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The Prehistory of North Africa spans the period of earliest human presence in the region to the beginning of the Early Dynastic Period of Egypt in c. 3100 BC. North Africa is defined by the United Nations to consist of the seven countries or territories situated between the Sahara desert and the Mediterranean: Algeria, Egypt, Libya, Morocco, Sudan, Tunisia, and Western Sahara.〔According to UN country classification here: http://millenniumindicators.un.org/unsd/methods/m49/m49regin.htm. The disputed territory of Western Sahara (formerly Spanish Sahara) is mostly administered by Morocco; the Polisario Front claims the territory in militating for the establishment of an independent republic, and exercises limited control over rump border territories.〕 Geographically, it can also be held to include the Saharan portions of Mauritania, Mali, Niger, and Chad. As modern humans are generally believed to originate in Africa, prehistoric North Africa may hold important clues in understanding the evolution and spread of the human race ==Saharan Climate and Human Migration== Human habitation in North Africa has been greatly influenced by the climate of the Sahara, which has undergone enormous variations between wet and dry over the last few hundred thousand years. This is due to a 41000-year cycle in which the tilt of the earth changes between 22° and 24.5°.〔Orbit: Earth's Extraordinary Journey documentary〕 At present (2000 AD), we are in a dry period, but it is expected that the Sahara will become green again in 15000 years (17000 AD). During the last glacial period, the Sahara was much larger than it is today, extending south beyond its current boundaries.〔Christopher Ehret. ''The Civilizations of Africa.'' University Press of Virginia, 2002.〕 The end of the glacial period brought more rain to the Sahara, from about 8000 BC to 6000 BC, perhaps because of low pressure areas over the collapsing ice sheets to the north.〔(Fezzan Project — Palaeoclimate and environment ). Retrieved March 15, 2006. 〕 Once the ice sheets were gone, the northern Sahara dried out. In the southern Sahara, the drying trend was initially counteracted by the monsoon, which brought rain further north than it does today. By around 4200 BC, however, the monsoon retreated south to approximately where it is today,〔(Sahara's Abrupt Desertification Started by Changes in Earth's Orbit ), Accelerated by Atmospheric and Vegetation Feedbacks.〕 leading to the gradual desertification of the Sahara. The Sahara is now as dry as it was about 13,000 years ago.〔 These conditions are responsible for what has been called the Sahara pump theory. During periods of a wet or "Green Sahara", the Sahara becomes a savanna grassland and various flora and fauna become more common. Following inter-pluvial arid periods, the Sahara area then reverts to desert conditions and the flora and fauna are forced to retreat northwards to the Atlas Mountains, southwards into West Africa, or eastwards into the Nile Valley. This separates populations of some of the species in areas with different climates, forcing them to adapt, possibly giving rise to allopatric speciation. In terms of human evolution, the Saharan pump has been used to date four waves of human migration from Africa, namely: * ''Homo erectus'' (ssp. ''ergaster'') into Southeast and East Asia * ''Homo heidelbergensis'' into the Middle East and Western Europe * ''Homo sapiens sapiens'' "Out of Africa theory" * The spread of Afro-Asiatic languages (Berber and Egyptian to North Africa and Semitic to the Arabian Peninsula and Middle East). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prehistoric North Africa」の詳細全文を読む スポンサード リンク
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