Doesn't that discount Adam and Eve in the process then? Or am I missing something?
And more importantly, did Adam and Eve have belly buttons? If not, why not? If so, why?
Not necessarily. The first known civilization started in Mesopotamia, and I think it's no coincidence that the Garden of Eden was in that region. I see Genesis as an explanation for our origins that was written for the audience of the time, who did not yet possess the tools to understand a more detailed explanation. In that context I would surmise that Adam and Eve were the founders of that civilization, IOW their predecessors were not quite fully human.