Region identified as homosexuality-influenced genes.
“Born This Way” is now backed by new research on the genetics of homosexuality. A study published on Nov. 17 in the Journal of Psychological Medicine is the strongest yet to find that homosexuality in men is significantly influenced by genetics. Its authors said that their findings are a stepping-stone for further research on the genetics of homosexuality, and that they may help fight homophobia through empirical understanding.
The study examined the genetic composition of 409 pairs of homosexual brothers, many of them twins, from the United States, Canada, and Great Britain. Comparing genetic differences between and within family members, in this case groups of brothers, can reveal which genes are involved with a given trait and which are not. Early genetic research on homosexuality found that it occurred more frequently in men with more homosexual relatives, and that identical twins are both homosexual more often than fraternal twins, suggesting a genetic background to sexual orientation.
The sample size of this study is three times greater than any previous research, which leads to more conclusive findings.
The study used Genome-Wide Linking Scans, a method that tests for genetic differences and commonalities between and within sample groups. It found five regions on the genome that corresponded with male homosexuality. Foremost among these was the Xq28 region of the X-chromosome, a group of 105 genes that had been implicated in past research on the genetics of homosexuality. This region was first implicated in male homosexuality in 1993, but it has seen conflicting evidence in research since that time.
How the Xq28 region links to homosexuality is still uncertain. The study’s authors suggest that it may be influenced by the gene region’s production of the vasopressin hormone and several types of neuropeptide, organic substances which are implicated in social and associative behaviours. How these compounds relate to homosexuality is also unknown, but they may be potential causative agents.
The Xq28 region may be an X-linked gene group, meaning that men inherit its characteristics from their mothers. Men have only one X-chromosome, which is always inherited from their mother, as opposed to women, who inherit one X-chromosome from each parent. Homosexuality is considered an evolutionary mystery: it doesn’t have an obvious evolutionary advantage because it doesn’t aid in reproduction. Homosexuality’s concordance with the X-chromosome in men may support the Sexually Antagonistic Hypothesis: that the same genes on the X-chromosome influence greater reproductive capacity in women and homosexuality in men, mitigating the evolutionary cost to having homosexual offspring.
The study’s findings focused on male homosexuality, so how the Xq28 gene region and its potential effects relate to female homosexuality was not analyzed. Sexuality exists on a continuum, commonly measured on the Kinsey Scale in psychological studies. Homosexuality in women tends to span this spectrum more than male homosexuality, which the authors suggest may be influenced by different genetic mechanisms from those which influence homosexuality in women.
A controversial element to research on homosexuality genetics is its implications into embryonic screening, or the testing of a human embryo for genetic predispositions to certain diseases or conditions that its parents can then choose to abort. The study’s authors assert that their findings cannot predict homosexuality, as they still don’t know which genes in the Xq28 genes affect sexuality, and because homosexuality is strongly multifactorial, being a combined product of genetic and environmental effects.
The concluding section of the study referenced past psychological research, showing that factual understanding of sexual orientation can prevent homophobia. Its lead author said that he hopes the study’s findings will increase societal understanding and acceptance of homosexuality.
The study was written by researchers from institutions around the United States and was led by Alan Sanders of the NorthShore Research Institute in Evanston, Illinois.