Deep inside South Africa's Rising Star Cave system, something extraordinary has been hiding in the enamel of ancient teeth for more than 200,000 years. Scientists have now pulled microscopic protein fragments from 23 teeth belonging to at least 20 individuals of Homo naledi—and found something that has upended everything they thought they knew about who was buried there.
The discovery, published in the journal Cell, reveals that none of the analyzed teeth carried the genetic signature of males. The Amelogenin-Y protein, which is uniquely coded by the male Y chromosome and present in human tooth enamel, was entirely absent from the sample. Researchers at the University of York's specialized chemistry facility verified that these proteins were genuinely ancient—not modern contamination—proving that something unusual happened in this cave.
"The lack of male markers within the group is truly fascinating," said Dr. Marc Dickinson of the University of York's Department of Chemistry. "It is incredibly exciting to gain a window not only into the biology of our ancestors, but also into how they lived."
Homo naledi itself is remarkable enough—an extinct cousin of modern humans that lived between 335,000 and 241,000 years ago, with an unusual mix of primitive and humanlike traits. But for more than a decade, scientists puzzled over why the adult fossils from the cave's Dinaledi Chamber looked so strikingly similar to one another, lacking the physical variations typically expected between males and females. Now, thanks to a minimally destructive acid-etching technique, they finally have an answer—and more questions.
Palesa Madupe, who conducted the research as a postdoctoral scholar at the University of Copenhagen, explained why teeth hold secrets that bones cannot. "Unlike those found in other remains like bone fragments, proteins in tooth enamel are preserved because dental enamel—the hardest tissue in the human body—shields proteins from environmental contamination even for millions of years," she said. "Our study helps explain the long-standing mystery of why Homo naledi lacked significant variation; it's probably because they could have all belonged to one sex."
That word "probably" carries tremendous weight. The findings open the possibility that Rising Star Cave represents the first known sex-specific burial site created by a non-Homo sapiens species—implying complex, symbolic mortuary practices once thought unique to modern humans. Alternatively, the Homo naledi population may have been so isolated that the male-specific genetic marker mutated or vanished entirely, meaning males existed but left no trace in their enamel.
What is not in doubt is that these ancient females—or genetically unique males—have prompted scientists to reconsider the origins of human society. As Dickinson noted, "Advances in ancient protein analysis are opening the door to a far richer and more nuanced understanding of ancient hominins." In the quiet dark of Rising Star Cave, it seems, our ancestors were doing far more than surviving. They were perhaps choosing who belonged among them—and why.