Humanity's claim to uniqueness just suffered another setback: scientists reported on Thursday that a newly discovered ancient species related to humans also appeared to bury its dead.
Fossils of the creature were unearthed in a deep cave near the famed sites of Sterkfontein and Swartkrans, treasure troves 50 km (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 (http://elifesciences.org/) and National Geographic magazine - 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.
"Today, we unearth our past. We are not exceptional. We are not the only ones who are able to bury our dead," South African Deputy President Cyril Ramaphosa said at news conference where the announcement was made a few kms (miles) from the site.
Paleoanthropologists concluded the species buried its dead, a trait previously believed to be uniquely human, through a process of elimination - a common approach in a field which often only has old bones to rely on.
The find - 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.
There was also no evidence that the creatures had been swept into the chamber by water.
"It does appear after eliminating all other possibilities that Homo naledi was deliberately disposing of its body in a repeated fashion," Berger told Reuters in an interview.
"That indicates to us that they were seeing themselves as separate from other animals and in fact perhaps from the natural world."
Of tools and chimps
Berger set aside another theory that they may have been hiding their dead deep underground simply to keep off scavengers and predators like the long-legged hyena, an animal known to have menaced our ancestors.
"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 - geology typically provides the smoking gun for the age of fossils.
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.
Reaching the chamber was no easy task, as the cave opening narrows to a width of only 18 cm (seven inches).
So Berger and his team issued a call on social media for people with caving skills and a background in paleoanthropology who could fit through such a small space.
From a global group of applicants, they put together a squad of "underground astronauts" who took part in the initial expedition in late 2013.
The surrounding area is a U.N. World Heritage site, named the "Cradle of Humankind" by the South African government because of its rich collection of hominin fossils.