28

“All right, then, what is its name?” Several of us were sitting around the breakfast table when Steve Churchill asked the question. It was time. With sediba, we had batted around ideas, listening to the sound of them and shooting them down, until we came to one that seemed to fit.

Everyone looked at me. “I was thinking of naledi,” I said. “It’s Sesotho for ‘star’—Rising Star. And we need a name for the 101 Chamber. I think we should call it the ‘Dinaledi Chamber’—that’s plural—it means ‘stars.’ ”

The others agreed. “Homo naledi,” Steve said. “I like the sound of it.”

Now we had named the creature that the bones represented—a new species, never discovered before. This declaration spun out a new string of mysteries, though, some familiar to us after the work on sediba. We already had proposed, just six years ago, that here in the Cradle, after more than 70 years of intensive exploration for hominin ancestors, we were adding a new species to the picture of human evolution. Now, it seemed, we had a second new species, represented by fossils in great abundance. Missing one species could be chalked up to bad luck. But missing two species started to look like a pattern. Only a tiny part of Africa had been subjected to the sort of intense paleoanth​ropological exploration that had brought sediba and naledi to view. What more could be out there waiting for us to find?

That question would have to wait, because now our team was fully occupied with another: How did the bodies get into the cave?

TOWARD THE END OF the workshop, Eric Roberts, Paul Dirks’s young colleague, arrived to help with the geological study of the site. Eric had come to collect more data from inside the cave, helping us understand how the Rising Star system was put together. Only by knowing more about the geology of the cave would we be able to establish how the fossils got into the Chamber. It had become our habit when starting to work with other scientists to size people up, literally, to see if they might be able to fit down the Chute. Eric had the right skill set and, importantly, the right physique. He would be our geologist inside the Dinaledi Chamber.

Our team had found soft chunks of reddish orange clay interspersed in some areas with the fossils, their color standing out in comparison to the dark brown sediment. Eric determined that the orange clay was in the Chamber first, before the naledi fossils were deposited there. Pieces of it still adhere to the walls of the Chamber, he observed, and as the fossil deposit formed, bits of the orange clay fell into the younger sediments. We had found traces of tiny rodents in the sediments around the fossils—mostly remnants of enamel from rodent incisors—but that was the only evidence of any kind of animal remains within the sediment where we found Homo naledi. Now Eric determined that these tiny pieces had probably come from the orange clay and had nothing to do with the hominin fossils at all.

The orange clay chunks told us something more. If the sediments had been carried in by water, they would have formed as a single muddy mass. Distinct chunks of the soft orange clay would never have lasted—they would have dissolved. The Chamber may have seen a gentle rise in the water table, but never a violent rush of water capable of carrying bones along with it.

Everyone on our excavation team had found the Dinaledi Chamber a silent place. Listening to the descriptions of people who had been inside, those of us on the surface had begun to imagine it as if it were a time capsule, virtually unchanged from the moment the unlucky hominins had ended up inside. But the geology suggests that the silence today is misleading. Dinaledi hadn’t been a peaceful place at all. It had a dramatic history. First, the Chamber had been partially filled with the orange clay material. Then, that was mostly removed—possibly washed out in the distant past, or slowly percolated downward through small drains in the floor of the Chamber. Later, the hominin remains came into the cave. These were slowly covered by a fine, chocolate brown sediment that made up the majority of the fossil deposit we had dug.

But there was more. The naledi fossils were embedded in the brown sediment that made up the floor of the Chamber, but Eric found clear evidence that this material had once extended much farther up the walls. In some areas, dripping water had created small deposits of calcium carbonate—flowstones—on top of the brown sediment floor. Some of the flowstones were now clinging to the walls of the Chamber, many inches above the current floor level, their edges broken where they had grown too thin to support their own weight. The conclusion was clear: The surface of the floor containing the hominin fossils was once higher. Floor drains were still at work, and sediment had been seeping down out of the Chamber, possibly carrying bits of Homo naledi with it.

During our excavation work so far, we had not given much attention to the Landing Zone, the area of the Chamber directly below the Chute. The team had found a few fossils in the area, including one tooth, but we had not excavated there. Eric found the area to be of key importance. A series of flowstones clung to the wall, tracing a record of ancient surfaces where water had dripped. Beneath and between them were remnants of sediment with bits of fossil bone. This area, the highest in the Chamber, seemed to represent a layer of the site that was now mostly gone, a layer that had once been above the present floor of the Chamber. This discovery made it very unlikely that the hominins could have arrived all at once in a single event.

We had seen other clues suggesting that the bones had entered the Chamber over some period of time and not as the result of a single mass death. For instance, as the team slowly worked down through the Puzzle Box, they had followed the path of a single femur downward through the sediment. For more than a week, they continued to excavate, never reaching the bottom of this bone, because it was vertically implanted, surrounded by hundreds of other bone fragments with a more horizontal orientation. Just as our team had to take the puzzle apart in a certain order, it seemed likely that the bones had come into the Chamber in a sequence, over time, and not all at once.

Jan Kramers had been working in his lab at the University of Johannesburg, analyzing the chemistry of the sediments around the fossils, while Eric Roberts and Paul Dirks were studying the particles and mineral fragments in the sediments. To most of us who had gone inside Rising Star, the floor of the cave, with its nondescript brown color, was just made of dirt. From one chamber to another, it might vary a bit in color and texture—in some places more rocky, in others more fine—but it was still just dirt. But the casual eye misses a complex landscape of different minerals, arrayed in pieces of different sizes. Under a microscope, these tiny mineral fragments began to show how the Dinaledi deposit had formed.

Jan found that the Dinaledi sediment samples were made up of tiny fragments of minerals rich in potassium and aluminum oxide, produced by slow weathering of the dolomite as the cave continued to form. These particles had an angular shape, with sharp edges that showed they could not have moved very far.

But when the team looked at the sediment from the floor of the Dragon’s Back chamber, they found a very different picture. That sediment was rich in silicon, and it was packed with many noticeable grains of quartz—particles that must have come from the outside environment above the cave. Even though they were microscopic, the bigger pieces had rounded edges, as if they had rubbed against each other as they were carried some distance. Some of those quartz particles probably came out of the breccia that was exposed in the Dragon’s Back chamber, a part of the cave whose geology both Eric and Paul had been able to examine closely.

Paul found that this part of the cave, including the tight squeeze known as Superman’s Crawl, had changed over time. At some point in the past, large piles of material had spilled into this area from outside the cave, transforming a larger cavern into the tight passages we now encounter. Superman’s Crawl, in other words, may not have been there when Homo naledi encountered the cave. One of the fills sloped all the way into the Dragon’s Back, and it contained fossils of other animals. This area looked a lot more like other caves in the Cradle, and although we could not yet be sure, it seemed possible that this part of the cave might have been easier for naledi to get through than it is for us today.

As we quickly learned, though, “easier” does not necessarily mean “very easy.” The sediment samples from the Dinaledi Chamber and Dragon’s Back were very different from each other. Particles were reaching the Dragon’s Back from outside the cave, tumbling some distance down through the caverns, but that sort of particle did not reach the Dinaledi Chamber. The Chamber was isolated, and always had been, so the soil around the hominin bones was distinctly different from any outside the Chamber. The ceiling of the Chamber was a solid layer of chert, with no substantial gaps or cracks that would allow a body to enter. Superman’s Crawl may have been differently configured, but the Dragon’s Back itself must have been in place before the bodies arrived, sealing in the Dinaledi Chamber from the outside environment, so that it was accessible only through small and indirect passages. The Chute that our team had been using was the only one of those passages large enough for anyone to get into the Chamber, now and in the age when the fossil remains were deposited.

People have often asked us whether some other entrance to the Dinaledi Chamber might have existed in the past. Another opening into the Chamber would have given naledi an easier route than the one our team was using, they suggest. We cannot rule out that some other entrance existed, and our geological team is still working to understand the entire cave system. But there is one thing we can say for sure: If there was any other entrance to the Chamber when naledi lived, it must have been just as hard to access as the Chute is for us now. If it had ever been easy to enter, there would be signs of other animals and larger sediment particles in the Chamber. The difficult entry helps to explain the evidence we have found.

AS THE TEAM OF anatomical specialists prepared to leave the workshop, heading off to finish their research papers, an even more detailed process of study began to unfold, bone by bone. Lucinda Backwell is what you might call a specialist in paleoforensics. The name for her work is taphonomy—the study of how fossil bone is changed by natural and artificial processes after an animal’s death. She and her colleagues study fossils intensely, often poring over their surfaces using high-powered microscopes, and then they go a step further and analyze what natural agents created any tiny markings or patterns of coloration they have found. In other words, she uses science to explain what is barely visible to the eye. Lucinda had found amazing things in the fossil deposit at Malapa, including parts of plants and insects, and those findings had prompted her to study the role of termites in the formation and taphonomy of fossil sites in southern Africa.

Some of the fossil sites in the Cradle represent thousands of years of leftovers from the meals eaten by large cats, especially leopards. These cats move their prey to trees to avoid the attention of lions and hyenas—and in the Cradle landscape, trees are often found near the openings of caves. Cats leave signs of chewing on bones—tooth marks and puncture marks. Likewise, hyenas create impressive fractures and even swallow and digest pieces of bone, leaving behind fossil bones etched with stomach acid. It’s an impressive sight to see a hominin fossil that has been ravaged by meat-eaters. In the Ditsong Museum in Pretoria, a fragment of skull from Swartkrans bears two puncture marks, an inch apart. The bone is displayed alongside the jaw of a leopard to show how the canine teeth match the holes perfectly.

Lucinda examined the Dinaledi bones under her microscope. Not a single one of them had any trace of a tooth mark, a puncture mark, or any other mark produced by carnivores or large scavengers. The bones preserved tiny marks from snails, which had scavenged their surfaces over the millennia to gather up calcium for their shells, but nothing from any large mammal.

At the same time, Patrick Randolph-Quinney, a forensic anthropologist, examined the breakage patterns of the bones. Fresh bones break like green tree branches, splintering along the grain of the bone tissue. When carnivores eat a carcass, that’s exactly how the bones break. The strength of bone comes from its mineral content—calcium and phosphorus mostly—held together with a framework made from a protein called collagen, which strengthens the bone much like steel rebar strengthens concrete. After an animal dies, its bones slowly lose the strength provided by that protein. Eventually the bones break differently, often across the grain and in short blocks, like toppled pillars from an ancient Greek temple.

The Dinaledi bones were broken—very few of them were anywhere near complete. But across the entire collection, not a single break showed the evidence of a fresh, green fracture. In other words, these bones broke long after the individuals died. As they lay there, their collagen slowly deteriorated. Sediment piled above them and trickled through, and the bones became brittle and fractured. There was no sign of a break from a carnivore, no sign of a sudden cave-in trapping them, no sign of an individual falling into a death trap. The geology of the cave itself broke these bones long after the individuals had died.

We thought long and hard about the possibility that water had moved or accumulated the bones. The Dinaledi Chamber is not far above the water table today, and the sediments contain so much moisture that we must allow the bones to dry out slowly after we excavate them. The Malapa situation was on our minds—we knew that hominins might have entered a cave seeking water. But if the Chamber had been a pool of water in the past, those discrete chunks of red-orange clay would never have remained in the sediment. The sediment from the Dinaledi Chamber was not like the sediment around the Dragon’s Back, which showed us that water did not flow downhill into the Dinaledi Chamber. We found so many body parts in perfect anatomical positions—including the complete hand and foot, several other partial hands and feet, and part of the leg of a child. That told us that these body parts must still have been enclosed in soft tissue, held together by tendons and ligaments, when they reached their current positions. If water had carried them through the cave, it would also have carried larger particles of sediment from the same area. We found the skeletons of young children, nearly every body part. These fragile bones would never have survived if a surge of water had carried them here.

At Malapa, we had proposed that the cave was a death trap—animals seeking water during a dry season might have come a bit far over the edge and fallen. The broken bones of the sediba individual provided solid evidence for it. Those hominins might have become trapped, one at a time, as they fell deeply from the surface. But Dinaledi was different. The sediments ruled out that the Chamber had ever been open to the outside. For naledi to fall into that Chamber by accident, they would first have had to delve deeply into the dark zone of the cave. We may not know for sure that they entered the Chamber through the Chute, but even if there was another entrance, it kept other animals out. In our view, the easiest way to explain the lack of other animals was that the Chamber was far enough into the dark, labyrinthine zone of the cave to exclude them.

Had naledi intentionally come into the depths of this cave? Back in November 2013 the idea had seemed inconceivable. Now as we pondered the strange lack of fauna and the richness of hominins at the site, it was almost inescapable. Like Sherlock Holmes, we had eliminated all the likely possibilities of how these hominin remains got into the Chamber. None of the explanations that worked for other caves in the Cradle worked for Dinaledi. The best hypothesis we had left was that naledi had put those bodies deliberately into the Chamber.

Some anthropologists place a special value on such behavior. It’s part of how they define modern humans. For nearly a century, archaeologists had argued about whether Neanderthals recognized mortality, understood death, or buried the remains of their dead. Neanderthals were fundamentally human, with a brain size and evidence for complex culture that rivaled those of modern humans. With Homo naledi, though, we were looking at a primitive creature with a brain only a third the size of a human brain today. Could it be possible that this species—clearly not human—still had the kind of awareness and social complexity that we see in our own species?

As we pondered this issue, we realized how misleading it could be to assume that the behavior we were seeing was exactly like human behavior. Chimpanzees and gorillas show clear signs of distress when individuals in their groups die or go missing. The same is true of most social mammals, including elephants and dolphins. But they do not seem to share any cultural practice of tending to the bodies of the dead and leaving them in a particular place. Our relatives among the apes seem to have all the emotional abilities necessary as a foundation for such behavior. If naledi, indeed, had such a practice, it may have been just the first step along a cultural transformation.

We struggled to think of ways to test the idea that naledi deliberately deposited their dead here. No other hypotheses made as much sense. If Homo naledi had gathered dead bodies in a single place, their motivation did not need to be the same as recent human cultures. In fact, cultures can be starkly different from each other: Some cultures leave grave goods with bodies—special objects to accompany the dead—but others don’t. Some expose the bodies for predators and scavengers to consume; others protect the bodies from those creatures. The sheer variety of possibilities made it hard to imagine a test.

Still, if naledi was repeatedly using the Rising Star cave system to deposit bodies, they may have spent time in other parts of the system for other purposes. We might find some evidence of habitation or other activity if we investigated other parts of the cave. If they were using the dark zone, they might have had light. That meant we might find evidence of fire.

And if this was really a behavior repeated within a Homo naledi population, it seemed unlikely that the Dinaledi Chamber would be the unique and only place where they had deposited bodies. If we looked, we might find other similar situations. We didn’t know yet what site 102 contained. That would be our next excavation priority.