JazzB1987 on 12 October 2012
There is no way to find out because there is no gene or brain defect or whatever. It is because of the way someone lived their life. The friends, family and experience etc shape the personality.
If you grow up with alot of sisters and played with barbies when you were little or if you were forced to watch e.g Sailor Moon because your older sister occupied the livingroom alot etc and you are shy and fail at getting a girlfriend etc chances are you will end up gay easier than a person with only brothers that is not shy and who watched Ninja Turtles and had no problems getting a girlfriend etc.
