Australasian Science: Australia's authority on science since 1938

Born This Way

By Guy Nolch

A study reporting a weak association between two genes and homosexuality could have powerful consequences.

On 7 December 2017 the Australian Parliament passed a historic bill legalising gay marriage. The process followed a nationwide postal vote in which 61.6% of the 12.7 million Australians who voted were in favour of same-sex marriage.

The Yes campaign had argued that marriage was a basic civil right that should be open to all regardless of their sexuality. The No campaign had appealed to those who believed that homosexuality was “unnatural” and should not be sanctioned in legislation.

Humans are complicated creatures, with every distinguishing characteristic existing along a continuum that makes each of us unique. None of us are “normal”, and this is entirely “natural” – including the many nuances of our sexuality.

Scientists have long sought an explanation for homosexuality, and now a genome-wide association study published in Scientific Reports (https://tinyurl.com/y8c2jtt4) has found a weak association with two genes. The first, SLITRK6, is a neurodevelopmental gene on chromosome 13 that is expressed in the diencephalon, a region of the brain that differs in size in men depending on their sexual orientation. The second gene, TSHR on chromosome 14, encodes the receptor for thyroid-stimulating hormone. The authors say this “could conceivably help explain past findings relating familial atypical thyroid function and male homosexuality”.

However, the study only involved 2300 men, which is small for a genome-wide association study. GWAS typically require more than 100,000 participants in order to find an association between the many genes that can contribute to a characteristic. “All that is required to see a genetic association in this study is for slightly more homosexual men to carry the genetic variant than heterosexual men, and many times this will simply be due to chance,” explained Dr Nina McCarthy of The University of Western Australia. “In addition, the reported associations between variants in genes and homosexuality are not statistically significant, and the authors themselves say that they are ‘best characterized as speculative’.”

It shouldn't be surprising that two genes would have a weak association with a characteristic as complex as sexuality, which is likely to be influenced by an array of biological and environmental factors. But those weak associations could have powerful consequences.

Already genetic test kits are available to the public, enabling people to determine their susceptibility to a variety of diseases. Not only is the predictive value of these tests highly questionable, but the potential for a genetic test leads us to the concept of homosexuality as a disease that could be treated.

While the notion of “gay genes” could equally lead to greater public acceptance that some people are simply “born this way”, that's not always the case. Dr Ilan Dar-Nimrod of The University of Sydney has found that “it can also lead people with anti-gay attitudes to polarise their views rather than mitigate them”. He says this “results in a heterosexual person feeling a clear ‘us’ and ‘them’ that... may fuel prejudice”.


Guy Nolch is the Editor and Publisher of Australasian Science.