David, you’re right about the hair-whorl study: It has been debunked, and the New York magazine article I read about it in did not describe how it was conducted:

How difficult is it to collect hair-whorl-direction data? [The man who conducted the study] explains that he, for one, got lucky:
“By chance I happened to be vacationing at a beach where a preponderance of gay men was fortuitously noticed. The subjects were considered to be homosexuals because of their public display of stereotypical interpersonal relationship deemed typical of homosexual men. This assessment was reinforced by the dearth of females and children on the beach . . . Conveniently, the gay men were highly concentrated in one area of the beach. Such considerations made it relatively easy to collect the data on groups of predominantly gay men with great confidence even though the subjects were not asked for their sexual preference.”

Yikes. Apologies for citing that. I usually know better than to go by popular-press accounts of scientific studies.

Nonetheless, I stand behind my assertion that “the evidence is simply overwhelming that something biological — perhaps genes, perhaps something having to do with the flush of testosterone that happens to males in the womb — is going on here.” (This is not an assertion that sexuality is purely biological.) The very study that debunked the hair-whorl pattern confirmed another potentially biological marker for homosexuality: Gay men tend to have more older brothers. Yet another marker seems to be that gay women have different digit ratios.

Also, I should stress that there’s a difference between sexual orientation and sexual behavior. One’s orientation dictates which gender one is most attracted to; the research is still coming together, but there’s a good argument to be made that male sexual orientation is somewhat fixed, while female orientation is more fluid. Nonetheless, when it comes to behavior, heterosexual males sometimes engage in sexual acts with other males for a variety of reasons — women aren’t available, homosexual behavior is ritualized in their culture, etc. Similarly, the stigmatization of homosexuality sometimes causes homosexual men to engage in heterosexual behavior.