Being adopted, this fear played at the back of my head. I didn't really start dating until I went to college, 7 hours away. I have since met my birthfamiles, who are Greek and Italian. I find it interesting that I've almost excusively dated Norwegian, Swedish, English, and Irish guys, and never a Greek or Italian!

I'm surprised that those twins ended up together: usually people detect genetic similarity in each other visually or chemically. Perhaps they were always incestuous, and would have been attracted to each other even if they hadn't been separated from each other. I have a disturbing example of this from my own life: the twin sister of a guy I dated once was extremely fond of him, and often behaved sexually towards him. She was very jealous of me. I doubt he ever thought anything except that she loved him as a brother, and what could I say? "Um, honey, I think your sister wants to have sex with you"?