*Edit*
Here are some fascinating videoclips from 60 Minutes on homosexuals and studies researching what causes someone to be gay or lesbian.
I never knew that the more brothers a guy has, the more likely he is to be gay unless he's a lefty--then he only has a 2% chance of being gay, just like firstborn sons. Don't believe me? Watch the clip. My only critique is they didn't give the statistics other than the firstborn son is only 2% likely to be gay.
Clip on why gay and lesbian couples want to be married.
