I ask because I'm trying to understand whether the prohibition against sibling marriage is due to genetic or emotional reasons.



Now, suppose Bob and Diana marry -- that would make Eve and Frank stepsiblings with no shared biological heritage.

Would the Old Testament law, in this case, prohibit Eve and Frank's marriage?


The prohibited forms of incest are found in Leviticus 18.

Verse 9 is of the most concern:


Verse 11, however is also interesting:



The complete list disallows:

  • your mother
  • any woman your father marries (honor)
  • your sister, or the daughters of either of your parents
  • your children's daughters (honor)
  • your father's wife
  • your daughter-in-law
  • your sister-in-law





This is not to say it's okay or not. There are plenty of specifics the Bible does not address specifically.

  • It does not specifically mention masturbation.
  • It does not mention whether or not it's okay to buy your wife flowers.

When there is no clear Biblical statement in a moral issue, such things are next determined based on extrapolating Biblical principles. But the answer to your question remains "there's nothing specifically forbidding it, and genetic similarity isn't cited as the reason for the prohibition on sexual relationships with close relatives."

I still don't know if that makes it okay, though. A better follow-up question that may have more definitive answers, could ask for the Catholic view on this, or another denomination.
