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

In 2015, scientists reported a startling discovery from the depths of a cave in South Africa: more than 1,500 fossils of an ancient, never-before-seen species of hominin.

Called Homo naledi, the creatures were short, with long arms, curved fingers, and a brain about one-third the size of modern humans. They lived at the time when the first humans roamed Africa.

Now, after years of analyzing surfaces and sediments in the evolving underground cavern, the same team of scientists is making another delightful announcement: Homo naledi—despite their small brains—buried their dead in graves. They lit bonfires to light their way down the cave, and marked the graves with inscriptions on the walls.

The discovery that small-brained hominins did human-like things was profound, said Lee Berger, a paleoanthropologist at the University of the Witwatersrand in Johannesburg and leader of the project. He suggests that big brains are not necessary for sophisticated types of thinking, such as making symbols, cooperating on dangerous expeditions, or even recognizing death.

“This is a ‘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 do you do? This is our moment now.”

But a number of experts in ancient inscriptions and burials said the evidence did not yet support these unusual conclusions about Homo naledi. They said the cave evidence found so far could hold a host of other explanations. The skeletons might have been left on the cave floor, for example. The charcoal and inscriptions found in the cave may have been left by modern humans who entered it long after the extinction of Homo naledi.

“The narrative seems to be more important than the facts,” said Maxime Aubert, an archaeologist at Griffith University in Australia.

Dr. Berger will describe the results in a Scientific meeting On Monday, the journal eLife will publish three papers detailing the evidence. A spokeswoman for the journal said the studies are currently undergoing peer review, and those reviews will be made public when completed.

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

“When you’re there, it’s like you’re on a different planet,” said Tibogo Makhopela, a geologist at the University of Johannesburg who joined the team in 2014.

The researchers found a wealth of bones, but getting to them took some risk. Some of the passages were so narrow that only the younger members of the team could cross.

Finally, the researchers found the bones of at least 27 individuals. It seemed unlikely to Dr. Berger and his colleagues that they would simply wash into the deep recesses of a cave.

in their 2015 reportResearchers have suggested that Homo naledi deliberately brought the bodies there but left them on the cave floor instead of burying them, an act archaeologists call “funerary storage.” This was still a provocative claim, given how primitive Homo naledi had come to be. Dr. Berger and his colleagues have argued that the species belongs to a lineage that split off from our ancestors more than 2 million years ago. While our lineage grew tall and acquired a large brain, theirs did not.

At first, scientists thought the fossils were spread evenly across the chamber’s floors. But when they dug more sediments in 2018, they noticed two more or less complete skeletons inside the oval depressions.

Nor is it as if the skeletons formed the depressions by sinking into the sediment. For example, an orange layer of clay surrounded the ovals, but was not inside them. Along the edges, the crack looked clean.

This discovery, along with other lines of evidence, led Dr. Mkhupila and his colleagues to conclude that the remains had been buried. “They all seem to paint the same picture,” he said.

Until now, only humans have been known to bury their dead, and Oldest known human grave It dates back 78,000 years. Homo naledi lived much earlier than that. Dr. Makhopela said that their fossils are at least 240,000 years old and could be as old as 500,000 years.

Scientists also found pieces of charcoal, burnt bones of turtles and rabbits, and soot on the walls of caves near the excavations. They suggested that Homo naledi used glowing coals to light their way into the caves and brought wood or some other fuel to light the fires. They may have cooked the animals as a meal, or perhaps as a ritual.

When these new discoveries came to light, Dr. Berger decided he had to take a look for himself in one of the rooms, known as Dinaledi, containing an alleged tomb. He had to lose 55 pounds before he could make it through the aisle. This past July, he was ready for the trip.

Dr. Berger went alone and examined the fossils. As he made his way, he passed one of the shafts. For his part, he noticed a set of hashtag-like grooves etched into the solid surface.

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

The two scientists immediately went to their phones and snapped the same photo: Carving in a cave in Gibraltar made by Neanderthals. It was strikingly similar to what Dr. Berger had just seen.

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

He argued that this type of cultural practice requires language of some kind. “You can’t do that without some complex connections,” he said.

But Maria Martinón Torres, director of Spain’s National Research Center on Human Evolution, said such speculation was premature based on the evidence presented so far. She said, “Hypotheses should be based on what we have, not on what we guess.”

Dr. Martinón Torres considered spools more likely in funeraries than in burials, noting that oval depressions do not contain complete skeletons in complete alignment. If Homo naledi brought carcasses into a cave and left them on the cave floor, the bones might separate from the carcasses. “Nevertheless,” she said, “I think the possibility of funerary caches of such antiquity is actually quite startling.”

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

It’s possible that Homo naledi did not bring in the bodies, either for temporary storage or burial, said Paul Pettit, an archaeologist at Durham University in England. The bodies may have been washed. “I’m not convinced the team has established that this was intentional burial,” he said.

As for the engravings and the fires, experts said it wasn’t clear if Homo naledi was responsible. It could have been the work of modern humans who entered the cave thousands of years later. “It’s all unconvincing, to say the least,” said Joao Zelhao, an archaeologist at the University of Barcelona.

One way to test these possibilities is to collect samples of petroglyphs, coal, and soot to estimate their age.

Dr. Hooks said these experiments were on the team’s to-do list but could take years because there were so many samples to test. Rather than wait, Dr. Hooks said, the team decided to present its data now and start a conversation with other scientists about how to move forward.

“For me, documentation and sharing are much more important than being right,” said Dr. Hooks.

If the researchers are right, the findings will challenge some of the most important assumptions about human evolution. Humans and Neanderthals had huge brains compared to those of early hominins, and paleoanthropologists have long hypothesized that greater size brought significant benefits. There must be some upside to overcoming the evolutionary problems of having big brains. They require a lot of extra calories to fuel them, and the large heads of infants put mothers at risk of dying in childbirth.

One of the benefits of a big brain may be complex thinking. Neanderthals left behind an impressive record of cooperative hunting and the use of tools and other skills. Modern humans make symbols, use language, and perform other feats of mental ability.

If hominins like Homo naledi could make carvings and dig graves, that means brain size isn’t necessary for complex thinking, said Dietrich Stout, a neuroscientist at Emory University who was not involved in the studies.

“I think an interesting question going forward is what exactly do big brains need,” said Dr. Stout.