Homo Naledi Burials: Critics Push Back

The scientific community is currently embroiled in a heated debate regarding Homo naledi, a small-brained human relative discovered in South Africa. In 2023, a team of researchers led by paleoanthropologist Lee Berger made headlines with a stunning claim: this ancient species buried its dead and carved symbols into cave walls. If true, this would rewrite the timeline of cognitive evolution. However, a significant number of experts are pushing back, arguing that the evidence provided does not support these sensational conclusions.

The Claims: Rituals by a Small-Brained Hominid

The controversy centers on the Rising Star cave system near Johannesburg, South Africa. Since 2013, Lee Berger and his team have excavated over 1,500 fossil specimens of Homo naledi. These hominids lived approximately 240,000 to 335,000 years ago and possessed brains roughly one-third the size of a modern human brain.

In mid-2023, Berger’s team released three pre-print papers through the journal eLife. Their central assertions were:

• Intentional Burials: They claimed to have found shallow, dug-out pits containing Homo naledi bodies in the Dinaledi Chamber and the Hill Antechamber.
• Rock Art: They identified cross-hatched geometric shapes (resembling hashtags) etched onto the cave walls, interpreting them as meaning-making symbols.
• Fire Usage: They suggested the use of fire to navigate the pitch-black tunnels.

These claims were released simultaneously with a Netflix documentary, Unknown: Cave of Bones, which presented the findings as fact. This coordination between scientific papers and mass media entertainment raised immediate red flags for outside observers.

The Scientific Rebuttal: Lack of Hard Evidence

The peer review process, which usually happens behind closed doors, was made public by eLife. The results were bruising for the Rising Star team. Four independent reviewers labeled the evidence “inadequate” and “incomplete.”

The primary criticism is that the researchers failed to rule out natural processes. To prove a burial, one must demonstrate that a hole was intentionally dug and then filled back in. Critics like María Martinón-Torres, a paleoanthropologist at the National Research Center on Human Evolution (CENIEH) in Spain, pointed out several flaws:

1. No Clear Cut Lines: The papers did not show distinct interruptions in the soil layers that would indicate a pit was dug.
2. Natural Depressions: The “pits” could easily be natural hollows in the cave floor where bodies accumulated.
3. Water Movement: Critics argue that water flowing through the limestone cave could have washed sediment around the bones, creating the illusion of a burial structure.

The consensus among the reviewers was that while the bodies were certainly in the cave, there is zero definitive evidence they were placed in dug graves.

The "Rock Art" Dating Problem

The second pillar of the controversy involves the engravings found on the dolomite walls. The Rising Star team asserted that because Homo naledi bodies were in the cave, the art must belong to them.

However, critics immediately highlighted a massive gap in the data: the engravings have not been dated.

Without radiometric dating or sediment analysis, there is no way to know when those scratches were made. The Rising Star cave system has been accessible to modern humans for thousands of years. The cross-hatchings could be:

• Graffiti from modern cavers or explorers in the last century.
• Art left by Stone Age Homo sapiens long after Homo naledi went extinct.
• Natural claw marks from animals.

Jamie Shreeve, formerly of National Geographic, and other science communicators noted that attributing undated art to a specific fossil species simply because they are in the same general location is scientifically unsound.

Taphonomy: The Missing Context

The field of study known as taphonomy focuses on what happens to an organism after it dies. This includes how bones decay, move, and settle in soil. This is where critics feel the Homo naledi papers failed most significantly.

In the eLife reviews, experts noted that the position of the bones did not necessarily suggest a curled-up, peaceful burial. Some skeletal parts were scattered or disjointed, which aligns more closely with natural decomposition or water transport than with intentional interment.

Michael Petraglia from Griffith University emphasized that extraordinary claims require extraordinary evidence. To prove that a creature with a brain the size of an orange performed complex rituals previously attributed only to large-brained humans (and perhaps Neanderthals), the geological and chemical analysis of the soil must be flawless. In this case, the data was largely descriptive rather than analytical.

Why This Debate Matters

The stakes of this debate are high because it touches on what makes humans unique. For decades, anthropologists believed that complex behaviors like mortuary rituals and symbolic art were unique to Homo sapiens and tied directly to our large brain size.

If Homo naledi practiced these rituals, it would imply that brain size is irrelevant to cognitive complexity. It would fundamentally change our understanding of evolution.

However, the pushback serves as a critical check on scientific sensationalism. By bypassing traditional peer review timelines to coincide with a Netflix release, the Rising Star team exposed themselves to intense scrutiny. The current scientific consensus remains skeptical: Homo naledi was a fascinating creature, but until better data emerges, the “burial” hypothesis remains just that: a hypothesis, not a fact.

Frequently Asked Questions

Did Homo naledi definitely bury their dead? No. At this time, the scientific consensus is that there is insufficient evidence to prove intentional burial. Most experts believe the bodies may have accumulated naturally or been dropped down chutes, rather than placed in dug graves.

How big was the brain of Homo naledi? Their brains were approximately 450 to 600 cubic centimeters. This is roughly one-third the size of a modern human brain and similar in size to an orange or the brain of an Australopithecus.

What is the “hashtag” controversy? Researchers found cross-hatched lines on the cave walls and claimed H. naledi made them. However, these markings have not been dated, so they could have been made by modern humans or other ancient humans at any point in history.

Why was the Netflix documentary criticized? Unknown: Cave of Bones presented the burial and art claims as proven facts before the scientific papers had completed the peer review process. When the reviews came back negative, the documentary was already out, potentially misleading the public about the scientific standing of the discovery.