Much seems to have been made of the protagonists' relationship being "incestuous" -- A simple definition of incest is sexual intercourse between closely related people -- But this construct implies intercourse that can lead to procreation and a conception that was observed to result in a high incidence of birth defects -- its development as a societal taboo is the result of millenniums of human experience. A review of the history of incest may be found in the "links" section.