with opposite Rh factors. The twins merge when one vanishes. Both twins cell lines/organs share the same body but not in harmony. One twin gets the brain, kidneys, liver, the other twin gets the reproductive organs, blood, and skin. Check that.
jon on August 28, 2015:
You need to seperate being homosexual and living a homosexual life style. As u mentioned, being homosexual is normal. This is the way he is been created. However, should he follow a homosexual life style? I am not yet convinced about it. The media nor the politicians nor the research has investigated the consequences. Think about someone who is klypomaniac? Is it his fault that he is klyptomaniac? no.. the research says it is genetic. should he live a klyptomanic life style? absolutely not. UK research shows increasing AIDS cases in homosexual men. Why it was it not a news in the main stream media? They don't really care the health and well being of homosexuals. What ever supreme court rules, they cannot change the natural fact that only a man and a woman can give birth to a child. Just few thoughts for brain :-)
Tuesday75 from Omaha, NE on June 01, 2015:
Very interesting article.
Sanxuary on January 16, 2013:
A true person knows how to negotiate a problem and uses facts and researches questions and answers. Instead of being ruled by emotions. You our one of the few real people who can write on this site that I have met so far. Thanks I was beginning to think people are marshmallows.
Thomas Swan (author) from New Zealand on January 15, 2013:
Thanks for the comment. The consensus lately is that it's never completely nature or nurture, it's both in varying proportions. Genes give us a greater susceptibility for developing particular traits. This, I hope, is reflected in my article. There will be genes that make someone more likely to become a paedophile at some point, though I expect they have very little direct influence, and will have many positive effects as well.
The problem is not science, it's the way the media reports science. To get a story, newspapers have to say "this gene causes homosexuality" because otherwise people wouldn't read it. Having said that, people usually don't read beyond the first paragraph anyway, and end up missing the important details about what the discovery means, thereby populazing the false idea that genes control everything. Scientists shouldn't agree to their results being published in that way, newspapers should be more responsible, and the public should be more interested in the actual science, but it will never happen, so this is what we have...
Sanxuary on January 15, 2013:
First of all I do not even think we are close to understanding DNA. We could all be carrying genes for a million things and never activate them. The gene debate is a really bad idea. Since there would have to be an opposite and that one could never be convinced to understand the idea of being whatever. Soon everything will be blamed on genes and not choices. Is there one for paedophiles and necrophiliacs. What I believe in is choice and everyone’s right to sanctuary. So stop trying to change everyone and allow everyone choices. There is no need for names and rocks people are what they are and it makes life interesting. In my Sanctuary you get my beliefs and in yours, It is your beliefs. That is what free will is all about, God did not want robots, but what is written is written but its up to you to wonder why. Changing it will not change a thing.
Thomas Swan (author) from New Zealand on October 23, 2012:
Thanks for the link KrisL, that was a good read. In particular, the fact about second-borns being more likely to be gay than first-borns. It would make sense for the first-born to have a higher chance of reproducing successfully because all parents have at least one child.
Thanks for the comment kathleenkat, I agree with jlpark's response.
Jacqui from New Zealand on October 23, 2012:
KathleenKat - perhaps that will be the case for her children. However, just having a gene doesn't necessarily make anyone anything. It may be a recessive gene, much like that for blue eyes, where if two people with a recessive 'gay gene' come together, they have a 25% chance of a gay child.
I personally think homosexuality is just another variant of human sexuality - much like asexuality, heterosexuality, pansexuality, and bisexuality are. None of these harm anyone else. It is part of what makes us human - difference.
kathleenkat from Bellingham, WA on October 22, 2012:
Curious...perhaps it was passed on, genetically, because homosexuality was a "no-no" for so long in our world's history. I knew a woman whose husband turned out to be gay. She had his children before he came out. If there is a gene, the children now have it.
KrisL from S. Florida on October 22, 2012:
I just found this interesting article relevant to your hub
Thomas Swan (author) from New Zealand on October 22, 2012:
Thanks for the comment jlpark. I agree that people fear what they don't understand. Religion takes this fear and amplifies it by adding caveats about divine implications. Science helps us understand if there is anything to be scared about. I agree it's important not to let emotions rule the way we see science. Scientists are curious and there is usually no intent to cause harm or offense.
Thomas Swan (author) from New Zealand on October 22, 2012:
Thanks for the comment KrisL! I should add that there are some studies that don't show sisters of gay men to have more children, so sexually antagonistic selection is still just a theory at this stage. It is however the most promising theory out there because of the supporting evidence for it so far. Clearly though there has to be more research to extract the reasons for some conflicting results. Ultimately, there is a lot of bias in research of this kind. Religious people and homosexuals take opposite standpoints before the results are known, and this often leads to bias. I agree that our culture is probably in the minority when it comes to forcing a sexual identity, and I think this is facilitated by religion. Pacific islanders and oriental cultures are two examples I can think of that differ from Westerners.
You make a very good point about animals. This is good evidence for an evolutionary explanation for homosexuality. I could guess and say that the same advantages proposed for homosexuality in humans (e.g. sexually antagonistic selection) are relevant for animals.
Thomas Swan (author) from New Zealand on October 22, 2012:
Thanks for the comments JKenny and Larry! You raise interesting points. I agree with Larry's point about there being a cocktail of different genes that influence where people reside on the continuum of sexuality. I would say everyone is bisexual to some degree, whether they are 99% heterosexual and 1% homosexual, or vice versa. I would add that environmental factors will play a role in whether those genes are "activated" or allowed to influence our lives. Some people may live their lives as heterosexuals without having the environment for their homosexuality to flourish. The first thing I learned as an evolutionary psychologist was it's never nature or nurture, it's always both, and how they interact.
Jacqui from New Zealand on October 21, 2012:
Thank you Thomas! Voted Up, and "Awesome".
It is interesting to read the studies which people have done. It is also interesting that it was thought to study people such as myself.
The old adage - "People fear what they do not understand" - I think that research into a subject - may it be for proving the existence of a gene, or that this is incorrect as there are both sides to every argument - is useful to help us understand the world around us, thus decreasing the fear of that which we suddenly now understand.
Whilst it could be seen as insulting that we as homosexuals need to be 'researched' to prove that we aren't evil, or mad, bad or scary...at the same time, at least someone is trying to help society understand something about it.
There is a large tome of a book, KrisL, about homosexuality in animals - I can't remember who it's by, but just that is HUGE. That may answer some of your questions.
Thank you Thomas again.
KrisL from S. Florida on October 21, 2012:
An excellent summary of the recent research. I hadn't heard about the fact that _sisters_ of gay men had more kids - fascinating!
Another social/evolutionary fact: only the minority of cultures over time have expected people to make an on/off choice of sexual identity. Except for a tiny minority of men who were impotent with women, most men who prefered intimacy with other men would have married and had children anyhow, and the same goes for women.
Another unanswered question is why homosexual behavior exists in non-human primates and also birds (who may form stable homosexual pairs). I have not read about that other mammals.
James Kenny from Birmingham, England on October 21, 2012:
Good point Larry, just goes to show how complex and complicated the whole issue of sexual orientation really is. The world is never just black and white.
Larry Fields from Northern California on October 21, 2012:
Outstanding hub, Thomas! Voted up and more.
Hi JKenny. You wrote:
"The problem with trying to establish whether homosexuality is genetic, is the fact that these scientists have missed the fact that there are people who develop a sexual attraction for both men and women."
Suppose that there are polymorphisms in a set of genes that predispose one to some particular sexual orientation over another sexual orientation. Suppose further that by the luck of the draw, an individual inherits a mixed hand in the set of Sexual Orientation Genes (SOGs). Depending on environmental factors in utero and in childhood, that person will probably have a mixed sexual orientation.
I'm not saying that they will necessarily have a 50-50 bisexual orientation. Suppose that a man is dealt a 70-30 hand of SOGs. He will probably be a heterosexual. But he may be attracted to women who have below-average female attributes, and greater-than-average male attributes, in terms of psychological outlook, musculature, facial structure, etc.
The genetics of sexual orientation are not necessarily either/or.
James Kenny from Birmingham, England on October 21, 2012:
A very interesting analysis Thomas. The problem with trying to establish whether homosexuality is genetic, is the fact that these scientists have missed the fact that there are people who develop a sexual attraction for both men and women. Does that mean that there is a bisexual gene as well? Like you say, homosexuality is the result of a complex range of factors that cannot be explained by genetics alone. Thanks for sharing.