by Alya Gorgi

West African archeology could write textbooks on human evolution differently

L’archéologie de l’Afrique de l’Ouest pourrait écrire autrement les manuels sur l’évolution humaine

New evidence confirms that notable and long-standing intergroup cultural differences shaped the later stages of human evolution in Africa.

Our species, Homo sapiens, appeared in Africa approximately 300,000 years. Objects that early humans made and used, known as Middle Stone Age (Middle Paleolithic) material culture, are present across much of Africa and are associated with a wide range of innovations.

Among these, it is necessary to mention the bow and arrow technology, tool shapes specialized, the transport over long distances of objects, such as marine shells and obsidian, objects of personal adornment, the use of pigments, finally the water storage, and art. Although it is possible that other ancestors of modern humans contributed to this material culture of Africa, some of the earliest stone tools from the Middle Stone Age have been unearthed along with the oldest fossils of Homo sapiens discovered so far.

According to textbooks, by about 40,000 years ago, the Middle Stone Age was long over in Africa. This is an important milestone in the history of our species: the end of the first and longest culture associated with humanity, and the foundation of all subsequent innovations and the material culture that defines us today.

Despite its central role in human history, we struggle to understand how the Middle Stone Age ended. Knowing this could tell us how different groups were distributed across the landscape, how they were able to exchange ideas and pass on genes, and how these processes shaped later stages of human evolution.

Unfortunately, large areas of Africa remain almost entirely empty on the map with regard to such distant prehistory, which does not facilitate the study of these cases. Research has tended to focus on regions such as East Africa, where the conservation of artifacts is deemed to be of a high standard, and risks therefore minimized and gains naturally maximized. However, due to the emerging consensus that all of Africa played a role in the origins of humanity, we can no longer afford to neglect large areas of the continent if we are to reconsider our evolution. in a realistic setting.

It is for these reasons that my colleagues and I focused on West Africa, one of the least understood African regions in terms of human evolution. Additionally, our recent works validate the previous statements of a rich Middle Stone Age past.

New work carried out in Senegal

In 2014, our work in Senegal led to the discovery of a site in the north of the country, which seems to suggest that the Middle Stone Age ended in this area much more recently than textbooks would suggest. In West Africa, several less ancient dates had been mentioned in the past, however this work had been largely dismissed due to problematic dating, carried out before the establishment of current standards.

The dating of Ndiayène Pendao indicates that the site had approximately 12,000 years old. Yet the material culture was traditionally Middle Stone Age, with no tools or means of production dating from the Late Stone Age (Upper Paleolithic). In 2016 and 2018, we returned to the field to search for sites in different regions of Senegal and along various river systems, near the tributaries of Senegal and the Gambia. Indeed, fresh water sources were essential for populations in the past, just as they are today; River terraces often also offer excellent conservation conditions and are therefore suitable places for research into archaeological sites.

The site of Laminia, in Gambia, had never been dated. We carried out a detailed assessment of its rock layers, in order to obtain dating samples that we could confidently link to the artifacts. Samples taken from this site date back 24,000 years, which confirms the presence of a less ancient Middle Stone Age in the region.

The Saxomununya site had an even bigger surprise in store for us. Like classic artifacts from the Middle Stone Age, such as the Levallois points and retouched scrapers, coming from this site, were unearthed on a new terrace of the Falémé river but also inside, it became obvious that the site was relatively recent. However, dating to 11,000 years brings the earliest Middle Stone Age into the Holocene epoch, the period following the last great ice age. It was the first time that such an ancient material culture had been discovered in such recent times in Africa. This find indicated that Ndiayène Pendao's results were neither the result of chance nor an error.

According to these results, the last known appearance of the Middle Stone Age dates back 20,000 years, which is astonishing. The work of Senegalese colleagues seems at the same time to evoke a first appearance of the Late Stone Age just as late, around 11,000 years ago, less ancient than in most other regions of Africa.

Why did the Middle Stone Age last so long and why did the Late Stone Age start so late?

Population growth

Part of the answer to the first question may lie in the fact that parts of West Africa appear to have been less affected by the extremes of repeated cycles of climate change. These factors may have created stable environmental conditions over a long period of time. Thanks to this stability, the “toolbox” refined and used successfully for millennia, perhaps did not need to evolve, independent of the complex society from which these tools originated.

As for the second question, its answer lies in the fact that this region of Africa was relatively isolated. To the north it meets the Sahara Desert, and to the east there are the rainforests of Central Africa, which were often cut off from the rainforests of West Africa during periods of drought. About 15,000 years ago, however, a considerable increase humidity and forest vegetation has been recorded in central and west Africa. Different areas could thus be connected, creating corridors conducive to the dispersal of human populations. This may have sounded the death knell for humanity's first and oldest cultural repertoire and initiated a new period of genetic and cultural mixing.

It is clear that the simple, unilinear model of cultural evolution toward “modernity,” which has long prevailed, is not supported by the evidence. Hunter-gatherer groups, rooted in technologically radically different traditions, may have occupied neighboring regions of Africa for thousands of years, and sometimes shared the same regions. Furthermore, it is possible that regions that had been isolated for a long time were important reservoirs cultural and genetic diversity. This fits well with genetic studies and may have been a determining factor in the success of our species. Our results remind us of the risks associated with refusing to take into account cartographic gaps.

Eleanor Scerri, independent group leader, Max Planck Institute for the Science of Human History

This article is republished from The Conversation under a Creative Commons license.