The Homo naledi discovery in a South African cave over thirteen years ago has revealed astonishing insights. Recent analyses of skeletal proteins suggest all samples examined were female, providing potentially the most compelling evidence of early human behavior yet.

Uncovered by a group of cavers in 2013 within the Rising Star cave system, approximately 40 kilometers northwest of Johannesburg, the fossils were situated in deep, hard-to-reach chambers. Since their discovery, researchers have tirelessly investigated how these remains came to rest in such a location.

Initial hypotheses emerged in 2015, proposing that H. naledi corpses were intentionally placed in the cave, as suggested by Lee Berger from the University of the Witwatersrand. Archaeological findings indicated potential grave digging within the cave and the use of torches to navigate the darkness, with claims of ancient rock paintings left behind in this burial space. However, these ideas have been met with skepticism.

The latest findings by Palesa Madupe at the University of Copenhagen involved extracting ancient proteins from H. naledi tooth enamel, enabling insights into the genetics of this long-extinct species, believed to have lived between 335,000 and 236,000 years ago.

Tooth enamel comprises around a dozen proteins, relatively understudied in evolutionary terms. However, certain proteins can reveal biological sex due to the presence of amelogenin proteins linked to X and Y chromosomes, with females typically containing only the X-linked (amelogenin A) allele.

Madupe and her team examined all 23 known H. naledi specimens and successfully identified amelogenin proteins in 20, all of which were female—a startling outcome. Madupe expressed initial concerns about potential errors in their analysis, yet repeated tests yielded the same result, leading researchers to ponder the absence of male specimens.

One explanation could be the rapid degradation of AMELY proteins, making some undetectable. However, Madupe suggests this is unlikely, especially considering that similar proteins dating back two million years were recently discovered in South African excavations.

Another theory suggests that H. naledi males might not express AMELY genes on their enamel. Examining existing literature, researchers note that such deletions can occur in current human populations, though infrequently. They calculated the likelihood of AMELY absence among a random sample of 20 individuals, positing that the odds would be exceedingly low at just 0.0000954 percent.

This points to one intriguing conclusion: all 20 fossilized remains could have belonged to females. Berger argues this indicates that the notion of a natural process leading to their arrival in the cave is untenable. Instead, he posits that the findings imply intentional placement of female corpses within the cave.

Many researchers support this conclusion. For instance, Emma Pomeroy from Cambridge University remarked, “This suggests either flawed analytical methods or intentional choices regarding H. naledi individuals.” Similarly, Bernard Wood from George Washington University hypothesizes there might be behavioral reasons behind why female remains were deposited in the cave.

Others remain more skeptical. Researcher Kimberly Fecke from George Mason University suggests cave access may have historically posed challenges for larger individuals, thus affecting the representation of males in the fossil record. Notably, the initial archaeologists who explored the cave were predominantly women.

In contrast, Michael Petraglia at Griffith University advocates the idea that social dynamics among H. naledi could have led to populations with higher female-to-male ratios for foraging activities.

However, other experts, like Eric Kruvezy from the University of Toulouse, express reservations about this theory, noting that in primate groups with uneven male-to-female ratios, one typically finds a balance of male and female infants. This discrepancy brings into question the potential for a largely female demographic in the cave.

Berger maintains that these findings bolster his hypothesis that H. naledi corpses were purposefully placed in the cave. Other researchers challenge this notion, with Wood asserting that simply placing a body in a rock crevice shouldn’t be equated with burial rituals, denying the existence of complex cultural beliefs in early hominins regarding mortality.

Finally, the pivotal question remains: what did H. naledi look like? Wood notes that while physiological traits can be surmised from female specimens, significant variation might be expected, especially considering other hominin species like Paranthropus boisei, where males displayed larger cranial features.