SF isn't a genre; SF is the matrix in which genres are embedded, and because the SF field is never going in any one direction at any one time, there is hardly a way to cut it off.
Larry NivenThere were timelines branching and branching, a mega-universe of universes, millions more every minute. Billions? Trillions? The universe split every time someone made a decision. Split, so that every decision ever made could go both ways. Every choice made by every man, woman, and child was reversed in the universe next door.
Larry Niven