Homo naledi represents a significant discovery in the study of human evolution. This ancient hominin, unearthed in South Africa, has challenged long-held assumptions about our family tree. Its surprising mix of features and puzzling placement in time has spurred new discussions among scientists. This find has reshaped our understanding of the diverse paths early human relatives may have taken.
The Astonishing Discovery
The discovery of Homo naledi began in 2013 within the Rising Star Cave system in South Africa’s Cradle of Humankind. Two cavers, Rick Hunter and Steven Tucker, stumbled upon numerous hominin fossils deep within the Dinaledi Chamber. This chamber is exceptionally challenging to access, requiring navigation through extremely narrow passages, one as constricted as 7.5 inches across, and a vertical drop of about 39 feet, often referred to as “The Chute.”
The challenging conditions necessitated a unique approach to excavation, leading to the recruitment of slender cavers and scientists, dubbed “underground astronauts,” to retrieve specimens. This team, led by paleoanthropologist Lee Berger, recovered a significant volume of fossils. Over 1,550 specimens were found from the Dinaledi Chamber, representing at least 15 individuals, the largest collection of a single hominin species ever found in Africa. An additional 133 specimens from at least three more individuals were later found in the nearby Lesedi Chamber.
A Mosaic of Traits
Homo naledi exhibits a unique blend of primitive and modern anatomical features, making its classification complex. Its brain size is notably small, ranging from approximately 465 to 610 cubic centimeters, comparable to earlier hominins like australopithecines and significantly smaller than modern human brains. This small brain size contrasts with its relatively human-like hands and feet.
Its hands possess wrist bones and a thumb similar to Neanderthals and modern humans, suggesting powerful grasping and potential stone tool use. However, its finger bones are significantly curved, a trait often associated with tree climbing. Its feet are largely adapted for upright walking, displaying many features found in modern human feet, yet retain some primitive characteristics like curved toe bones and a flatter arch. The species also had more ape-like shoulders and a flared rib cage. Adult individuals are estimated to have weighed between 40 and 55 kilograms and stood between 140 and 160 centimeters tall.
Unraveling Their Age
Dating Homo naledi fossils was challenging due to the absence of volcanic ash layers, typically used for precise radiometric dating. Early estimations, based on their primitive appearance, suggested an age of 1 to 2 million years, but this proved inaccurate.
To establish a reliable chronology, researchers employed multiple dating techniques. Uranium-thorium dating was used on cave flowstones, and electron spin resonance (ESR) dating was applied directly to Homo naledi teeth. These methods, combined with paleomagnetic dating of sediments, revealed a surprisingly young age. The remains are now dated to between 236,000 and 335,000 years ago, placing them in the Middle Pleistocene epoch. This timeframe is intriguing because it overlaps with the emergence of early Homo sapiens in other parts of Africa.
Rethinking Human Ancestry
The existence of Homo naledi and its relatively young age have significant implications for our understanding of human evolution, challenging the traditional linear progression of hominin development. Its unique combination of small brain size and human-like body features suggests a more complex, branching “bush” rather than a straight line in our evolutionary history, with multiple hominin species co-existing. This discovery indicates that diverse forms of hominins, some with traits previously considered ancient, persisted much later than once thought, alongside species with larger brains.
Beyond their physical characteristics, recent research suggests Homo naledi may have engaged in complex behaviors, including the deliberate disposal of their dead within the deep, inaccessible chambers of the Rising Star Cave system. Evidence, such as skeletal remains found in crouched positions within depressions, some potentially with associated stone tools, has led to claims of intentional burial. If confirmed, this would represent the oldest known instance of such mortuary behavior, predating similar practices attributed to Neanderthals and early modern humans by tens of thousands of years. This interpretation, though still debated, raises significant questions about the cognitive capabilities of small-brained hominins and expands our understanding of the origins of symbolic thought and meaning-making in our ancient relatives.