Thousands of bones of Homo naledi recovered in South Africa's chamber of secrets show unique features – and may be the relics of an ancient burial site

It’s an anatomical mosaic John Hawks

ONE thousand four hundred bones, 140 teeth, belonging to at least 15 individual skeletons – and that’s just what was recovered in a single short field session.

The early human fossil record isn’t normally this rich. For a century, palaeoanthropologists have generally learned to make do with slim pickings – part of a face here, a jawbone fragment there. Now, from the depths of a cave in South Africa, has come a monster cache of hominin bones from a previously unknown early species of our own genus, Homo.

This is what Homo naledi could have looked like National Geographic Society

“It’s unique,” says Fred Spoor at University College London, who has seen casts of some of the finds.

The sheer number of bones and their location hint at something even more astonishing: the bodies they belonged to appear to have been left deliberately in the cave. This has never been seen before in such a primitive human, and could have big implications for understanding the origins of modern human behaviour (see “Did ancient hominins bury their dead?“).

The first signs that something unusual was unfolding came in October 2013, when Lee Berger at the University of the Witwatersrand in Johannesburg, South Africa, advertised for people with good archaeological skills and a lack of claustrophobia to come forward. The successful applicants flew to South Africa a few weeks later to help remove hominin bones and teeth from the cramped Dinaledi chamber in a cave system a few tens of kilometres from Johannesburg (see diagram).

There are still thousands more remains in the cave, according to Berger. “Once we realised the full potential, we decided the best thing to do was to lock down the site, and engage the entire community to make a decision on what to do there next,” he says.

But what has been recovered so far tells an extraordinary tale. The species the bones belonged to had a unique mix of characteristics. Look at its pelvis or shoulders, says Berger, and you would think it was an apelike Australopithecus, which appeared in Africa about 4 million years ago and is thought to be an ancestor of Homo. But look at its foot and you could think it belonged to our species, which appeared just 200,000 years ago.

Its skull, though, makes clear that the brain was less than half the size of ours, and more like that of some species of Homo that lived about 2 million years ago.

“It doesn’t look a lot like us,” says Berger. Even so, he and his colleagues think that, on balance, the features of the skull, hands and teeth mean the new species probably does belong in our genus. They have named it Homo naledi (eLife, DOI: 10.7554/eLife.09560).

“It may not be that closely related to us, but could have had a cognitive ability essentially equal to ours.”

Its anatomy suggests it is one of the earliest members of our genus to evolve, but frustratingly, we don’t yet know exactly how old the skeletons are. They might turn out to be 2 or 3 million years old, dating back to the time when Homo first came on the scene.

But even if they prove to be much younger – 100,000 years old, say – that would be significant, says Berger. It would make them a human version of the coelacanth, he says: an ancient species that survived, unchanged, into essentially modern times. “Whatever the age, it’s exciting.”

The team refers to the fossils’ mixture of features as “anatomical mosaic”. We have previously seen such a mosaic in Australopithecus sediba, a 2-million-year-old hominin that Berger and his colleagues excavated in 2008 from the Malapa cave, a few kilometres away. “Naledi is almost the mirror of sediba,” says Berger. “Almost everywhere in the sediba skeleton where you see primitive features, in naledi you see derived features. And almost everywhere that sediba is derived, naledi is primitive.”

Although it was just about possible to dismiss A. sediba, with its assortment of ancient and modern features, as a quirk of human evolution, the new find hints that such “mosaicism” is not the exception in early humans but the rule, says Berger.

That has implications for how we interpret other early human fossil finds representing the transition from Australopithecus to Homo, he says. These fossils generally amount to just a few fragments rather than complete skeletons. “Both sediba and naledi say you can’t take a mandible [lower jaw], a maxilla [upper jaw] or a collection of teeth and try to predict what the rest of the body looks like,” he says.

Homo naledi hands Peter Schmid

But Spoor says H. naledi could really be a localised exception. “If you have lots of bones scattered all across East Africa, that might actually give you a better indication of what’s going on in terms of human evolution over a widespread region,” he says.

Not that this viewpoint diminishes the importance of the find. “The contribution of these fossils is fantastic,” says Spoor. “I don’t think many people will have a problem with the interpretation: it’s a new species and I think it does belong in the genus Homo.”

Inevitably, though, there are dissenting views. “To me, having studied virtually the entire human fossil record, the specimens lumped together as Homo naledi represent two cranial morphs,” says Jeffrey Schwartz at the University of Pittsburgh in Philadelphia.

Ian Tattersall at the American Museum of Natural History in New York shares that view. Last month, he and Schwartz wrote an article calling for researchers to think carefully about classifying new fossils as belonging to Homo.

As for the Dinaledi finds, Schwartz and Tattersall point out that although the foreheads of some of the new skulls are gently sloped, one skull has a taller forehead with a distinct brow ridge – suggesting two species are present. “Putting these fossils in the genus Homo adds to the lack of clarity in trying to sort out human evolution,” says Schwartz. Berger disagrees, saying this can be explained by differences between males and females of the same species.

Either way, all can agree that the new find is a remarkable addition to the human fossil record. “This is an amazing assemblage of fossils that should keep paleoanthropology buzzing for a long time,” says Tattersall.

Face view of Homo naledi skull with virtual reconstruction in blue. Heather Garvin

Dean Falk at Florida State University in Tallahassee is especially excited by the fact that Berger’s team has produced a cast of Homo naledi‘s small brain. Images of it hint at interesting features close to one brain region associated with speech in modern humans, she says.

Berger says it’s possible that for the first time, we have found another creature not that closely related to us, yet with a cognitive ability “different but essentially equal to ours”.

The find is also a reminder that the fossil record still has rich treasures to offer, he says. “This stuff is still out there, and it’s out there in abundance.”

Some 1500 bones and teeth at the bottom of an inaccessible cave in South Africa comes from a new species of early humans. Here are some of the finds and a look at how they were recovered:

Did ancient hominins bury their dead? The discovery of more than 1500 fossilised human bones and teeth in one place is unusual (see main story), but what’s missing from the site is also extraordinary. Besides a few rodent fossils and the remains of an owl that probably fell into the Dinaledi chamber by mistake, there are no other vertebrate species present. How so? Lee Berger at the University of the Witwatersrand in Johannesburg, South Africa, and his colleagues looked at various explanations. Carnivores could have brought the human remains to the chamber, but there are no gnaw marks, and it’s rare for just one species to be targeted. The ancient humans could have fallen in by accident – but few would wander deep enough into the caves to stumble upon the chamber’s entrance. What’s more, the remains include those of infants, making this idea even more implausible. Only one scenario works, they say: Homo naledi deliberately disposed of its dead in the chamber. Perhaps the bodies were gently dropped down the shaft (see diagram) which researchers squeezed through to recover the bones (eLife, DOI: 10.7554/eLife.09561). There are precedents for this. At Sima de los Huesos in the Atapuerca mountains of Spain, for example, 28 hominin skeletons were recovered from a deep pit. But these hominins were big-brained – they looked and behaved rather like us. H. naledi had a brain less than half the size of ours. “It’s fair to say that naledi individuals recognised their own mortality and the other self that comes with death,” says Berger. The find is likely to “squash the sacred cow” that this sort of behaviour requires a big brain, he says.

Key human fossil discoveries With a discovery of a new early human, we look back at major finds that defined our understanding of human evolution The history of early human fossil finds is a long and messy one, and as the new Homo naledi find shows, it remains a work in progress. The sheer number of H. naledi bones and teeth found is remarkable, as often fossils are just tiny fragments of the skeleton. Here’s a timeline of some key finds and what they taught us about our deep past. 1829 First Neanderthal bones are discovered in what is now Belgium. Subsequently we learned that Neanderthals lived alongside our species, looked a little like us and even interbred with our species 1891 The first H. erectus fossils are found in Java. We now think the species appeared at least 2 million years ago in Africa and, again, looked distinctly human 1924 The discovery of the first Australopithecus remains in South Africa shifts the focus of study to Africa. Clearly more primitive than humans, australopiths appeared about 4 million years ago and walked on two legs, although they also had large teeth, small brains and long arms like those of apes 1960 Excavations in Olduvai Gorge in Tanzania reveal a possible Australopith-human halfway house – a species later named H. habilis, with a small brain but a skeleton slightly more human-like than an australopith. It appeared a little over 2 million years ago 1974 The now famous Lucy skeleton is found in Ethiopia, later dated to around 3.2 million years. It remains arguably the most famous Australopithecus ever found 2008 Astonishingly well preserved 2-million-year-old australopith remains, later named A. sediba, are found in a cave in South Africa. Controversially, some see the species as a better “missing link” to our genus than H. habilis 2015 A jawbone unearthed in Ethiopia could, some suggest, be the oldest fossil of our Homo genus. The find narrows down the transition from Australopithecus to Homo to around 2.8 to 3 million years ago

This article appeared in print under the headline “Deep cave yields a new human”

For more about the cave’s discovery, read: Bone bonanza: Chamber of secrets yields human remains

Learn more about human evolution: Click here to read a collection of articles on human evolution