A new study of gay men in the United States has found new evidence that sexual orientation is influenced by genes, researchers in Chicago said yesterday. The study, which is so new it hasn't even been published yet, was carried out by Dr. Michael Bailey of Northwestern University. Bailey outlined the findings Thursday in a meeting of the American Association for the Advancement of Science.
The Guardian reports:
Scientists tested the DNA of 400 gay men and found that genes on at least two chromosomes affected whether a man was gay or straight.
A region of the X chromosome called Xq28 had some impact on men's sexual behaviour - though scientists have no idea which of the many genes in the region are involved, nor how many lie elsewhere in the genome. Another stretch of DNA on chromosome 8 also played a role in male sexual orientation - though again the precise mechanism is unclear.
Researchers have speculated in the past that genes linked to homosexuality in men may have survived evolution because they happened to make women who carried them more fertile. This may be the case for genes in the Xq28 region, as the X chromosome is passed down to men exclusively from their mothers.
The Telegraph adds:
Dr Bailey said: "Sexual orientation has nothing to do with choice. Our findings suggest there may be genes at play - we found evidence for two sets that affect whether a man is gay or straight. "But it is not completely determinative; there are certainly other environmental factors involved. "The study shows that there are genes involved in male sexual orientation.
"Although this could one day lead to a pre-natal test for male sexual orientation, it would not be very accurate, as there are other factors that can influence the outcome."
Dr Alan Sanders, associate Professor of Psychiatry at Northwestern University, who led the study said that it was it was an 'oversimplification' to suggest there was a 'gay gene.'
"We don't think genetics is the whole story. It's not. We have a gene that contributes to homosexuality but you could say it is linked to heterosexuality. It is the variation."
As Zack Ford notes at ThinkProgress, these results confirm earlier studies and show an emerging scientific consensus that biological, pre-natal factors play a significant determinative role in the development of a person's sexual orientation:
This jibes with other research that found environmental factors in the womb likely also have an effect on sexual orientation. For example, a Canadian study found that men with older brothers are more likely to be gay, which suggests maternal biological changes that happen with each additional son. Another study identified sex-specific genetic markers called "epi-marks" that can be triggered during fetal development, causing fluctuations in the DNA expression that impacts sexual development.
h/t: Joe. My. God.