Homo Naledi May Have Made Etchings On Cave Walls And Buried Their Dead

Evidence has been released suggesting that the mysterious hominin species known as Homo naledi buried their dead and left symbolic drawings above them. The implications of such a finding are revolutionary, suggesting intelligence similar to our own in a species with brains not much larger than those of chimpanzees. However, some paleontologists are cautious, arguing the case is not yet proven.

For months, Professor Lee Berger of the University of Witwatersrand has been teasing the world with hints to have made his biggest discovery yet. From the man responsible for two of the most important breakthroughs in human evolution this century, that's not something to take lightly.

Now, preprints of two papers have been released, but have not yet completed peer review, accompanying a conference talk. Their content certainly has the potential to live up to Berger's boasts, provided his joining of certain dots proves correct. Berger claims to have found the oldest evidence of burial by a human species, accompanied by fire and the carving of symbols.

Berger led the team that discovered the bones of H. naledi, stunning the world in 2015. However, he had to do it from the surface, as the passageway deep within the Rising State cave system in which the fossils were found was too tight for him (or indeed most men) to enter. Eventually, after losing 25 kilograms (55 pounds) Berger was able to squeeze down to reach the bones – although he risked his life and severely damaged his shoulder in the process. Even then, one of the chambers in which H. naledi remains have been found proved beyond him.

Nevertheless, he told ABCNews it was all worth it. "These are the most ancient interments yet recorded in the hominin record, earlier than evidence of Homo sapiens interments by at least 100,000 years," Berger and co-authors write in one of the forthcoming papers.

That would be big news under any circumstances. However, if the finding was from close relatives such as Neanderthals, with brains only modestly smaller than our own, it would not be too shocking. H. naledi, on the other hand, had hands and feet remarkably similar to our own, but brains so small that when first discovered they were thought to have lived two million years ago, subsequently revised to one million.

More recently, however, it has become clear H. naledi were present around 250,000 years ago, indicating they overlapped with Homo sapiens, although we have no evidence our species and H. naledi interacted.

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Dogs bury bones, and so in a way do floods, so if H. naledi covered up their dead it would not necessarily prove high intelligence. However, the preprints report what appear to be shallow graves, along with geometric shapes and something like a hashtag (#) carved on smooth surfaces of a nearby pillar, which the authors interpret as a sort of commemorative gravestone. "That would mean not only are humans not unique in the development of symbolic practices, but may not have even invented such behaviors," Berger told AFP.

The shapes include squares, triangles, and even patterns that resemble ladders, all made in hard dolomite rock that couldn't be carved without strong tools. Lines are typically 5-15 centimeters (2-6 inches) long and the markings often appear to have been buffed before and after with sand and pigment. The preprint describing the engravings in detail refers to them as 241-335,000 years old, but this is based on the previously established ages of some of the bones, rather than direct measurements of the markings.

Berger noticed soot on the ceiling of the cave and charred bones on the floor, bolstering his previous claims H. naledi must have used fire to move about in a location no sunlight can reach. Other members of the team found what they call a hearth elsewhere in the system, although none of these were covered in the preprints. Australian raptors have reportedly developed the capacity to spread fire to their benefit, but bringing it into a cave system that would have been difficult to access, even for a species smaller-bodied than our own, implies far greater control.

While anthropologists not involved in the research acknowledge its potential significance, some have also warned against leaping to conclusions. Understandably, not every anthropologist is willing to take the risks Berger did to reach the site, which has hindered independent verification and analysis of the finds. The passageways can't be widened without threatening the caves’ structural integrity.

Griffith University's Professor Michael Petraglia questions Berger's confidence the engravings were made by H. naledi in the absence of any way to date them. "It is unlikely that any other hominin population made these engravings," the authors write. "No physical or cultural evidence of any other hominin population occurs within this part of the cave system, and there is no evidence that recent humans or earlier hominins ever entered any adjacent area of the cave until surveys by human cave explorers during the last 40 years."

However, the absence of evidence is not necessarily evidence of absence, and Petraglia disputes the possibility the fire and markings were the work of H. sapiens can be ruled out. "I have no reason to believe, at this stage, that Homo naledi controlled fire, and I await convincing scientific evidence to prove this is the case," Petraglia told Scientific American. Other anthropologists have expressed doubt about some or all of the major claims made in the preprints, noting the absence of tools and arguing that floods could create the appearance of burials.

Some techniques that might confirm or undermine Berger's claims could damage the site, so the debate may not be settled for a while to come.

Both papers have been submitted to the journal eLife. They are currently available on BioRxiv here and here. Related work was presented Monday at the Richard Leakey Memorial Conference.