anthropology explains the zhus

Min Zhu before his fall from grace
Certain high Azande nobles, are permitted to wed their own daughters, and brother-sister marriages were preferred in the old Hawaiian aristocracy and in the Inca royal family. In none of these instances, however, could the general population contract incestuous unions, for these were a symbol and prerogative of exalted status. Among the Dobuans, intercourse with the mother is not seriously regarded if the father is dead; it is considered a private sin rather than a public offense. The Balinese of Indonesia permit twin brothers and sisters to marry on the ground that they have already been unduly intimate in their mother’s womb. Among the Thonga of Africa an important hunter, preparatory to a great hunt, may have sex relations with his daughter—a heinous act under other circumstances. By their special circumstances or exceptional character these cases serve rather to emphasize than to disprove the universality of intra-family incest taboos.