The stone tools at Bété I are believed to have been created by Homo sapiens more than 100,000 years ago. © Jimbob Blinkhorn, MPG
Our species has been living in tropical forests for a surprisingly long time.
While these environments had previously been thought of as a barrier for our ancient relatives, new research suggests that some Homo sapiens were living in them from at least 150,000 years ago.
Ancient humans might have been living in rainforests for more than twice as long as expected.
Stone tools found in Cote d’Ivoire suggest that some Homo sapiens were living in the rainforests of western Africa over 150,000 years ago. This is tens of thousands of years earlier than the previous record for rainforest-dwelling humans.
Dr Eslem Ben Arous, the lead author of the study published in the journal Nature, says that the findings appear to overturn the idea that dense rainforests were a barrier to early human movements.
“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,” Eslem explains.
“Our research pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate.”
Professor Chris Stringer, an expert in human evolution who wasn’t involved in the study, says that the new finding is a “surprising” twist in the tale of our species.
“We have evidence of such adaptations in Homo sapiens outside of Africa from more than 40,000 years ago, but so far nothing definitely as old within Africa,” says Chris.
“While we have to remain slightly cautious of these results in the absence of any fossil remains of Homo sapiens found at the site, it seems very likely that these tools were made by early members of our species.”
Rainforests appear to have been more important in the evolution of our species than realised. © Fabian Plock/ Shutterstock
Rainforests are some of the most biodiverse places on Earth, with a vast array of resources including plants and animals. Until relatively recently, however, it was believed that ancient humans couldn’t cope in these environments.
For many years, researchers thought that early members of our species would have preferred to live in grasslands and more open landscapes. They argued that it would have been easier for these humans to find food and navigate in these environments rather than in dense tropical forests.
This idea stuck around, in part, because of the difficulty of investigating human evolution in rainforests.
“The visibility and accessibility of sites in tropical forests have been a limiting factor in the study of prehistory in these regions,” Chris says. “This is particularly true where regions are more remote, the forests are denser and there are fewer transport networks to reach them.”
Not only are these areas difficult for scientists to access, but the humid conditions of tropical forests don’t lend themselves to preserving fossils. The fossils which have been found are generally preserved in caves where they are protected from the hot and humid environment outside.
Caves such as Tam Pà Ling in Laos and Lida Ajer in Indonesia have preserved fossils that act as important milestones as Homo sapiens migrated around the world. The remains also tell us other information about these ancient humans, such as their omnivorous diet.
Bété I has been lost to mining following the recent excavation, but scientists are hopeful similar sites in Africa are still to be found. © Jimbob Blinkhorn, MPG
Another promising tropical site is Bété I, which is located around 20 kilometres north of Abidjan in Cote d’Ivoire.
Bété I was first excavated in the 1980s by a team of researchers from Cote d’Ivoire and the Soviet Union. They discovered a variety of stone tools among the layers of sediment, but dating techniques at the time couldn’t reveal their age.
But recently, interest in the site has been reignited after climate models showed that a rainforest might have been present at Bété I for over 100,000 years. A new team of researchers teamed up with Professor Yodé Guédé, who was a member of the original expedition, to re-explore the site.
Using more modern dating techniques, the researchers were for the first time able to accurately date the different layers of Bété I. Larger stone tools, such as picks, were found in a layer dated to around 150,000 years ago, while more delicately shaped tools were only about 20,000 years old.
Sediment from the layers with tools was examined further for signs of the plant life that was alive at the time. Pollen from trees and palms such as African elemi and oil palm accounted for up to 80% of the samples.
Along with analysis of other plant material, this suggests that the humans living at Bété I were living in a wet tropical forest. This is a type of environment that includes rainforest, swamp forests and riparian forests near bodies of water.
The researchers can't be certain exactly which type of tropical forest it is, though rainforests persist in the region today.
Unfortunately, further investigation of the site, to resolve questions like these, is now almost impossible. The original tools discovered by the 1980s expedition have been lost, while Bété I itself has now been destroyed by mining.
Despite this setback, the team are confident that more early signs of Homo sapiens living in rainforests will be uncovered in the coming years.
Museum science is helping to answer where, when and how humans evolved.
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