Well… I took a class called human population biology and it went into the specifics about how scientists believe how someone becomes a homosexual. I can’t cite specific information right now… but I can tell you, in the world of academia, it is accepted that being gay or lesbian, or bisexual is biological. It has to make some sense too… like you said, if your not part of the norm your going to face abuse and in America its pretty brutal. Why would someone want to choose to deal with that?
As for the second part… I agree that some of those things you have to be molded into, but a large part has to be genetics as well. When you said pro athletes I thought of the manning family. Father was a pro quarterback and has two sons that are pro quarterbacks and one that was supposedly better than the other two, but had to stop playing due to injury. Nature and nurture. You don’t have three sons that are high caliber players with luck.