As Jdawg said, I don't believe homosexuality is a choice, although I personally believe that one's environment may affect one's attractions. And environment is a very vague term, however, and it can encompass everything from brain chemistry to social settings. In terms of being 'pushed into a sexual group', this may happen, but from what I've seen of society, I think most people are 'pushed' into conforming with society's mores; I have heard of a religious group that would 'convert' gay people to become straight, for instance.
There is also the fact that many people with homosexual attractions end up having a straight marriage, only to later break up. A little while ago, I read an article in a newspaper regarding a woman who'd gotten married to a guy only to have to break up with him later when she found that he'd been cheating on her; with guys. She later finds a group dedicated to helping people who have this type of thing happen to them.
I also believe that people's sexuality is something that is at times not completely rigid; the idea that one can only be 'straight' or 'gay' is blown out of the water by the fact that there are also people who are both (bisexuals), for starters.
Why not 20 for both? or 16? Seriously, what are you basing your decision on?