Sahara Pump Theory

Carvings of fauna common in the Sahara during the wet phase, found at Tassili in the central Sahara

The Sahara Pump Theory is a hypothesis that explains how flora and fauna left Africa to penetrate the Middle East and then Europe and Asia. The theory observes that African pluvial periods are associated with a "wet Sahara" phase, during which larger lakes and more rivers exist. This causes changes in the type of animals found in the area. Regardless of the aridity of the greater Sahara, migration along the river corridor was halted when, during a desert phase 1.8-0.8 Ma, the Nile ceased to flow completely and possibly flowed only temporarily in other periods

Mechanism

During periods of a wet or "Green Sahara", the Sahara and Arabia become a savanna grassland and African flora and fauna become common. Following inter-pluvial arid period, the Sahara area then reverts to desert conditions usually as a result of the retreat of the West African Monsoon southwards. Evaporation exceeds precipitation, the level of water in lakes like Lake Chad falls, and rivers become dry wadis. Flora and fauna previously widespread as a result retreat 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 north-east across the Sinai into Asia. This separates populations of some of the species in areas with different climates, forcing them to adapt, possibly giving rise to allopatric speciation.

Plio-Pleistocene

In the Plio-Pleistocene migrations to Africa included Caprinae in two waves at 3.2 Ma and 2.7-2.5 Ma; Nyctereutes at 2.5 Ma, and Equus at 2.3 Ma. Hippotragus migrated at 2.6 Ma from Africa to Siwaliks. Asian Bovid moved to Europe and to and from Africa. Primate Theropithecus experienced contraction and its fossils are found only in Europe and Asia, while Homo and Macaca settled wide ranges.