The null hypothesis is that animals, including humans, moved where they could, when they could, regardless of any inconvenience for theorists of recent prehisto

The null hypothesis is that animals, including humans, moved where they could, when they could, regardless of any inconvenience for theorists of recent prehistory. All we can know about the prehistory of present populations from genetics is their direct ancestry. Who was in the Americas before those ancestors, but did not breed with them, is lost to us until we find actual remains. Pretending to know there weren't any is a mistake made over and over again, yet never learned from.