The discovery of at least 15 individuals’ bones in a South African cave has been hailed as a major find
More than 1,500 fossils from the Rising Star cave system in South Africa have been named as a new human species, Homo naledi, one which displays a unique combination of human and non-human traits throughout the skeleton.
In September 2013, two cavers discovered bones in an almost inaccessible chamber deep within the Rising Star cave system, about 25 miles from Johannesburg in South Africa. Two months later a team led remotely by palaeoanthropologist Lee Berger of the University of Witwatersrand (remotely because only excavators much slenderer than Berger could squeeze themselves into the chamber) was recovering a haul of fossil human bones. The extraction of the remains was widely publicised, along with numerous videos and live feeds, and I’m sure I wasn’t the only one who thought that the coverage had more hype than substance.
But in two papers published in the online journal eLife, we can see what the fuss was all about as Berger and an international team of collaborators have reported the discovery of more than 1,500 human fossils, representing at least 15 individuals ranging from infants to the aged.
The remains have been assigned to a new human species called Homo naledi (naledi means “star” in the Sotho language). However, despite the wealth of information about the physical characteristics of H. naledi that this collection provides, many mysteries remain. How old are the fossils? Where does H. naledi fit in the scheme of human evolution? And how did the remains arrive deep within the cave system?
In one paper, Berger and colleagues describe how the collection displays a unique combination of primitive and derived characteristics. For example, the small brain size, curved fingers and form of the shoulder, trunk and hip joint resemble the prehuman australopithecines (“southern apes”) and the early human species Homo habilis (“handy man”). Yet the wrist, hands, legs and feet look most like those of much more recent Neanderthals and modern humans. The teeth have some primitive features (such as increasing in size towards the back of the tooth row), but they are relatively small and simple, and set in lightly built jawbones. In several ways the material looks most similar to the small-bodied examples of the primitive human species Homo erectus found at Dmanisi in Georgia, which have been dated at 1.8 million years old. However, the rich H. naledi sample includes bones that are poorly known in other early human species such as H. habilis and H. erectus, so it is difficult to assess how similar these species were throughout the skeleton.
Unfortunately, the naledi fossils have not yet been dated, but if they are more than 2 million years old, which Berger suggests could be possible, the species might lie close to the very origin of our genus Homo (“humans”). However, if they are less than 100,000 years old, it would mean that the species survived until relatively recently, just like Homo floresiensis (nicknamed “the hobbit”) far away in Indonesia (another species which combines a small brain with small teeth). Because naledi is only known from one site, it is unclear whether it was restricted to southern Africa, but if it was more widespread, scientists may need to re-examine other diminutive fossils from across Africa which have often (and perhaps wrongly) been attributed to a small form of H. erectus.
In a second paper in eLife, Berger and colleagues describe the setting of the fossils: the Dinaledi chamber (“chamber of stars” in Sotho). This cavity lies 80 metres into the Rising Star system, and must have always been in darkness. The circumstances parallel those of an accumulation of 6,500 human fossils found in the Sima de los Huesos (“pit of the bones”) in the Sierra de Atapuerca in Spain. In both cases there is no associated evidence suggesting humans lived so deep in these caves. Because the Atapuerca team recovered bones of the hands, feet and spine that could be articulated – reconnected as they were in life – they proposed that the remains of at least 28 early Neanderthals had been intentionally thrown into the pit, where the bodies had decayed.
After considering alternative explanations ranging from whether the remains could have washed there to being dragged there by predators, Berger’s team favour a similar scenario to that proposed for the Sima. However, they also recognise that the intentional disposal of bodies is a complex behaviour for a creature that had a brain no bigger than a gorilla’s (about 500cc in volume).
Even without a date, the mixed human and non-human traits of the naledi skeletons provide yet another indication that our genus Homo had complex origins. The distinctive combination of primitive and derived characteristics in different early human species perhaps even indicates that the genus Homo is “polyphyletic”: in other words, some members of the genus might have originated independently in different regions of Africa.
If this is the case, it would mean that several of the species currently placed within the genus Homo would need to be reassessed, and perhaps reclassified as non-human. While many have concentrated on east Africa as the key and perhaps sole region for the origins of the first humans, the continuing surprises emerging further south serve to remind us that Africa is a huge continent that even now is largely unexplored for its early human fossils.
Professor Chris Stringer is merit researcher in the Department of Earth Sciences at the Natural History Museum in London. This article was adapted by the author from his commentary, The many mysteries of Homo naledi, published in eLife on 10 September
Our evolutionary cousins from all across the planet
Homo sapiens may have been the last-minute lucky winners in the race to dominate Earth but for most of the past two million years it is clear there were many – and mysterious – ways to be a human. These included:
■ The Hobbit Man of Flores. Discovered in 2003, Homo floresiensis lived on Flores in the East Indies until around 17,000 years ago. The species was probably on average only about 3ft 6ins (1m) in height but had large feet and teeth. They also had tiny brains yet made stone tools, hunted elephants and may even have made fire.
Other stone tools found on Flores suggests the species could have lived there for the past 800,000 years. Why it disappeared is a mystery. Equally, it is unclear how the species arrived on Flores. It may have evolved from an early ancestor of modern humans, an African species called Homo erectus, or possibly even an earlier apeman species. But how it managed to travel to Indonesia is a mystery.
■ Denisovan humans. A finger bone found in Denisova cave, in the Atlas Mountains in Siberia, was first thought to be of a Neanderthal, our closest evolutionary “cousin”. But DNA tests carried out by the Swedish biologist Svante Pääbo showed the bone belonged to a completely new species of humans, which were named after the cave. These were thought to have thrived until relatively recently in eastern Asia. Pääbo also discovered that modern men and women in Melanesian countries such as Papua New Guinea carry between 4% and 6% of the DNA of Denisovans.
■ Australopithecus sediba. Discovered by Matthew Berger, Lee’s son, in Malepa in South Africa, sediba people are thought to have thrived around 2 million years ago. Crucially, they have skeletons indicating that apemen were then changing from arboreal animals to upright walkers. However, sediba people walked oddly, turning their feet inwards and putting their weight on the outer edges of each foot. Some scientists suggest this indicates that upright walking – one of the defining features of our species – may have evolved more than once during human evolution.
■ And then there are the Neanderthals. Believed to have died out in Europe around 40,000 years ago, the species’ relationship with humans has always been controversial. Early ideas suggested we evolved from them, a notion that was dispelled several decades ago. We were separate species. However, recent work by Pääbo and others indicates that Neanderthals do live on – in our DNA. About 2-4% of the DNA of humans who originate from outside Africa is reckoned to be Neanderthal, suggesting the latter and our own ancestors made love not war on several occasions in our prehistory. This probably occurred as modern humans were emerging from their African homeland and encountered Neanderthals in Europe or the Levant.