A new study is reporting confirmation of previous findings that there is a correlation with regions on the X chromosome and sexual orientation for males.
Male sexual orientation influenced by genes, study shows Genes examined in study are not sufficient or necessary to make men gay but do play some role in sexuality, say US researchers
A study of gay men in the US has found fresh evidence that male sexual orientation is influenced by genes. 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.
This is yet another confirmation of the work of Dean Hammer in 1993 that caused such a stir. Like most scientific research, this study raises more questions than it provides proven answers. Any research on genetic effects on any human characteristics must be evaluated in the context of the rapidly changing field of molecular biology. When the human genome was first sequenced one of the surprising results was the very large amount of DNA that was something other than genes that code for specific proteins. At the time it was getting labeled as junk DNA. Shortly thereafter the new field of epigenetics began to discover control mechanisms that turn the expression of specific genes on and off. There are some indications that environmental variables play a role in determining these effects. It seems to be where nature and nurture overlap.
There is a growing body of work on the role of epigenetics in determining sexual orientation. One telling complication is that while in identical male twins there is an increased probability that both will have the same sexual orientation, it is not an absolute certainty. Since they have identical copies of DNA, if it were directly a cause and effect of genes, it should always be the same. It seems probable that multiple influences play a role in determining the eventual outcome.
Another interesting issue is raised by the difficulties that have been encountered in confirming the same pattern of chromosomal correlation for lesbians as has been done with gay men. Hammer originally did a separate study on lesbians that appeared to find the same pattern, but subsequent efforts have not replicated the findings. The research has been limited and on a small scale so it is by no means a conclusive finding. However, if "sexual orientation" should turn out to work differently in women than in men, it would suggest that it may that people don't necessarily have something that is a specific and clearly defined orientation.
The political debates about civil rights for lesbians and gays, like most political debates, don't leave much room for dealing with scientific complexities and uncertainties. Advocates are attempting to counter the medieval sophistry of the religious right who typically see scientific exploration as a threat to divinely ordained "truth". They stake their claims on the belief that anything other than traditional heterosexuality is a disordered choice. The counter argument tends to get framed in terms of claims that there is clear scientific proof that they are wrong. There is certainly a growing body of evidence to support the notion that homosexuality is a naturally occurring phenomenon and no scientific evidence to support the counter argument. However, the answers are not yet tied up in a tidy conclusive package and probably won't be for sometime to come. Exploring the complexities of human diversity is much more interesting than trying to shove it all into tight little boxes.