Largest discovery of early human remains in remote cave
That is not just because a new species has been added to the Homo family of which humans are the sole living members, but because of the record number of fossilised bones found in the cave, including those of at least 15 infants, children, adults and elderly individuals.
Another key reason is because the bodies appear to have been intentionally deposited in the cave by our early ancestors, although such a gesture of respect to the dead had been thought to be solely a more recent human attribute.
Discovery of the new species, dubbed Homo naledi, was announced on Thursday by an international group of more than 60 academics and scientists from a dozen different countries, including some from the Croatian Natural History Museum and Nazarbayev University in Kazakhstan.
They were led by Dr Lee R Berger, an American paleo-anthropologist and professor of human evolution studies at the University of the Witwatersrand in Johannesburg, South Africa.
Berger said Homo naledi was a reference to the cave where the bones were found – the Rising Star cave system at the Cradle of Humankind World Heritage site in South Africa: ‘naledi’ means ‘star’ in the local South African Sesotho language.
Record number of fossil bones
In two papers published in the open-access journal eLife, the researchers said more than 1,550 fossil bones had been found in the cave. This is the largest number of such fossils discovered at any African site and one of the largest anywhere in the world.
Even so, Berger told a media conference that what had been found so far probably represented only a small fraction of the fossils still to be recovered. He suggested that the discovery and how the bones had been deposited could change existing views of human behaviour.
The initial find was made two years ago, following a tip-off from cave explorers who said they had glimpsed “lots and lots of old bones” through a crack in a limestone wall deep in the Rising Star cave.
The remains covered the earthen floor beyond the narrow opening and, as Berger and his team found after two expeditions to the site, seemed to be a large, dark chamber for the dead.
The fossils – they have yet to be dated – were laid out in the chamber 90 metres from the cave entrance and accessible only through the narrow entranceway. The material was recovered in two expeditions in November 2013 and March 2014 and then subject to intense examination in the months since then.
During the first expedition, more than 60 cavers and scientists worked together over 21 days in what Marina Elliott, one of the excavating scientists, described as “some of the most difficult and dangerous conditions ever encountered in the search for human origins”.
Elliott was among six women selected as ‘underground astronauts’ from a global pool of candidates after Berger issued a call on social media for experienced scientists or cavers who could fit through the 18-centimetre-wide cave opening.
Social media continued to play a role in the project, as the team shared expedition progress with a large public audience, schoolchildren and scientists.
“With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage,” Berger said.
Although a reconstruction of the new species suggests it could be one of the most primitive members of our genus, he said it also had some surprisingly human-like features – enough to warrant placing it among our ancestors.
According to the eLife paper, Homo naledi had a tiny brain about the size of an orange perched atop a very slender body that stood about 1.5 metres tall and weighed some 45 kilograms. The teeth are described as similar to those of the previously earliest-known members of our genus, such as Homo habilis, as are most features of the skull.
The shoulders are more similar to those of apes although the small hands suggest tool-using capabilities with their extremely curved fingers. In fact, the fingers are said to be more curved than almost any other species of early hominin, “clearly demonstrating climbing capabilities”.
These contrast with the feet, however, which Berger said were “virtually indistinguishable from those of modern humans”. This, combined with long legs, “suggests that the species was well-suited for long-distance walking and these features distinguish Homo naledi from any previously known species”.
Intentional body disposal
Dr Paul Dirks of Queensland’s James Cook University and a lead author of the eLife paper, said the cave had always been isolated from other chambers and had never been open directly to the surface.
“What’s important for people to understand is that the remains were found practically alone in this remote chamber in the absence of any other major fossil animals,” Dirks said.
He said out of more than 1,550 fossil pieces recovered, only a dozen were not hominin, and these pieces were isolated mouse and bird remains, meaning that the chamber attracted few accidental visitors.
The paper notes that the bones have no marks of scavengers or carnivores or any other signs that animals or natural processes such as moving water carried the individuals into the chamber.
“We explored every alternative scenario, including mass death, an unknown carnivore, water transport from another location, or accidental death in a death trap, among others,” Berger said.
“In examining every other option, we were left with intentional body disposal by Homo naledi as the most plausible scenario. This suggests the possibility of a form of ritualised behaviour previously thought to be unique to humans.
The fossils were subject to close analysis at a workshop in May last year where more than 50 experienced scientists and early-career researchers turned up to study what they called a “treasure trove of fossils” and to prepare scientific papers.
Berger said much remained to be discovered in the Rising Star cave. “This chamber has not given up all of its secrets. There are potentially hundreds if not thousands of remains of Homo naledi still down there.”
As well as the report in the eLife journal, the discovery is also reported as the cover story in the October issue of National Geographic and in a NOVA/National Geographic Special.