Kinsey- famous sex researcher, came to the conclusion that sexual preference was on sort of a scale. imagine bisexual as being a "5" on the scale, with heterosexual as a "0" and homosexual as a "10". He stated that most people weren't exclusively hetero- or homo-sexual, we are all kind of a mix. I think that is probably true, although his research has been criticized on it's methodologies- so you can't be totally sure what he concluded was all that significant. You should check out the movie done on him that came out pretty recently, it's called "Kinsey, Let's Talk About Sex". It is a great documentary, but very sexually explicit- which is fitting for the type of guy he was. It's a great movie.