And Paul Pettitt, an archaeologist at Durham University in England, said it was possible that Homo naledi did not bring the bodies in, either for caching or burying. The bodies might have washed in. “I’m not convinced that the team have demonstrated that this was deliberate burial,” he said.

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

One way to test these possibilities would be to collect samples from the engravings, charcoal and soot in order to estimate their age.

Dr. Hawks said that these experiments were on the team’s to-do list but could take years because there were so many samples to test. Rather than waiting, Dr. Hawks said, 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 to share than it is to be right,” Dr. Hawks said.

If the researchers are right, the findings will challenge some of the most important assumptions about human evolution. Humans and Neanderthals have huge brains compared with those of earlier hominins, and paleoanthropologists have long assumed that the bigger size brought major benefits. There would have to be some upside to outweigh the problems, evolutionarily speaking, of having big brains. They require a lot of extra calories to fuel, and an infants’ large heads put mothers at risk of dying during childbirth.

One benefit of a big brain might be complex thinking. Neanderthals have left behind an impressive record of cooperative hunting, tool use and other skills. And modern humans make symbols, use language and perform other feats of brainpower.

If a hominin like Homo naledi could make engravings and dig graves, it would mean brain size was not essential to complex thought, said Dietrich Stout, a neuroscientist at Emory University who was not involved in the studies.

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