Is Rising Star Cave still a mystery, or did our long-lost cousins the hominins go there to make graves for their dead?

According to a series of recent studies by the species' discoverers, University of Witwatersrand paleoanthropologist Lee Berger and his colleagues, Homo naledi, a diminutive, primitive-appearing relative of our species, may have marked the graves of its dead with etchings on cave walls and buried its corpses. Even on Netflix, there is a documentary that tells the tale of Homo naledi death ceremonies.

Other scientists, however, are dubious about whether the evidence actually supports interment rather than just the erosion-caused sedimentation of remains. No one disputes the significance of these fossils or the location; the argument is on what the fossils reveal about these little hominins and how certain we can be given the data at hand.

A Deep Cave With Shallow Graves?

When Berger and his colleagues announced in 2015 that they had discovered a new species of hominin, it caused debate since it is a big claim to make. Homo naledi, although having a considerably older-looking resemblance to modern humans, may have roamed the South African plains around 300,000 years ago, according to dating.

Berger used a unique method to disseminating his discovery from the beginning. And in the eight years that have passed, Berger and his associates have made even stranger claims about Homo naledi: that these diminutive, small-brained hominins had intentionally carried their dead into the Rising Star Cave System, that they had used fire to light their way, and most recently, that they had actually buried their dead in shallow pits and then carved marks on the cave walls nearby.

In light of the facts at hand, other paleoanthropologists disagree, but Berger and his colleagues continue to stand by their assertions.

Awesome Evidence is Required for Awesome Claims

Pre-prints are research papers that scientists have finished writing but have not yet had peer review or been accepted for publication by a journal. The most recent claims, that Homo naledi not only carried its dead into the caves but actually buried them there in shallow graves in the dark, were first published in a set of pre-prints. Before scientific study is published, it is customary for a team of scientists who weren't engaged in the project to read the manuscript and review the data. Instead of just accepting one other's word for it, scientists check each other's work through peer review.

The papers are currently being reviewed at an open-access journal called eLife, and the four anonymous reviewers, who are also paleoanthropologists and were chosen by the journal's editors for their expertise in studying hominin fossils, are highly doubtful that Homo naledi actually dug graves deep underground.

The conclusion of anonymous Reviewer #2 was, "While I understand the relevance of examining probable planned burials in Homo naledi, I do not think that in its present form, the data presented in this study is as substantial as it should be.

The specific issues raised by the reviewers range from the lack of a schematic showing the arrangement of the bones to the failure to consider erosion as a potential explanation for their placement in the cave. In the end, it comes down to the general conclusion that while there is no proof that Homo naledi buried its dead, there is also insufficient proof to conclude with certainty that they did. Berger was extremely transparent with his data in 2015, but the reviewers claim that this time around, he and his colleagues completely omitted certain important information from the report.

Other paleoanthropologists who weren't engaged in the Rising Star research or the review process have also commented. Most of them are dubious, though not about the possibility that Homo naledi buried its dead but rather about the certainty that it did.

On the study's eLife page, Berger and his coworkers' responses to reviewers are available. They also want to revise the manuscript and add further evidence. Berger has been far less circumspect in his press interviews. One thing is certain: the discussion is just getting started, and we'll get to watch it unfold in real time rather than over the course of years of slowly exchanging opposing journal articles.