By Bryan Caplan
Ryan Sorba, author of The “Born Gay” Hoax, was recently booed at the CPAC convention. Since I recently read all of the main twin and adoption studies of sexual orientation, I wondered what he had to say. He focuses on Bailey and Pillard’s 1991 twin study, which he correctly reports, “found that 52% of the identical twin brothers of gay men were gay, as were 22% of fraternal twin brothers, and 11% of genetically unrelated brothers.” Sorba’s critique:
[I]n order to show that “homosexuality” is genetic using identical twins, one must demonstrate that when one twin is “gay” the other will also be “gay” 100% of the time. The results of this twins study however, fell a long way short of the mark.
If the claim is that 100% of the variance in orientation is genetic, then Sorba’s right. But by this standard, no complex human trait is genetic! Identical twins are not 100% identical in height, IQ, personality, or criminality, either. In each of these cases, however, identical twins are much more similar than fraternal twins, indicating that these traits have strong genetic components. We are not “born gay” any more than we are “born tall,” but our genes definitely push us in these directions. Sorba’s just attacking a straw man.
His other complaint is better: “[T]his study shows that unrelated step‐brothers are both ‘gay’ more often than genetically related brothers.” This is indeed a piece of evidence against the genetic hypothesis. If Sorba had merely observed that the results of this study were “inconsistent” and then turned to the broader literature (which confirms a strong genetic component, a mild family environment component, and a lot of randomness), I’d commend him. But instead, he bizarrely picks one hole in one study, then claims complete vindication for environmentalism.
HT: David Boaz