Ancient human relatives buried their dead in caves, new theory claims

In 2015, scientists reported an astonishing discovery deep in a South African cave: more than 1,500 fossils of an ancient hominid species that had never been seen before.

The creatures, called Homo naledi, were small, with long arms, curved fingers and a brain about a third the size of a modern human. They lived around the time when the first humans roamed Africa.

Now, after years of analyzing the surfaces and sediments of the extensive underground cavern, the same team of scientists is making another rousing announcement: Homo naledi – despite their small brains – have buried their dead in tombs. They lit fires to light their way through the cave, and they marked the graves with carvings on the walls.

Lee Berger, a paleoanthropologist at the University of Witwatersrand in Johannesburg and the leader of the project, said the discovery that a small-brained hominin did such human things was profound. It suggests that big brains aren’t essential for advanced forms of thinking, he said, such as making symbols, collaborating on dangerous expeditions or even recognizing death.

“This is the ‘Star Trek’ moment,” he said. “You go out, you meet a species, it’s not human, but it’s just as complex for humans. What are you doing? That is our moment, now.”

But some experts on ancient engravings and burials said the evidence didn’t yet support these extraordinary conclusions about Homo naledi. The cave evidence found so far may have a range of other explanations, they said. For example, the skeletons may have been left alone at the bottom of the cave. And the charcoal and carvings found in the cave may have been left behind by modern humans who moved in long after Homo naledi went extinct.

“It seems that the story is more important than the facts,” said Maxime Aubert, an archaeologist at Griffith University in Australia.

Dr. Berger will describe the findings on a scientific meeting on Monday, and three articles detailing the evidence will be released by eLife magazine. The studies are currently undergoing peer review, a spokeswoman for the journal said, and those reviews will be made public when they are complete.

The remains of Homo naledi were discovered in 2013 by two South African cavers exploring the Rising Star cave. Dr. Berger organized an expedition into the complex system of chambers and tunnels, which stretches for miles underground.

“When you’re there, it’s like being on another planet,” said Tebogo Makhubela, a geologist at the University of Johannesburg who joined the team in 2014.

The researchers found a treasure trove of bones, but reaching them required risky caving. Some passageways were so tight that only smaller members of the team could get through.

All told, the researchers found bones from at least 27 individuals. It seemed Dr. Berger and his colleagues are unlikely to have just washed into the deep recesses of the cave.

In their Report 2015, the researchers suggested Homo naledi had brought the bodies there on purpose, but left them at the cave floor instead of burying them, an act archaeologists call “burial caching.” That was still a provocative claim, given how primitive Homo naledi looked. Dr. Berger and his colleagues argued that the species belonged to a lineage that split from our own ancestors more than two million years ago. While our lineage grew big and got a big brain, theirs didn’t.

At first, the scientists thought the fossils were spread evenly across the chamber floors. But when they excavated more sediment in 2018, they found two fairly complete skeletons resting in oval depressions.

And it didn’t look like the skeletons had formed the depressions by sinking into the sediment. For example, there was an orange layer of mud around the ovals, but it wasn’t in it. Around the edges, the break looked clean.

This finding, as well as other lines of evidence, led Dr. Makhubela and his colleagues now conclude that the remains were buried. “They all seem to paint the same picture,” he said.

Until now, only humans were known to bury their dead, and the oldest known human grave dates from 78,000 years ago. Homo naledi lived much earlier than that. Dr. Makhubela said their fossils were at least 240,000 years old and may be as old as 500,000 years.

The scientists also found bits of charcoal, burnt turtle and rabbit bones, and soot on the cave walls near the fossils. They suggested that Homo naledi used glowing coals to light their way into the caves and brought wood or some other fuel to burn fires. Perhaps they cooked the animals as a meal, or perhaps as a ritual.

When these new discoveries came to light, Dr. Berger decided that he should take a look for himself at one of the chambers, known as Dinaledi, which contained a supposed tomb. He had to lose 55 pounds before he could fit down the hall. Last July he was ready for the trip.

Dr. Berger went in alone and examined the fossils. As he walked out, he passed a pillar. On its side, he saw a series of hashtag-like grooves etched into the hard surface.

Getting out was harder than getting in. “I almost died,” Dr. Berger said, but he managed to escape with a torn rotator cuff. Two members of the team, Agustín Fuentes of Princeton University and John Hawks of the University of Wisconsin, waited for him in the adjoining room. Dr. Berger showed them pictures of the grooves he had made.

The two scientists immediately went to their phones and pulled out the same image: an engraving in a cave in Gibraltar made by Neanderthals. It was strikingly similar to what Dr. Berger had just seen.

Based on the growing number of fossils scientists are finding in Rising Star, Dr. Fuentes, it appears that Homo naledi may have visited the cave for hundreds of generations, trekking together into the dark depths to bury their dead and mark the spot. with art.

This kind of cultural practice, he argued, would have demanded some sort of language. “You can’t do that without complicated communication,” he said.

But María Martinón-Torres, the director of Spain’s National Research Center of Human Evolution, said such speculations were premature based on the evidence presented so far. “Hypotheses should be built on what we have, not what we suspect,” she said.

Dr. Martinón-Torres considered funerary caching more likely than burials, pointing out that the oval depressions did not contain complete skeletons that were completely aligned. If Homo naledi had brought the bodies into the cave and left them at the bottom of the cave, the bones could have separated as the bodies disintegrated. “Still, I think the possibility of burial caching with this antiquity is already staggering,” she said.

“I am very optimistic that they have burials, but the jury is still out,” said Michael Petraglia, the director of the Australian Research Center for Human Evolution. Dr. Petraglia wanted to see a more detailed analysis of the sediment and other types of evidence before judging whether the ovals were burials. “The problem is that they are ahead of science,” he said.

And Paul Pettitt, an archaeologist at the University of Durham in England, said it’s possible Homo naledi didn’t bring the bodies in, either for caching or burial. The bodies may have washed ashore. “I am not convinced that the team has shown that this was an intentional burial,” he said.

As for the carvings and the fires, experts said it wasn’t clear Homo naledi was responsible. It was possible that they were the work of modern humans who entered the cave thousands of years later. “The whole thing is inconclusive to say the least,” said João Zilhão, an archaeologist at the University of Barcelona.

One way to test these possibilities would be to take samples of the engravings, charcoal and soot to estimate their age.

Dr. Hawks said these experiments were on the team’s to-do list, but could take years because there were so many samples to test. Instead of waiting, Dr. Hawks, the team decided to present its data now and start a conversation with other scientists about how to proceed.

“For me, it’s much more important to document and share than to be right,” said Dr. Hawks.

If the researchers are right, the findings will challenge some of the key assumptions about human evolution. Humans and Neanderthals have huge brains compared to those of earlier hominids, and paleoanthropologists have long assumed that the larger size brought great benefits. There should be an advantage to outweigh the problems, evolutionarily speaking, of having a big brain. They need a lot of extra calories to fuel, and a baby’s big head puts mothers at risk of dying in childbirth.

An advantage of a large brain can be complex thinking. Neanderthals left an impressive record of cooperative hunting, tool use and other skills. And modern man makes symbols, uses language, and performs other brainteasers.

If a hominid like Homo naledi could make engravings and dig graves, that would mean brain size isn’t essential for complex thinking, said Dietrich Stout, a neuroscientist at Emory University who was not involved in the studies.

“I think the interesting question going forward is what exactly big brains are needed for,” said Dr. Naughty.