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New discoveries suggest that a cryptic early human species, Homo naledi, exhibited behaviors such as burying their dead and creating cave wall carvings, predating similar practices observed in modern humans.

Despite having brains approximately one-third the size of contemporary human brains, the now-extinct Homo naledi demonstrated these complex behaviors.

These findings could revolutionize our perception of human evolution, as these activities were previously thought to be exclusive to larger-brained species like Homo sapiens and Neanderthals.

Three research that have been approved for publication in the journal eLife in-depth the findings; preprints of the manuscripts are accessible on BioRxiv.

The Rising Star cave system in South Africa, part of the UNESCO World Heritage Site known as the Cradle of Humankind, was the location of the first Homo naledi fossil discoveries during 2013 excavations. This area is significant for its rich trove of ancient human ancestor species fossils, which are shedding light on the history of human evolution.

Dr. Lee Berger, a paleoanthropologist, and a National Geographic Explorer in Residence, together with his team of “underground astronauts,” have persisted in their exploration of the vast and perilous cave network in an effort to gain a more thorough understanding of these extinct hominins, our early human forebears.

The research group has now unearthed Homo naledi remains, including both adults and children, that appear to have been purposefully positioned in a fetal pose within cavities in the cave and subsequently covered with earth. These burials predate the earliest known Homo sapiens burials by a minimum of 100,000 years.

While examining the cave burials, the researchers also discovered numerous symbols etched into the cave walls. These symbols are believed to date back between 241,000 and 335,000 years, although further tests are being conducted to establish a more exact timeline.

The symbols consist of intricately engraved patterns resembling hashtags and other geometric designs. Comparable symbols have been discovered in other caves, created by early Homo sapiens 80,000 years ago and Neanderthals 60,000 years ago. These were presumably used as a method of recording and communicating information.

“These recent findings suggest intentional burials, the use of symbols, and meaning-making activities by Homo naledi. 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,” said Berger, lead author on two of the studies and coauthor on the third, in a statement. “That would mean not only are humans not unique in the development of symbolic practices, but may not have even invented such behaviors.”

Navigating the intricate and sprawling network of the Rising Star cave system and its inner chambers is no task for the timid.

Dr. Tebogo Makhubela, the leading geologist of the studies and a senior lecturer of geology at the University of Johannesburg, states that the team has charted over 2.5 miles (4 kilometers) of these caves. The caves boast a vertical depth of 328 feet (100 meters) and stretch more than 656 feet (200 meters).

This cave system presents perilous vertical descents and minuscule passages such as the Superman’s Crawl, a narrow tunnel 131 feet (40 meters) long and just 9.8 inches (25 centimeters) wide. This necessitates researchers to inch their way forward on their bellies, explains Dr. Keneiloe Molopyane, a National Geographic Explorer and the lead excavator of the Dragon’s Back Expedition (named after a particular feature within the cave).

To gain access to the precarious chambers of the cave in 2022, Berger had to shed 55 pounds (25 kilograms).

“It was the most awful and wonderful experience in my life,” Berger said. “I almost died coming out of there, but it was obviously worth it to make some of these discoveries. But, I think an important part of that, though, is that the journey would not be nearly as difficult, I think, for Homo naledi.”

Homo naledi exhibited certain human-like characteristics, such as bipedal locomotion and object manipulation using their hands. However, the species was marked by smaller cranial dimensions, lesser height, a more slender and robust build, according to Berger.

According to Dr. John Hawks, a professor of anthropology and paleoanthropology at the University of Wisconsin-Madison, Homo naledi’s shoulders — designed more suitably for climbing — and dental features bore resemblances to those of earlier hominins, such as Australopithecus.

Researchers have discovered numerous Homo naledi fossils scattered across the caves, including remains from infants to elderly adults, which aids in understanding the species as a whole population, stated Hawks. As the team ventured further into the depths of the caves, it became apparent that Homo naledi utilized extensive areas of the cave system.

In 2015, when Berger and his team first announced the discovery of Homo naledi, they hypothesized that this species might have intentionally placed their dead inside the cave. However, the notion of a hominin with a smaller brain engaging in such behavior sparked considerable controversy.

By 2018, the team began to uncover evidence that substantiated the theory of Homo naledi purposefully burying their deceased. They found cave surface indents resembling dug-out pits, within which were body remains arranged in fetal positions.

According to Berger, other burial sites were dug into hillsides horizontally and included bodies, demonstrating that the remains weren’t accidentally transported there.

“It’s not a body that died in a depression or hole. It was a whole body that was covered in dirt and then decayed within the grave itself, in part demonstrating that it was buried at the time as a whole flesh entity, but not by some dramatic collapse or being washed in,” Berger said. “We feel that they’ve met the litmus test of human burials or archaic human burials and the most ancient human burials, and therefore describe them as graves or burials by the nonhuman species, Homo naledi.”

The team subsequently uncovered carvings on the wall and an artifact within a grave.

Inside one of the burial sites, a rock resembling a tool was found adjacent to the hand of an adult Homo naledi. Above the graves in a connecting passage, an antechamber houses a wall adorned with rock carvings.

The deeply engraved geometric patterns are visible on the dolomite rock walls, which register a hardness of 4.5 to 4.7 on the Mohs Hardness Scale used by scientists to measure a mineral’s resistance to scratching. Given that dolomite’s hardness is halfway to that of a diamond (which sits at the pinnacle of the scale), Berger explains that carving into the walls would have required a substantial amount of time and effort.

The team asserts that the carvings were likely the work of Homo naledi, not Homo sapiens, given the absence of any proof indicating human presence within these caves.

According to Berger, Homo naledi was able to illuminate their activities inside the dark caves by using fire. This claim is supported by various remnants distributed across the caves, such as soot, charcoal, and burnt bone fragments, which suggest active fire-making.

Agustín Fuentes, a National Geographic Explorer, on-site biocultural specialist, and the lead author of the third study, mentioned that the evidence of burials and symbols suggests that Homo naledi was capable of participating in substantial behaviors.

Researchers are unsure of the symbols’ meanings or whether the symbols served as a kind of communication among the species.

“What we can say is that these are intentionally made geometric designs that had meaning for naledi,” Fuentes said. “That means they spent a lot of time and effort and risked their lives to engrave these things in these places where they’re burying bodies.”

The naledi discoveries imply that there may be other factors involved in the complicated behavior that was long thought to be exclusive to humans, according to Fuentes.

“The challenge here, then, is that we now know that Homo naledi, in addition to Homo sapiens and Neanderthals and Denisovans and a few others, were engaging in the kind of behavior that we, even just a few decades ago, thought was unique to us,” he said. “That means we need to rethink the timing of fire use, of meaning-making and of the burial of the dead in hominin history.”

The research team contends that it was Homo naledi, rather than Homo sapiens, who created the carvings, given the lack of any evidence suggesting human entry into these caves.

Berger points out that Homo naledi was capable of shedding light on their activities within the pitch-dark caves by making use of fire. Various evidence scattered throughout the caves, such as soot, charcoal, and charred bone pieces, supports this assertion by indicating the practice of fire creation.

Agustín Fuentes, a National Geographic Explorer, on-site biocultural specialist, and the main author of the third study, noted that the burial and symbolic engravings suggest Homo naledi’s capacity for engaging in sophisticated behavior patterns.

“I would certainly like to see attempts at dating the evidence for the engravings and for the fire, but if these huge claims turn out to be well-founded, they have profound implications for our reconstructions of human evolution,” Stringer said.

These discoveries caused several inquiries, including the possibility that such behaviors originated from an ancient common progenitor predating Homo naledi and humans. Furthermore, it leads to questioning why we possess such large brains “if human-like behavioural complexity can be achieved with a brain less than half that size,” stated Stringer.

The groundbreaking work of Berger and his team on the discovery of Homo naledi and its potential impact on the human evolutionary tree is featured in Netflix’s “Unknown: Cave of Bones”. In addition, Berger and Hawks have coauthored a book, “Cave of Bones: A True Story of Discovery, Adventure, and Human Origins,” which will be available beginning August 8.

The research team is continuing their efforts to learn more about Homo naledi, including its age, if it lived closer to humans than previously believed, and whether any DNA has been retained in the bones discovered in the cave network.