Conundrum: Could sexual preference be a choice?

Andrea calls in from San Francisco. She is a biologist and has been thinking about the question of why people are gay. She knows a lot of gay people in the city and has had many discussions with them about how gayness comes about. She has tried to argue that being gay is a choice, but the majority of the gay people she knows reject this claim. Society doesn't tolerate homosexuality very well, and some people wouldn't have chosen to be gay if they felt they could have a decision in the matter. Even so, Andrea has consistently stuck to the idea that choice should supercede biology. She asks whether she should abandon this line of argument.