It was an announcement that astounded the world of science and made headlines around the globe. Researchers reported last month that they had discovered burials, carved symbols and tools made by an ancient species of small-brained humans. The finds, in South Africa’s Rising Star cave system, suggested Homo naledi displayed sophisticated behaviour almost a quarter of a million years before modern humans began making graves and art, even though this primitive species had brains little bigger than those of chimpanzees.
The revelations were described online in papers that had still to be peer-reviewed but were nevertheless hailed by the authors as an intellectual revolution, a paradigm shift that challenged previous assumptions about human evolution. Religion and art were in our lineage long before we developed big brains, it was argued.
“We now face the prospect that a creature before humans was contemplating an afterlife. It completely changes how we have to think about human evolution,” said anthropologist Lee Berger, who has led the Rising Star investigations.
The claim certainly raised key questions about human nature. If small-brained creatures like H. naledi could already make fire, art, tools and graves, what was the function of all the extra grey matter modern humans evolved? The question raised prospects of an intriguing scientific debate.
Then the tide turned. Peer reviews of the H. naledi study appeared. These papers are “imprudent and incomplete”, announced one last week. “These claims are inadequate, incomplete and are largely assumption-based – rather than evidence-based,” warned another, while a third dismissed the papers because they “do not present convincing evidence”.
As a result, Berger’s team has found itself at the centre of a scientific storm. “I have no issue with the idea that non-Homo sapiens species disposed of their dead, but I do have an expectation that there is robust scientific evidence to support such statements before scientists go on massive media campaigns regarding these ideas,” said palaeoanthropologist Andy Herries of La Trobe University in Melbourne, Australia.
This point was backed by Paige Madison, a researcher at Arizona State University. “To push a notion that is so unsubstantiated that it has met with rejection by the scientific community is irresponsible,” she said.
Exaggerating the intellectual prowess of H. naledi, as featured in a recent Netflix documentary, could detract from study of the site in future, added Prof Chris Stringer of the Natural History Museum, London. “Rising Star is such a great site and the naledi material is so wonderful that there was really no need to over-egg the pudding,” he said. “It’s going to cause problems of credibility in future, which may even affect funding for more work.”
Homo naledi’s resting place was found by recreational cavers in a chamber, littered with bones, in the Rising Star caves near Johannesburg in 2013. Berger, then at the University of the Witwatersrand in Johannesburg, organised an expedition, enlisting six female paleoanthropologists slim enough to pass through an 18cm-wide rock gap to access the chamber. The remains of several small, human-like individuals were discovered, since named naledi after the local Sesotho word for star, and their remains dated as being around 300,000 years old. Homo naledi were around 1.5m (5ft) tall, slim, walked upright but were adapted to climbing, and had brains the size of an orange.
It was unclear how their remains got deep into the cave system, however. There were no signs that predatorsbrought them into the chamber or that underground streams swept them there. So Berger’s team concluded that the bones had been deliberately placed, an idea it has since pushed to its extreme according to the Netflix documentary, Unknown: Cave of Bones, screened last week and which highlights the team’s investigations into Homo naledi.
The bones, they maintain, were not merely dumped in the cave but carefully placed in scraped hollows and covered with soil. For good measure, a slice of stone in the hand of an H. naledi child is interpreted as being a tool, scratch marks around the cave were said to be attempts at art, and darkened patches of soil were pinpointed as hearths.
None of these claims impress reviewers of the papers written by Berger and his team, however. Other interpretations of these findings have not been adequately explored, detractors argue. “The consequences of rushing publication with such a significant unsubstantiated find will likely result in perilous ramifications,” said one reviewer.
Berger, whose book Cave of Bones will be published by National Geographic next month, is unrepentant. In an interview with the Observer last week, he insisted his team’s recent research was solid and reliable. The Rising Cave research is not just the work of one or two scientists but is backed by dozens of researchers. “Their scientific opinions should not be outweighed by two or three or four reviewers. That is not the way it works,” Berger said.
Not every scientist is convinced by this stance, however. “Rather than engaging with concerns, the team appears to be denying problems with their methods and analysis and are attacking peer reviewers’ motives in an attempt to undermine their criticism,” said Madison.
Nevertheless, Berger remained adamant that his team would be vindicated. “We haven’t stopped working in the chamber, and more evidence is coming. We will continue to present more evidence and we will keep these criticisms under our belts but I will say to those critics who demand more evidence: we will deliver that evidence, so be careful what you wish for.”
