What it feels like to turn human evolution on its head

In 2013 a collection of fossils was found deep in a cave in South Africa in a region dubbed the Cradle of Humankind. These fossils would turn human evolution on its head.

Homo naledi was first introduced to us in 2015, a previously unknown human ancestor whose fossils were found in the Rising Star Cave system in South Africa. The find shows that the landscape of human evolution is more complex than previously thought.

“These [fossils] are really turning human evolution on its head a little bit and that’s exciting times,” explains geologist and Associate Professor Eric Roberts. “The reason why it’s interesting and significant to people in general is that it’s about our origins, it’s about understanding the complexity of our origins.”

The complexity is surrounding naledi’s morphology – the bone and skeletal structure – and the age of the fossils. Based on physical features of the skull, paleoanthropologists initially declared that the fossils were two million years old, however they were found in mud, not rock, which indicated they were much more recent.

“Right from the beginning we had a bet with the paleoanthropologists that these things weren’t going to be two million years old – it was going to be much younger because the geology didn’t fit,” says fellow geologist, Professor Paul Dirks.

Eric at work inside the chamber. Photo: Marina Elliott, Supplied.

Paul and Eric, along with their geology and earth science colleagues at JCU, have been providing essential expertise to place dates on the fossils, which they believe to be between approximately 236 000 to 341 000 years old.

“Our contribution has all been about proving the importance of geology and how much geology can add to understanding this whole story about human life,” says Paul.

“Not just the dating itself, which is of course very important, but also about providing context.”

The context is significant because it’s the first species of hominin in Africa in the last half a million years that potentially lived side by side with either Homo sapiens, or primitive Homo sapiens.

Add to this that naledi’s morphology clearly suggests it was capable of using stone tools, then this find also opens up an important archaeological perspective.

“Any stone tools found from that time period in Africa are always automatically ascribed to Homo sapiens cultures,” Paul explains. “And here we’ve got an animal that is not Homo sapiens and it has hands that probably can use stone tools. So which tool was a Homo sapiens stone tool and which was naledi? And did naledi learn from Homo sapiens or did Homo sapiens learn from naledi?”

To be involved in such a significant discovery has been exciting for Eric and Paul, who both feel very privileged to be part of it.

“If you think about science, there’s a wonderful element of discovery,” Eric says.

“It’s thrilling. It’s exciting. And hominins are among the most celebrated of all fossils.”

“It’s nice to be involved with something that you know that people are interested in,” Paul adds. “It offers such an opportunity to make your own area of interest so much more interesting to people as well.”

The excitement and enjoyment of working on such a discovery began early when Paul and Eric found themselves crawling through the Rising Star cave system, which is often very narrow, and experienced the feeling of the unknown that goes with it.

“You don’t know whether you’re going to be able to fit and that adds a whole other element,” Eric says. “Not only if you’re going to be able to fit, but will you be able to get yourself back up? And I can say both of us have been stuck on more than one occasion. Not threateningly stuck, but enough to keep the adrenalin going. That’s exciting.”

Eric and JCU post-doc Hannah Hilbert-Wolf. Photo: Marina Elliott, Supplied.

When Eric arrived to make his first journey into the chamber where naledi was found in 2013, he was greeted by two professional cavers, who decided to play good cop, bad cop with him.

“One of them’s saying, ‘you’ll make it, I don’t think it’ll be a problem’ and the other one’s looking at me saying, ‘I think you’ll make it but I’m not really sure’,” he says. “One of them goes first and the other follows me and I get in there, and it’s pretty terrifying to be honest, but after you get into it and you start moving, you sort of settle down.”

The route is physically demanding and includes vertical climbs down and places where it’s so tight you barely fit, while you need to angle your body to get though. But once into the fossil chamber, Eric said it was an honour.

“It’s amazing,” he says. “I’ve worked on fossil sites all over the world and they’re always exciting, but there’s a whole different order of significance when you look across this chamber floor and you see hominin fossils scattered across the floor.”

Naledi’s significance doesn’t end with its place in human evolution, or human archaeology. There’s also the potential for an anthropological perspective.

In southern Africa, there are folk tales of the tokoloshe. A mythical being that lives underground and comes out at night to sneak around and steal things.

“There’s a lot of legends in the world,” Paul says. “And increasingly, as research progresses, we are starting to realise that some of these legends ultimately have a core of truth attached to them somewhere.”

These tales are likely to have been completely misinterpreted and retold so many times that they don’t look like the original anymore but somewhere there is something that may hark back to a real observation.

“Now that the age potentially overlaps with humans, I’m sure this will surface again that we’ve found tokoloshe,” Paul says.

“Look at how far Aboriginal spoken history goes back here. They still know about the ice ages. They still tell the legends of being able to walk out to Magnetic Island. That’s the same sort of time period.”

Before entering the cave in 2016. L-R: Paul Dirks, Eric Roberts, Jelle Wiersman (JCU PhD student), Marina Elliott (University of the Witwatersrand), Hannah Hilbert-Wolf (JCU post-doc), Jess Robbins (JCU PhD student). Photo: Marine Elliott, Supplied.

Paul and Eric are keen to remain involved on this project, which they hope will lead to more exciting discoveries.

“This is not the end of it,” Paul says. “We know there are other hominids that haven’t been described yet, which we just need to go and look at. This is an incredible situation to be in.”

“For us to be able to work out the context of such a unique and unusual fossil discovery is wonderful,” Eric says. “It’s a wonderful detective story in a way. “

And Paul’s bet with the paleoanthropologists about naledi’s age?

“I get a big bottle of wine out of it,” he says.

Cover image: Eric Roberts working with JCU post-doc Hannah Hilbert-Wolf. Photo: Marina Elliott, Supplied

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