Buried for Females Only? Ancient DNA Hints at Strange Rituals

Twenty-three ancient teeth recovered from South Africa’s Dinaledi Chamber contained no trace of Amelogenin-Y, a protein marker encoded by the male Y chromosome. This finding suggests that the Homo naledi individuals interred in the Rising Star Cave system may have been exclusively female, challenging long-standing assumptions about the physical variation within the species.

The absence of male genetic markers

For over a decade, scientists have puzzled over the uniformity of adult Homo naledi fossils found in the chamber. The remains displayed almost none of the sexual dimorphism typically expected between males and females. To address this anomaly, researchers from the University of York, the University of Copenhagen, and more than ten other international institutions conducted the first proteomic analysis of these extinct hominin fossils.

The study, published in Cell, utilized a minimally destructive acid-etching technique to extract microscopic peptides from the enamel of the 23 teeth, which represented at least 20 distinct individuals. The team specifically targeted Amelogenin-Y to determine if any male specimens were present among the samples. Their analysis yielded no evidence of this male-specific protein.

Preservation through dental enamel

To ensure the recovered proteins were genuinely ancient and not the result of modern contamination, specialists at the University of York’s chemistry facility analyzed their amino acid composition. Palesa Madupe, who completed the research as part of her postdoctoral work at the University of Copenhagen, highlighted the unique preservation capabilities of tooth enamel.

“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 stated. She noted that this makes enamel ideal carriers of genetic information from deep time, potentially solving the mystery of why Homo naledi lacked significant variation: “it’s probably because they could have all belonged to one sex.”

Implications for burial customs

If the Dinaledi Chamber served as a burial site reserved solely for females, it would represent the first known instance of sex-specific burial practices by a species other than Homo sapiens. Such a custom implies complex, symbolic treatment of the dead, a behavior previously thought to be unique to modern humans. This discovery raises new questions regarding how Homo naledi organized its society.

Dr. Marc Dickinson from the University of York’s Department of Chemistry described the lack of male markers as “truly fascinating.” He emphasized that the findings provide a rare window into both the biology and the lived culture of our ancestors. According to Dickinson, advances in ancient protein analysis are opening doors to a richer understanding of hominin history.

Alternative biological explanations

Despite the absence of Amelogenin-Y, the researchers caution that this does not definitively prove every sampled individual was female. They identified a potential biological alternative: if the Homo naledi population was highly isolated, the gene encoding the protein could have mutated or been deleted. In this scenario, males might have been present in the chamber but possessed teeth lacking the usual male marker.

Homo naledi, discovered in 2013 within the Rising Star Cave system, lived between 335,000 and 241,000 years ago. The species exhibited an unusual mix of primitive, ape-like traits alongside human-like features. The current study examined the largest extinct hominin population yet analyzed through protein methods.