Rethinking what makes us human

Research by Lee Berger and UW-Madison’s John Hawks gets a new book and Netflix documentary

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Books

What separates humans from the rest of the animal kingdom? The use of tools was once a criterion. But chimps, dolphins and even crows have rebuffed us on that. Surely burials of our dead, a command of fire, cave art, and the making of stone tools from a blunt rock still set us apart? Maybe not. A book out last month, Cave of Bones: A True Story of Discovery, Adventure, and Human Origins, along with a new companion Netflix documentary, suggests that we are not alone in these accomplishments and likely weren’t even the earliest, not by a long shot. 

Meet Homo naledi. Short of stature — just over four-and-a-half feet tall — and thin-limbed; bipedal and upright like the rest of the genus Homo, with a brain a third of the size of our species’; and compelled to descend deep into the dark earth to place their dead in shallow graves. And that may not even be the most remarkable thing about these human-like non-humans. The dates for naledi figure to be at least 250,000 years ago, possibly more, meaning they trod the earth at the same time as the earliest humans. 

National Geographic explorer Lee Berger, director of the Centre for the Exploration of the Deep Human Journey at the University of Witwatersrand in Johannesburg, and UW-Madison’s own John Hawks, Vilas-Borghesi Distinguished Achievement Professor of Anthropology, co-authored Cave of Bones, based on their research within the Rising Star cave system, part of an UNESCO world heritage site in South Africa. Both the book and documentary blend the thrill of CSI sleuthing a cold case and a physical adventure worthy of Indiana Jones, with a layperson-accessible underpinning of hard science and excited speculation. 

The discovery of naledi at Rising Star in 2013 defies belief: a collection of bones from more than 25 individuals, an extraordinary amount for a single site, and from a human-related species never before encountered. In some cases, they lay right out in the open on the cavern floor. Nevertheless, collecting them proved a bit of a challenge.

The Netflix documentary, Unknown: Cave of Bones, opens with ominous music and footage of jagged, narrow cave passages, their sharp surfaces revealed in spotlit patches with the weighty darkness around the edges of the shot. We meet Berger’s “Underground Astronauts,” research assistants who are climbers and necessarily short and lithe to negotiate the narrowest crevices and belly crawls. The film jumps back and forth in time from 2014 to 2022. The team is four years into the dig before they find an arrangement of bones in an oval-shaped depression — a burial. As the researchers talk about what they’ve learned from these bones, sepia-toned pointillist animation, based on that evidence, eerily brings naledi to life. 

The setting may trigger anyone who’s claustrophobic. “You don’t get anywhere without the rock squeezing on you,” says Hawks. “It is a cave that is very tactile.” Hawks and Berger watch through monitors as they are both too tall and bulky to get to the farthest reaches of the chambers. That is, until Berger privately commits himself to lose 40 pounds so he can contort and scratch his way the last 12 meters down The Chute to enter the farmost space, the Dinaledi Chamber, for one vital visit — a harrowing experience, even more so in the book, as he gets stuck for a long time. No spoilers here, but his finds there suggest even more human-like behavior, and calls to question some of our beliefs of our exceptionalism. 

The book opens with a prologue that teases Berger’s dramatic squeeze into Dinaledi, before chapter one takes us back to the beginning, setting the stage of the cave system. Hawks explains how even decades ago we’d had to revise our “March of Progress” ideas about human evolution, the image of a parade beginning with a small ape and ending with modern humans. The discovery of Homo naledi raises even more questions about the rise of culture. 

With just over 200 pages, Cave of Bones is not an intimidating brick, and the characters feel as important as the science, putting the reader there for group decisions about how to proceed and what their finds may mean. It has elements of a page-turner, and the tangible thrills from the big reveals are at least equal to those of the fine production quality of the documentary.

“You can’t convey in film the internal,” says Hawks, “the sort of thoughts and states that somebody has when they’re challenged beyond maybe their limit. [Berger’s description of] what he was going through is really powerful.” And the science side, Hawks contends, is just as internal. “It’s wonderful when we’re working on something that’s super visual,” he says. “But going to the state of, ‘okay, but how did it get this way? And how do we show that?’ I think is also one of those processes that benefits from a book.”

Hawks’ work on the ancient genomes of Neanderthals brought him into contact with Berger and back into field work. He says the two were both interested in “opening up the science to a broader population” and finding “ways to make it possible for collaborations to grow bigger than they had by sharing data.”

Their work together got Hawks deeply involved in South Africa. At Rising Star, he studies the bones, matching them with individuals. Among them is “Neo,” a half-complete naledi skeleton found in what appears to be a grave more than 241,000 years old. 

Dates can be elusive or at least broad-ranged. Radiocarbon dating only serves as far back as 50,000 years ago, and while alternative methods can examine rock formed around a fossil or crystals formed in teeth, the estimates are still imprecise and have limitations. “Some of it we know is between about 335,000 years and 241,000 years. That’s 100,000 years of wiggle room,” says Hawks. “It’s like ‘When was the Battle of Hastings?’ Well, you know, 500 A.D. to 1500 A.D., somewhere in that range.” But even the minimum age in that “wiggle” range is startling. The earliest evidence of a possible human burial dates back about 100,000 years, and current evidence suggests “commonplace mortuary practices” are a mere 35,000 years old. 

The nature of the find has also made an impact on future work. No one had imagined to find such remains so deep in a cave, let alone lying exposed on the floor. “Our team began to hire cave explorers,” says Hawks, and they’ve since gone into more than 600 cave sites in the region finding even more hominin remains. “The world is a big place and we’ve only started to scratch the surface of what is in the underground spaces.” 

With modern communication, field work is not as remote as it once was. “We are doing some really cool work now with a group in Copenhagen who are focused on biomolecules, but we do work on geology, geochemistry with labs in Australia and South Africa. So it’s really global.” They can’t get DNA from these bones, but are hopeful to work with protein evidence. Those types of analyses require a collaboration with different labs with different kinds of techniques, says Hawks.

But beyond the analysis of bones and burials, one thing remains certain: “We didn’t evolve in isolation. We evolved with other species that were like us in some ways and yet really different,” says Hawks. “We are the last survivors of a diverse group, and most of that group has become extinct. I think that’s a big message for humanity.”