- A new study published in Nature provides the earliest evidence that our human ancestors lived in the tropical rainforests of Africa
- The study involving University of Sheffield researchers dates humans living in rainforests back to 150,000 years ago, 80,000 years earlier than found in other rainforests sites around the world
- Luminescence and Electron Spin Resonance dating techniques were used to date sediments containing Middle Stone Age tools found at an archeological site in Côte d'Ivoire, Africa, to a time when tropical rainforests existed across the region
- The study argues that tropical rainforests were not a barrier to the spread of modern humans and supports the theory that human evolution happened across a variety of regions and habitats.
The earliest evidence of humans living in tropical rainforests in Africa, around 150,000 years ago, has been published in a new study in Nature.
Humans were thought to have not lived in rainforests until relatively recently due to them being thought of as natural barriers to human habitation.
However the new study - published by an international team led by the Max Planck Institute of Geoanthropology, with contributions from the University of Sheffield - found that humans were living in rainforests within the present-day Côte d'Ivoire around 150,000 years ago.
The study puts the evidence for humans living in rainforests anywhere in the world, back by 80,000 years, and argues that human evolution happened across a variety of regions and habitats.
The team re-excavated an archaeological site from the 1980s currently found within rainforest, in which stone tools had previously been found deep within sediments but could not be dated. They then applied new scientific methods to the site which were not available during the original study.
Ancient pollen, silicified plant remains (phytoliths) and leaf wax isotopes from site sediments were also analysed and found to indicate that when humans were dropping their stone tools in the region, it was a heavily wooded wet forest, typical of humid West African rainforests.
Professor Mark Bateman, from the University of Sheffield’s School of Geography and Planning, used a dating technique called Optically Stimulated Luminescence, to discover the burial age of individual grains of sand from eight samples throughout the site. His work showed that the archaeological site extended back from 12,000 years ago right through to around 150,000 years ago. These results were then corroborated by Electron Spin Resonance dating.
Professor Bateman, said: “The stone tools found at the site were thought to be from the Middle Stone Age, so they could have been as old as 500,000 years, or as young as 10,000 years.
“Key to finding when they were being used was the application of modern dating techniques to the sediments in which the stone tools were found.
“It is incredibly interesting to take a grain of ancient sand and be the first to know when it was deposited. It is even more so when the age of the sand changes what we know of how, and where, our ancient ancestors lived.”
Lead author of the study, Dr. Eslem Ben Arous from the National Centre for Human Evolution Research (CENIEH), said: “Before our study, the oldest secure evidence for habitation in African rainforests was around 18,000 years ago, and the oldest evidence of rainforest habitation anywhere came from southeast Asia at about 70,000 years ago.”
“This pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate.”
Professor Eleanor Scerri, senior author of the study and leader of the Human Palaeosystems research group at the Max Planck Institute of Geoanthropology, said: “Several recent climate models suggested the area could have been a rainforest refuge in the past as well, even during dry periods of forest fragmentation. So we knew the site presented the best possible chance for us to find out how far back into the past rainforest habitation extended.
“This work reflects a complex history of population subdivision, in which different populations lived in different regions and habitat types.
“We now need to ask how these early human niche expansions impacted the plants and animals that shared the same niche-space with humans. In other words, how far back does human alteration of pristine natural habitats go?”
Professor Bateman, added: “There are other sites waiting to be investigated that could provide equally as exciting results. However this study was completed just before the site was destroyed by mining activity, highlighting that being able to do work such as this is vitally important in being able to further study the history and evolution of the human species.”
