Johannesburg - For hundreds of thousands, even millions of years, they were hidden. No plants shared their tomb. No other animals. They lay beside each other inside the abyss, in a cave system named Rising Star, inside a chamber called Dinaledi – Sesotho for “the stars”.
Despite its name, there was no access to the skies inside the pitch black cave, a cave so remote it would take a 45-minute crawl through the Dragon’s Back to reach a crack 12m long and 17.5cm wide which opened into it.
Inside the chamber lay one of the greatest discoveries in the history of science – a palaeontological treasure trove.
For Lee Berger, research professor in human evolution and the public understanding of science at the University of the Witwatersrand, it started with a photo.
In September 2013, Rick Hunter and Steve Tucker, two amateur cavers, were exploring the Rising Star cave system, which lies near Sterkfontein and Swartkrans in Gauteng and is one of the most explored valleys in Africa.
The Rising Star has been known for almost 50 years. It had been mapped, people thought, completely. Almost every palaeontologist in the country has searched for fossils in this valley.
But they missed the biggest find.
The cavers went into the pitch black and found the Dinaledi chamber. They saw bones lying on the floor. A week later, they took a picture.
On a laptop, Berger saw a picture he thought he’d never see as a scientist: “I saw a mandible, the mandible of a primitive hominin, lying on the floor of this chamber. That shouldn’t be. We find our fossils in hard dense rock.”
“I thought for certain what I was looking at was a skeleton. Possibly the skeleton of an early hominin. That alone is unprecedented. You shouldn’t see that sort of thing,” he said.
Berger knew immediately something extraordinary lay in the deep, dark cave, but he couldn’t fit into the 17.5cm gap to look.
He needed scientists who could. So Berger sent out a plea on Facebook.
He asked for skinny scientists who were willing to drop everything and come to South Africa for a month.
On November 10, a team of 60 scientists went to the cave, six went in. Within hours, the first material came up.
“By the second morning, we knew I’d been wrong about everything. It wasn’t a single skeleton; it was multiple skeletons,” Berger said.
By the end of the 21-day expedition, the team had recovered the largest amount of individual hominin specimens discovered in Africa. The 1 550 bones came from at least 15 individuals both young and old.
The floor of the chamber was covered by the bones of what the scientists now know is a new species of human relative.
It is a hominin, a type of prehistoric creature that is part of the early human family tree. But, it is not a human, Berger explains. If you were standing next to this species, you would not mistake it for a human being.
The scientists named them Homo naledi – “star people” – after the cave system in which they were found.
But the true mystery of Homo naledi isn’t just in the bones they left behind. It lies in where they were found – that dark abyss where nothing else has lived or died. How did Homo naledi get there? “We have studied this chamber,” said Berger. “We’ve eliminated the normal causes for the accumulation of fossils like this.”
The bones have sat in a deep remote cave never opened directly to the surface of the earth. All the sediment inside comes from within the chamber. Homo naledi was well and truly alone. The scientists concluded that the bodies of Homo naledi were brought into the cave by relatives, deliberately placed there – they buried their dead – an action thought to be the sole preserve of humans.
What isn’t known is how they got in. Did they climb in with their curved fingers? They must have used fire. But the living naledi went into the dark zone, at considerable risk to themselves to put their dead there.
Berger said there is also evidence that the bodies were placed there over time. The way they lay, all alone, has also created another mystery. We have no way of knowing how old Homo naledi is. There is no rock overlying them, no rock under them. There is no datable sediment around them.
“It is an extraordinary circumstance,” said Hawks. “Naledi seems to be a type of time traveller. We can tell from their physical features that they must sit at the base of our lineage. They are so primitive in many ways.”
Berger said that if our present understanding of the origins of our genus is correct, then Homo naledi must originate from a time prior to 2.5 million years ago.
Homo naledi also could have continued down through time and may only be hundreds of thousands of years old. Nobody knows.
“They may go back into deep time. Whatever it is… we have enough fossils and evidence to take us on a very long journey,” said Berger.
Berger and the team have hinted that they’ve found something else in the fossil treasure trove of the Cradle of Humankind.
And in the words of one professor, “the best is yet to come”.
The find, and that of Australopithecus sediba in 2008, has inspired the scientific world.
Also thrilled about the discovery was Terry Garcia, the National Geographic Society’s chief science and exploration officer.
“For decades we have sent adventurous men out to map the world, and almost every dot has been filled. And even until this day, when it seems as if science has answered all the questions, there are still mysteries and wonders we haven’t seen. This is an example. I believe the 20th century is the great age of exploration.”
There is nobody who believes this more than Berger, who said they found Naledi in a cave system that is one of the most researched in the world.
“I had many sleepless nights thinking how I had spent 17 to 20 years roving the area searching for fossils. And I missed this,” he said.
Berger said palaeontologists believed 15 years ago that there were no new discoveries to be made. Scientists believed it was safest to conduct science in a lab.
“This site has been dug continuously since 1948. It is the most well-known fossil site on the continent, and we missed this. This shows us there is no substitute for exploration.”
He had stopped exploring for five years when his son found Sediba. “Now we are continuously exploring. Will we make more discoveries? We already have.”