Homo naledi is an extinct species of hominin, first discovered in 2013 in South Africa. This species has sparked considerable interest and debate among scientists, as the initial find consisted of over 1,550 fossil specimens from at least 15 individuals. This wealth of remains has provided an unprecedented look into an ancient human relative that presents a unique mosaic of primitive and modern features. The discovery continues to challenge our understanding of human evolution.
The Discovery in the Rising Star Cave
The story of Homo naledi began within the Rising Star cave system in the Cradle of Humankind, a UNESCO World Heritage site in South Africa. In 2013, recreational cavers exploring the system squeezed through a narrow vertical chute and stumbled upon a chamber deep underground, littered with fossil bones. This chamber, now named the Dinaledi Chamber, was exceptionally difficult to access, lying about 30 meters below the surface.
The cavers contacted paleoanthropologist Lee Berger, who assembled a specialized team to excavate the site in a safe and scientifically rigorous manner. Due to the extreme inaccessibility of the fossil chamber, he recruited a unique crew of slender scientists, dubbed “underground astronauts,” who had the caving and excavation skills to navigate the passages.
The team recovered a trove of hominin fossils, one of the largest such assemblages ever found in Africa. The bones belonged to males and females from infancy to old age. Further exploration later revealed another chamber, the Lesedi Chamber, containing more Homo naledi remains, including a well-preserved adult male skeleton.
Physical Anatomy of Homo Naledi
Homo naledi possessed certain features similar to early hominins like the australopithecines, such as a small braincase. The cranial capacity of Homo naledi was only between 465 and 610 cubic centimeters, roughly a third of the size of a modern human’s brain.
Its shoulders were positioned in a way that would have facilitated climbing, and its fingers were distinctly curved, another adaptation for an arboreal, or tree-climbing, lifestyle. This suggests that Homo naledi may have spent a significant amount of time in the trees. The structure of its torso and pelvis also retained some primitive characteristics seen in earlier hominins.
In contrast, other parts of the skeleton were surprisingly modern. The wrists, hands, and thumbs of Homo naledi showed adaptations for fine manipulation and dexterous hand use, similar to modern humans and Neanderthals. Its legs and feet were long and structured for efficient, long-distance walking with a modern bipedal gait.
Dating and Evolutionary Context
One of the most surprising aspects of the discovery was the age of the fossils. Initial analysis of the bones’ anatomy led many to believe they were much older, but direct dating of the remains and surrounding sediments, published in 2017, revealed them to be between 335,000 and 236,000 years old.
This unexpectedly young age places Homo naledi in the Middle Pleistocene, meaning it was alive at the same time as early Homo sapiens in Africa. The presence of a small-brained, primitive-looking hominin alongside anatomically modern humans suggests that the evolutionary landscape of the time was far more complex, with multiple hominin lineages coexisting.
The precise position of Homo naledi on the human family tree remains a subject of ongoing scientific discussion. One possibility is that it represents a relic species, an ancient lineage that survived for a very long time. Another scenario suggests it could be more closely related to modern humans, branching off from a more recent common ancestor. Its exact relationship to our own species is still unclear.
Debates Over Complex Behavior
The context of the fossil discoveries has led to some of the most contentious debates surrounding Homo naledi. The research team, led by Lee Berger, has proposed that the hominins intentionally placed their dead in the remote and inaccessible chambers of the Rising Star cave. This hypothesis suggests a form of deliberate body disposal or mortuary practice, a behavior previously thought to be unique to larger-brained species like Neanderthals and Homo sapiens.
The argument for intentional placement rests on the fact that the chambers are extremely difficult to reach and that there is little evidence of the bones being washed into the cave by water or dragged in by predators. The remains of at least 15 individuals were found in the Dinaledi Chamber, and the discovery of what appear to be deliberately dug pits containing collections of bones has bolstered this claim. If this interpretation is correct, it would be the earliest evidence of such behavior in the hominin record by a significant margin.
More recently, the research team has put forward even more striking claims: the discovery of charcoal and burnt bone fragments suggesting the controlled use of fire deep within the cave system, as well as markings on the cave walls that have been interpreted as deliberate engravings or rock art. These assertions are debated within the scientific community. Skeptics argue that the evidence for burial is not definitive and that other natural processes could explain the accumulation of bones.
The claims of fire use and engravings face similar scrutiny, with other researchers calling for more rigorous analysis to rule out natural causes for the markings and the presence of charcoal. The possibility that a small-brained hominin could engage in such complex, meaning-making behaviors is significant, but the evidence is still being carefully evaluated by the broader scientific community.