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behind an enduring legacy of rock engravings and rock paintings depicting the animals
they knew so well. With the onset of plant and animal domestication by small groups
of Neolithic herders and farmers some 10,000 years ago, the focus of the paintings
changed. Cattle camps, showing herds of brindled cattle guarded by men with bows-
and-arrows and dogs, were now painted on suitable smooth rock faces in mountainous
areas throughout the Sahara (Muzzolini, 1995 ; Coulson and Campbell, 2001 ). Some of
these paintings showwomen in their finery, riding oxen just as they do today among the
Baggara cattle-owning tribe of western Sudan during their summer migrations north
into the desert to search for fresh pasture and to escape the biting Tabanidae flies that
herald the onset of the rains further south. Others show papyrus or reed canoes similar
in design to those still made and used on Lake Tana near the Ethiopian headwaters
of the Blue Nile. The plains adjacent to high mountains were preferred occupation
sites for these Neolithic pastoralists and their proto-historic successors ( Figures 17.5
and 17.6 ). Small lakes and permanent springs were a guarantee of survival in years
when the summer rains failed. The cattle herders ranged as far as Jebel 'Uweinat
in south-east Libya, the Tassili sandstone plateaux in southern Algeria and the Aır
Massif in Niger.
The nature of the interactions between prehistoric peoples and their environment
remains the subject of enduring archaeological enquiry. Given the former presence
of domesticated cattle, sheep and goats in areas no longer able to sustain them, it is
tempting to speculate that they themselves may have accelerated their exodus from
the desert. An obvious question to ask is: To what extent did Neolithic overgrazing
by large herds of hard-hoofed cattle, sheep and goats accelerate soil erosion by wind
and water and initiate humanly induced processes of desertification, especially in the
drier second-half of the Holocene? At Adrar Bous in the central Sahara, the rate of
sedimentation evident in small valleys around the central granite massif was an order
of magnitude greater than it had been during earlier phases of human occupation,
suggesting that a combination of grazing pressure allied with progressive (or rapid)
climatic desiccation may have caused the increase in erosion, a situation likely to be
true of other parts of North Africa at this time (Williams, 1984b ; Williams, 1988 ), as
well.
Coastal shell middens provide another important, unambiguous source of inform-
ation about human occupation of arid lands. For example, the extensive Neolithic
and younger shell midden sites along the arid coasts of Mauritania (Petit-Maire,
1979a ; Petit-Maire, 1979b ) or Peru contain stone tools and other Neolithic artefacts
(Sandweiss et al., 2001 ) and clearly indicate a human presence at the time they were
accumulating. In Peru, the shells and fish otoliths (Andrus et al., 2002 ) have been
used to determine changes in the temperature of the seawater along the coast, which
also varies between El Ni no and La Ni na years (see Chapter 23 ), being warmer in
the former and cooler in the latter (Quinn and Neal, 1987 ). The sudden accumulation
of shell middens along this now arid coast some 5,000 years ago has been used as
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