The concept of genre has also been extended beyond language-based texts, so that we customarily speak of genres in relation to art, music, dance, and other non-verbal methods of human communication.
For example, in art we are familiar with the genres of painting, drawing, sculpture and engraving. In addition, within each genre, sub-genres have developed. For painting, sub-genres might include landscape, portraiture, still life and non-representational works. Some of the recognized sub-genres of fiction include novels, short stories and novellas. Presumably, any number of sub-levels can exist for any one genre, and new sub-genres may be invented at any time. Recently, genre theories have been promulgated for texts about every kind of human activity. In each, genres and sub-genres can be identified.
This proliferation of genre analysis for various purposes means that we must include all kind of text in an investigation of the usefulness of genre.
The old "fight or flight" reaction of our evolutionary heritage once played a major role in the life of every human. Our ancestors lived and died by it. Then someone invented the fascinating game of civilization, and things began to calm down. Development pushed wilderness back from settled lands. War, crime, and other forms of social violence came with civilization and humans started preying on each other, but by and large daily life calmed down.