The UK Guardian gives us a tale wherein the fiance breaks it off with his girlfriend when he walks in on her doing the nasty with her biological dad. And she finds it a normal thing to do. Can sex between blood relations ever be acceptable? The reality of genetic sexual attraction (GSA) is slowly creeping into public consciousness primarily because of the talk that equates consensual incest with gay sex.
On one hand, there's the situation wherein siblings or fully conscious relatives get it on with each other. (Parang Flowers in the Attic, which people keep on telling me to read, but I haven't seen a copy of it in your friendly neighborhood Booksale bins.) On the other hand, in the age of sperm donorship, it is possible for two people to meet up and have an affair and then realize than they're related. According to experts, if you were separated at birth (or something like that), there's a high 50% chance that you will get obssessed with your sibling and/or very close relative.
So apparently, this isn't soap opera territory anymore, like amnesia and killing people. But given the chance, if you were allowed to marry your sibling, would you do it? A huge majority still says 'Eewww, hell no!' but then again, in some states, if said parties can't procreate anymore, maybe they'd be allowed to.
I'm just chewing on this because I had to reread Kathyryn Harrison's The Kiss some weeks back and most of the articles coming out on GSA mention the book. The Kiss was a memoir which came out in 1997, and chronicled the author's affair with her father starting at age 20. It more or less verifies what the experts (the so few of them) who did say that close blood relatives separated at birth have the tendency to have GSA.