A new study has revealed that when humans were still living exclusively in Africa, before migrating to Eurasia and ultimately to the rest of the planet, they were more flexible and adaptable than previously believed. This is because evidence shows that ancient humans had taken up residence in the tropical rainforests of Africa 150,000 years ago, or 80,000 years before this was supposed to have happened.
Until now it was thought that humans had avoided the rainforests for as long as possible, because of the difficulties of living in such a wet, dark, and potentially dangerous environment. But the international team of researchers involved in the new study discovered that this wasn’t true. It was in an area of ancient rainforest in the West African state of Côte d'Ivoire that evidence of human habitation dating back 150,000 years was found, forcing a reevaluation of how human evolution and development actually proceeded in the Upper Paleolithic period.
The research project that made this surprising discovery was led by scientists from the Max Planck Institute of Geoanthropology, and also included researchers from the University of Sheffield. The results were published in the journal Nature.
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The Unexpected Antiquity of the Rainforest Dwellers
The research team re-excavated an archaeological site from the 1980s in the West African rainforest. Stone tools had been found embedded deep into sediment, but they could not be dated. The researchers relied on new scientific methods to analyze the site in depth, which had not been possible during past studies.
Different views of the site of the discovery of ancient human rainforest occupation. (Arous, et.al/Nature).
Among the substances that the scientific team analyzed were grains of ancient pollen, silicified plant remains, and leaf wax isotopes, all of which were found in the rainforest in sediment. What the results of this study revealed is that the human toolmakers had lived at a time when the area was covered by tropical forest. This forest had been thickly wooded and wet, with high humidity levels typical of the humid West African rainforests, then and now.
With this established, the next step for the research team was to get some accurate dates for the ancient deposits.
This responsibility fell to Professor Mark Bateman from the University of Sheffield’s School of Geography and Planning, who used a dating technique called Optically Stimulated Luminescence to achieve good results. This test allowed him to calculate the true burial age of individual grains of sand from eight samples taken from different locations at the site.
This approach proved to be highly productive. It showed that the archaeological site had a history extending as far back as 150,000 years, an unexpected result that has been corroborated by Electron Spin Resonance dating.
“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,” Professor Bateman explained in a press release issued by the University of Sheffield. “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.”
This testing proved humans had lived in the rainforest long before it was thought to have been possible or desirable.
Piece of stone tool found at archaeological site. (University of Sheffield).
“It is incredibly interesting to take a grain of ancient sand and be the first to know when it was deposited,” Professor Bateman said. “It is even more so when the age of the sand changes what we know of how, and where, our ancient ancestors lived.”
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The results obtained were groundbreaking, and the were also stunning.
“Before our study, the oldest secure evidence for habitation in African rainforests was around 18,000 years ago,” said Dr. Eslem Ben Arous from the National Centre for Human Evolution Research (CENIEH), the new study’s lead author. “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.”
Climate models had suggested the area the researchers studied could have been a rainforest in the past, maintaining that status during drier periods. This is why the scientists carried out their study where they did, as they were hoping to find solid evidence of human habitation.“
Early Humans Rising to the Challenge
What was discovered showed the remarkable resilience and adaptability of early modern humans, who were able to survive in challenging circumstances and adjust their living patterns based on the climates they encountered. This flexibility would obviously serve them well tens of thousands of years later, when they migrated to Eurasia and had to survive in very different climates.
Largely unspoiled section of Kakamega rainforest in Kenya, Africa. (Doron/CC BY-SA 3.0).
“This work reflects a complex history of population subdivision, in which different populations lived in different regions and habitat types,” said Professor Eleanor Scerri, senior author of the study and leader of the Human Paleosystems research group at the Max Planck Institute of Geoanthropology. “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.”
Top image: Section of largely unexplored central African rainforest intersected by the Kivu River.
Source: MONUSCO Photos/CC BY-SA 2.0.
By Nathan Falde
