After the evolution of homo sapiens sapiens approximately 150,000 to 100,000 years ago in Africa, the continent was mainly populated by groups of hunter-gatherers.[18][19][20] These first modern humans left Africa and populated the rest of the globe during the Out of Africa migration dated to approximately 50,000 years ago, exiting the continent either across Bab-el-Mandeb over the Red Sea,[21][22] the Strait of Gibraltar in Morocco,[23] or the Isthmus of Suez in Egypt.[24]
Other migrations of these modern humans within the African continent have been dated to that time, with evidence of early human settlement found in Southern Africa, Southeast Africa,North Africa, and the Sahara.[25]
The size of the Sahara has historically been extremely variable, with its area rapidly fluctuating and at times disappearing depending on global climactic conditions.[26] At the end of the Ice ages, estimated to have been around 10,500 BC, the Sahara had again become a green fertile valley, and its African populations returned from the interior and coastal highlands in Sub-Saharan Africa, with rock art paintings depicting a fertile Sahara and large populations discovered in Tassili n'Ajjer dating back perhaps 10 millennia.[27] However, the warming and drying climate meant that by 5000 BC, the Sahara region was becoming increasingly dry and hostile. Around 3500 B.C., due to a tilt in the earth's orbit, the Sahara experienced a period of rapid desertification.[28] The population trekked out of the Sahara region towards the Nile Valley below the Second Cataract where they made permanent or semi-permanent settlements. A major climatic recession occurred, lessening the heavy and persistent rains in Central and Eastern Africa. Since this time, dry conditions have prevailed in Eastern Africa and, increasingly during the last 200 years, in Ethiopia.
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