In the Biblical Period, the idea of what constituted a prohibited degree of kinship for sexual relations seemed to have broadened. Among the ancestors of Israel there occurred an unusual number of marriages that are incestuous by later standards; evidently this was not merely condoned, but favored, as ensuring good stock. Thus Abraham married his paternal sister, Jacob married to sisters, and Amram, Moses’ father married his aunt. As late as the time of David, marriage to a half sister was condoned.

In Jewish Law the general prohibition against incest with one’s “near of kin” (Lev. 18:6) has been held to be limited to the following degrees of consanguinity:

  • Parents
  • Mother-in-law
  • Stepmother
  • Sister and half sister (but not a stepsister)
  • Granddaughter
  • Aunt
  • Wife of father’s brother
  • Daughter-in-law
  • Brother’s wife
  • Stepdaughter and step granddaughter
  • Wife’s sister during the lifetime of the former

A list of another 20 degrees of consanguinity was later drawn up, however, by way of analogy – albeit not to create additional criminal offenses, but as additional prohibitions of intercourse and impediments to marriage.

The punishment for the various offenses of incest varies going from death by stoning to flogging. Incest is one of the three cardinal offenses (together with murder and idolatry) which a man may not commit even in order to save himself from certain death; nor in order to save another person’s life; nor can there be any justification for its commission on any medical grounds.