This happened when I was in my late teens.  (A few ears ago)   For years it was alledged that heroin users started with pot and then progressed to heroin.  This was a false assumption and an argument against it was a study that showed that most heroin users started off with tobacco.  Now this was during the sixties when probably the majority smoked.  Not sure how it would be today with smoking  down to 25%?   Since the majority smoked back then you probably could make the case that anything started with tobacco.