Why are we gay? Is it by nature or nurture? Lahn Straney examines the evidence and asks: ‘does it matter?’
Is homosexuality the result of nature or nurture? While the former suggests some underlying biological cause, the latter suggests sexuality to be a consequence of some combination of environment, upbringing and choice.
While the question generally polarises people, the science of sexuality is a complex and interesting area of biological and ethical research.
Studies of twins are a useful starting point for understanding the human condition and the role that genetics and the environment plays. Studies from the early 90s revealed that 52% of the identical twins of homosexual men were also homosexual – much higher than the 10% expected in the general population.
Detractors of genetic mechanisms contend that this could be due to twins sharing the same environmental upbringing. However in the same study it was also found that, despite sharing the same upbringing, only 11% of adopted boys raised with a homosexual brother identified as homosexual, consistent with figures in the general population.
Genetic research into homosexuality almost certainly won’t reveal a ‘gay gene’. Current evidence indicates that homosexuality is multi-factorial and genetically influenced but not determined.
This may give the false impression that people, at least in part, choose to be gay. The fallacy in this assertion lies in a false impression that genetics have a monopoly on biological conditioning.
One biological but non-genetic piece of the puzzle is related to fraternal birth order, said to explain about one seventh of the prevalence of homosexuality in men.
Research has repeatedly shown that older brothers increase the odds of homosexuality in later-born males. The favoured mechanism is an immune-response from the mother. When a mother is carrying her first son, the placental barrier prevents exposure to the son’s proteins. Upon delivery, inevitable mixing of blood will expose the mother to the male-specific proteins.
Recognising these proteins as ‘foreign’, the immune system produces antibodies which the placenta may transport to subsequent offspring in the uterus. This purportedly results in an increasing effect of ‘anti-male’ antibodies on the sexual differentiation of the brain in each succeeding male foetus. Interestingly however, this mechanism appears to only occur in right-handed men, which is particularly curious given left-handedness is associated with an elevated likelihood of homosexuality in men and women.
Taken together, the body of scientific literature strongly supports a biological basis for homosexuality. However, in an evolutionary sense, the persistence of homosexuality in the population still seems somewhat of a paradox.
If indeed homosexuality has some genetic basis, and homosexual people are less likely to produce offspring, then eventually the gene(s) should become less common and eventually be lost.
As an attempt to explain this inconsistency, some contend that there is less difference in child rearing numbers than assumed, while others argue there has been simply not enough time, in an evolutionary sense, to see any marked reduction in homosexuality.
More complex conjectures contend that homosexuals play a role in supporting the family unit in rearing children and thus family genes are preserved. Still other theories suggest some association between male homosexuals and increased fertility of female relatives.
While there is no shortage of theories, there is currently insufficient evidence to support one over any other.
At this point it seems prudent to take a step back. In attempting to answer the question of nature versus nurture we have sidestepped a more important question; namely, what does it matter?
Many will argue that determining the biological basis will prove that we do not choose our sexuality. At the heart of this argument is the contention that, given gay people do not choose their sexuality, they deserve to be accepted for who they are.
This begs the question; if someone chooses to be gay do they have any less entitlement to the rights of every other citizen? The answer is of course no.
Modern ethics dictates that an inalienable right of all human beings is the right to pursue personal happiness so long as they bring no harm to others. Given this, is there any real imperative in uncovering the biological mechanisms for homosexuality?
Advocates will further argue that a biological mechanism will result in wider social acceptance and better protection against discrimination. However the notion that identifying a biological cause for homosexuality would reduce homophobia is unrealistic. We have long known that race is genetic and yet racism persists.
Furthermore, by identifying causes we risk pathologising homosexuality, and may also inadvertently provide the basis for treating it as a condition. Worse still, genetic markers of homosexuality could increase the capacity for discrimination through genetic testing.
Nevertheless, curiosity is an embedded and necessary part of human nature and we have a right and interest to know the reasons that we are the way we are. So while biological research should continue, we must begin to consider the ethics and utility of such knowledge.
The battle for gay rights is not in the laboratory but in increasing understanding and acceptance among the people around us.
An evidence-based biological explanation of sexuality may help progress understanding but society must remember that the acceptance of a person’s sexuality is not dictated by a biological explanation but by the fact that all human beings are entitled to the same rights and respect.
Why are we gay? Is it by nature or nurture? Lahn Straney examines the evidence and asks: ‘does it matter?’ 
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