Homo naledi finds are up-ending what we know about being human
Findings indicate some cultural behaviour unique to humans and Neanderthals were also present in the extinct species Homo naledi.
Discoveries from a subterranean cave system in South Africa are prompting palaeoanthropologists to rethink what makes us human. New findings reveal a small-brained human relative known as Homo naledi buried its dead and carved symbols on walls inside the system. Both these behaviours were previously associated with our species or the big-brained Neanderthals with which we interbred.
“We’re looking at cultural behaviour that is very human in a species that has a brain a third the size of ours,” said John Hawks, a University of Wisconsin-Madison palaeoanthropologist and co-author of the research released last week.
“It is going against the idea that brain size is what made us human. We’re also understanding more and more that our species wasn’t alone,” he added.
Chris Stringer, research leader in human origins at the Natural History Museum in London who wasn’t involved in the new work, said he had previously been sceptical of the claims for complex behaviours in Homo naledi.
“But the considerable evidence presented now for possible burials and wall engravings cannot be easily dismissed,” Stringer said.
If the claims from the new research turn out to be well-founded, he added, it has profound implications for our understanding of human evolution.
The findings indicate that some aspects of what was considered to be late-developed and sophisticated cultural and symbolic behaviour were also present in a much more primitive human relative that had a separate evolutionary history, he said.
“And they must indeed have been achieved with an ape-sized brain.”
Fossil evidence suggests Homo naledi lived between 241,000 and 335,000 years ago inside a cave system known as Rising Star, located near modern-day Johannesburg. Its lower body, feet, hands and teeth had aspects that appeared humanlike, yet its average 45kg, 150cm frame carried a brain the size of an orange – similar to that of chimpanzees.
“We’ve never had a creature that manifested the complexity of us that wasn’t us,” said Lee Berger, a palaeoanthropologist and an explorer in residence at National Geographic who co-authored the new research. Homo naledi, he added, is “threatening to the very clearly defined narrative of the rise of human exceptionalism”.
Berger and Hawks helped publicly reveal the species in 2015 after an international effort to explore and excavate the labyrinthine Rising Star (naledi means “star” in South Africa’s Sesotho language).
More than 1500 bones belonging to Homo naledi individuals were found in one chamber of the cave system, and the abundance of bones enabled the research team to reconstruct a composite skeleton and more than a dozen partial ones. They also found evidence they used fire, including hearths and charred bones.
Though Rising Star may have looked different hundreds of thousands of years ago, currently its subterranean chambers can be reached only by slithering and squeezing through narrow passages – including a vertical chimney less than 30cm wide known as “the chute”. Berger – who previously couldn’t make the journey – initially recruited shorter, smaller researchers to go into the cave system, where they set up cameras and recording equipment to monitor the area for researchers watching in an above-ground command centre.
At the time, one of the biggest mysteries surrounding Homo naledi’s discovery was how so many bones turned up in the remote cave system. Palaeoanthropologists – including professors Andy Herries from Melbourne’s La Trobe University and Paul Dirks from James Cook University – explored ideas including whether a group of these individuals unexpectedly died there all together, or whether a mudslide or flood carried the bones in, or – as Berger and Hawks’ team proposed in 2015 – Homo naledi used Rising Star as a place to deliberately dispose of their dead.
That theory was considered controversial, Berger said, so the researchers launched more excavations to examine the extent of the bone beds therein. Further exploration of other chambers within Rising Star – more than 4km of the system, which is at least 100m deep, have been mapped so far – revealed bodies, including those belonging to children, in different depressions that the researchers said had been intentionally dug.
“I could see the outline of this disturbed area that clearly interrupted the stable cave floor,” Berger said. “Whether you call it a grave or not, it is a dug hole with a (Homo) naledi body in it that has been covered by dirt from that hole.”
The teams brought back one of the interments, safely encased in a plaster jacket, above ground where it was then studied using methods including CT scanning. The examination revealed that the bones all belonged to the same individual, which supports the idea that they had discovered a buried body, and not bones from different individuals.
“The idea of dealing with death in ritualised fashion is actually one of the last precious things attached to being human,” Berger said, adding that the remoteness of Rising Star supports the idea that Homo naledi was doing something quite similar.
“They didn’t want their dead in an easy-to-get-to space,” he said. “We don’t either.”
Hawks has never descended into the narrowest passages of the cave system, but Berger finally achieved that goal last year after losing 25kg.
When Berger was down there, he observed another remarkable example of Homo naledi’s cultural behaviour.
Inside one of the chambers last July, team members found engravings that had been gouged into a part of the hard dolomite wall that appeared to be smoothed out before being carved.
The engravings included crisscross patterns resembling a modern hashtag that were made with a pointed tool.
Stringer said he would like to see attempts to date the engravings. According to Hawks, the team has found evidence of a foreign substance embedded within the grooves of the ancient hashtag, and that efforts are under way to further test that substance and discern whether the engravings are contemporary with nearby burials. The significance, and intended meaning, of the symbols inside Rising Star has yet to be determined, the researchers said, but the act of engraving intentional designs is widely considered a major cognitive step in human evolution.
Similar ancient hashtags have been documented at a Neanderthal site in Gibraltar that is just tens of thousands of years old.
“They are uncannily similar, and they are 8000km apart, you know, it is just crazy,” Hawks said.
One explanation, according to Berger, is that such crisscross symbols “are deeply shared by our last common ancestor and sit inside of us”.
THE WALL STREET JOURNAL
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