While some postevangelicals run screaming from what Gen 1-2 says about the creation of man, the account is rather remarkable, if you think it about. It may be so familiar to us that we miss it.
The account teaches monogenesis: all humans descend from a single pair of ancestors. If, however, you think Genesis is just pious fiction, and the narrator was guessing at the origin of man, why would he posit monogenesis rather than polygenesis?
After all, in the view of postevangelical scholars, the narrator had no idea how man actually originated. Indeed, he couldn't–given his lake of scientific knowledge.
But if we grant their assumption for the sake of argument, then wouldn't be at least as likely if not more so that the narrator would posit polygenesis? To my knowledge, it's not uncommon for some people-groups to view themselves as intrinsically superior to other people-groups. And they use a theory of racial superiority to justify the conquest and subjugation of other people-groups. It would be very convenient to ground that pretension in a theory of separate origins. Different people-groups originated independently of each other, which accounts for the (alleged) superiority of one in relation to the other.
Although this may be more commonly associated with European imperialism and American slavery, the general attitude is hardly confined to that. To my knowledge, the Japanese traditionally view themselves as superior to other people-groups, and that justified their wars of conquest. Likewise, consider Aristotle's theory of natural slavery. I've also read that some African and South American tribes teach polygenesis.
Take another comparison: in Greek mythology, some men are fathered by gods. Yet there's a pecking order in the pantheon. If Zeus is your father, I assume that might put you a few notches above somebody who was fathered by Hermes, or somebody who had merely human parents. You have a superior or inferior pedigree.
If the Pentateuch is pious fiction, surely it would be very logical for the narrator to make the Israelites a separate and superior race. To say the Israelites and Canaanites were created independently of each other, which is why God treats both groups differently.
But, of course, that's not the actual story. Rather, all people-groups share a common origin in Adam. That threads its way through the creation of Adam and Eve, the survivors of the flood, the Table of Nations, and so forth.
I don't think it's coincidental that the Pentateuch teaches monotheism as well as monogenesis. Polytheism and polygenesis naturally go together inasmuch as each god or goddess of sufficient power could create a human or humanoid breeding pair or population. In Genesis, by contrast, there's only one Creator.
Evolution teaches polygenesis. On that theory, although humans have a common ancestor, they don't have an absolute point of common origin. Rather, they're an offshoot of the evolutionary tree of life. They have animal ancestors. In addition, there's interbreeding between different hominids.