There was a particularly infamous case in Greece, ca 1980-1981, in a small village of the Pelloponese, where practically every child in the village has been fucked again and again by pretty much everybody in its clan, as part of some old bucolic tradition and point of view on "elder-young" relationship. The final outcome was (I think) a mass absolution, and the case has been hidden under the carpet so well that it's hard to track down any data on it. The village's name is "Douneika". If you want to do the research yourself, be my guest.