A creation in its truest form serves as a critique of all previous creations, and more locally (music/film/etc), serves as the pedestal for competitive growth. In effect, when we write a song, it is a commentary on all the songs we've ever heard before, and to an even greater extent, on a more primal level, every sound we make is in reaction to all previous sounds we've heard. We then- as consumers- base our taste in music and sounds on how relevant the said musician's critique of former musics is to our own critique. We are, after all addicted to our own models of the universe, so it's only natural that we'd be obliged to serve those models with similar or more complex versions of the same model. Genres seem to be the best way to describe this phenomenon.