I’m quite late in addressing a finding published in July in Psychological Bulletin. As I was unable to find access to the original report, my sources linked here are second hand.
Psychology Today reports that Dr. Kenneth Zucker of the University of Toronto has found that gay men and women are more likely to be left-handed than the general public at large.
The findings, reported in the Psychological Bulletin, lesbians have a 91 percent greater chance of being left-handed or ambidextrous than straight women, while gay men are 34 percent more likely than straight men to not be right-handed.
There does not seem to be a causal relationship between sexual orientation and handedness. The vast majority of left-handed people are heterosexual and the vast majority of gay people are right-handed.
However, this finding is interesting considering the predominance of the claim from ex-gay ministries that “No one is born gay”. As Science Daily puts it:
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.
It is my belief that sexual orientation is the result of a complex interplay of a number of factors, at least some of which are pre-birth. The determinants could include genes, hormones, and/or environmental factors. However, all credible sources suggest that these are set in place very early and, if not before birth (as I suspect), then within the first few years of life. The correlation between handedness and sexual orientation is consistent with that assumption.
NARTH reviewed the report and was unable to refute it. They did, however, caution that meta-analysis can be performed poorly (though they did not suggest that it was in this case) and that as the results were only 31% and 91% different from the control groups, this was intriguing but not decisive (Their 31% differs from the Psychology Today report of 34%):
The latest study is intriguing. Nevertheless, the main routes to homosexuality would not likely be through the route that has caused some people to be left-handed.
NARTH discounts the ever-growing preponderance of evidence that in at least some persons sexual orientation is primarily determined by pre-birth factors with a reference to “main routes”.
This study should cause more than a little concern for those seeking to instill cultural and legal preference for reorientation of sexuality. It serves as a stong linking reminder. Many people recall the efforts made to reorient left-handers to right-handed behavior. These efforts to force children to go against their natural inclinations led in many cases to serious problems.
As well as the obvious feelings of inadequacy and insecurity this produced, left-handed children that were forced to switch to use of the right hand often experienced bed-wetting and developed speech impediments.
Also, (similarly to most ex-gay efforts) they didn’t work.
Fortunately left-handedness is no longer viewed as sinister (pun intended) or a defect in and of itself. The efforts to make left-handed children use their right hand have come to be viewed as unnecessary and cruel. And though there is no identifiable genetic “cause” of left-handedness, most people have come to see it as “natural”. Eventually, I believe, sexual orientation will come to be viewed the same.