Here is some information to start the discussion. This tells us that the Nile Valley was not peopled until after the wet period of the Holocene and that some of the inhabitants were cattle herders/collectors/fishermen fleeing the dessication of the Sahara. It also points out that the entire Sahara area was uninhabited until 8-9000 BC.
S.K. McIntosh and R. J. McIntosh. 1983. “Current Directions in West African Prehistory,”
Annual Reviews in Anthropology 12: 215-58.
These southerly areas today bear the hallmark of the 20,000 to 12,000 dry period—massive almost continuous fields of longitudinal dunes extending 4000 kilometers from the Atlantic littoral to the Sudan republic (108,202, 204, 251). At this time the Sahara shifter 450-500 kilometers south (164, 265), dunes were active 60 latitude further south than today (93) and the Chad Senegal and Niger Basins were subjected to dune erection over former lacustrine deposits (81,163,203,210,21,137,255). A low, saline Lake Bosumtwi (lowest level 17,500-15,000) lay in a landscape of grass savanna, where forest was reduced to valley remnants (251; M.R. Talbot, personal communication). As arid as this Late Glacial Phase became, it was by no means as severe as that before 40,000.
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[Late Stone Age LSA] During the hyperarid episode lasting from 20,000-12,000 B.P., the Sahara down to 150 was uninhabited. Most of the population in West Africa at that time probably lived south of 110 N. When the wadi channels began to flow with water again between 10,000 and 8,000 B.C., grasslands and large grazing mammals repopulated the Sahara, as, presumably, did hunter/collectors. Archaeological traces of these groups are rare, however. They are probably represented by small scatters of punched blade industries known from a handful of Saharan sites.. This industry is well described at Wadi Greboun in the Aïr (45), where a small group of hunter/collectors camped briefly on the banks of an early Holocene lake. Similar aggregates with distinctive, asymmetrically shouldered Ounanian points have been found at Adrar Bous, near Arawan, and further north in the Fezzan and Maghreb (16, 45). It appears that these industries are earlier than 6500 B.C. Confirmation of this chronology has recently come from Roset’s work (207a) in the Temet basin in the northeast Aïr, where a blade industry associated with stone bowls and pestles has been dated to about 7600 B.C. In Egypt’s Western Desert, Terminal Paleolithic industries with backed bladelets and Ounanian points date to 7000-6800 B.C., and apparently represent the first occupation of the area since the Aterian (270, pp. 108-10, p. 277). The affinity of these blades and bladelet industries with earlier Epipaleolithic material in North Africa indicates that large parts of the Sahara were recolonized from the North in the early Holocene (47, p. 564). Mori (169) has suggested that the well-known Saharan rock engravings of elephants and wild buffalo (Homiocera (Bubalus) antiquus) were created at this time. Muzzolini, however, argues that the so-called Bubalus style is contemporaneous with other Saharan rock art dating to the second half of the Holocene (174,175).
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Kuper, R. and S. Kröpelin 2006 “Climate-Controlled Holocene Occupation in the Sahara: Motor of Africa’s Evolution,”
Science 313: 803-807.This is an excellent paper
Fig. 3. Climate-controlled occupation in the Eastern Sahara during the main phases of the Holocene. Red dots indicate major occupation areas; white dots indicate isolated settlements in ecological refuges and episodic transhumance. Rainfall zones are delimited by best estimate isohyets on the basis of
geological, archaeozoological, and archaeobotanical data. (A) During the Last Glacial Maximum and the terminal Pleistocene (20,000 to 8500 B.C.E.), the Saharan desert was void of any settlement outside of the Nile valley and extended about 400 km farther south than it does today. (
With the abrupt arrival of monsoon rains at 8500 B.C.E., the hyper-arid desert was replaced
by savannah-like environments and swiftly inhabited by prehistoric settlers. During the early Holocene humid optimum, the southern Sahara and the Nile valley apparently were too moist and hazardous for appreciable human occupation. (C) After 7000 B.C.E., human settlement became well established all over the Eastern Sahara, fostering the development of cattle pastoralism.
(D) Retreating monsoonal rains caused the onset of desiccation of
the Egyptian Sahara at 5300 B.C.E. Prehistoric populations were forced to the Nile valley or ecological refuges and forced to exodus into the Sudanese Sahara where rainfall and surface water were still sufficient. The return of full desert conditions all over Egypt at about 3500 B.C.E. coincided with the
initial stages of pharaonic civilization in the Nile valley.