Ancient human relative Homo naledi used fire, cave finds suggest

South African paleoanthropologist and National Geographic explorer Lee Berger describes finding soot-covered walls, charcoal fragments, burnt antelope bones and rocks arranged like hearths in the Rising Star cave system, where nine years earlier the team discovered the bones of a new member of a human family, Homo star.

The control of fire is considered a crucial milestone in human evolution, providing light for navigation in dark places, enabling activity at night and leading to cooking food and subsequent increase in body mass. When exactly the breakthrough occurred, however, is one of the most contested questions in all of paleoanthropology.

“We’re probably looking at the culture of another species,” said Berger, who bucked scientific convention by reporting the findings not in a peer-reviewed journal but in a press release and Carnegie Science Lecture at the Martin Luther King Jr. Memorial Library in Washington on Thursday. In an interview with The Washington Post, Berger, a professor at the University of the Witwatersrand in Johannesburg, said the official documents were under review and added: “There are a series of big revelations coming out in the next month.”

He emphasized that his team’s findings this summer answer a critical question raised when they announced the initial find of 1,500 fossil bones: How this ancient species found its way into a cave system about 100 to 130 feet underground, a place that is damn hard to reach and, in his words, “terrifyingly dangerous”?

The research team now believes that H. naledi used small fires in chambers in the cave system to light its way. Berger based the claim in part on his personal journey through the cave’s narrow passages, which required him to lose 55 kilograms.

He further argues that the use of fire by a human relative with a brain slightly larger than a large orange upsets the traditional story of our evolution. For years, experts have portrayed evolution as a “ladder” that moves upward toward species with larger brains and greater intelligence, while leaving smaller-brained species to die out.

But evidence is mounting that the process may have been messier than previously thought, a view that would be supported if indeed this smaller-brained contemporary of the early Wise man was advanced enough to use fire.

Berger’s lecture, accompanied by photographs from the cave but not carbon dating and other traditional scientific methods, drew criticism, as did some of his previous claims about H. naledi fossils.

“There is a long history of claims about the use of fire in South African caves,” said Tim D. White, director of the Center for the Study of Human Evolution at the University of California, Berkeley, who is a former critic of Berger. “Any claim of controlled fire will be met with considerable skepticism if it comes via a press release rather than data.”

Past reports of early human use of fire, even those accompanied by scientific evidence, have proven controversial. In 2012, archaeologists using advanced technology reported “unequivocal evidence in the form of burnt bones and cremated plant remains that burning took place at Wonderwerk Cave” in South Africa approximately 1 million years ago. Critics questioned this age estimate, and scientists revised the date back to at least 900,000 years after using a sophisticated technique called cosmogenic nuclide dating.

White said rigorous studies must date both the fire evidence and the H. naledi bones if Berger’s team is to prove they both come from the same period. Other studies should show not only the presence of fire, but also its controlled use. Testing will need to establish that the material thought to be soot is actually soot and not discoloration caused by chemicals or other factors.

Berger acknowledged that one of the big challenges for him and his colleagues will be dating the materials they have found. So far, they said the H. naledi bones date back to between 230,000 and 330,000 years ago, although Berger emphasized that those dates should not be seen as the first or last appearance of the species.

White seemed most skeptical about the lack of stone tools found in the caves. He said archaeologists would expect to find thousands of stone tools at a site where human relatives used fire for light and cooking.

“I will tell you at this stage that there are no stone tools that we have found in the presence of a hearth,” Berger said in the interview. “It’s a strange thing.” However, he told the Carnegie Science lecture audience, “Fires don’t start spontaneously 250 meters away in a damp cave, and animals don’t just wander into the fire and burn themselves.”

He said stone tools were found in the general landscape outside the caves. He also rejected criticism that what the team found did not constitute evidence of an ancient hearth.

“We found dozens of outbreaks, not just one,” Berger said when asked about the evidence during the interview. “It’s 100 percent. No doubt. … Now we’re entering a phase where it’s moving from just bones to a rich understanding of the environment they lived in.”

Berger previously ran into controversy when initially announcing the discovery of H. naledi, when he suggested that these ancient relatives had deliberately used the caves as a place to lay their dead. Despite the debate, Berger repeated the claim several times during the lecture, admitting that it “may not have been very well received by most of the academy.”

Other researchers said that while much testing remains to be done, the latest findings at Rising Star are impressive.

“I think it’s great. It seems very convincing,” said Richard W. Wrangham, a professor of biological anthropology at Harvard University and author of the 2009 book.Ignite: How Cooking Made Us Human.”

“Of course it’s fascinating because of the small and generally mysterious nature of these people.”

Wrangham said that when the discovery of H. naledi was announced, he was discussing the dark caves where the bones were found with one of Berger’s colleagues and remarked, “Surely that must mean they had light.”

Still, Wrangham said he remains puzzled by one question: “How did they put up with the smoke? Was there a current that pulled the smoke out of the cave?’

Wrangham said he was willing to take Berger’s word for the use of fire based on the early evidence. He said the strongest evidence for early control of fire, however, comes from an archaeological site in Israel called Gesher Benot Ya’aqov, where experts say early human relatives used fire cook fish about 780,000 years ago.

During the lecture, Berger also shared vivid descriptions of some of the 50 H. naledi individuals the team found.

He describes the fossil bones of a hand “curled in a death grip”; the skull of a child found sitting on top of a shelf in the rock; and the skeleton of another child tucked into a niche in one of the chambers. The dramatic images required an equally dramatic journey through a crevice in the dolomite that tapers to just seven inches and requires extreme contortion of the explorer’s body.

“You’re basically kissing the earth,” said Keneilo Molopyane, a 35-year-old researcher at the University of South Africa’s Deep Human Journey Research Center. The explorers, she continued, were coming out on a dangerous ridge about 65 feet above the cave floor. It’s pitch black inside, with ‘bats flying by on either side of you. If you fall, you belong in the cave.”

The reward, however, is a feeling Molopyane remembers vividly from his first descent into the cave system: “Oh my God. I’m the first person to see these remains in I don’t know how many thousands of years and now I’m touching them.”

Berger said about 150 scientists from around the world are involved in the effort to excavate, date and study the remains and artifacts found in the Rising Star cave system.

Asked to speculate on the interactions and possible conflicts that may have occurred between H. naledi and H. sapiens, Berger replied: “Everything you just asked, within the next 36 months we will have answers.”