Marriage and the Bible -- Part 4 -- Abraham Marries His Sister

You know for all the talk of how Issac was the child of promise and he is, one of the interesting things about his parents Abraham and Sarah was that they had the same father. Two different mothers (another polygamist relationship) but they were brother and sister as well as husband and wife. Incest by the time Moses writes the Law but at this point apparently there is no such thing.
Who one can and cannot marry based on family relationship is something the Bible does deal with but the interesting thing about Genesis is that such concerns do not seem to be prevalent. The issue of why Sarah could not conceive may be as much an issue of family genetics as it was her own biology. Even to today the most common arranged marriage in many countries is to a member of the family.
The biblical issue is what is allowed and why. As time goes on the Bible becomes restrictive about who one can marry in the family but it does not completely get rid of it. If Moses is using Genesis as a basis for the Law that follows then it is interesting that Abraham's marriage to His sister will be illegal later. Changing nature of the God-man relationship? Probably.

Next: Abraham the Polygamist