A new analysis of ancient proteins in Homo naledi fossils suggests the Rising Star cave site in South Africa may contain remains of an entirely female population, raising questions about the species’ social structures and burial practices. Researchers found no evidence of amelogenin Y, a protein linked to male sex chromosomes, in 23 teeth samples from 20 individuals, according to a study published in Cell and reported by ScienceAlert and National Geographic. The findings, which contradict earlier assumptions about the species, have sparked debate among paleoanthropologists about whether the site represents intentional burial or a unique demographic anomaly.
The All-Female Enigma
The study, led by researchers including Palesa Madupe of the University of Copenhagen, focused on proteins preserved in dental enamel, which is more durable than other tissues. "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," Madupe explained in a National Geographic report. By analyzing amelogenin X (present in both sexes) and amelogenin Y (unique to males), the team found no traces of the latter in any of the 23 teeth examined.
Proteomic Breakthroughs
"This makes them ideal carriers of genetic information from deep time," Madupe said, citing the ScienceAlert article. However, the absence of amelogenin Y does not definitively prove the site is all-female. "Absence of evidence is not evidence of absence," cautioned Lee Berger, the paleoanthropologist who discovered the Homo naledi fossils in 2013, in a Smithsonian Magazine interview. The team proposed two possibilities: either the population was predominantly female, or the males lacked the AMELY gene entirely.
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Rising Star’s Burial Debate
The discovery has reignited discussions about whether the Rising Star cave site represents the earliest known human burial ritual. The Dinaledi Chamber, accessible only through a narrow "chute," contains over 1,500 fossils from more than a dozen individuals. "When these results came out, there were a lot of quite nervous scientists. This was not what we expected," Berger told CNN, as reported by Smithsonian Magazine.
The lack of male remains challenges traditional assumptions about hominin reproduction, which relies on both sexes. "Clearly, there had to be males, otherwise the species would not exist," said study co-author Enrico Cappellini, a paleoproteomicist at the University of Copenhagen’s Globe Institute, per Smithsonian Magazine. Yet the team found no evidence of male fossils in the chamber. "Either scenario would have very interesting implications for the biology and evolution of H. naledi," the researchers wrote in their Cell paper, as cited by ScienceAlert.
Unanswered Questions
Each source highlighted distinct aspects of the study.
The Smithsonian Magazine article added a layer of irony, pointing out that the initial excavation team, led by Berger, was composed entirely of women. "I think that’s one of those great, beautiful ironies of science and exploration," Berger reflected, as noted in the National Geographic report. Meanwhile, ScienceAlert underscored the broader implications for understanding Homo naledi’s place in human evolution, suggesting the species’ lack of sexual dimorphism could explain the absence of male markers.
A Cave Still Unraveling
Despite the findings, the mystery remains unsolved. "Only a definitively male skeleton could answer that question," said Madupe in National Geographic. Berger estimated that dozens of additional skeletons might still be hidden in the Rising Star cave system, though accessing them would require overcoming the chamber’s treacherous "chute."
The study’s authors also acknowledged the need for further research. "It is wonderful to see how ancient proteins open up the window of prehistory a little wider, bringing us closer to our hominin cousins," said archaeologist Kiri Douglas in a National Geographic interview. Meanwhile, critics like evolutionary biologist John Hawks, quoted in ScienceAlert, argued that the findings should be interpreted cautiously, given the limited sample size and potential biases in protein preservation.
