Researchers that evaluated hundreds of sets of brothers, some of whom were non-identical twins, say they found evidence that supports a predisposition for homosexuality in a person's genes, but other scientists question the data.
The researchers conducted genomic analysis on 409 pairs of homosexual brothers in the largest study of its kind to date and identified two areas where they think they found a genetic link to homosexuality among the men. The genomic linkages were found on chromosome 8 and chromosome Xq28, according to the study published in the journal Psychological Medicine. Other studies previously evaluating these regions as being associated sexual orientation in men have seen mixed results.
"It erodes the notion that sexual orientation is a choice," Alan Sanders, lead author of the study and behavioral genetics researcher at NorthShore University HealthSystem Research Institute, told New Scientist of his findings.
According to the science news site, the only thing all 818 men involved in the study had completely in common was that they were gay. With other traits being variable among the study subjects, any shared differences of one nucleotide — single nucleotide polymorphisms — in their genetic code were associated with sexual orientation by the researchers, New Scientist reported.
The most common SNPs among these men were found in a region of the X chromosome and on chromosome 8. Going forward, researchers compared the differences spotted in these locations between gay and straight men in order to "narrow down to fewer genes" that could be related to sexual orientation, Saunders told New Scientist.
"This study knocks another nail into the coffin of the 'chosen lifestyle' theory of homosexuality," Simon LeVay, who has researched other factors that seem to be shared in homosexual individuals, said, according to New Scientist. "Yes, we have a choice in life, to be ourselves or to conform to someone else's idea of normality, but being straight, bisexual or gay, or none of these, is a central part of who we are, thanks in part to the DNA we were born with."
Experts not involved in the study were more skeptical.
Neil Risch, a genetics expert at the University of California, San Francisco, said the data are statistically too weak to demonstrate any genetic link. Risch was involved in a smaller study that found no link between male homosexuality and the X chromosome .
Dr. Robert Green, a medical geneticist at Harvard Medical School, called the new study "intriguing but not in any way conclusive."
Kelly Servick for Science magazine wrote that the type of DNA analysis used in the study might serve to call some of the findings into question because it has "largely been superseded by other techniques."
Sanders agreed that finding a specific gene, rather than a region that holds many genes, would have been better, but using this technique he was able to replicate and support earlier research that associated these regions with sexual orientation in men, Servick reported.
The Associated Press contributed to this report.
Front page image via Shutterstock.