Scientists Shed Light on Mysterious Habits of Small-Brained Extinct Humans

An extinct human species that lived around 300,000 years ago may have been more similar to us than scientists first thought.

New research has found that this species, Homo naledi, buried their dead deliberately and carved symbols inside caves, marking the earliest recorded occurrences of these behaviors by at least 100,000 years.

This behavior was previously only thought to be performed by Neanderthals and modern Homo sapiens.

These findings were revealed in three preprints published to the preprint server bioRxiv by paleoanthropologist Lee Berger and his colleagues. Berger discovered the existence of this hominid species Homo naledi only eight years prior, inside the Rising Star cave system northwest of Johannesburg in South Africa.

These human cousins are thought to have lived some time between 241,000 and 335,000 years ago, and have features distinct from our human species, including a brain only around one-third the size of ours, and a smaller body stature.

Berger and his team have found evidence for deliberate burial, including 1,800 bone fragments inside an underground chamber, only accessible via a 7.5-inch-wide slot, laid out in a seemingly careful way as opposed to being dumped.

"We've found the cultural space of a non-[modern] human species," Berger told National Geographic.

"These burial features meet evidentiary standards used for recognizing burials of H. sapiens. The recognition of burials in these chambers within the cave system prompts us to evaluate the broader array of H. naledi remains for evidence of mortuary activities," the authors wrote in the preprint titled "Evidence for deliberate burial of the dead by Homo naledi."

Some have suggested that these bodies may have entered the cave by other means, being washed in by a flood or dragged in by a predator, or even moved in by later Homo sapiens. However, no traces of gnaw marks were found, and the cave sediments revealed no signs of water deposition. They also found no traces of other human species.

"Some authors have argued that mortuary behavior is unlikely for H. naledi, due to its small brain size. The evidence demonstrates that this complex cultural behavior was not a simple function of brain size," the authors wrote.

"While we cannot at this time exclude H. naledi as part of the ancestral makeup of humans, its overall morphology suggests that its common 380 ancestors with today's humans and Neandertals go back a million years or more.

In the second preprint, titled "241,000 to 335,000 Years Old Rock Engravings Made by Homo naledi in the Rising Star Cave system, South Africa," the authors discuss how they also found markings on the cave's walls. These markings seem to have been erased and reengraved, possibly indicating that they were made across a long period of time.

In a third preprint, "Burials and engravings in a small-brained hominin, Homo naledi, from the late Pleistocene: contexts and evolutionary implications," the authors examine how and why these small-brained humans gained behaviors so similar to that of modern humans. It has been previously assumed that our more complex behaviors accumulated with our brain size. If Homo naledi did bury their dead and decorate cave walls, these findings challenge that assumption.

"The association of these activities in subterranean spaces accessed and modified by the small-brained species Homo naledi impacts assertations that technological and cognitive advances in human evolution are associated solely with the evolution of larger brains," the authors wrote.

The papers are still in preprint, however, so they are yet to be published officially in a peer-reviewed journal. Berger tells National Geographic that they will soon be published in the journal eLife, but they decided to go public before that point to keep the process transparent.

"Your readers will be able to watch as the authors—our large team—interact with reviewers and editors as part of the open access policy," Berger said. "Effectively, we're letting people in to watch the review process and the way peer review works."

More research needs to be done on H. naledi's behaviors to determine just how different from us they were, and to determine if they performed other unexpected activities, such as the use of fire.

"If this species was adapted to living in caves and going deep into caves, which is the implication in Rising Star, then there must be more evidence of it in many other sites in South Africa," anthropologist Chris Stringer told National Geographic.

"I might have been one of those people who's been skeptical about the idea that a small-brained creature like Homo naledi could be going deep into the cave to dispose of its dead," he said. "But I have to say, on the amount I've seen so far, that yes, it does change my view on the balance of probability."

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