Homo Naledi: A Mystery Buried Deep in the Cradle of Mankind

by Rajiv Reddy

“In my wildest dreams, I would never have thought that caving would take me to what’s happening here. You could almost call this a bit of an accident,” chuckled Steve Tucker, a thin, wiry caver who, along with his friend, happened to make the most astonishing human fossil discovery in over half a century—and undoubtedly the most perplexing. He stumbled upon the remains of a previously undiscovered human ancestor species, Homo naledi, whose origin and behavior continue to puzzle the scientific community.   

One Friday evening nearly two years ago, a pair of recreational cavers, Steve Tucker and Rick Hunter, entered a cave called Rising Star, located 30 miles northwest of Johannesburg, South Africa, hoping to explore a less trodden passage. This region has produced so many fossils of our early ancestors that it has come to be known as the Cradle of Mankind. Deep in the cave, Tucker and Hunter maneuvered through a crevice merely ten inches tall. The passage is notoriously named Superman’s Crawl because one can only fit through by holding one arm tightly against the body while extending the other above the head, like the Man of Steel in flight.  

The two cavers found themselves in a large chamber and climbed up a jagged slope of rock known as the Dragon’s Back. At the top, they dropped through a vertical chute only eight inches wide into a breathtaking cavity brimming with stalactites: the Dinaledi chamber. Hunter decided to take out the camera to capture the spectacular sight when suddenly Tucker felt something against his foot. It was a bone. Upon greater scrutiny, he realized that the whole floor was littered with them. They appeared to be human, but it wasn’t until Tucker found a mandible that he was sure these remains were Hominid.  

That same night, Tucker and Hunter contacted Lee Berger, an anthropology professor at the University of the Witwatersrand with their thrilling news and were invited to his house. When they knocked on his front door, jawbone fossil in hand, Berger called National Geographic and broke out the beers. Berger had some major findings over the span of his 20-year career, but he knew that he had something extremely special on his hands. What he did not know at the time was that it would revolutionize our understanding of human evolution and inspire unprecedented questions about our identity.  

The next few months involved putting together a qualified team to unearth and study the remaining specimens from the Dinaledi chamber where the mandible was found. Once assembled, the remains formed much of a complete skeleton. This dumfounded Berger. At the time, only a handful of full early hominid skeletons had been unearthed. Berger could see that the bones did not belong to a modern human being. Certain features, like the jawbone and teeth, were far too primitive. So what was this? How old was it? And how did it get there? 

Berger, with a team of over 50 experienced scientists, worked tirelessly to answer these questions. The initial step was to analyze the 190 teeth collected, as tooth analysis is usually enough to identify a species. The results were baffling: some features, like the molar crowns, were astonishingly humanlike while others, like the premolar roots, were oddly primitive. This hodgepodge of primitive and advanced features was consistent across the skeleton as a whole. A modern hand, fitted with curvy fingers for climbing. Hunched, apish shoulders but a modern pelvis. Primitive thigh bones, which became modernized as you moved towards the feet. But then there was the head. While the general morphology of the four skulls studied looked advanced, the braincases themselves were tiny – a mere 560 cubic centimeters for the males and 465 cubic centimeters for the females, less than half the size of our own. It became clear that these were not human beings but a primitive species with humanlike body parts.  

Named after the Dinaledi chamber in which it was found, Homo naledi posed challenges beyond perplexingly mismatched features. For example, where does Homo naledi fall along the spectrum of human evolution? Because the fossils were not buried in volcanic ash or in flowstone layers, dating the fossils based on their surrounding sediment was not an option. That left radioactive dating as the only viable route. As of September 10, 2015, no form of radioactive dating has been conducted on the Homo naledi remains. For now, we cannot ascertain Homo naledi’s age, but Berger and his team insist that its anatomy suggests it originated at or near the start of the Homo genus around 2.5 to 2.8 million years ago. They believe Homo naledi to be the transition between Australopithecines, ancestor species of modern hominids, and Homo species, like ourselves. 

Just as perplexing as Homo naledi’s identity is the question of how the skeletal remains ended up in such an incredibly remote chamber. Paleoanthropologists and researchers tested the merits of multiple theories. Conceivably, a group of Homo naledi could have lived in the chamber or found themselves trapped in it. However, the distribution of bones seemed to indicate that they were deposited there over a long period of time, rather than all at once. Perhaps the remains had been washed into the chamber by a stream of water. If this were true, the stream would have also brought in rubble and stone, none of which are present at the site. Having exhausted these likely explanations, Berger and his team arrived at their current conclusion: the bodies of deceased Homo naledi were deliberately placed in the chamber, which served as a burial site. Research shows that the narrow cavities Tucker and Hunter used to reach the chamber were once walkable, substantiating the theory that Homo naledi dragged corpses into the chamber to be buried.  

In order to believe this, we must also accept that torches or fires were used to light the way into the chamber through complete darkness. While the notion that such primitive, small-brained creatures could exhibit such complex behaviors is refuted by many researchers, no other explanation seems to be supported. “There isn’t a lot of subjectivity here,” says Eric Roberts, a geologist from James Cook University in Australia, having examined the chamber himself. “The sediments don’t lie.”  

Intentional disposal of the dead usually confers respect on the departed, brings closure for the living or aids in the transition to the afterlife. These sentiments represent the hallmark of humanity. Until now, it was thought that the first human burials took place a mere 100,000 years ago, long after the estimated age of Homo naledi. Berger claims, "Until the moment of discovery of 'naledi,' I would have probably said to you that it was our defining character. The idea of burial of the dead or ritualized body disposal is something utterly uniquely human." Homo naledi’s ability to perform ritualistic behavior such as burial suggests that they pondered their own mortality. This line of thinking completely alters our evolutionary perspective of what it means to be uniquely human.  

On September 10, 2015, nearly two years since Tucker and Hunter fortuitously discovered Homo naledi, Berger first announced his team’s startling findings to the public in a news conference. That same day, two research articles describing the new species were published in the biological science journal eLife, causing a buzz in the scientific community. 

To date, Berger and his team have uncovered remains from 15 distinct individuals, including infants, babies, toddlers, teens, young adults and even elderly individuals. Although intensive research has been conducted to assess the origin, anatomy and age of the species, many mysteries remain. "The chamber has not given up all its secrets," Berger says. "There are potentially hundreds if not thousands of remains of Homo naledi still down there." Years of careful exploration lie ahead, while other scientists will continue to challenge Berger’s controversial conclusions.  

Amidst the opposing theories, researchers will eventually piece together a consistent image of Homo naledi. It may take years or even decades. But until then, few will dispute that Homo naledi plays a truly significant role in the story of humanity.