Homo naledi is an extinct species of hominin, a group that includes modern humans and our close ancestral relatives. First identified in 2015 from a large fossil collection in South Africa’s Rising Star Cave system, this species has challenged our understanding of the human family tree. Its unique combination of anatomical traits and surprisingly recent existence have made it a subject of intense scientific debate.
Discovery Within the Rising Star Cave System
The story of Homo naledi began in September 2013, when recreational cavers Rick Hunter and Steven Tucker explored an unmapped section of the Rising Star cave system. They navigated a narrow, 12-meter-long vertical chute and entered a chamber 30 meters underground, where they found the floor covered in fossil bones. Recognizing the potential of their find, they brought photos to paleoanthropologist Lee Berger, who organized an excavation.
Accessing the Dinaledi Chamber was difficult, requiring excavators small enough to fit through passages as narrow as 20 centimeters. Berger recruited a specialized team of six scientists who were also experienced cavers. Their work led to the recovery of over 1,550 fossil specimens from at least 15 individuals, the largest single collection of a hominin species found in Africa.
In a subsequent discovery within the Lesedi Chamber, another 133 specimens were found, representing at least three more individuals. The context of the finds, deep within a dark and nearly inaccessible cave network, raised questions about how the remains came to be there.
Anatomical Portrait of Homo naledi
Homo naledi presents an anatomical puzzle, with a mosaic of features that combines traits seen in primitive australopithecines with those of more recent Homo species. The species had a small body size, with an average height of about 144 centimeters, and a body mass similar to that of small-bodied modern human populations.
The cranium of Homo naledi is one of its most distinct features. It housed a small brain with an endocranial volume of only 465 to 610 cubic centimeters, comparable to the brain size of an Australopithecus. Despite this small size, the overall shape of the skull shares similarities with early Homo species like Homo erectus, and its dentition is small and simple.
The rest of the skeleton continues this pattern. The hands and wrists are human-like, suggesting tool-using capabilities, but the fingers are long and curved for climbing. The shoulders and torso are also more like those of an australopithecine. In contrast, the pelvis is flared like an Australopithecus, yet the long legs and modern-looking feet were adapted for upright, bipedal walking.
Unexpectedly Recent Existence
When Homo naledi was first discovered, its blend of features led many scientists to hypothesize that it was a very old species. The scientific dating of the fossils, announced in 2017, was a surprise. Using multiple independent techniques, researchers determined that the remains from the Dinaledi Chamber were deposited between 335,000 and 236,000 years ago.
This young age places Homo naledi in the Middle Pleistocene, a period when early Homo sapiens and other archaic human species were already in Africa. The revelation that a small-brained hominin with a primitive body plan survived for so long challenged the view of human evolution as a linear progression. It showed that more advanced species did not simply replace more primitive ones.
The existence of Homo naledi alongside our own direct ancestors demonstrates that human evolution was more complex and diverse than previously thought. It indicates that multiple hominin lineages coexisted, each with its own set of adaptations. The late survival of this species raises new questions about the ecological landscape of Africa during this period.
Potential Behaviors and Cultural Practices
The location of the fossils has led to the debated hypothesis of deliberate body disposal. Proponents, including Lee Berger, argue the chambers were always dark and difficult to access, making accidental falls or predation unlikely. The absence of other animal fossils and predator marks on the hominin bones supports this view. This suggests the bodies were intentionally placed in the cave, a behavior previously associated only with larger-brained species.
This hypothesis is not without its critics, who propose alternative explanations. Some scientists suggest the individuals could have become trapped in the cave and died, or that their bodies were transported into the chambers by flowing water. Researchers continue to analyze the geology and sediments of the cave system to better understand how the deposits were formed.
More recently, the discussion has expanded to include claims of even more complex behaviors. As of 2023, Berger’s team has put forward preliminary evidence suggesting Homo naledi may have created engravings on the cave walls and used fire for illumination. These claims are contentious and are undergoing intense scientific scrutiny. Notably, despite hand anatomy well-suited for toolmaking, no stone tools have been found in direct association with the remains.
Homo naledi’s Place in the Human Story
The combination of features and recent age of Homo naledi make it difficult to place within the human family tree. Scientists debate whether it represents an early branch of the genus Homo that survived for a long time or if it has a more recent common ancestor with other human species.
The existence of a small-brained, partially primitive hominin alongside early modern humans challenges the idea that larger brain size was the only successful evolutionary strategy. Homo naledi shows that the path of human evolution was not a simple line, but a complex process with multiple hominin species coexisting.
The species highlights the potential for future fossil discoveries to reshape our understanding of the hominin lineages that shared the planet with our ancestors. Homo naledi has added a new and unexpected character to the human story, illustrating the rich complexity of our evolutionary past.