Many cosmologies and creation myths from different cultures all over the world explain how each of their respective peoples came into being from their own gods or supernatural forces, and were thus native to each region.
Why do no stories seem to recall a great migration out of an African motherland to wherever each of our ancestors ended up?
Or any other major migration for that matter?
The earliest migrations out of Africa took place over 200 000 years ago, the latest at around 50 000 years ago.
Dating orally transmitted stories is a fickle task. Looking comparatively at Indo-European myths, one has been able to reconstruct certain mythic motives probably used during the proto-Indo-European (PIE) times, very roughly around 4000 BC. Some of those motives are the Sky Father, the Horse Twins and the Serpent Slaying Myth. Certain reflexes of these motives were not recorded until the 13th century, as in the case of the Icelandic myths, which means the themes had astoundingly been transmitted orally for over 5000 years.
One could therefore assume that the mythic tradition of the Indo-Europeans at around 4000 BC was atleast stable, which could imply a certain age even then. But even if one assumes that these myths are double the age, being very generous, that would only land you at around 9000 BC. There is still a gap of 40 000 years to the latest migration out of Africa. That gap only is our very-generously-estimated-age-of-PIE-myths times four, and more.
Adding to that, there has been mass migrations under the time of the PIE mythic tradition that haven't been preserved in memory, the foremost one being the PIE mass migration itself. The mythical themes of the PIE survived, but the memory of their arrival didn't.