28-02-2025
African rainforests were home to humans much earlier than thought: 150,000 years ago
African rainforests were home to humans much earlier than thought: 150,000 years ago
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Scientists have long believed that hundreds of thousands of years ago, humans first learned to thrive in East African grasslands before spreading out and adapting to new environments.
But a new study published this week found some of our ancestors managed to survive in a tropical rainforest in West Africa much earlier than was previously known.
A team of researchers found evidence that humans were living at a site in southern Côte d'Ivoire, a region of present-day rainforest, about 150,000 years ago in an environment generally believed to be a barrier to human occupation, according to the study published Wednesday in Nature.
"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," study author and archaeologist Eslem Ben Arous, of Spain's National Centre for Human Evolution Research, said in a statement. "This pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate."
Though its widely believed that humans first originated about 300,000 years ago from one part of Africa, we understand very little about the continent's history, according to Eleanor Scerri, leader of the Human Palaeosystems research group at the Max Planck Institute of Geoanthropology and a co-author of the new study. As the evidence of early humans living in Asian rainforests emerged, she began investigating the possibility the same phenomenon had occurred in West Africa.
A challenging route to finding evidence
Finding evidence of this theory presented a challenge, Scerri said, because the preservation of ancient botanical materials is notoriously poor in rainforests, and Africa's rainforests see so little rainfall it's possible they may not have been considered rainforests thousands of years ago.
As she began her research, Scerri came across a decades-old book written in Russian about a deeply buried site next to a river in Côte d'Ivoire. More recent climate research suggested the area may have been "a rainforest refuge in the past as well," Scerri said previously.
But when the site was first uncovered in 1982 by a joint Ivorian–Soviet expedition led by archaeologist professor Yodé Guédé of the Université Félix Houphouët-Boigny, the team didn't have the tools to determine the age of the stone tools they found or what the environment was like when people lived there.
The research was strong, but Scerri said "because it was published in Russian and because it was West Africa, no one was interested, and no one knew about it."
So Scerri and her colleagues tracked down Guédé who, now in his 80s, guided them back to the vast trench. The timing couldn't have been better: The team managed to cut back the vegetation and collect samples in March 2020 before they had to leave the country because of the COVID-19 pandemic and they were able to return briefly before the site was ultimately destroyed by quarrying.
"One of the most rewarding things was just to see the happiness on Professor Guédé's face that this project that goes back to the 1980s, he was finally able to close that chapter," she said.
New techniques lead to exciting discoveries
Over the next few years, Ben Arous developed new techniques to date quartz grains from the oldest layer of sediment in which tools were found while a separate lab verified the results with another technique called luminescent dating. "It's around 150, 160,000 years old, which was exciting because it's like one of only two sites in West Africa that are that old," Scerri said.
Next, the team examined the isotopes from the waxy coating of leaves, which Scerri said are "surprisingly indestructible," solidified plant remains and ancient pollen. The evidence indicated the site wasn't just small forested area, but a heavily wooded one home to key rainforest trees like oil palms and hunteria.
Scerri said the team is still working to examine sediment samples and stone tools taken from a site near the trench and more exploration of West Africa needs to be done to understand these artifacts. She said the findings challenge the longstanding narrative that we "had to learn how to overcome different ecosystems as we sort of grew up as humans."
"It reinforces the idea that humans have multiple roots across Africa, and that from our inception almost we were a species that could and did survive in very, very different ecosystems," Scerri said. "And the same skills that allowed us to do that, are the same skills that have put us on the moon and have us looking forward to going to Mars. It's human adaptability and our ingeniousness, coming up with ways in which you can adapt to radically different environments, is unknown in any other animal."
