Bonobo genes are the genetic factor. That is, in times of stress they start to think of... things that aren't violent (like sex). I can't really see something as fancy as death feedback being plausible genetically. There might be some factors that could be partially affected genetically, like nausea when seeing blood or paralysis in front of violent behavior. However, I don't see it being fully genetic with creatures as complex as humans. The existence of fiends in fact means it can't be. I doubt fiends become fiends by having a mass of genes spontaneously altered in their brain and elsewhere in their endocrine system.