On an unremarkable day in 2013, two professional cavers decided to squeeze through a passageway in South Africa that they had never gone through before. They contorted themselves through more than 650 feet of rocky and dangerous passageways, as narrow as seven inches wide in some parts, before dropping down into a cave quite literally covered in hominin fossils. These fossils would later reveal the existence of Homo naledi, a new species of human ancestor that has a similar hand, foot, and skull shape to humans but with apelike shoulders and a tiny brain.

Paleoanthropologist and National Geographic Explorer-in-Residence Lee Berger put together a team of six anthropologists, archaeologists, and paleontologists to retrieve these bones. Because of