The Rising Star cave system is located in South Africa and is part of the Cradle of Humankind World Heritage Site. It has been well mapped and explored by curious cavers for many years, but without any noticed fossil remains there.
In September 2013, that changed when two South African cavers, Rick Hunter and Steve Tucker, found and entered a remote, unmapped chamber and found the first-known fossil bones of what is now called Homo Naledi strewn across the chamber’s floor.
Working with Lee Berger, Hunter, and Tucker hoped to find new cave areas with evidence of our fossil ancestors. Berger reacted to the discovery quickly and created an excavation to explore the contents of the new, extremely difficult-to-get-to site, named the Dinaledi Chamber.
During the summer of 2023, researchers published a new series of papers regarding further discoveries, claiming that this ancient human species buried their dead, could make fire, used tools, and even created art. These papers and theories sparked a heated debate between other researchers and peer reviews that stated the research posted by Berger’s team was ‘imprudent and incomplete’ and ‘largely assumption-based.’
Berger’s team and the Homo naledi discovery found themselves at the center of a scientific storm of debate.
Who Were the Homo Naledi?
Dating back to the Middle Pleistocene 335,000-236,000 years ago, Homo naledi is an extinct hominin species discovered within the Rising Star Cave system in 2013 in the Gauteng province, South Africa.
Homo naledi has some similarities to Homo sapiens, or modern humans, while also sharing several characteristics found within Australopithecus, the genera homo (which includes modern humans), Paranthropus, and Kenyanthropus evolved from.
It is currently estimated that H. naledi were around five feet, or 1.5 meters tall, slim, and walked upright but were adapted to climbing and had brains the size of an orange.
Why Homo Naledi Theory is Controversial
The discovery of small-brained humans that have persisted longer than science estimated could suggest that the H. naledi brain might be more cognitively complex than earlier thought. H. naledi’s confusing mix of anatomical details known in early species of our genus, such as Homo erectus and Homo habilis, yet their brains were much smaller than typical in these species. However, aspects of H. naledi’s teeth resemble a much earlier species that branched from our family tree, 3.2-million-year-old Australopithecus afarensis.
This mix of features is called anatomical mosaic in evolutionary biology. Over the last century, paleoanthropologists have learned that human evolution was not a gradual progression from an apelike ancestor to modern humans. We developed small canine teeth and a more upright posture very early in our lineage, then our pattern of walking upright next. Somewhere in the middle of our evolutionary tree, ancestors and relatives went on to evolve larger molar and premolar teeth—a trend that reverted as soon as the first member of our genus, Homo, began hunting and making stone tools. Only then did our ancestors develop social sharing that led to language, which we believe is unique to modern humans. In short, the general thought is that our brains evolved later, our legs early, and all the species in our ancestry have their mosaic of features from this.
H. naledi’s hands, arms, and shoulders, combined with a wrist and fingertips, were more human-like than those of H. habilis. Yet, H. naldi’s fingers were curved, resembling those of the earliest hominins and living apes. Researchers trying to recreate the full skeleton of H. naledi within a program often show a shoulder canted upward on the trunk suitable to a climbing species and an upper arm twisted in a way, unlike other human relatives.
These details appear to show that H. naledi was both a climber and a possible toolmaker with its narrowed rib cage.
What makes H. naledi controversial is the claim that the findings in the cave are evidence of H. naledi being capable of creating fire, observing burial rites, and creating art and stone tools, which means H. naledi’s mosaic conflicts with previous storylines.
If these claims are valid, and if small-brained ancestors could already make art, fire, tools, and graves, then what is the actual reason and function why we grew bigger brains as modern humans evolved?
Debate continues as researchers and scientists attempt to understand how H. Naledi’s remains got so deep into the cave system, while Berger’s team believes they were deliberately placed, meaning H. Naledi could be the oldest known gravesite of human ancestors. This could further overturn what we thought to be known about developing human beliefs, culture, and symbolism.