A reconstructed Homo naledi skeleton made from the bones of multiple individuals. (Credit: Lee Roger Berger research team)

In 2013 a couple of spelunkers, caving 100 feet underground in South Africa, wriggled down a narrow vertical chute. They dropped into an uncharted chamber and in the flickers of their headlamps saw human-like bones scattered across the ground. It was a new species of hominin.

The fortuitous discovery in the Rising Star Cave system led to one of the most spectacular an