Brendan Zietsch receives funding from the Australian Research Council. He is senior author on the paper discussed. What has been elusive is knowledge of what specific gene, or genes, are involved. But a later study did not replicate this finding, and subsequent follow-ups yielded mixed results.
Twins Separated at Birth Reveal Staggering Influence of Genetics
Scientists quash idea of single 'gay gene' | Genetics | The Guardian
A new study of twins provides the strongest evidence yet that homosexuality has a genetic basis, researchers say, though they say other factors like social conditioning may be important. The study, published in the December issue of The Archives of General Psychiatry, adds to evidence that sexual orientation does not result from a maladjustment or moral defect, one author said. Michael Bailey, an assistant professor of psychology at Northwestern University in Evanston, "which is exactly the kind of pattern you would want to see if something genetic were going on. Bailey was referring to brothers by adoption.
No individual gene alone makes a person gay, lesbian or bisexual ; instead, thousands of genes likely influence sexual orientation, a massive new study of the genomes of nearly half a million people suggests. The biological factors that contribute to sexual orientation are largely unknown, but many scientists suspect that genetics plays a role, given that same-sex sexual behavior appears to run in families and is seen more often in identical twins than in fraternal twins. Same-sex orientation remains criminalized in more than 70 countries, some with the death penalty, often stifling those willing to disclose such personal information.
The relationship between biology and sexual orientation is a subject of research. While scientists do not know the exact cause of sexual orientation , they theorize that it is caused by a complex interplay of genetic , hormonal , and environmental influences. Biological theories for explaining the causes of sexual orientation are favored by scientists. The influence of hormones on the developing foetus has been the most influential causal hypothesis of the development of sexual orientation. The presence of the Y-chromosome in males prompts the development of testes, which release testosterone, the primary androgen receptor-activating hormone, to masculinize the fetus and fetal brain.