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By Ian Randall
Deputy Science Editor
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Humans were living in rainforests roughly 150,000 years ago, some 80,000 years earlier than was previously thought—and may have been an important center for early human evolution.
This is the conclusion of an international team of researchers who re-examined an archaeological site in West Africa from which stone tools of previously uncertain age—including picks and smaller retouched tools—had been uncovered.
Rainforests represent a major world biome, the researchers explain, but one that humans were not thought to have occupied until relatively recently.
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"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," said lead author and archaeologist Eslem Ben Arous, of Spain's National Centre for Human Evolution Research, in a statement.
"This pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate."
While we know that humans first originated in Africa some 300,000 years ago before dispersing across the globe, it is unclear exactly how the environments in which our distant relatives lived might have affected our evolution.
According to the team, rainforests have long been overlooked as a setting for the development of our species—with the biomes long thought of as natural barriers to human occupation.
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In their study, Ben Arous and her colleagues studied a site dubbed "Bété I" in what is today the Republic of Côte d'Ivoire, near West Africa's southern coast.
The site was first excavated back in 1982 by a joint Ivorian–Soviet expedition headed up by archaeologist professor Yodé Guédé of the Université Félix Houphouët-Boigny, who was also involved in the new research.
The original dig—which carried on until the early nineties—unearthed layers containing stone tools at the site which today lies within a rainforest.
The tools were subsequently lost during the Second Ivorian Civil War in 2011; and at the time, it was not possible to precisely date the tools nor determine the ecology of the region at the time that the sediments were deposited.
"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," explained paper co-author and Max Planck Institute of Geoanthropology (MPI-GEA) archaeologist professor Eleanor Scerri in a statement.
"We knew the site presented the best possible chance for us to find out how far back into the past rainforest habitation extended."
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"With Professor Guédé's help, we relocated the original trench and were able to re-investigate it using state of the art methods that were not available thirty to forty years ago," added paper author and MPI-GEA archaeologist James Blinkhorn.
The team's investigation turned out to be very timely, for the site was since been destroyed by mining activity during the COVID-19 pandemic.
"The site was given protected status. Unfortunately, the loss happened regardless of this," Scerri told Newsweek.
Analysis of quartz grains from the layers where the stone tools were recovered revealed that such were deposited some 150,000 years ago.
Examining pollen, leaf wax and silicified plant remains known as "phytoliths" from soil samples collected at the site, the researchers determined that—at the time of the ancient human occupation—the region was heavily wooded, with the samples consistent with the types of vegetation found in humid West African rainforests.
Furthermore, the team notes, the low levels of grass pollen detected confirmed that the site was not just located in a narrow strip of forest, but lay within a dense woodland.
The findings pose questions not only about how living in rainforests might have shaped the lives of our ancient relatives, but also how they in turn shaped the rainforest around them.
"Convergent evolution shows beyond doubt that ecological diversity sits at the heart of our species. This reflects a complex history of population subdivision, in which different populations lived in different regions and habitat types," said Scerri.
"In the textbook view, we evolved in the grasslands and had to learn how to overcome different habitats gradually. Even our early forays out of Africa have been cast as 'Africa's grasslands growing' rather than humans moving into different habitats beyond Africa," she told Newsweek.
"What we have discovered in our results is that this view cannot be true, and for a very early stage, unexpectedly early, people were living in radically different ecosystems in Africa, the home of our species, and adapting to them."
It it likely, the archaeologist continued, that groups adapted to rainforests would not have frequently encountered others adapted to semi-arid savannahs and grasslands.
She added: "Ecosystem diversity and our adaptations to radically different ecosystems also likely moderated how people interacted, and how genes were exchanged—the processes that underlie evolution."
The discovery, Scerri says, opens many a new avenue of questions.
"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 the human alteration of pristine natural habitats go?" she mused.
Guédé added: "This exciting discovery is the first of a long list, as there are other Ivorian sites waiting to be investigated to study the human presence associated with rainforest."
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Update 02/03/25, 2:07 p.m. ET: This article was updated with additional information and comments from Eleanor Scerri.
Reference
Ben Arous, E., Blinkhorn, J. A., Elliott, S., Kiahtipes, C. A., N'zi, C. D., Bateman, M. D., Duval, M., Roberts, P., Patalano, R., Blackwood, A. F., Niang, K., Kouamé, E. A., Lebato, E., Hallett, E., Cerasoni, J. N., Scott, E., Ilgner, J., Alonso Escarza, M. J., Guédé, F. Y., & Scerri, E. M. L. (2025). Humans in Africa's wet tropical forests 150 thousand years ago. Nature. https://doi.org/10.1038/s41586-025-08613-y
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