 A good account of perversion might have to be prescriptive, capturing the core of perversion but not necessarily capturing all our beliefs about it (it should explain why our beliefs are mistaken when they are). Furthermore, it will likely be a psychological account, a preference to have sex with or involving certain types of object that are anti-life, such as bodily waste and corpses, and that are biologically odd, such as inter-species sexual intercourse. Evolutionary biology and evolutionary psychology would have to play crucial roles.