Around a decade ago, an astonishing assortment of hominin bones was discovered in the depths of South Africa's Rising Star Cave. Within two years of the discovery, researchers had determined that the bones represented a new species, which they named Homo naledi. Short, stout and small-brained, the species trampled through South Africa between 335,000 and 241,000 years ago and behaved brutishly.
Well, that's what most paleoarchaeologists and paleoanthropologists who read about the discovery assumed. But three pre-print papers from the same team that discovered and described the species are starting to test those behavioral assumptions, asserting that H. naledi individuals buried their dead in caves and carved cave walls.
Posted to the BioRxiv pre-print repository at the beginning of the month, the three papers should appear in the journal eLife pending their peer review. And if their findings stand up to the scrutiny, they may mean that smaller-brained hominins participated in some of the same sophisticated behaviors as bigger-brained hominins.
A Grave Assertion
The initial H. naledi find featured at least 1,550 specimens from at least 15 individuals, making South Africa's Rising Star Cave one of the most important archaeological sites in the world. And now, after a few additional years of combing through the cave's complicated interior, researchers are painting an increasingly impressive picture of H. naledi and its activities, suggesting that the species dealt with death in a surprisingly sophisticated way.
Citing a combination of anatomical, stratigraphic and taphonomic analyses, the team says that the species dragged their dead deep into the Rising Star Cave, where they buried the bodies in intentionally dug graves and decorated the walls with abstract scrapes.
"These recent findings suggest intentional burials, the use of symbols, and meaning-making activities by Homo naledi," says Lee Burger, a paleoanthropologist at the University of Wits and an author behind the three pre-prints, according to a press release. "It seems an inevitable conclusion that, in combination, they indicate that this small-brained species of ancient human relatives was performing complex practices related to death."
According to the researchers, the findings suggest that bigger-brained hominins weren't the only ones burying bodies and carving cave walls, nor were they the first, with Homo naledi making graves and art over 100,000 years before Homo sapiens. In fact, the oldest undisputed discoveries of H. sapiens burials and drawings both date back to between 80,000 and 70,000 years ago, well after H. naledi had faded from the fossil record.
During their initial discovery of H. naledi, researchers had already started to suspect that the Rising Star bones had been deliberately deposited inside the cave. In one of their first descriptions of the bones, they theorized that H. naledi individuals had brought the bodies to the cramped cavern intentionally, dropping them or dragging them inside and discarding them in haphazard, unburied heaps.
But as researchers continued their investigation of the cave in 2018, they discovered an accumulation of bones in what appeared to be a deliberately dug depression, around 10 by 20 inches in size and around 3 inches in depth.
Analysis of the bones revealed that the majority of the accumulation (over 80 separate specimens) represented a single H. naledi individual whose body was, by all appearances, placed and preserved in a fetal position, raising the possibility of an intentional burial. An analysis of the depression revealed that the soil around the body had been disrupted and filled with soil of a separate sediment composition, increasing that possibility.
According to the researchers, several other potential burials have been identified inside the cave, as well, with some seeming to contain single skeletons and others seeming to contain several skeletons all at once. And adding to the cave's surprises are the abstract shapes scratched into its interior walls, which resemble art made by H. naledi's bigger-brained relatives, Homo neanderthalensis and Homo sapiens.
Though these carvings have yet to be dated, the researchers say that they may have been made between 335,000 and 241,000 years ago, the same span of time in which H. naledi crammed the cave with the deceased.
Dead Wrong or Dead On?
The authors of the three pre-prints say that their findings could challenge fundamental theories about the foundations of human behavior, suggesting that the development of a bigger brain was not necessary for the development of complex thought and action.
"What we've uncovered forces us to rethink a whole set of assumptions about hominins and human evolution," said Agustin Fuentes, an anthropologist at Princeton University and another author behind the pre-prints, according to a press release. "Much of what we assumed was distinctively human, and distinctively caused by having a large brain, may not be either of those things."
But despite the potential significance of these discoveries, some researchers remain skeptical, stating that the team arrived at their conclusions without completely ruling out a variety of alternative scenarios regarding the positioning of the remains and the timing of the art.
According to these skeptics, the Rising Star bodies may have accumulated in natural depressions in the cave floor due to natural forces, having been washed in by water, for instance. Alternatively, they may have been tossed into the depressions by H. naledi individuals, as has been previously proposed, only to be subsequently buried by the natural shifting and settling of sediment inside the cave.
Weakening the findings further, some researchers add that the scratches along the walls of the cave are not necessarily the work of H. naledi, since they could have been created by H. neanderthalensis or H. sapiens artists, thousands of years after the tiny-brained hominin had died out.
Ultimately, skeptics stress that the best way to uncover the truth is through continued investigation. While future digs and further study of the cave's contents could clarify the origin of the depressions and the positioning of the bodies within those depressions, formal dating could determine whether it was H. naledi or one of the species' later, bigger-brained relatives who was the artist behind the art.