Fossils of the creature were unearthed in a deep cave near the famed sites of Sterkfontein and Swartkrans, treasure troves 50km (30 miles) northwest of Johannesburg that have yielded pieces of the puzzle of human evolution for decades.
“It was right under our nose in the most explored valley of the continent of Africa,” said Lee Berger of the Evolutionary Studies Institute at Johannesburg’s University of the Witwatersrand.
The new species - described in the scientific journal eLife - has been named ‘Homo naledi’, in honour of the “Rising Star” cave where it was found. Naledi means “star” in South Africa’s Sesotho language.
Paleoanthropologists concluded it buried its dead - a trait previously believed to be uniquely human - through a process of deduction.
Africa’s largest single collection of hominin (human and human-related) fossils was made up of 15 individuals, from infants to the elderly, pieced together from more than 1,500 fragments.
Virtually no other remains from other species were found there and the bones bore no claw or tooth marks - suggesting they were not the leftovers from a predator’s larder or death trap.
“It does appear after eliminating all other possibilities that Homo naledi was deliberately disposing of its body in a repeated fashion,” Berger said.
“That indicates to us that they were seeing themselves as separate from other animals and in fact perhaps from the natural world.”
He set aside another theory that they may have been hiding their dead deep underground, simply to keep off scavengers like the long-legged hyena. “They are only selecting their own dead. If they were doing that they would put everything in it that would attract a predator or a scavenger,” he said.
This is not the first time that the study of our relatives, extinct or living, has yielded evidence that humans do not have the monopoly on certain kinds of behaviour.
Jane Goodall in 1960 famously observed chimpanzees, our closest living relative, using grass stems for termite “fishing”, the first recorded use of a crude tool by non-humans.
Homo naledi, discovered in the cave in September 2013, had a brain slightly larger than a chimpanzee’s, but its age remains an enigma, said Berger.
This is because the specimens found were deliberately taken to the chamber, and so there are no rocks or sentiments under or overlaying them, he added.
There are also no fossils with them from other animals that could provide clues. “But we can see from their physical morphology or appearance where their species originates in time. If our present understanding is correct, then that must be in excess of 2.5 million years,” said Berger.
The surrounding area is a UN World Heritage site, named the “Cradle of Humankind” by the South African government because of its rich collection of hominin fossils.
Rick Potts, director of the human origins programme at the Smithsonian Institution’s Natural History Museum, who was not involved in the discovery, said without an age, “there’s no way we can judge the evolutionary significance of this find”.
“If the bones are about as old as the Homo group, that would argue that naledi is “a snapshot of ... the evolutionary experimentation that was going on right around the origin” of Homo, he said. If they are significantly younger, it either shows the naledi retained the primitive body characteristics much longer than any other known creature, or that it re-evolved them, he said.
Eric Delson of Lehman College in New York said his guess is that naledi fits within a known group of early Homo creatures from around 2 million years ago.
Besides the age of the bones, another mystery is how they got into the difficult-to-reach area of the cave. The researchers said they suspect the naledi may have repeatedly deposited their dead in the room, but alternatively it may have been a death trap for individuals that found their own way in. “This stuff is like a Sherlock Holmes mystery,” declared Bernard Wood of George Washington University in Washington DC.
Visitors to the cave must have created artificial light, as with a torch, Wood said. The people who did cave drawings had such technology, but nobody has suspected that mental ability in creatures with such a small brain as naledi, he said.
Potts said a deliberate disposal of dead bodies is a feasible explanation, but he added it’s not clear who did the disposing. Maybe it was some human relative other than naledi, he said.
Not everybody agreed the discovery revealed a new species. Tim White of the University of California, Berkeley, called it questionable. “From what is presented here, [the fossils] belong to a primitive Homo erectus, a species named in the 1800s.”