Scientists announced on Tuesday that the Rising Star cave system – the home of homo naledi – had yielded a series of startling new finds: not least that there was still a great deal more exploring to be done, that modern humans may have known homo naledi a lot better than we previously thought, and perhaps most amazingly, a skull intact enough to allow facial reconstruction. By MARELISE VAN DER MERWE.
Scientists announced on Tuesday a series of further discoveries in the Rising Star cave system, the outcome of further research into site where homo naledi was found. The results follow a three-year expedition in the Cradle of Humankind. More specifically, the researchers are sticking to their guns: naledi, they say, disposed of their dead.
The research, consisting of three papers published in the journal eLife, firstly describes the age of the naledi fossils found in the Dinaledi Chamber, which they say is considerably younger than expected, suggesting homo naledi may have come into contact with modern man.
Second, it announces the discovery of a second chamber, Lesedi, in the Rising Star cave system, containing further specimens of homo naledi virtually identical to those first found in the Dinaledi chamber in 2015.
Third, it describes the discovery of remarkably well-preserved remains in the additional chamber, including a child and a partial skeleton of an adult male, with what the team calls a “spectacularly well-preserved skull” – complete enough to enable a facial reconstruction. “We finally got a look at the face of homo naledi,” said Peter Schmid of Wits and the University of Zurich, who spent hundreds of hours reconstructing the bones.
The research was completed by a large team from the University of the Witwatersrand (Wits), James Cook University, Australia, the University of Wisconsin, Madison, United States, and over 30 other institutions – a total of 52 scientists. The team was led by Professor Lee Berger of Wits, who is also National Geographic Explorer in Residence.
Photo:Professor Lee Berger, leader of the Rising Star expedition, Research Professor in Human Evolution and the Public Understanding of Science Evolutionary Studies Institute at University of the Witwatersrand in Johannesburg, South Africa. Photo: Wits University.
The skeleton was nicknamed “Neo”, meaning “gift” (Berger told Daily Maverick he would not be surprised to see some Matrix-inspired memes surfacing).
“To have a skeleton is just so beautiful. It is extraordinary,” he said. According to Berger, the skull is one of the most perfectly preserved ever found – comparing it, perhaps not so subtly, to that of the famous Lucy, for whom one of Berger’s more vocal critics, Tim White, is best known.
Berger believes that with thousands of fossils likely remaining in both the Lesedi and Dinaledi Chambers, there are decades of research potential. “We are going to treat ongoing extraction of material from both of these chambers with extreme care and thoughtfulness and with the full knowledge that we need to conserve material for future generations of scientists, and future technological innovations,” he says.
It’s difficult to pinpoint exactly what is most significant about the latest developments. Berger says from a scientist’s perspective the importance lies most in the promise of what’s to come. Berger has been one side of a well-documented media duel with the equally respected White, who – among others – met the discovery of homo naledi with some scepticism. But Berger believes that a new era of discovery is just beginning. “It is a remarkable time to be a young paleo-anthropologist,” he says. “This has profound implications for the field.”
Naledi sceptics have raised a number of questions since the haul of some 1,500 specimens surfaced a year and a half ago. Most commonly, the critics have been reluctant to accept that homo naledi disposed of their dead, a behaviour that was believed only to have originated with more advanced species. Wits postdoctoral fellow Aurore Val (and former student of Berger) published the first critique in a peer-reviewed journal, the Journal of Human Evolution. She argued that it was simply impossible to establish reliably that homo naledi really had disposed of their dead there, most notably because the fossils’ age had not yet been determined and that the original researchers could not know what the caves were like when the remains entered it. She added that analysis had not been thorough enough to rule out that the remains had been brought in by water or carnivores. Cave systems can change substantially over time and access to the chambers where the remains were found was extremely difficult. (Some of the entrances are smaller than 20cm and at one point, Berger got stuck at an awkward 90% angle in a 25cm gap, having to be extracted by the wrists.) Why, then, would homo naledi make the treacherous journey to dispose of their dead?
But the team is sticking to its guns. For one thing, says Berger, the sheer abundance of homo naledi fossils – including the extraordinarily well-preserved skeleton of Neo, one of the most complete skeletons of a hominin ever discovered, plus the remains of at least one child an another adult – raise the question of how on earth they got there. The absence of larger animal bones and signs of carnivore damage to the homo naledi fossils lends credence to the theory that they were not washed in by water or dragged in by animals, the team argues. They believe it is precisely its inaccessibility that makes the cave system a likely tomb.
The Lesedi Chamber (Setswana for “light”), third in the system, is over a hundred meters from the Dinaledi chamber. “What are the odds of a second, almost identical occurrence (of a body turning up) happening by chance?” asks researcher John Hawks (Wits/University of Wisconsin-Madison).
And so there remains the question of behaviour. The age of the homo naledi remains, adds Berger, tells an unexpected story. Homo naledi, first announced to the public in September 2015, lived sometime between 224,000 and 236,000 years ago, meaning there is a chance they lived alongside homo sapiens. This would mean the dating of homo naledi provides the first evidence that another species of hominin may have survived alongside the first humans in Africa – a scenario Berger describes as “bizarre”.
“We can no longer assume that we know which species made which tools, or even assume it was modern humans that were the innovators of some of these critical technological and behavioural breakthroughs in the archaeological record of Africa,” says Berger. “If there is one other species out there that shared the world with ‘modern humans’ in Africa, it is very likely there are others. We just need to find them.”
At the very least, this claim is likely to raise questions from the scientific community. When homo naledi first emerged, critics raised eyebrows at whether the discovery could drive a major reinterpretation, or rather whether naledi was an outlying species confined to one region. At the time, Bernard Wood of George Washington University told Scientific American he agreed homo naledi was a significant discovery, but that – like the small-brained species homo floresiensis from Flores, Indonesia, it could simply be a relic population that may have evolved some odd traits.
Photo: Homo naledi may have lived at the same time as the first modern humans. Left: ”Neo” skull of Homo naledi. Right: Omo 2 skull, one of the earliest modern humans. Photo: Wits University/John Hawk
Nonetheless, the given naledi date is surprisingly recent. The fossil remains have primitive features that are shared with some of the earliest known fossil members of our genus, such as homo rudolfensis and homo habilis, species that lived nearly two-million years ago. On the other hand, it also shares some features with modern humans. After the description of the new species in 2015, experts predicted that the fossils should be around the age of these other primitive species. Instead, the fossils from the Dinaledi Chamber are barely more than one-tenth that age.
Paul Dirks of James Cook University and Wits, lead author of the paper The age of homo naledi and associated sediments in the Rising Star Cave, South Africa, worked with 19 other scientists from laboratories around the world to establish the age of the fossils, using six independent dating methods. The fossils – which were eventually classified as late Middle Pleistocene – may have survived for as long as two-million years alongside other species of hominins in Africa, he argues.
This was when “modern human behaviour” began in southern Africa, says Berger – behaviour which had, until now, been attributed to the rise of modern humans and thought to represent the origins of complex modern human activities such as burying the dead, self-adornment, or the making of complex tools.
The significance, explains Berger, is that this primitive species, with its small brain, perhaps made contact with modern humans. “We see the archaeological signs in Southern Africa; the rise of modern human behaviour.”
There will, no doubt, be questions around the dating, but it appears the team is ready and waiting. The dating process was particularly challenging and was painstakingly undertaken, not least because the findings could have such controversial ramifications, they say. “It was done very carefully, once we realised this was going to be very young,” explains Berger.
They used a combination of optically stimulated luminescence dating of sediments, with Uranium-Thorium dating; and palaeomagnetic analyses of flowstones to establish how the sediments relate to the geological timescale in the Dinaledi Chamber.
Direct dating of the teeth of homo naledi, using Uranium series dating (U-series) and electron spin resonance dating (ESR), provided the final age range. “We used double blinds wherever possible,” says Professor Jan Kramers of the University of Johannesburg, a uranium dating specialist. Direct dating is seldom used unless it is absolutely unavoidable, due to the risk of destroying the material, says Berger.
Dr. Marina Elliott, Exploration Scientist at Wits and one of the original “underground astronauts” on the 2013 Rising Star Expedition, says she had always felt that the naledi fossils were “young”. “I’ve excavated hundreds of the bones of homo naledi, and from the first one I touched, I realised that there was something different about the preservation, that they appeared hardly fossilised.”
Hawks explains: “I think some scientists assumed they knew how human evolution happened, but these new fossil discoveries, plus what we know from genetics, tell us that the southern half of Africa was home to a diversity that we’ve never seen anywhere else”.
Berger agrees. Asked if he can think of a location offering a similar richness, diversity or explorative potential anywhere else, he struggles. Not really, he says. “Recently, the fossil hominin record has been full of surprises, and the age of homo naledi is not going to be the last surprise that comes out of these caves, I suspect,” he adds.
The original fossils, as well as those from the original Rising Star expedition, will be on public display at the Maropeng Visitors’ Centre, Cradle of Humankind World Heritage Centre, from 25 May. The exhibit will be the largest ever display of original fossil hominin material. DM
Photo:“Neo” skull of Homo naledi from the Lesedi Chamber. Photo: Wits University/John Hawks