Humans were living in a tropical rainforest in West Africa 150,000 years ago. The finding pushes human habitation of tropical forests much further back in time, suggesting our ancestors were able to live in a wide variety of terrains.
It has generally been thought that humans evolved in open grasslands and savannahs, says at the Max Planck Institute of Geoanthropology in Jena, Germany. Instead, she says, our ancestors were highly adaptable. āEcological diversity is at the heart of our species.ā
Scerri and her colleagues have re-excavated a site called BeĢteĢ I in Anyama, Ivory Coast. BeĢteĢ I was investigated in detail in the 1990s by a Russian-Ivorian team led by Francois YodĆ© GuĆ©dĆ© at the Institute of African History, Art and Archaeology in Abidjan, Ivory Coast. The first excavation found stone tools that indicated the presence of ancient humans, but was not able to reliably date the site.
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Accompanied by GuĆ©dĆ©, Scerri and her team visited BeĢteĢ I in March 2020, aiming to apply modern methods to determine the age of the tools and whether the site was a rainforest at the time of its occupation.
The timing, at the start of the covid-19 pandemic, was unfortunate. āWe left for five weeks of fieldwork and came back after oneā, having obtained a few samples, says at the University of Liverpool in the UK. In their absence, the area was quarried. āBy the time we could arrange to get back to the site, it had been destroyed.ā
The sediments at BeĢteĢ I were laid down in distinct layers. , now at the National Human Evolution Research Centre in Burgos, Spain, used two methods to date them: optically stimulated luminescence and electron spin resonance. Both gave similar results. āWe establish the complete chronology of the site,ā says Ben Arous. The tool-bearing layers formed over a range of dates from 146,000 to 55,000 years ago.
The researchers also studied plant remains trapped in the sediments. They found traces of large trees like African elemi (Canarium schweinfurthii) and African oil palm (Elaeis guineensis), as well as dense shrubs. Some of the plants were typical of forests that flood seasonally, suggesting BeĢteĢ I became a swamp for part of each year.
āIt is genuinely tropical forest,ā says at University College London. āAnd I think the dating is pretty convincing as well.ā
Previously, the oldest evidence of humans living in African tropical forests was ā although in other regions, like and the Philippines, people were tens of thousands of years earlier. Regardless, BeĢteĢ I is by far the oldest confirmed instance of humans living in dense forests.
The notion humans could not live in tropical forests was always dubious, says Shipton. One hypothesis argued that Homo sapiens groups could only live in tropical forests if they had reciprocal relationships with people outside. āI never found that particularly convincing,ā he says. Tropical forests have their challenges, but humans can live in the Arctic, he points out.
The question is how far back in the human story these forests go. The classic narrative is , while the ancestors of chimpanzees and bonobos ā our closest living relatives ā stayed among the trees. In this view, some humans eventually returned to the forests after millions of years on the grasslands.
In contrast, Scerri and Blinkhorn argue the lack of evidence of humans in forests has more to do with the difficulty of finding it: tropical forests often donāt preserve anything, and even when artefacts and bones do survive, the dense trees are difficult to work in. For this reason, Scerri says living in forests may be an ancient habit. āIt wouldnāt surprise me if it went a lot further back,ā she says.
Dwelling in tropical forests may have required ancient people to develop new behaviours and tools, but so far thereās no clear sign of that at BeĢteĢ I. Some of the tools are unusually large āchunkersā, Scerri says. They might be something to do with chopping down trees, she says, or perhaps for digging up tubers for food. āWe can only speculate.ā
Nature
