A study of men in Ontario, Canada provides a new twist on the connection between sexual/relational orientation and right or left-handedness.
Whereas earlier studies showed that gay men (and lesbians) were 39 percent more likely than heterosexuals to be left-handed, the new data “provides evidence that gay or bisexual men also have an elevated incidence of extreme right-handedness.”
To complicate matters, another factor is involved – the often-reported finding that having older brothers may be a predictor for men being gay. In the new study, results indicate that the number of “older brothers moderates the relationship between handedness and sexual orientation.” That is, the extreme right-handedness finding is only seen in men with no or few older brothers.
“These new research findings add further weight to the idea that biological factors play a significant role in the development of sexual orientation,” said Robert-Jay Green, Executive Director of the Rockway Institute, a national center for lesbian, gay, bisexual, and transgender research and public policy at Alliant International University.
The study was conducted by Anthony F. Bogaert of Brock University in St. Catharines Ontario and published in the journal Neuropsychology (2007, Vol. 21, No. 1, 141-148). Bogaert asked about the sexual attractions and behavior of 538 gay or bisexual men and 373 heterosexual men. The men were questioned about their right or left hand usage for 10 physical activities. They also were asked if they had biological brothers.
Most of the men were right-handed. However, the gay and bisexual men had a higher likelihood of both left-handedness and extreme right-handedness when compared to the heterosexual men. “The number of older brothers increased the likelihood of being gay or bisexual in moderate right-handers only,” Bogaert wrote. “In both non-right-handers and in extreme right-handers, older brothers either did not increase or lowered the likelihood of being gay or bisexual.”
Bogaert went on to conclude: “If elevated extreme right-handedness is an indication of early neurodevelopmental anomalies, then an elevation of this handedness pattern in gay or bisexual men gives additional evidence that one route to same-sex attraction is through early developmental stressors” (during pregnancy) “or through a factor correlated with such stressors.”
However, Bogaert wrote, “a genetic explanation can also be forwarded.” He noted that genes have been linked to both handedness and sexual orientation. Specific genes have been linked to handedness and immune system functioning, but this relationship has not been sufficiently researched. Immune reactions are suspected in the male birth order findings.
“In conclusion,” he continues, “the main findings—evidence of extreme right-handedness in gay men, along with the moderating effect of older brothers at both ends of the handedness continuum—potentially move forward two important research programs (on handedness and birth order) related to men's sexual-orientation development.”