Since probably 3500 BCE, the Saharan and Sub-Saharan regions of Africa have been separated by the extremely harsh climate of the sparsely populated Sahara, forming an effective barrier interrupted by only the Nile in Sudan, though the Nile was blocked by the river 's cataracts. The Sahara pump theory explains how flora and fauna (including Homo sapiens) left Africa to penetrate the Middle East and beyond. African pluvial periods are associated with a Wet Sahara phase, during which larger lakes and more rivers existed.
what geographical feature limited contact between sub-saharan africa and the outside world
the extremely harsh climate of the sparsely populated Sahara