But the discovery's location also highlighted another surprising finding: that members of our species, Homo sapiens, were thriving in the tropics tens of thousands of years ago.
But that perspective has been changing over the past few decades. Sulawesi's ancient rock art is one of several clues that modern humans may have lived in tropical rainforests for hundreds of thousands of years. That would mean modern humans could have been living in these hot, wet regions since soon after the emergence of our species in Africa around 300,000 years ago.
Conventional wisdom held that modern humans emerged from one parent population in an East African savanna and did not encounter rainforests until around 12,000 years ago, after agriculture emerged to support survival in these climes. The lack of H. sapiens fossils from Africa's tropics appeared to support this view.
These populations periodically met and exchanged genes and ideas, but they also spent long periods apart, adapting to different ecosystems and evolving diverse traits. In this new understanding, the earliest members of our species may have evolved not just in the grassy savanna but in tropical rainforests, too.
Tropical rainforests were long considered too challenging for early members of our species to have lived in. (Image credit: Richard McManus via Getty Images)
Because rainforests come with their own set of environmental pressures, people who lived there may have evolved traits to handle those challenges. When different early human populations came together, tropical rainforest dwellers would have contributed different gene variants than populations from open savannas. The ability to adapt to a variety of environments, including rainforests, may have come in handy later, when H. sapiens spread out of Africa and into tropical Southeast Asia, including places like Sulawesi.
Rainforests are terrible for fossil hunters
Unfortunately, the highly acidic soil in rainforests degrades organic material like bones. This makes evidence of ancient humans, such as fossils, or human activities, like bone arrows or potential woven fiber baskets, exceptionally rare in rainforests.
The lack of long sediment sequences also significantly reduces the odds of finding fossils at all, said Antonio Rosas, a paleobiologist at the National Museum of Natural Sciences in Spain who has been searching unsuccessfully for such fossils in Equatorial Guinean rainforests since 2014. "To be honest, I think I gave up the possibility of finding fossils properly," Rosas said.
In Africa, stone tools reveal humans were in coastal tropical forests in what is now Kenya roughly 78,000 years ago, the tropical rainforests of what is now Equatorial Guinea from around 45,000 years ago, and the rainforests of what is now the Democratic Republic of the Congo around 18,000 years ago.
Stone tools like this one, excavated in the Ivory Coast, reveal that humans were present at the rainforest site roughly 150,000 years ago. (Image credit: Jimbob Blinkhorn, MPG)
The antiquity of these quartz tools — which were a mix of flakes and heavy-duty picks and choppers — show that early H. sapiens were capable of designing technology to survive in dense tropical forests. Dense forests weren't a barrier for early humans at that time, Ben Arous said.
Direct evidence
By analyzing the isotopes of elements found in human tooth enamel, researchers can reveal whether our distant relatives actually lived in rainforests. That's because closed, dense canopy rainforests have low levels of sunlight and high carbon dioxide, and the ratio of isotopes of elements in a person's teeth can reveal if they spent a lot of time in those conditions as a child.
Similar evidence is currently lacking from African rainforests. But the ability to adapt to many different environments, including rainforests, and the capacity to develop highly specialized traits for such environments is "what's unique about our species," Roberts said.
Without preserved DNA or fossils, anthropologists guess by looking at contemporary populations living in the tropics. Many modern-day rainforest inhabitants are small, because it may help them cool off more easily, reduce their caloric needs, and make it easier to move in dense rainforests.
There is evidence in multiple rainforest dwelling populations, including in those Gabon hunter-gatherers, of selection against specific pathogens.
Ancient DNA may be the key
But some scientists hope to someday find evidence of these adaptations in ancient DNA.
Researchers can find ancient DNA lurking in the environment by analyzing sediment cores from tropical lakes. (Image credit: Annett Junginger)
Bálint and his colleagues recently reviewed ancient environmental DNA (aeDNA) recovered from tropical environments. They found 113 studies reported aeDNA in tropical and subtropical habitats between 1998 and 2025, including 1 million-year-old aeDNA extracted from a lake in Indonesia. This DNA came mainly from nearby plants, not from ancient humans. But because people leave "millions of DNA traces" in their environment during their lifetime, human DNA should also be present and retrievable, Bálint said in the statement.
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"There is enough evidence now to justify investigating areas that used to be well off the human origins map, considered to be very far from the main stage of human evolution," Scerri said.
The question now is how much further back in time people were living in rainforests and using their resources. "We consider ourselves to really be scratching the surface," Scerri said.
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