I sense that Jonathan, on decorum, fitness, is onto something that could be productive.
The concept presupposes that a literary text occupies a place in a larger field, a context. That it is necessarily both an echo, to some extent, and a mode of address or indication toward something else.
Maybe most shifts in style depend on a new sense of decorum. That is, if there's a fitness in relation to experience or reality, then, as our general sense of reality changes, the old styles or old forms of decorum will no longer ring true. (Maybe some forms of decorum never change, though - built as they are on our direct responses to certain basic kinds of experiences. Laughter in comedy is just a special application of humor in general.)
Complex artworks are structured around complex forms of decorum. I remember reading an essay about Melville's Confidence-Man, which argued that the thing is a fantastic meditation/spoof on the generic expectations of literary forms.
Complex critical projects are probably built around systematic and layered senses of decorum.