As anyone who reads Andrew Sullivan knows, John Derbyshire is probably the most (what Andrew (and other gays) call) “homophobic” writer at National Review.

Apparently, in response to a post yesterday about the genetic origins of homosexuality, he got an email from a (vociferously non-conservative) supposed expert in the field, who wrote:

…if it were a genetic disease defense, it would have a certain very simple and identifiable inheritance pattern, and it certainly does not have that pattern. Identical twins would both have it, but the chance that a homosexual man’s identical twin is also homosexual is only about 20%.

I have a theory about the genetic basis of human sexual orientation, that I never hear anyone discuss, but to me makes perfect sense, and fits the facts (including the one quoted above, assuming that it is indeed a fact). I discuss it here, and in comments to this post.

Simply put, some are born homosexual, some (probably more) are born bisexual, and most are born heterosexual. For the first and third groups, their sexuality is indeed thrust upon them. Errrr…so to speak.

If that’s true, then the twin studies might actually provide some insight into the relative genetic component, assuming they’re separated twins. If two separated twins (the cite above doesn’t indicate whether they were separated or not) turn out to both be homosexual, that to me is a good indicator of homosexuality with either a genetic basis, or uterine environmental basis, or both. Of course, the only way to truly determine the genetic basis may be to allow human cloning…

In any event, it seems to me that my theory would dictate that the cases in which one twin is homosexual, and the other not, are cases in which both were born bisexual, and for various post partum environmental reasons, made different choices as to partners. It also explains why some homosexuals can be “cured,” and others can’t. The ones who can be were never homosexual in the first place–they always had a choice and simply decided to start choosing differently.

Long story short, this “expert’s” provision of this “fact” (and I’m pretty sure I’ve seen different numbers) has little relevance to the debate, unless you really do have the simplistic viewpoint that all people are either purely homosexual, or heterosexual, with nothing in between.