During Bible study we read through the Scripture passages about family members having children from family members - one in particular I noticed is Genesis 19:36: "Thus both the daughters of Lot were with child by their father."
The question raised from our Bible study member was this: At what time period, historically, did people realize/consider the health concerns of this and when did it shift to not allowing children with people of one's family? As well as the focus of monogamy vs. polygamy?
So I ask a few questions on several levels as follows: When did the wider social norms change? When did a new awareness begin and when did new thoughts and morals/ethics form around it?
These our good questions. You are correct, Heather, in thinking in terms of progressive revelation. God does not give a timeless word sheet that ignores where people are in their development and thought. There is strong condemnation of incest, however, such as Lev. 18.6-18. Scholars differ in how to date the legal materials.
A point that I would make is that the historical materials of the Bible are not necessarily normative. They are historical. At times an action would be followed by punishment or blessing thus likely bringing the normative in. It is possible that the Moabites and Ammonites, who were the descendants of this sexual action, are being given a negative status by it (Gen. 19.37-38). If so, the action would be under criticism.