After the destruction of Sodom and Gomorrah, the only survivors, Lot and his two virgin daughters, lived in a cave. One night the daughters plied their father with wine, and the elder daughter seduced Lot in order to 'preserve the seed of [their] father'. The following night they got him drunk again, and the younger daughter took her turn. Lot apparently had no memory of the events, although nine months later his daughters gave birth to two sons, Moab and Ben-ammi.

Abraham and Sarah had the same father but different mothers. Sarah married her half-brother in Ur, and they remained together until she died, at the age of 127.

Abraham's brother, Nahor, married his niece, the daughter of his dead brother Haran and the sister of Lot.

Amram married his father's sister, and Aunt Jochebed bore him two sons, Aaron and Moses.