All Identified Homo Naledi Skeletons: Evidence Suggests They Are All Female

In a remarkable revelation, fossils of Homo naledi discovered in a South African cave 13 years ago have provided unexpected insights. Recent protein analysis indicates that all identified remains may be female, presenting one of the clearest indications yet of the unique burial practices of this ancient species.

Initially uncovered by cavers in 2013, H. naledi fossils were found in deep, challenging chambers of the Rising Star cave system, located about 40 kilometers northwest of Johannesburg. This pivotal discovery has fueled ongoing research to unravel the mysteries surrounding their entombment.

Among the intriguing hypotheses, first introduced in 2015, posits that H. naledi individuals were intentionally placed in the cave. Lee Berger and his colleagues from the University of the Witwatersrand have bolstered this theory, citing archaeological findings that suggest deliberate actions, such as grave digging and torch use to navigate the dark caverns; intriguing rock paintings have also been observed.

For the latest analysis, Palesa Madupe at the University of Copenhagen extracted ancient proteins from H. naledi tooth enamel. This protein analysis offers valuable genetic insights into an ancient human species believed to have existed approximately 335,000 to 236,000 years ago.

Tooth enamel contains a limited variety of proteins, which can help determine the sex of ancient individuals. Specifically, the amelogenin protein can signal whether the gene came from the X chromosome or the Y chromosome. Typically females exhibit signals from the amex gene whereas males display signals from both amex and Amelie.

Madupe and her research team analyzed proteins from 23 known H. naledi individuals, successfully recovering amelogenin protein from 20 specimens. Curiously, the absence of the Amelie signal suggests that all analyzed individuals were female—a highly anomalous result. Madupe expressed initial skepticism, fearing methodological errors. However, replicating the analysis yielded consistent findings, prompting the question: Why are there no male remains?

One potential explanation is that male Amelie-bearing proteins may have degraded faster than their amex counterparts. Madupe deems this hypothesis unlikely, noting previous findings of male enamel proteins in 2 million-year-old South African teeth.

Another possibility is that males in the population did not express Amelie genes in their enamel. Literature suggests this can occur in modern humans, albeit rarely. Nonetheless, researchers determined that encountering an entire sampled population devoid of male representation is statistically improbable.

This leads to a profound implication: all analyzed ancient humans could indeed be females. Berger believes this ruling out of natural processes implies a deliberate burial of female H. naledi remains within the cave.

Many researchers echo this sentiment. Emma Pomeroy from Cambridge University suggests that the analysis reveals intentional choices regarding burial practices. Bernard Wood from George Washington University also posits behavioral aspects behind the selective placement of female corpses in the cave.

However, cautions remain among some researchers, such as Kimberly Fecke, who points out the challenges of cave access—especially for larger males. Michael Petraglia, from Griffith University, adds that social structures within H. naledi could naturally lead to skewed sex ratios in fossil collections.

Competing views arise from Eric Kruvezy at the University of Toulouse, who argues that unexplained demographic patterns among the remains challenge standard community profiles. Berger maintains that these findings lend credence to the notion of purposeful interment of H. naledi remains.

As noted by Pomeroy, these ongoing discoveries prompt further questions regarding the appearance and behavior of H. naledi. Scholars continue to speculate on the potential differences in morphology between male and female specimens.