Homo naledi: The Rising Star Cave Discovery in South Africa

Homo naledi is an extinct species of early human discovered in 2013 in the Rising Star cave system, about 50 kilometres north-west of Johannesburg in South Africa. Its fossils, more than 1,500 pieces from at least 15 individuals in the first excavation alone, revealed a creature with a brain little larger than a chimpanzee’s but hands and feet much like ours. When dating in 2017 showed that it lived only around 335,000 to 236,000 years ago, Homo naledi became one of the most surprising discoveries in the study of human origins.

Background: the Cradle of Humankind

The Rising Star cave lies in the Cradle of Humankind, a UNESCO World Heritage Site since 1999 that has produced many famous fossils, including Mrs Ples and Little Foot from nearby Sterkfontein. The dolomite hills are honeycombed with caves, and the area had been explored by palaeontologists and recreational cavers for decades.

Lee Berger, a palaeoanthropologist at the University of the Witwatersrand, had already made headlines in 2008 when his young son found the fossils later named Australopithecus sediba at Malapa, elsewhere in the Cradle of Humankind. Encouraged by that success, Berger asked local cavers to look out for fossils in the region’s caves.

Discovery in the Dinaledi Chamber

On 13 September 2013 two cavers, Rick Hunter and Steven Tucker, squeezed through a tight gap known as Superman’s Crawl, climbed over a jagged ridge called the Dragon’s Back, and lowered themselves down a narrow vertical fissure, the Chute, about 12 metres long and in places only around 18 centimetres wide. At the bottom, some 30 metres below the surface, they found a small chamber whose floor was scattered with bones, including part of a human-like jaw.

Because so few experienced scientists could fit through the Chute, Berger advertised on social media for skinny researchers with caving and excavation experience. Six women were selected: Marina Elliott, Elen Feuerriegel, Alia Gurtov, Lindsay Hunter, Hannah Morris and Becca Peixotto, who became known as the “underground astronauts”. In November 2013 and March 2014 they worked in the chamber in shifts, linked by cables to a command centre on the surface where other scientists followed every move on video.

Working conditions were extreme. The chamber was dark, cramped and humid, every tool and bag of sediment had to pass through the Chute, and the excavators spent hours at a time underground. Rather than digging quickly, the team mapped and photographed each bone before lifting it, often brushing away sediment with paintbrushes and toothpicks, so that the position of the remains could later be studied in three dimensions.

The excavations recovered about 1,550 hominin specimens, an exceptionally large haul. Almost all the bones belonged to the same kind of creature, with only a few remains of birds and rodents mixed in, a highly unusual pattern for a fossil cave.

Naming a new species

Some 50 early-career researchers were invited to Johannesburg in May 2014 to study the material in an intensive workshop. On 10 September 2015 the team announced the new species, Homo naledi, in the open-access journal eLife. “Naledi” means “star” in the Sesotho language, and the chamber was named Dinaledi, “chamber of stars”. The fossils came from at least 15 individuals, from infants to elderly adults.

Homo naledi turned out to be a strange mosaic. Adults stood around 1.5 metres tall and weighed perhaps 40 to 55 kilograms. Their brains were small, roughly 465 to 560 cubic centimetres in the Dinaledi skulls, comparable to australopiths. Yet the wrist and the long, strong thumb were human-like, and the feet were almost modern, suited to long-distance walking. At the same time the fingers were strongly curved, the shoulders adapted for climbing, and the flaring pelvis recalled much older species. The teeth were small and simple, more like those of later humans.

A surprisingly young species

In 2015 the fossils had no reliable date, and many observers assumed that such a primitive-looking species must be around two million years old, close to the origin of the genus Homo. One statistical analysis of its anatomy, published in 2016, estimated an age of roughly 900,000 years.

In May 2017 the researchers published dates obtained by uranium-thorium and electron spin resonance dating of three Homo naledi teeth, combined with uranium-series dating of flowstones and palaeomagnetic analysis. The fossils turned out to be between about 335,000 and 236,000 years old. That made Homo naledi a contemporary of the earliest known Homo sapiens, such as those at Jebel Irhoud in Morocco, and of the large-brained human from Kabwe in Zambia.

The Lesedi Chamber and “Neo”

Alongside the dating, the team announced a second chamber in the Rising Star system, the Lesedi Chamber, “chamber of light”, more than 100 metres from Dinaledi. It contained the remains of at least three further individuals, including a remarkably complete adult skeleton nicknamed “Neo”, meaning “gift” in Sesotho. Neo’s skull had a brain volume of around 610 cubic centimetres, at the upper end for the species.

In 2021 the team described parts of the skull and teeth of a child of about four to six years, nicknamed “Leti”, from the Setswana word “Letimela” meaning “the lost one”. The bones lay in a tiny passage leading off the Dinaledi system. Each new find added to the puzzle of how so many bodies came to be so far inside a dark and almost inaccessible cave.

The burial debate

From the start, the team argued that the bodies had not been washed in by water or brought by predators: the bones showed no tooth marks, there were few other animals, and the chamber appears to have always been hard to reach. In 2015 the researchers proposed “deliberate body disposal”, meaning that Homo naledi repeatedly carried its dead into the dark zone of the cave.

In June 2023 Berger and colleagues went further. In three preprints submitted to eLife, they reported what they interpreted as dug graves containing bodies in the Dinaledi Chamber and in a nearby antechamber, geometric engravings on the cave walls, and traces of soot suggesting the use of fire to light the way. These claims would imply complex, possibly symbolic behaviour in a species with a brain about a third the size of ours.

Independent reviewers and many other specialists were sceptical. They argued that the papers did not adequately rule out natural processes for the sediment patterns, that the engravings had not been shown to be made by Homo naledi or dated, and that the evidence for fire was thin. As of the mid-2020s these burial and engraving claims had not won general acceptance, and the debate continues.

Why Homo naledi matters for human evolution

Homo naledi shows that a small-brained human species survived in southern Africa long after larger-brained humans had appeared elsewhere. It undermines a simple story in which brain size steadily increased along a single line leading to us. Instead, Africa around 300,000 years ago was home to several kinds of humans, each with its own mix of primitive and advanced traits.

Its place on the family tree is uncertain. Some researchers think Homo naledi descended from an early branch of Homo that split off around two million years ago and survived in isolation; others link it more closely to Homo erectus or later species. Because no ancient DNA has been recovered from the fossils, anatomy is the only guide. Another open question is what tools Homo naledi used. No stone tools have been found with the fossils in the deep chambers, although its hands look well suited to making and handling them. Some researchers have suggested that Homo naledi could have made some of the Middle Stone Age tools found at other sites in the region, but this remains speculation without direct evidence.

The project also changed how fossils are shared. Berger’s team published in open-access journals and released 3D scans of many bones online, allowing scientists, teachers and students around the world to study and print them. That openness, along with the dramatic cave expeditions, made Homo naledi one of the best-known fossil finds of the 21st century.

By the numbers

Timeline

• c. 335,000-236,000 years ago: Homo naledi remains accumulate in the Dinaledi Chamber.
• 2013, 13 September: Cavers Rick Hunter and Steven Tucker find bones in the Dinaledi Chamber.
• 2013, November: The first Rising Star expedition recovers hundreds of fossils.
• 2014, March: A second excavation season brings the total to about 1,550 specimens.
• 2015, 10 September: Homo naledi is announced in the journal eLife.
• 2017, 9 May: Publication of the dates and of the Lesedi Chamber and the “Neo” skeleton.
• 2021, November: The child’s skull “Leti” is described.
• 2023, June: The team claims evidence of burials and engravings; the claims are widely disputed.

Why it matters

Homo naledi proves that the human family tree was far bushier and more surprising than once believed, with small-brained and large-brained humans living in Africa at the same time. Whether or not it buried its dead, its discovery has reshaped debates about what made our ancestors human, and it shows how much may still lie hidden in caves that scientists thought they knew.