Genetics determine homosexuality. Study biology and psychology. You'll find that data and research points towards nature rather than nature. You choose what college to attend. You choose what food to buy at a food market. You choose whether or not to watch a movie. Choice is free will. You do not choose your sexual orientation. A gay man does not choose to get an erection at the sight of a naked man. A gay man does not choose to be aroused by male pheromones which are odorless, tasteless and invisible except only to the nervous system. Choice has nothing to do with it. Nature does.