Three Canadian researchers have shown that left-handedness is more common in gay men and in lesbian women than in comparable heterosexual persons. Drs. Martin L. Lalumière, Ray Blanchard, and Kenneth J. Zucker, of the Centre for Addiction and Mental Health (CAMH) and the University of Toronto, reached this conclusion by means of a meta-analysis -- a statistical technique for combining the results of many previous studies in order to reach a reliable conclusion.
The study, published in the July issue of Psychological Bulletin, combined the results from 23,410 heterosexual and homosexual men and women. The results for both sexes were statistically significant; however, the tendency toward increased levels of left-handedness was markedly greater for lesbian women than for gay men.
The importance of these results lies in their theoretical implications. Handedness is determined early in development -- probably before birth. Therefore, the correlation of handedness and sexual orientation demonstrates that at least some influences on adult sexual orientation operate quite early, maybe even before an individual is born. The results also suggest that there may be at least one cause of homosexuality that is common to both gay men and lesbian women. This is in contrast to much other biological research on sexual orientation, which has usually suggested that sexual orientation in men is influenced by different factors than sexual orientation in women.
Although the findings of increased left-handedness in homosexual persons are quite reliable, they are small in absolute magnitude, and they have no application besides providing clues to the origins of sexual orientation. Handedness could not be used to decide whether someone else (or oneself) is gay, lesbian, or heterosexual.
The Centre for Addiction and Mental Health is Canada's largest centre in the area of mental health and addictions. A World Health Organization Centre of Excellence and a teaching hospital fully affiliated with the University of Toronto, the Centre was established in 1998 through the merger of the Addiction Research Foundation, the Clarke Institute of Psychiatry, the Donwood Institute and the Queen Street Mental Health Centre.