Kings. Brother-sister marriage was limited to the royal family in most periods of ancient Egyptian history. The king thus imitated the god Osiris, who married his sisters Isis and Nephthys. An explanation provided by early scholars of this practice, that kingship passed through the female line, has been disproved by the Egyptologist Gay Robins. Betsy M. Bryan has suggested that incestuous marriage had the practical value of keeping property within the royal family. The best-known examples of brother-sister marriage were practiced by the Ptolemaic kings. Because these rulers were actually Greek, perhaps they emphasized the imitation of Osiris's marriages to validate their claims to the Egyptian throne.

NonRoyal Intrafamily Marriage. Though elite members of Egyptian society often married cousins, or their father's or mother's siblings, brother-sister marriage was not commonly practiced. Egyptologist Jaroslav Cerny has demonstrated that some of...