Smoking is almost always curiosity and social pressure to start, but it is physically addictive. Thus, the desire to quit needs to be pretty strong. My parents smoked...my younger brother smoked.... I never did. There 'may' be some genetic factor involved in my having no desire to start, but... *shrug*

I doubt there is a gene that says: "roll up some plant material in a piece of paper and set fire to it."
We are, however, genetically programmed to have various degrees of sexual desires, or there wouldn't be these discussions... *wry smile*. The concern now is learning in what ways the programming might differ, due to hormonal variations or other conditions that would 'tend' someone to be gay.