A 15-meter deep trench in the Ivorian soil has provided several new pieces of the puzzle to human history. In the 1980s, Soviet researchers excavated a ditch in the West African rainforest, where several Stone Age finds were made. However, the technology at the time did not allow for an effective dating of the objects. So in 2020, during the beginning of the pandemic, an international research team returned to the site.
There is a stream nearby, which is in perfect size for humans. It's not a large, scary one with crocodiles and hippos, but large enough for people to easily get their water there, says Eleanor Scerri at the German Max Planck Institute.
Fantastic preservation conditions
What's special about the site is also that it's a rainforest and, according to climate models, has been so for hundreds of thousands of years. The sediment layers contained stone tools. With the help of modern technology, the oldest could be dated to 150,000 years. Furthermore, the researchers' sediment samples could confirm that it was indeed a rainforest at the site at that time.
We have fantastic preservation conditions, to the extent that we could see the pollen-containing anthers, which plants release directly. So we know that those plants were locally present, says Scerri.
At the same time, they didn't find much evidence of grass, which would have been there if it were smaller forest clearings or gallery forests following a stream.
So we know it's a deep, dense jungle and that people lived there. Moreover, the stone tools are unusual.
Previously, researchers have believed that rainforests were a kind of barrier for early humans. The finds are more than twice as old as the previous oldest evidence, which also comes from Southeast Asia.
Life for early humans was very different there compared to living on more open grasslands.
You see other people and animals from a distance. In the rainforest, you must have other hunting methods, she says, adding that modern hunter-gatherer people in rainforests use nets and traps.
Returned to the site
Scerri believes that the rainforest people were probably separated from their cousins on the savannah.
Humans are very adaptable, but also specialists. Once you've adapted to an area, you tend to stay there.
The researchers found finds on the excavation site that were significantly younger, 20,000 years old. There are also finds dated to the younger Stone Age (10,000–2,000 before our time), and even younger pottery shards.
So people have returned to this site again and again. Probably because it's a pretty nice place, she says.
No Eden's paradise
Eleanor Scerri argues that the research contributes to rewriting the map of human origins. The oldest humans are believed to have emerged 300,000 years ago. The prevailing image has been that humans emerged in a specific type of landscape in East Africa, "almost like an Eden's paradise". But Scerri and her colleagues believe that humans may have emerged in several places in Africa in different ecosystems, before eventually migrating from the continent.
The image of humans initially living in harmony with nature is also likely to be much more complex – that early humans probably influenced animals and nature through their presence.
Now we know that humans didn't avoid the African rainforests. It gives us some context for understanding behaviors that go beyond life in Africa – that we have a unique adaptability that helps us move into all the different environments that exist in the world today. It's part of the story of how we eventually ended up on Antarctica and the moon, she says.
The international research team has examined sediment layers and finds from tools created by humans from an excavation site in Côte d'Ivoire.
The researchers have used electron spin resonance and luminescence dating (OSL) to date the tracks. It has been complemented with analyses of leaf axis isotopes, phytoliths, and pollen found in the sediments to determine what type of vegetation was present at the site.
The fact that the tools were found in the rainforest 150,000 years ago shows that the jungle was not a barrier for early humans. The study is published in the journal Nature.
