3.2 Developments in other parts of the world during the period 4000- 2000 BC.
To provide some background to the developments at the Tassili plateau during the  4000- 2 000 BC period, developments in other parts of the known world, during the same period, are briefly summarized as follows:
During the period 4000 – 2000 BC mankind made rapid progress and it is in this period that in locations with favorable circumstances the transition occurred from the Neolithic period or Stone Age to the Bronze Age. The small traditional societies depen- dent on hunting gathering and simple dry land farming which existed in 4000 BC  developed during the fourth millennium into city civilizations with complex community organizations and sophisticated technologies, including the development of writing, the invention of  the wheel, mathematics, astronomy, irrigated agriculture and related technologies. References: 6 & 13
Thus, for example by 3000 BC in Uruk, a town in Sumer, South Mesopotamia, present day Iraq,  a complex city civilization had developed, based on irrigated agriculture. Writing, book keeping, mathematics, astronomy, medical science and many other technologies, including the invention of the wheel and the making of bronze tools and weapons had been developed. Uruk was trading with locations as far apart as Afghanistan for lapis lazuli, the Indus valley for carmelian, Anatolia and Persia for metal ores, gold and silver and the Zagros and Libanon for cedar wood. Uruk exported to these places grain, leather, dried fish, dates and textiles. Some authors suggest that the Uruk civilization actually established colonies in some of these locations to facilitate and safeguard its trade. Much information is also available about some of the kings of Uruk among whom Gilgamesh is the most famous, as several poems about his adventures have survived till this day.
Also in Egypt similar developments had occurred and by 3000 BC already kingdoms existed in South and North Egypt which in 2 700 BC merged into one country under the First Dynasty. Also here in Egypt writing, the invention of the wheel, astrology, mathematics and irrigated agriculture was already well developed by 3000 BC.
In the Indus valley, in Mohenjo-Daro and Harappa, similar developed societies were reported by 2700 BC. The same applies for developments in China in this period. For example, silk cultivation was already well established by about 3 000 BC. In Europe during this period traditional permanent or semi permanent farming systems developed.
When we are discussing the Sahara pastoralists living in the period from 4000-to 2000 BC, it may be useful to realize that we are already talking about modern man, who was gradually developing technologies, tools and equipment to improve his living conditions. Location specific opportunities were different between geographical areas, explaining why pastoralists were living in the stone-age in the Sahara in the same period as highly developed bronze-age civilizations existed in Sumer and in Egypt.