We know where the bodies ended up, but not how they got there
In the limestone depths of South Africa's Rising Star cave, a decade of excavation has yielded not just bones, but a deepening riddle about what it means to bury the dead. New protein analysis of Homo naledi teeth reveals that every individual tested was female — a finding so unexpected that researchers ran the data twice. Whether this reflects ritual, biology, or behavior, it forces a reckoning with how we understand the minds of our small-brained ancestors and the origins of symbolic thought.
- Scientists expected a mixed-sex population, but ancient protein analysis of 20 Homo naledi individuals returned the same result every time: no male marker, only females.
- The discovery has unsettled the field, with researchers describing 'nervous scientists' and a scramble to rule out laboratory error before accepting the data.
- Three competing explanations are now in tension — sex-segregated burial rituals, a rare genetic mutation, or natural female-only foraging groups — each carrying radically different implications for Homo naledi's cognitive life.
- Skeptics urge restraint, warning against projecting complex ritual behavior onto a hominin with a brain barely larger than a chimpanzee's, while excavation leaders point to the absence of juvenile males as evidence against simple behavioral explanations.
- The mystery of how these bodies arrived in the cave, and where the males went, remains entirely unresolved — leaving Rising Star as one of the most contested and consequential sites in human evolutionary science.
Deep in South Africa's Rising Star cave, researchers have spent over a decade recovering fossils of Homo naledi — a small-brained hominin that appeared, improbably, to bury its dead with deliberate care. When the species was first announced in 2015, it already challenged assumptions about which ancestors were capable of ritual behavior. A new analysis has made the puzzle stranger still.
Using paleoproteomics — the study of proteins preserved in ancient tooth enamel — a team led by Palesa Madupe searched for a protein found only on the male Y chromosome. Across twenty usable samples, the marker was absent in every case. All tested individuals were female. Lead excavator Lee Berger admitted the team ran the data twice out of disbelief, and reflected that the signs had been there all along: the fossils showed almost no variation in size or shape, a uniformity so unusual that the species was once described as the least sexually dimorphic ancient hominin ever found.
The explanations on offer are each unsatisfying in their own way. Perhaps Homo naledi practiced sex-segregated burial, reserving this cave for females alone — a level of social and symbolic organization that strains credibility for a creature with such a small brain. Perhaps a genetic mutation eliminated the male-determining gene across the population, though researchers consider this vanishingly unlikely at such a scale. Or perhaps these were simply female foraging groups, sheltering in caves as some chimpanzee groups do today.
Anthropologist Michael Petraglia cautioned against over-interpreting the sex distribution, suggesting small-brained hominins might naturally form female-heavy groups in certain environments. Berger pushed back: if the species merely foraged in sex-segregated parties, juvenile males should appear somewhere at the site — but none have been found. The cave has yielded only females and children of indeterminate sex.
Where the males went, how the bodies arrived, and what any of it reveals about Homo naledi's inner life remain open questions. As one researcher put it, we know where these individuals ended up — but not how they got there, nor how they lived. Rising Star continues to offer more mystery than resolution.
Deep in the twisting passages of South Africa's Rising Star cave system, researchers have been pulling fragments of bone and tooth from the rock for over a decade. What they found was strange enough to upend assumptions about human ancestry: a species called Homo naledi, with a brain barely larger than a chimpanzee's, that seemed to bury its dead with deliberate care. Now a new analysis has made the puzzle even stranger.
In 2015, scientists first announced the discovery of Homo naledi at a chamber called Dinaledi within the cave complex. The fossils were abundant and remarkably well-preserved. What caught researchers' attention was not just the species itself, but the apparent behavior it displayed. Despite its small brain, Homo naledi appeared to have carried its dead into the cave intentionally, arranging them in a way that suggested ritual. Some researchers even proposed that the species had carved symbols into the rock walls—a marker of cognitive sophistication once thought to belong only to humans.
Then came the protein analysis. A team led by Palesa Madupe at the University of Copenhagen's Globe Institute examined tooth enamel from 23 samples representing individuals at the site. Using a technique called paleoproteomics—the study of ancient proteins—they looked for a specific protein called amelogenin that appears only on the male Y chromosome. In all twenty usable samples, the male marker was absent. Every individual tested was female.
The finding rattled the field. Lee Berger, the paleoanthropologist who has led excavations at Rising Star, said researchers ran the data twice to rule out error. "When these results came out, there were a lot of quite nervous scientists," he recalled. "This was not what we expected." Looking back, Berger acknowledged he should have noticed something was off earlier. The adult fossils showed almost no variation in size or shape—a uniformity so striking that when the team first described the species in 2015, they called it the least sexually dimorphic ancient hominin ever found. Males and females typically differ noticeably in body size and features. Homo naledi did not.
The implications are disorienting. One explanation is that Homo naledi practiced sex-segregated burial rituals, deliberately placing only females in the cave while males were treated differently or buried elsewhere. This would suggest a level of social organization and symbolic thinking that seems improbable for a creature with such a small brain. But there are alternatives. The male-determining gene could have mutated or been deleted in the population—a phenomenon that has occurred in some living human males and even in Neanderthals, though researchers say it would be extraordinarily unlikely to happen in half of twenty individuals. Or, as some skeptics propose, Homo naledi may have simply lived in female-only foraging groups, similar to patterns observed in chimpanzees, where small parties of females with offspring sometimes shelter in caves.
Michael Petraglia, an anthropologist at Griffith University who has long questioned whether Homo naledi truly buried its dead intentionally, urged caution about reading too much into the sex distribution. He noted that small-brained hominins might naturally form female-heavy groups while foraging in particular areas. Berger countered that if the species lived in sex-segregated groups, he would expect to find juvenile males at the site—but no baby boys have been recovered, only children of indeterminate sex and multiple females.
The discovery raises questions that may take years to answer. Why would only females be present at this location? How did the bodies arrive there? Where did the males go? Ryan McRae, a paleoanthropologist at the Smithsonian, captured the paradox: "We know where the bodies of the Homo naledi individuals ended up, but we do not know how they got there nor where or how they lived." The Rising Star cave remains one of the most contentious sites in human evolutionary science—and this latest finding has only deepened the mystery.
Notable Quotes
When these results came out, there were a lot of quite nervous scientists. This was not what we expected.— Lee Berger, paleoanthropologist leading excavations at the site
Either scenario, namely the absence of Homo naledi males in the Rising Star cave system or a systematic deletion of their AMELY gene, is fascinating and would have deep implications for understanding the biology and evolution of this species.— Enrico Cappellini, paleoproteomics researcher at University of Copenhagen
The Hearth Conversation Another angle on the story
So they found twenty teeth, tested them all, and every single one came from a female. That seems almost too clean. Did they consider that this might be a fluke?
They did. Berger said they ran the data through two separate labs and checked it twice because they were skeptical themselves. The technique is solid—it's been used on fossils millions of years old. But yes, the uniformity is what makes it so unsettling.
If Homo naledi had a brain the size of a chimp's, how are we supposed to believe it had the cognitive ability to perform ritual burials? That seems like a contradiction.
That's exactly what divides the field. Some researchers think the all-female finding actually supports the burial theory—it suggests deliberate, organized practice. Others say a small-brained species might just naturally form female foraging groups, like chimps do, and the cave became a shelter where they happened to rest.
But Berger has a point about the children, doesn't he? If it was just natural grouping, wouldn't you find some young males?
That's his strongest argument. He's saying the absence of juvenile males is hard to explain by chance alone. But his critics say we're still making huge assumptions about what the presence or absence of bones really tells us about how these creatures lived.
What happens next? Do they keep digging?
Almost certainly. The Rising Star site has been productive for over a decade. But the real work now is figuring out what the pattern means—and that's going to require more evidence and a lot of careful thinking about what we can and cannot infer from bones alone.