I would say that in way of documenting the period, by humanly, it had to be a fairly local exercise. I find it interesting that world wide so many people are so focused, and live their whole lives, base upon what happened in a few square miles of the middle east (OK in one area about the size of Texas - that is not the whole world. Rest your hopes on very small place?)
What if every culture had it's own Adam and Eve. Each has their own belief and documentation of the creation of people.
Inbreeding to such an extent to populate the whole world has real problems.
How were such a variety of all races and cultures introduced to only on blood line? We went Scandinavian, Latino, Chinese, Black, White, ect. from only one blood line?
What if the world at that time was a petri dish of experiments? Maybe a few regional floods/meteors/disasters cleaned the slate a few times to start over?
Genesis is only one local regional story of creation. Why in the world do people in California hang their hat, and hope, and faith, on stories from the middle east?