The biggest ever comparative study of stone tools dating to between 130,000 and 75,000 years ago found in the region between sub-Saharan Africa and Eurasia shows marked differences in the way stone tools were made, reflecting a diversity of cultural traditions. The study identified at least four distinct populations, each relatively isolated from each other with their own different cultural characteristics.
     Researchers took over 300,000 measurements of stone tools from 17 archaeological sites across North Africa, including the Sahara, and combined the stone tool data with a model of the North African environment during that period which showed that the Sahara was then a patchwork of savannah, grasslands and water, interspersed with desert. They also mapped out known ancient rivers and major lakes. They were then able to draw new inferences on the contexts in which the ancient populations made and used their tools, showing how early populations of modern humans dispersed across the Sahara along the ancient rivers and watercourses.
     Lead researcher Dr Eleanor Scerri, visiting scholar at the University of Oxford, says: "This is the first time that scientists have identified that early modern humans at the cusp of dispersal out of Africa were grouped in separate, isolated and local populations. Stone tools are the only form of preserved material culture for most of human history. These stone tools reveal how early populations of modern humans dispersed across the Sahara just before they left North Africa. While different populations were relatively isolated, we were interested to find that when connected by rivers, they share similarities in their tool-making suggesting some interaction with one another."
     Dr Scerri continues: "Not much is known about the structure of early modern human populations in Africa, particularly at the time of their earliest dispersals into Eurasia. Our picture of modern human demography around 100,000 years ago is that there were a number of populations, varying in size and degree of genetic contact, distributed over a wide geographical area. This model of our population history supports other theories recently put forward that modern humans may have first successfully left Africa earlier than 60,000-50,000 years ago, which had been the common view among scholars. Our work provides important new evidence that sheds light on both the timing of early modern human dispersals out of Africa and the character of our interaction with other human species, such as Neanderthals."
     Co-author Dr Huw Groucutt says: "The question of whether there was an early successful exit from Africa has become one of whether any of the populations discovered in this paper went in and out of Africa for some or all of this time. A crucial next step involves fieldwork in areas such as the Arabian Peninsula to understand how these populations spread into Eurasia."

Edited from PhysOrg (18 August 2014)