On September 13, 2013, local cavers Rick Hunter and Steven Tucker set out to explore the Rising Star cave system, located about an hour’s drive northwest of Johannesburg, South Africa. The cavers had no idea they were about to make a once-in-a-lifetime discovery. About 120 meters (400 feet) into the cave, Hunter and Tucker climbed up Dragon’s Back, a narrow spine of rock crested with spikes (see Rising Star Cave). At the top, Tucker moved into a crack in the cave floor so Hunter could step over him. As he did, Tucker realized that what he was standing in wasn’t a crack at all, but a vertical chute into a previously unmapped part of the cave. 

The cavers shimmied down the chute—just 20 centimeters (8 inches) wide in some sections—and dropped down into a chamber. “That’s where we saw the bones,” says Hunter. It quickly became clear that the cave floor was dotted with human-like remains: bone fragments, a semicircle of skull, and a jawbone studded with teeth. “They seemed human, but not human,” says Hunter. “They were so strange.”

The cavers took photos of the site to show to a local geologist, who alerted scientist Lee Berger. Berger is a paleoanthropologist (scientist who studies the origins of humankind) at the University of the Witwatersrand in Johannesburg. He took one look and knew what the cavers had stumbled upon—the bones of an extinct human ancestor.

Berger wondered: Who were the ancient people who ended up in the cave, and what could they tell us about human evolution?

Berger couldn’t wait to see the bones. But he couldn’t hope to fit through the tight passage himself to retrieve them. He needed a team of skilled excavators made up of people small enough to be able to squeeze through the chute. The group would have to be comprised of highly specialized anthropologists (scientists who study humans) and archaeologists (scientists who study the past). He got to work assembling a team he could trust. 

Berger posted a plea for help on Facebook asking for experts who were “skinny and preferably small” with caving and climbing experience. “I saw the post and I thought, ‘That’s me,’” says Alia Gurtov, an anthropology graduate student from the University of Wisconsin-Madison who has excavated the remains of ancient human relatives all over the world. By November 2013, Gurtov and five other female scientists were on planes headed for South Africa. 

Most paleoanthropologists go their entire careers without discovering remains of ancient human ancestors. The few who do usually find no more than a tooth fragment. The fossils for some entire species amounts to a few pieces of bone. So Gurtov and the team were shocked by what they discovered in the cave. “Every time we uncovered one bone, we found another—there were so many that getting them out was like a game of pick-up sticks,” says Gurtov.

By the end of the three-week excavation, they had discovered bones from at least 15 individuals—of all ages, ranging from infants to the elderly. “It is one of the most significant discoveries for human evolution in all of Africa,” says Gurtov.

So far, the scientists have pulled more than 1,500 bones out of the cave, but 90 percent of the chamber hasn’t been excavated yet. The evidence they’ve gathered so far indicates that groups of this ancient human may have lived in caves that dot the area, using their strong hands to clamber over rocks and up steep slopes. 

As the scientists squirmed through the dark, twisted tunnels to get to the remains, they couldn’t help but wonder: How did the bones get there in the first place?

They wondered if animals had dragged the bodies into the cave to eat—but there were no tooth marks on the bones or remains of other prey. So far there’s only one explanation that hasn’t been ruled out: H. naledi may have intentionally brought their dead into the Rising Star cave and laid them to rest in the chamber. 

The story of H. naledi is just beginning to unfold. Researchers recently discovered more fossils in another part of the cave 200 meters (650 feet) from the first site. “Lots of new finds are on the horizon!” says anthropologist Lindsay Hunter of the Rising Star team.