The Sahara Pump Theory is one which is used to explain the various phases by which African flora and African fauna have left that continent to penetrate the Middle East and possibly, thereafter, the rest of the world. African pluvial periods are associated with a "wet Sahara" phase, in which large lakes and many rivers are found. During these periods, the Sahara becomes a Savannah grassland and African flora and fauna become common. During the following inter-pluvial dry arid period, the Sahara reverts to desert conditions usually as a result of the retreat of the West African Monsoon southwards. Evaporation exceeds precipitation, level of water in lakes like Lake Chad falls, and rivers become dry wadis. Flora and fauna previously widespread retreats northwards to the Atlas Mountains, southwards into West Africa, or eastwards into the Nile Valley and thence either south east to the Ethiopian Highlands and Kenya or northwestwards acros the Sinai into Asia. This separates populations of some of the species on areas with different climates, forcing them to adapt, possibly giving rise to allopatric speciation.
The Saharan pump has been used to date four waves of human emigration  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 Semitic languages.
- ↑ Van Zinderen Barker E. M. (1962-04-14). "A Late-Glacial and Post-Glacial Climatic Correlation between East Africa and Europe". Nature 194: 201 - 203. DOI:10.1038/194201a0.
- ↑ Stokes Stephen, "Chronology, Adaptation and Environment of the Middle Palaeolithic in Northern Africa" http://www.human-evol.cam.ac.uk/Projects/nafrefched/efched.htm
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