Handedness, homosexuality and… Rh- blood

Many studies in the 1980s and 1990s had asked whether there was any relationship with handedness, and we, like others, had concluded that there was not. However, a meta-analysis of 20 studies, including our own, with a grand total of 6182 homosexual men altered that situation, male homosexuals having a significantly higher likelihood of being left-handed. The earlier studies had mostly failed through being too small, a typical study having about 300 homosexual men, and hence being under-powered. That was later confirmed in the large BBC Internet study of sex and sexuality, where 4616 male homosexuals showed a significant excess of left-handedness, with a similar effect found in the 2008 female homosexuals.

— McManus, Chris, “Half a century of handedness research: Myths, truths; fictions, facts; backwards, but mostly forwards”, Brain and Neuroscience Advances (2019)