There are numerous genres as in literature so in the other fields of arts /and any types of artistic creations/ like battle genre, horror, comedy, etc. Many genres we can find as in Ancient Greece so much more previously in some tribe primitive drawings and in such theatre as Kabuki, etc. Anyway, it is clear that genres came from the deepest dark times of the human era. Probably, it won't be surprice to have known that even during Dinosaurus era there were some kind of genre creations.
Each genre isn't unique completely, so counless examples of different pieces of creation have more than one element that can be interpreted as a specific genre element. That's why such occasions as the betrayal or the killing, or the investigation belong to not just one type of genre, but to many of them. Those elements /specific situations/ are bricks for the genre, however, styliscis it can differ, and depending on who's the author and how skilled is he /what kind of talents he has, etc/ he can draw the different type of expression, i.e. he's able to present something extraordinary or unusual even for a pretty-founded genre. Let's take such narrative as Macbeth and such a view/method as one; both of them can be combined into erotic genre. But, that has to be notified it's not necessary that combining two these elements we will have erotic genre. In some plays there are nude or naked elements are presented, however they are not taken as erotical.
I'm curious about the question of what allow those genre to appear? And why people do in similar genres? Why some people are trying to mix genres? -- Generally, what are all those influences are behind genres? Thanks.