During long time ago, Sahara as known today as Saharan Desert used to be a woodland and during the period until 5,000 BC has gone through slow transformation into desert due to global warming. Before that, the Earth was far colder and most of it was uninhabitable or very harsh, especially in Central and Northern Europe. As climate changed, Into Europeans moved into Europe and created subsequent civilizations.
When Africa was far colder, there was a point of perfect steppe environment where you could prosper. Yakub punished black people, gave it to white men. After which, Proto Indo European linguistical conquest.
As it got hotter, livestock probably died and people left the regions and suffered famine.