When fossil hunters unveiled the remains of a mysterious and archaic new species of human found deep inside a cave in South Africa two years ago, the scientific community was stunned. Since then, bodies of the long-lost family members have piled up.In work published on Tuesday in the journal eLife, the team reveals how high that pile has become. They now have the remnants of at least 18 Homo naledi, as the species is named. The most recent haul of bones, found in a cave chamber 100 metres from the first, includes a nearly complete adult skull.
Tests on the material found the bones to be between 335,000 and 236,000 years old, making them far younger than many scientists had expected. “It means that this species of primitive hominid was actually around at the same time as Homo sapiens,” said Lee Berger, the lead scientist at the University of Witwatersrand in Johannesburg.
The bones, remarkably, show few signs of disease or stress from poor development, suggesting that Homo naledi may have been the dominant species in the area at the time. “They are the healthiest dead things you’ll ever see,” said Berger.
Homo naledi stood about 150cm tall fully grown and weighed about 45kg. But it is extraordinary for its mixture of ancient and modern features. It has a small brain and curved fingers that are well-adapted for climbing, but the wrists, hands, legs and feet are more like those found on Neanderthals or modern humans. If the dating is accurate, Homo naledi may have emerged in Africa about two million years ago but held on to some of its more ancient features even as modern humans evolved.
“This is astonishingly young for a species that still displays primitive characteristics found in fossils about two million years old,” said Chris Stringer at the Natural History Museum in London, who was not involved in the research.
The age of the bones, and their discovery in the Rising Star cave system on the edge of the Cradle of Humankind World Heritage site near Johannesburg, has led Berger to speculate that some ancient stone tools found in the region might have wrongly been attributed to Homo sapiens. Instead, they might be the work of Homo naledi, he said.
No stone tools have ever been found with Homo naledi bones, but Stringer does not rule out the possibility that the species may have made them. “It seems highly likely that its handiwork is present in the archaeological record of southern Africa, but currently unattributed,” he said.
Another question raised by the remains is how they got to their final resting place. Berger does not believe that the creatures got there by accident. “I think the discovery of this second chamber adds to the idea that Homo naledi deliberately disposed of its dead in the deep underground chambers in the Rising Star cave system,” he said. “I can’t see any other way, other than them going into these remote chambers themselves and bringing bodies in.” To do that, he suspects, they were also able to control fire.
Others are not so confident. Stringer said he and many other experts doubted that Homo naledi, with a brain the size of a gorilla’s, was capable of such complex behaviour. “Perhaps further exploration will reveal other, closer, entrances or sinkholes which were temporarily open, through which the remains could have been introduced by accidental or natural processes?” he said.
According to Jessica Thompson, a palaeolithic archaeologist at Emory University in Atlanta, what the bones do make clear is that human evolution was not the straightforward, linear progression from one species to another that it is often made out to have been. “It doesn’t start out with something that looks like a monkey, and the something that looks like an ape, and then something that looks like a human, and then all of the sudden you’ve got people,” she said. “It’s much more complicated than that.”