Some 25 miles outside of Johannesburg, South Africa, there is a famous paleoanthropological site known as the Cradle of Humankind. So many hominin bones were found in the region that it was designated a UNESCO World Heritage site in 1999. Among the many limestone caves in the region is the Rising Star cave, where cavers discovered fossils representing a new hominin species, Homo naledi, in 2015. Only H. naledi remains were found in the cave, suggesting the possibility that the bodies had been placed there deliberately, although this hypothesis proved to be a bit controversial.
Now the same expedition team has announced the discovery of H. naledi bodies deposited in fetal positions, indicating intentional burials. This predates the earliest known burials by Homo sapiens by at least 100,000 years, suggesting that brain size might not be the definitive factor behind such complex behavior. The team also found crosshatched symbols engraved on the walls of the cave that could date as far back as 241,000–335,000 years, although testing is still ongoing.
Taken together, the discoveries provide evidence of a major cognitive step in human evolution in terms of mortuary practices and meaning-making. The team described these new findings during a virtual press conference and in three new preprints posted to the BioRxiv, which will be published later this year in the journal eLife.
"I think we are facing a remarkable discovery here of hominids with brains a third the size of living humans, and slightly larger than chimpanzees, burying their dead—something previously only found in large-brained hominids—as well as etching meaning-making symbols on the wall," said Lee Berger, a paleoanthropologist and National Geographic Explorer in Residence who leads the Rising Star Project. "This would mean not only are humans not unique in the development of symbolic practices, but [they] may not even have invented such behaviors."
Naturally, there are skeptics. For instance, María Martinón-Torres, director of Spain’s National Research Center on Human Evolution, told the New York Times that such speculations were premature based on the evidence presented so far, suggesting that funerary caching was a more likely scenario than burials. “Hypotheses need to be built on what we have, not what we guess,” she said. “Still, I think the possibility of having funerary caching with this antiquity is already stunning."
The story of Homo naledi technically begins millions of years ago, when the cradle's network of limestone caves first formed. As Lydia Pyne wrote for Ars in 2018:
Caves in that area of South Africa form as water percolates through the cracks and fissures of the region’s dolomite rock and slowly erodes the rock away, forming underground caverns of all shapes and sizes. As water flows through these caves, it leaves behind deposits of calcium carbonates—easily recognizable as concrete-hard breccias or sheet-like deposits of flowstone found along cave walls. In the Rising Star cave system, this resulted in a network of chambers, including those where researchers have recovered Homo naledi fossils.
Recreational cavers had been exploring parts of the Rising Star system since the 1960s. But Berger hired a team of cavers in 2013 to survey the cave more thoroughly to map out any chambers with potentially significant fossils. That team included Rick Hunter and Steven Tucker, who used a 1985 map to guide their explorations. The duo managed to worm their way through a previously unmapped slot just 18 centimeters (7 inches) wide and found themselves in one of the cave chambers. There, they saw a treasure trove of fossilized bones. "When we first saw the mandible, we thought, 'Maybe this was the last guy that came down to the chamber and didn't make it out,'" Hunter told Ars in 2018.
The reality was potentially much more significant. Excited by the discovery, Berger hired an additional team of six women with both scientific and caving experience to excavate the site (using toothpicks and sometimes porcupine quills, among other tools). The entire three-week excavation played out live on Twitter.
These are not easy sites to access. In fact, the chute labyrinth along one portion of the route to the Dinaledi Chamber is known as "Superman's Crawl" because most cavers can only manage to squeeze through by extending one arm above the head while holding the other tight against the body. It's basically a narrow, vertical 12-meter (39-foot) long "chimney" with an average width of 20 cm (7.9 inches).
"You have to crawl on your belly because there's not enough space for you to be on your hands and knees," said Keneiloe Molopyane, an archaeologist and biological anthropologist at the University of Witwatersrand and one of the team's "underground astronauts." Berger lost 55 pounds to finally make his way into the Dinaledi Chamber for the first time last year, describing the journey as "the most awful and wonderful experience in my life." That chute opens into the so-called "Dragon's Back Chamber," in which cavers must navigate a treacherous 15-meter (49-foot) dolomite ridge.
That first excavation, and a second one the following year to excavate the so-called Lesedi Chamber, yielded 1,350 fossils and fossil fragments, although thousands more bones remain at the site. Berger and John Hawks, an anthropologist at the University of Wisconsin-Madison, set up a collaborative workshop of early career scientists to analyze all those fossils. Based on that analysis, Berger and his collaborators concluded that the fossils represented a previously unknown species of extinct hominin, which they dubbed Homo naledi. ("Naledi" means "star" in a local language and references the Rising Star cave system in which it was found.)
As previously reported, a typical adult of Homo naledi stood about 1.5 m (4.9 feet) tall and weighed only 45 kg (about 100 lbs). Its skull was very small, with a cranial volume similar to that of the larger Australopiths; every species of Homo except the hobbits (H. floresiensis) had a larger brain. Its shoulders are also ape-like, which is commonly interpreted as indicating it retained the ability to climb trees; the rib cage is constructed like that of Australopiths. Yet many features align it more closely with Homo. The feet and ankles are largely similar to those of modern humans, although its hips looked Australopith-like. Meanwhile, some of the leg bones have features unique to the species. Overall, Berger and his team concluded that it was able to stride efficiently.
Despite its small size, the skull has many features similar to those of our own genus. The fingers are long and curved yet appear to have the ability to perform fine-scale manipulations, potentially allowing H. naledi to use tools. Its jaw looks like those of other early members of our genus, but the teeth were small and similar in size to those of humans. In the end, the authors conclude that many of the features that form integrated systems—like the jaw and teeth or foot and ankle—are similar to other members of our own genus.
In 2017, Berger's team announced the discovery of even more skeletons in the Rising Star cave system, bringing the overall total to 21 individuals and more than 2,000 fossil fragments. With those new skeletons came some hard dates based on uranium-series dating: only about 250,000 years ago, possibly making H. naledi a contemporary of the earliest modern humans. Those dates upset just about everything we thought we knew about recent human evolution, our genus' use of tools, and how all those skeletons ended up buried in the cave in the first place. "This species persisted and survived alongside other species that were much more human-like, including our own early members of our species, Homo sapiens," said Berger. "That scenario is something we did not anticipate when we began work in this cave system."
The specimens discovered so far include the most complete individual partial skeleton yet found, dubbed "Neo," as well as the partial skeleton of a child (DH7) between 11 and 15 years old (by human aging metrics). So along with Neanderthals, Homo erectus, Australopithecus afarensis, and A. sediba, anthropologists were also able to study a juvenile H. Naledi skeleton to shed some light on the evolutionary origins of our own species’ lengthy childhoods. Humans take much longer to grow up than other great apes, which may be related to our larger brains and more complex cognitive skills. Anthropologists are still trying to understand exactly when and how that reality came about.
The chambers in which these skeletons were found are remote enough that almost no other animals ever reached them. Only H. naledi remains have been found, and there is no evidence the bones were transported there via water flows. "Our earlier work has shown that H. naledi was using potentially very broad parts of the Rising Star cave system, that it was familiar with these spaces, and it was doing something very interesting to exclude the bones of other kinds of animals," said Berger.
The clear implication is that these skeletons were unlikely to have gotten there by accident. Instead, they were probably placed in the cave. And since H. naledi belongs to our own genus, the most likely explanation is that other members of this population were the ones doing the placing, deliberately disposing of their dead. The cave wasn't necessarily always this remote or difficult to access, but it's clear that there must have been some effort involved in getting individuals to the location.
That said, as Ars Science Editor John Timmer noted back in 2015, "It's tempting to over-interpret this as a sort of burial, but it's dangerous to try to infer the mental processes in a species where we have no understanding of the mental capacity." Indeed, Berger was careful not to claim it was an actual burial at the time of discovery. But in 2018, the team discovered two new burial features overlapping with the originally discovered remains that changed their interpretation significantly.
Specifically, they identified depressions deep in the chambers of the cave system, in which the bodies of H. naledi adults and several young children had been deposited in a fetal position, suggesting that the intent was to bury the dead. One feature had clearly been dug horizontally into a slope, according to Berger. Furthermore, according to Berger, "This burial has depth, demonstrating it's not a body that died in a depression or hole," he said. "It was a whole body that was covered in dirt and then decayed within the gravel itself, not by some dramatic collapse or being washed in. We feel they've met the litmus test of the most ancient human burials."
The other feature held the remains of a teenage child, most likely around 13 years old by human metrics, as well as other younger children, although the latter are still being analyzed, with the findings to be reported in a future publication. The teen's remains included a tool-shaped rock artifact near the hand. "We believe it's a chert or dolomite substance, and it may have characteristics of being a manufactured lithic artifact," said Berger, and it's something that will be investigated once the artifact is extracted for further testing.
An even more exciting discovery awaited. On July 28, 2022, Berger and his team found etchings engraved in a crosshatch pattern on Panel B in the Hill Antechamber. The patterns include geometric figures like squares, ladders, triangles, crosses, and X's. More crosshatch etchings were found on a second Panel A, which also showed evidence of earlier etchings behind it, obscured (perhaps deliberately) by covering the surface with cave dirt. Some of the engravings appeared to fluoresce slightly, suggesting that some substance had been applied, similar to the 78,000-year-old carved ochre art found in Blombos Cave. The surface also showed signs of having been prepared by hammerstones prior to the engraving.
Dating rock engravings is a complex and challenging process. But Berger et al. argue that contextual evidence rules out these etchings having been made by natural forces, given the fossil algal stromatolite rock found at the bottom of the Panel A engraving. The rock is incredibly tough, ranking about 4.7 on the Mohs hardness scale (about half as hard as diamond). The etchings are too deep to have been made naturally. "You can hit this rock with a rock hammer and it bounces off," said Berger. "To scratch it would have had to be with an object as hard or harder, and it would take an extreme amount of effort."
Add in prior evidence found of fire in the Rising Star cave system—charcoal, silt, burnt bone—and there is a solid case to be made that the engravings were made by H. naledi. "These are not the kind of graffiti or engravings that humans do," said Berger. "There's no evidence of humans in the proximal spaces other than our entry into this space. There are burials of this species directly below, graves they dug. The engravings were not done in one sitting, they're done over time, and there's [evidence of] erasure. They actually put material or sand over it and carved through at a later period."
This, too, has other scientists expressing cautious skepticism. “It is premature to conclude that symbolic markings were made by small-brained hominins, specifically H. naledi,” Emma Pomeroy of the University of Cambridge told New Scientist. “While intriguing, exciting and suggestive, these findings require more evidence and analysis to support the substantial claims being made about them.”
The authors are careful not to speculate much about what these mysterious engravings might suggest about the development of language and communication among H. naledi and are especially cautious about what the symbols might mean. It's much too easy to erroneously see meaning in a pattern that is more in keeping with our human history.
"What we can say is that these are intentionally made geometric designs that had meaning for H. naledi," said Agustin Fuentes, an anthropologist at Princeton University and co-author on all three new papers. "What that meaning is, and how that correlates with, let's say, different neural cognitive processes for expression of information through oral or other forms of language—we simply don't know. But at the end of the day, this is intentional meaning-making. They spent a lot of time and effort and risked their lives to engrave these things in these places where they’re burying bodies. How does that relate to language? I don't know if that's a question we can answer."
