New research has shown that humans were living in African rainforests more than 100 thousand years earlier than previously thought.
An international team of researchers are re-writing our understanding of how our prehistoric ancestors lived after they found evidence that people were living in a rainforest in modern day Cote D‘Ivoire around 150 thousand years ago.
The study, led by the Max Plank Institute of Geoanthropology, has been published in Nature.
Humans originated in Africa around 300 thousand years ago, but the ecological and environmental contexts of human evolution are still little understood. In the search for answers, rainforests have often been overlooked, generally thought of as natural barriers to human habitation, until now.
“Before our study, the oldest secure evidence for habitation in African rainforests was around 18 thousand years ago and the oldest evidence of rainforest habitation anywhere came from southeast Asia at about 70 thousand years ago,” explains Dr. Eslem Ben Arous, researcher at the National Centre for Human Evolution Research and lead author of the study. “This pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate.”
“Our study has identified the oldest known association between humans and rainforests and has highlighted the importance of Africa’s diverse regions and ecosystems in human evolution,“ Dr Sarah Elliott, a Paleoecologist at Bournemouth University, added.
Stone tool (Credit: Jimbob Blinkhorn, MPI-GEA)The study site was first investigated by co-author Professor Yodé Guédé of l'Université Félix Houphouët-Boigny in the 1980s. Results from this initial study revealed a deeply stratified site containing stone tools in an area of present-day rainforest. But the age of the tools – and the ecology of the site when they were deposited there – could not be determined.
This new study set out to re-investigate the site in Cote D’Ivoire using technology that was not available forty years ago.
The researchers used several dating techniques, including Optically Stimulated Luminescence and Electron-Spin Resonance, on mineral grains in the sediments to arrive at a date roughly 150 thousand years ago.
The original study trench (credit: Jimbob Blinkhorn, MPI-GEA)At the same time, sediment samples were separately investigated for pollen and leaf wax isotopes. Dr Elliott also examined micro-botanical silica phytolith remains from the site to help build up a reconstruction of the ecosystem.
Analyses indicated the region was heavily wooded, with pollen, silica phytoliths and leaf waxes typical for humid West African rainforests. Low levels of grass pollen and grass phytoliths showed that the site wasn’t in a narrow strip of forest, but in a dense woodland.
“We now know that people in prehistoric times lived in a variety of ecosystems, including rainforests and we can now start to ask questions about human alteration of these environments, and how the plants and animals in these wet tropical rainforests may have been altered in the deep-past,“ Dr Elliott concluded.
