This we know because the six women who entered the cave excavated one of the richest collections of hominin fossils ever discovered—some 1,550 fossil fragments, belonging to at least 15 individual skeletons. To find one complete skeleton of a new hominin would be hitting the paleoanthropological jackpot. To find 15, and perhaps more, is like nuking the jackpot from orbit.

John Hawks

The early hominins included the australopiths, with their sturdy builds, long arms, short legs, and small brains. A couple of million years ago, they were joined by the first members of our genus Homo, with their longer legs, stiffer walking feet, more dextrous fingers, and much larger brains. And some curious species harbor traits that are typical of both lineages.

In 2008, Berger found one such mosaic in South Africa’s Malapa cave: a new hominin called Australopithecus sediba. He spent the next five years studying it. The project became so all-encompassing that in 2013, Berger, an explorer at heart, realized that he had stopped exploring. To rectify that, he enlisted two cavers, Rick Hunter and Steve Tucker, to explore other South African caves that might yield important fossils. The Rising Star Cave was one of them.

When the duo entered it in October 2013, they weren’t expecting much. Cavers had thoroughly explored the system for some 50 years, and the chances of finding anything new were low. Tucker did so by accident. During a rest, he wedged himself in a crevice—and found that his feet didn’t touch the bottom. The crevice, it turned out, led to an absurdly narrow shaft, which descended for 12 meters before opening into a chamber. When Tucker dropped into it, he found bones. He took out his Go-Pro and snapped some shots.

When Berger saw the pictures, he was amazed. He was clearly looking at the skull and jawbone of a hominin, maybe an Australopithecus. “That evening, I couldn’t sleep,” he says. At 2 in the morning, he called Terry Garcia, the National Geographic Society’s chief science and exploration officer, who had funded Berger’s digs before. “If you ever believe in me, believe in me now,” Berger said. “Terry said: Do whatever you need to do.”

Berger quickly rounded up a team of scientists—and six skinny cavers. Marina Elliott was the first and oldest of them on the scene. When she first saw Berger’s ad, she was finishing off a Ph.D. at Simon Fraser University and had already done a lot of fieldwork in Siberia and Alaska. “I was predisposed to extreme environments,” she says. “Telling me that I’d have to do climbing, that it would be underground, and that it would be strange and potentially dangerous… it appealed.” She was joined by five others: Elen Feuerriegel from Australia, and Americans K. Lindsay Eaves, Alia Gurtov, Hannah Morris, and Becca Peixotto.

By November 7th, a month after Berger’s ad went up, a 60-person camp had assembled next to the Rising Star cave. Three days later, the team ventured inside. “We knew the fossils were going to be super-important. They clearly weren’t human,” says John Hawks from the University of Wisconsin–Madison, whom Berger recruited. “We thought we were going to excavate one skeleton. Because what else would you find?”

After entering the cave, the team almost immediately hit several narrow, pitch-black corridors, a knife-edge ridge called the Dragon’s Back with steep drops on either side, and finally that 12-meter chute. “It’s a long crack, punctuated by shark-teeth protrusions,” says Elliott. “I remember looking down and thinking: I’m not sure I made the right decision.”