The stone tool styles that took Homo Sapiens out of Africa and across much of the world were gradually replaced with new implements, and were thought to have been abandoned entirely by 30,000 years ago. New discoveries reveal that in West Africa this transition was not made until long after the rest of the world, with replacements only appearing around 11,000 years ago.

Long before H. Sapiens' arrival on the scene other early human species had refined stone tool use to a fine art. The first bones of our own species are associated with the appearance of a distinctive style of flaking tools, scrapers, and grinding stones anthropologists refer to as the Middle Stone Age. As the name suggests, there was also a Later Stone Age, marked by much smaller tools and ostrich eggshell beads. These first appeared around 67,000 years ago, and by 30,000 years ago were thought to have replaced the larger tools that served humanity for almost 300,000 years everywhere in Africa.

Dr Eleanor Scerri of the Max Planck Institute for the Science of Human History has challenged this belief based on sites she has examined in Senegal in particular. "West Africa is a real frontier for human evolutionary studies – we know almost nothing about what happened here in deep prehistory,” Scerri said in a statement. “Almost everything we know about human origins is extrapolated from discoveries in small parts of eastern and southern Africa,"

Scerri partnered with Dr Khady Niang of Senegal’s University of Cheikh Anta Diop to study Senegal's sites where humans tarried across the nation’s diverse environments, which range from thick rainforest to desert fringes. In Scientific Reports they describe abundant Middle Stone Age tools at sites near two of the nation's major rivers. Using Optically Stimulated Luminescence (OSL), which measures how long an object has been buried away from sunlight, one of these was dated at 21,000-24,000 years ago, the other 11,000 years old.

Scerri, Niang and co-authors note this is consistent with their previous discovery of a Middle Stone Age tools at another 11,600-year-old Senagalese site. Other sites across West Africa have not been as precisely dated, but they could be as young as 20,000-25,000 years old.

Co-author Dr Jimbob Blinkhorn attributes the tools’ survival to the region’s isolation from the rest of humanity at the time. “To the north, the region meets the Sahara Desert," he said. "To the east, there are the Central African rainforests, which were often cut off from the West African rainforests during periods of drought and fragmentation.”

"This matches genetic studies suggesting that African people living in the last 10 thousand years lived in very subdivided populations," Niang added.

Moreover, the climate of Western Africa appears to have been more stable during the last Ice Age than the rest of the continent. Without the pressure of changing conditions people living in the region may have had little need to abandon the tools that served their ancestors so well. Not until the Holocene had nearly begun did greater humidity expand West Africa’s forests, possibly linking them to those in Central Africa and sparking a cultural exchange.