Homo naledi: Who are these strange star children?

“THEY are non-human," declares palaeoanthropologist Lee Berger  about the latest, controversial discoveries at the fossil burial site of Homo naledi in the Rising Star cave system in the Cradle of Humankind. How do I translate non-human? Not-human? So what is human-like? And who, or what, was the strange Homo naledi?

We define our humanity by our DNA codes and share 99.5% of our DNA with the extinct Neanderthals. Modern anatomically modern humans and Neanderthals could interbreed. The remnants of their DNA are found in the genes of Europeans. Now Lee Berger comes along and says the latest research on the enigmatic Homo naledi suggests they are non-human.

In 2008, just after Berger's controversial discovery of Homo sediba, I walked with him over the grassy hills of the Cradle of Humankind. Lee was as excited as a little boy with birthday presents. He explained how satellite photography, laser technology and terrain radar are used to identify new palaeontological sites.

In 2013, he struck gold. In an almost inaccessible cave system, now known as Rising Star, Berger's team discovered a treasure trove of fossil bones from an unknown species that he named Homo naledi, or star children. Hundreds of bones from deep in the cave's dark passages showed that the species were small in stature with a brain about a third of the size of modern humans. It was the find of the century. But who were they?

Intelligent life

Classical theory on the evolutionary development of humans says we started with small brains that gradually grew bigger over a few million years. Australopithecus africanus, including the Taung Child and Mrs Ples from Kromdraai, had brains of about 450g. The brain of Homo habilis was 600g. Homo erectus, the wanderer who travelled widely to Asia, had a 950g brain. And modern humans' brains average 1,350g.

As brains grew, intelligence emerged. Yet now Homo naledi comes along with a brain one-third the size of ours but with human-like hands and feet and behaviour indicative of a modern “culture". Their brain size should have placed them among prehistoric early humans about
2-million years ago. But modern dating techniques — thermoluminescence and electron spin resonance — show they lived as recently as 250,000 years ago.

“They looked like they should have lived millions of years ago but they were actually existing 250,000 to 350,000 years ago, the same time modern humans were evolving," Berger said in Washington at the National Geographic Society, which funded the research. “It's a remarkable thing. My mind is blown. Much of what we thought about the origin of intelligence and the cognitive powers of having a big brain clearly just died."

In London, Chris Stringer of the Natural History Museum declared: “The evidence is impressive. These humans were taking carcasses, bodies of fellow naledis, down deep into the cave, and they must have had artificial lighting. This is remarkable behaviour for a creature that’s got an ape-sized brain. It suggests organisation, because this is not something a single individual would have done, it must have been a group activity. And it’s obviously happened multiple times. That implies the existence of what we might call a culture — a different species, not closely related to us.”

Discoveries that astonished the world

The Rising Star system was discovered by amateur cave explorers in 1999. In 2008, with their help, Berger mapped the underground caverns and passages. But it was only in 2013 that a team of female palaeontologists — they all had to be small in stature — could crawl through the treacherous tunnels to open the Dinaledi chamber for scientists. The narrow passageways were sometimes only 20cm wide. What they saw in the light of their headlamps astonished the world: an underground burial site with hundreds of fossil skeletons.

Then came new discoveries. A rock passage led to a second chamber, dubbed Heuwel. And a narrow passage about 100m from Dinaledi led to a third, Lesedi (Tswana for “light"). There, scientists found the fossilised body of a child and an almost complete adult skull.

“Finally, we come face to face with Homo naledi," wrote Peter Schmid of Wits and Zurich universities, who spent days reconstructing the bones. With his typical flamboyant style, Berger named the adult skull Neo, Keanu Reeves' character in The Matrix.

Berger and his team also found evidence of soot and burnt animal bones, indicating that the naledis used fire — quite possibly for light in the underground tunnels. And they discovered shallow graves hollowed out in the cave floor, where the deceased were laid to rest and covered with soil.

So many questions

Not all scientists are convinced of Berger's claims. He is known for “breaking news" statements that often raise seasoned eyebrows. Bernard Wood of Washington University, for example, believes Homo naledi, like Homo floresiensis — a species of dwarf humans from Indonesia — is a mishmash of various species in Africa. Nothing to get excited about.

A former student of Berger, Aurore Val from Wits, is also not convinced the bones were buried there. She believes we know too little about the condition of the cave a quarter of a million years ago. The current cramped and suffocating narrow passages could have been caused by geological shifts.

But Berger and his team stand their ground. And like a determined general leading his troops, Berger took on the impossible task. He would go and see for himself.

In the underground depths

I know Berger as a fairly well-built man with no chance of squeezing through the dark tunnels. But he went on a strict diet, shed 25kg, and made his way into the cave. A terrifying experience. I quote his own words:

“I’ve sat there [before the chute labyrinth] many, many times thinking to myself: what have I done? I’m contemplating my choices in life. I want to call my mum… My adrenaline is pumping and my mouth is dry, and I need that last sip of water, the last sip to get me through what I’m going to see next... the chute labyrinth, the tiny space that separates the adventurous from the not-so-adventurous… That dreaded labyrinth is essentially a crack in the ground with large dolomite points sticking out of it, grabbing you, preventing you from falling to your death as you descend; and of course you have to use these points to help you ascend to the surface.”

He made it to the Dinaledi Chamber. There, in his headlamp's light, he saw a rock pillar with strange scratch marks on it. This pillar led to the Heuwel Chamber and later to Lesedi. On rock walls above the alleged graves, the team discovered enigmatic etchings, carved into the hard rock. Circles and crosses, crude symbols and long lines. What could they mean? We still don't know, says Berger. But they are similar to engravings made by Neanderthals and modern human cave-dwellers.

Did Homo naledi have contact with the primitive humans, our ancestors? It seems so, says Berger. Is it ritual “rock art" at their graves? We don't know, he says. Ultimately, the key to their origin lies in their DNA. Three attempts to extract DNA from the fossil bones have failed so far. “But we will keep trying," says Berger. “And one day, we will know who these strange star children of Southern Africa are."

The search continues

There are still so many unanswered questions,  but in Berger's words, “we can no longer assume that we know which species made which tools, or even assume it was modern humans that were the innovators of some of these critical technological and behavioural breakthroughs in the archaeological record of Africa. If there is one other species out there that shared the world with ‘modern humans' in Africa, it is very likely there are others. We just need to find them."

He believes there are kilometres of undiscovered cave tunnels beneath the Cradle of Humankind that still need to be investigated. To do so, Berger has assembled an impressive team: 52 scientists from international universities. But they won't just plunder the caves for research, says Berger. “We, as humans, have to decide how we're going to approach the space of another species that they clearly saw as critically important to them."

Lee Berger is not a man who hesitates to trumpet his discoveries. He is flamboyant, challenging, self-assured and not always popular. But I admire him. He is not afraid to speak his mind. And he makes things happen.

♦ VWB ♦

BE PART OF THE CONVERSATION: Go to the bottom of this page to share your opinion. We look forward to hearing from you!