Wedged in a narrow crevice about 150 feet underground in South Africa's Rising Star cave system, Becca Peixotto squeezed between the rocky walls to work her way around a bend. Inch by inch she wriggled her body through the twisting passage, turning nearly upside down to reach a small ledge where a scientific treasure awaited—the teeth and bone fragments of a child who lived more than 240,000 years ago, an enigmatic human relative known as Homo naledi.

The find adds to nearly 2,000 bones and teeth of H. naledi recovered from Rising Star since cavers stumbled upon the first fossils in 2013. The remains of the child—estimated to have died between four and six years old—include six teeth and