Nature Versus Nurture

During Friday's class the long standing debate of nature versus nurture was brought up. It is obvious that peoples opinions differ on the subject and sides are taken but the subject led me to question which category homosexuality falls under. Does someone become gay because of predetermined circumstances that take place during conception and through birth? Or, can someone become gay under outside influences? Also, if it is predetermined before birth, then how is it actually determined? I know what I believe and I am sure that this is a touchy subject for some but it is a valid question.

So, is it nature or nurture?