Such beliefs are geographically widespread and observed throughout recorded history. For example, many tribes in Southern Africa explicitly refer to the right hand as the “male hand” and the left as the “female hand". In Hinduism and Hatha Yoga, the right-hand side of the body is considered male, and the left side female. In ancient Jewish Kabbalah traditions, the left-hand pillar of the Tree of Life is the female pillar, and the right-hand pillar the male. The ancient Celts saw the left-hand side as female and sacred and linked to the Moon. The cult that grew up around Pythagoras in Ancient Greece connected the right side with masculinity, force and goodness. Christianity derived many of its doctrines from these and many other ancient traditions, but made the additional leap of associating the female left with weakness and even evil.
Most studies conclude that males are more likely to be left-handed than females, and this appears to apply regardless of the culture or society. The difference is not huge, though. One major study has pegged male left-handedness at about 11.6% and female 8.6%; others indicate respective percentages of 13% and 11%, 14% and 10%, etc. A 2008 meta-analysis of 144 other studies found that men are, on average, about 23% more likely to be left-handed than women, which is roughly consistent with these results. The commonly-quoted notion that men are twice as likely to be left-handed than women is demonstrably false and of unknown provenance.
Various possible reasons and explanations have been put forward for the discrepancy between men and women, including testosterone levels (see the section on Biological Theories of Handedness), the Fighting Hypothesis (see the section on Handedness and Combat), etc, but no convincing cause has been found. Indeed, it seems to fly in the face of recent evidence that women's brains are generally marked by more inter-hemispheric connections, while male brains show more intra-hemispheric activity (left-handers typically show more inter-hemispheric communication or “cross-talk”).
A relationship between handedness and sexual orientation - specifically that homosexuals are more likely to be left-handed than heterosexuals - has been proposed by several researchers over the years. In fact, the idea goes back to a hypothesis of Sigmund Freud at the end of the 19th Century or, more accurately, to his disciples Wilhelm Stekel and Wilhelm Fliess, whose less-than-scientific assertions struck a chord with many chauvinists.
A link between homosexuality and left-handedness perhaps suggested itself due to a series of striking (although quite likely coincidental) similarities, both statistical and qualitative, between the two phenomena. For example, both affect around 10% of the population (at least according to some measurements); both describe positions on a continuum rather than an all-or-nothing proposition; both are difficult to define and measure; both lack an obvious evolutionary advantage; and both have mysteriously persisted, and even prospered, even in the face of persecution. Interestingly, “left-handed” was American slang for homosexual for much of the 20th Century.
A meta-analysis by Martin Lalumiere et al in 2000 showed an incidence of left-handedness of 39% in homosexuals (nearly four times the expected rate). But the evidence is at best mixed - for example, a 2002 study indicated a correlation between homosexual women and left-handedness, but not men, while a 2003 study showed just the opposite (a correlation for homosexual men but not women) - and no convincing explanations of the link have been put forward.
A 2001 study by Richard Green and Robert Young suggests that individuals with gender identity disorders (transsexuals) were significantly more likely to be left-handed (or at least less exclusively right-handed) than the general population. The study conjectured that elevated levels of testosterone during pregnancy may have decreased the asymmetry in the fetal brain, resulting in a greater tendency to left-handedness. A 2008 study also showed higher than average left-handedness among paraphiliacs (people who have extreme or atypical sexual urges, such as towards inanimate objects, children, unusual situations, etc).