The discovery in the cave of stars

In September 2013, two recreational cavers — Rick Hunter and Steven Tucker — exploring the Rising Star cave system came through a passage known as “Superman’s Crawl” (requiring cavers to extend one arm ahead and squeeze through on their side) and descended a vertical shaft approximately 12 metres deep and 18 cm at its narrowest point. At the bottom, they found the floor carpeted with fossils. They photographed the fossils and sent the images to paleoanthropologist Lee Berger of the University of the Witwatersrand, who recognised immediately that the bones were hominin. Berger advertised in November 2013 for “small, slightly built cavers” who were also scientists — maximum height approximately 150 cm, maximum shoulder width approximately 25 cm. Six women were selected: the “Underground Astronauts,” who worked in the narrow chamber for weeks while communicating with Berger’s team on the surface via video link.

The species was announced in September 2015 in two papers in eLife. The morphology was baffling: the brain (465-610 cubic centimetres) was barely larger than a gorilla’s. But the feet were almost identical to those of modern humans; the hands combined curved, climbing-adapted fingers with a thumb capable of precision grip; and the teeth were distinctly Homo-like. The primitive brain led early estimates toward approximately 2 million years. Uranium-thorium and electron spin resonance dating published in 2017 instead placed the Dinaledi Chamber fossils at 335,000-241,000 years — contemporaneous in Africa with the earliest Homo sapiens, whose oldest known remains (Jebel Irhoud, Morocco) date to approximately 300,000 years ago.

The most controversial aspect is the taphonomy: why are 15+ hominin individuals in a chamber with no other fauna, no evidence of carnivore activity, and no catastrophic event? Berger’s team argues that Homo naledi must have deliberately placed its dead in the chamber — mortuary behaviour previously documented only in Homo sapiens and Neanderthals, both with much larger brains. In 2023, Berger’s team announced possible engraved geometric marks on the cave walls of the Lesedi Chamber, suggesting symbolic behaviour in a small-brained hominin, compounding the debate about cognitive capacities in Homo naledi.