Glaciation: Why biodiversity does not support the out of Africa theory.

Scientists believe human beings came out of Africa originally partly because the greatest genetic diversity is found in Africa.
However the genetic diversity can be explained away with glaciation. Twenty thousand years ago, most now temperate regions were under ice and thousands of years earlier they were burstling with life. The people had to evacuate themselves to the south in Africa, South America and etc until the ice started to recede again thousands of years later and people started to return. There was nobody living in Europe twenty thousand years ago but there were people there thousands of years earlier.
The places where biodiversity is low worldwide are relatively newly colonized living spaces and that is the reason for the low biodiversity in those places. It will happen again in the future as people will need to leave their land because of ice. Glaciation happens once in a while and we have no idea yet what causes it.

Hypothetically.