Single ‘gay gene’ remains elusive
A STUDY of almost 500,000 people, involving a Queensland researcher, has failed to find evidence of a single "gay gene".
Although twin research has shown that sexual preference is influenced by DNA, previous studies have been too small to confidently identify specific genes involved.
The latest international study, which analysed DNA from individuals living in the UK, US and Sweden, found five genetic markers significantly associated with homosexual behaviour, including one involving sex hormone regulation.
However, study author Brendan Zietsch, of the University of Queensland, said that their collective influence on sexual preference was so small, they could not be used to predict whether a person was gay or straight.
"What we found was that there is no one 'gay gene'," Dr Zietsch said. "Instead, there are many, many genes that influence a person's likelihood of having had same-sex partners."
Dr Zietsch said that along with the five DNA markers identified in this study, the researchers were highly confident of there being hundreds, or even thousands, of other locations in the human genome that were also involved in sexual preference.
"Overall, our results reveal a highly complex genetic influence on same-sex sexual behaviour," he said. "Because of this complexity, we cannot meaningfully predict a given person's sexual preference from their DNA - nor was this our aim.
"It is important to note that sexual preference is influenced by genes but not determined by genes. Non-genetic influences are also important, but we know little about these and our study does not shed light on them."
Research biologist Craig Smith, who researches sexual development at Monash University, but was not involved in the genetic analysis, described it as "one of the largest and most statistically rigorous studies of its kind".
"While the findings are important for our understanding of human sexuality, we shouldn't be terribly surprised by them," Associate Professor Smith said.
"Complex human traits such as sex, sexuality and gender identity will involve many genes. There is very unlikely to be one gene governing any of these traits.
"What about nurture? The current study was focused on the genetics side and makes no conclusions about the potential role of environment. The authors state that their results overwhelmingly point towards the richness and diversity of human sexuality."
Retired medical geneticist Bob Williamson, an honorary fellow at Melbourne's Murdoch Children's Research Institute, said no-one would be surprised that sexual attraction was "in part determined by genes and in part by environment".
"This is true for every form of human behaviour," Professor Williamson said.
"Some individuals who are gay or lesbian will be more influenced by the genetics side, some will be more influenced by environmental factors. We know that the proportion of people who are same-sex attracted varies from time to time, and from country to country, much too quickly to be only genetic.
"These genome-wide studies are great for giving leads for future research, but cannot be used to tell us about individuals. Scientists who work in controversial fields such as this must speak up, advocate, and ensure their findings are not used, falsely, to discriminate against anyone who is gay or lesbian."
The study, which also involved American and European researchers, is published today in the international journal, Science.