The Israelites were YHWH's chosen people; set apart from other civilizations (Deuteronomy 7:6). This provides the explanation for all of the laws that the Israelites were to follow - like what foods to eat - because it visibly showed how the were different from those around them. Obviously, Genesis would also need to provide an explanation for what the neighboring tribes did that would make them abominable to YHWH. In the beginning of Deuteronomy 7, the Israelites are called to utterly destroy the neighboring tribes and to not marry off their children with members of the other tribe. Genesis provides the framework and rationalization for Israelites to follow YHWH's commands later on. Knowing that the other tribes did testable things, such as
