A relationship between handedness and sexual orientation has been suggested by a number of researchers, who report that heterosexual individuals are somewhat more likely to be right-handed than are homosexual individuals. The relationship between handedness and sexual orientation has been suggested within both sexes and may reflect the biological etiology of sexual orientation; work by Ray Blanchard has linked the relationship to the fraternal birth order effect, which suggests that a man with several older biological brothers is more likely to be homosexual.
Lalumière et al. conducted a meta-analysis of 20 studies with a total of 6,987 homosexual and 16,423 heterosexual participants. They found that homosexual men had a 34% greater odds of not being right-handed, and homosexual women had a 91% greater odds.
Williams ''et al''., 2000
In a study involving 382 men no significant association emerged between handedness and sexual orientation.
Mustanski ''et al''., 2002 study
Mustanski et al. examined sexual orientation and hand preference in a sample of 382 men and 354 women. Although a significantly higher proportion of homosexual women was found to be left-handed compared to heterosexual women, no significant differences were found between heterosexual and homosexual men with respect to hand preference.
Lippa, 2003 study
Lippa examined sexual orientation and handedness in a sample of 812 men and 1,189 women. Homosexual men were 82% more likely to be non-right-handed than heterosexual men, but no significant differences were found between heterosexual and homosexual women in terms of handedness. When combining men and women into one large sample, homosexual individuals were 50% more likely to be non-right-handed than heterosexual individuals.
Blanchard ''et al''., 2006 study
Blanchard et al. argued that the fraternal birth order effect appears to be limited to right-handed men. Moreover, the same study indicates that left-handed men without older brothers are more likely to be homosexual than non-right-handed men who have older brothers. As Blanchard et al. said in their report,
BBC survey
In a multinational online survey, it was found that gay men and lesbians are more likely to be left-handed than heterosexual men and women. Bisexuals of both sexes more often described themselves as ambidextrous than gay or heterosexual individuals of the same sex.
Blanchard, 2008 ''Archives of Sexual Behavior'' study
A subsequent study by Blanchard found that both right-handed homosexual men and left-handed heterosexual men had a statistically significant number of older male siblings, but that there was no significant observable effect either for right-handed heterosexual men or for left-handed homosexual men.
Blanchard, 2008 ''Laterality'' study
Blanchard discussed ways in which the fraternal birth order effect and handedness could be explained in terms of the maternal immune hypothesis. In this, the mother is assumed to grow more immune to male antigens with each pregnancy, and thus produce a greater number of "anti-male" antibodies. He suggests two possibilities: Either that non-right-handed fetuses are less sensitive to the antibodies, or that the mothers of left-handed fetuses do not, for some reason, produce them.
In a sample including 694 gay men and 894 straight men, it was found that 13.9% of gay men and 15.9% of straight men were not right-handed, a non-significant difference. The study replicated the 'older brother effect' for homosexual men, but unlike Blanchard, it found that the effect applied to both right-handed and left-handed gay men, being in effect stronger for the latter than for the former.
Kishida and Rahman, 2015
In a sample of 478 heterosexual men and 425 homosexual men, gay men were found to show a significantly greater likelihood of extreme right-handedness and non-right-handedness compared to heterosexual men.
A 2014 Internet study attempted to analyze the relationship between self-identification as asexual, handedness and other biological markers, in comparison to individuals of other sexual orientation groups. A total of 325 asexuals, 690 heterosexuals, and 268 non-heterosexuals completed online questionnaires. The study asserts that asexual men and women were 2.4 and 2.5 times, respectively, more likely to not be right-handed than their heterosexual counterparts.
