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. 鈥淓cological diversity is at the heart of our species.鈥�
Scerri and her colleagues have re-excavated a site called Be虂te虂 I in Anyama, Ivory Coast. Be虂te虂 I was investigated in detail in the 1990s by a Russian-Ivorian team led by Francois Yod茅 Gu茅d茅 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 Gu茅d茅, Scerri and her team visited Be虂te虂 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. 鈥淲e left for five weeks of fieldwork and came back after one鈥�, having obtained a few samples, says at the University of Liverpool in the UK. In their absence, the area was quarried. 鈥淏y the time we could arrange to get back to the site, it had been destroyed.鈥�
The sediments at Be虂te虂 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. 鈥淲e establish the complete chronology of the site,鈥� 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 Be虂te虂 I became a swamp for part of each year.
鈥淚t is genuinely tropical forest,鈥� says at University College London. 鈥淎nd I think the dating is pretty convincing as well.鈥�
Previously, the oldest evidence of humans living in African tropical forests was 鈥� although in other regions, like and the Philippines, people were tens of thousands of years earlier. Regardless, Be虂te虂 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. 鈥淚 never found that particularly convincing,鈥� 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 鈥� our closest living relatives 鈥� 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 don鈥檛 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. 鈥淚t wouldn鈥檛 surprise me if it went a lot further back,鈥� she says.
Dwelling in tropical forests may have required ancient people to develop new behaviours and tools, but so far there鈥檚 no clear sign of that at Be虂te虂 I. Some of the tools are unusually large 鈥渃hunkers鈥�, Scerri says. They might be something to do with chopping down trees, she says, or perhaps for digging up tubers for food. 鈥淲e can only speculate.鈥�
Nature
