How old is Homo naledi?

Back in September 2015, a new species of early human - Homo naledi - was announced to the world. The remains were found in the aptly named ‘Cradle of Humankind’ near Johannesburg, South Africa at the Rising Star cave system. Since their discovery they have changed the way that we think about human evolution. Now another chamber has been discovered containing yet more remains and analysis of the skeletons within has shed light on what Homo naledi looked like and where they fit into the timeline of evolution. Tom Crawford spoke to the lead researchers…

Lee - I’m Professor Lee Berger; I’m a research professor at the University of Witwatersrand in Johannesburg, South Africa and Explorer in Residence at the National Geographic.

We’ve discovered first a new chamber with more Homo Naledi about 100 metres from the original chamber - it’s called the Lesedi chamber. It’s got multiple individuals in it including a partial skeleton of Homo Naledi, an adult male we call Neo, which means ‘gift’ by the way. It’s not after the matrix character. We also have finally dated Homo naledi for the Dinaledi chamber; the fossils that we announced in September, 2015. And, contrary to what I think practically, every scientist who had seen or studied the remains thought these individuals are not millions of years old as they probably should have been by their anatomy, but they are relatively young, between 2 and 300,000 years approximately. That places them in the presence, potentially, of modern humans who we believe are evolving in Southern Africa at that time and certainly, we’ve seen first what we used to think of as the first archaeological evidence of modern human behaviour.

Tom - Homo naledi: is this some sort of primitive human species in some sense?

John  - Yeah, exactly right. I’m John Hawks and I’m a Professor of Anthropology at the University of Wisconsin, Madison and at Vitz University in South Africa.

When we look at Homo naledi, and we have a better skeletal record now of naledi now than we do of any other fossil hominin except for the Neanderthals and modern humans. So we know a lot about it and its human-like in some aspects. It’s human-like in its hands and wrists in many ways, in its feet. It's human-like in body size and it’s got very small human-like teeth which indicates something about its diet.

But much of the rest of the skeleton is very primitive. It has a brain about a third the size of modern human brains. It has a very primitive early homo-like skull and parts of the trunk are very primitive also, so it has this mixture of characteristics. It’s been very difficult for us to try to figure out exactly how it’s connected to us but it’s clear that its origin, its branching from our evolution, has to be something like 2 million years ago, so that’s where people were thinking it would be.

Tom - But you’ve now shown that it’s much more recent than that?

John - Exactly right. That lineage may have originated two million years ago - it looks like it. But this population existed in the very recent past - 200, 300,000 years ago. So it shows that there was a lineage that lasted up to two million years that was in Africa evolving at the same time that our ancestors and, potentially, and other lineages of archaic humans are evolving. It’s a very complicated scenario, and even five or ten years ago we would have said this is probably a very simple scenario. So this has really shocked us and shocked many in the field.

Tom - You mentioned this was a new cave that you’ve discovered. So was this branching off from the old cave system?

John - The Rising Star system as a whole has up to two kilometres of passageways underground that we’ve got mapped. Now our first discovery, the Dinaledi chamber was not on the map and it was a very difficult descent down into it and very surprising that we found bones lying on the surface. As we were excavating that, our exploration team said I think I’ve seen something like this somewhere else, and the original two discoverers of the Dinaledi chamber, Steve Tucker and Rick Hunter showed us the Lesedi chamber and it also had skeletal material on the surface. It wasn’t as obvious and it had been missed before but we began to explore that, we began to do very limited skeletal excavations in it and preserved some of the best Homo naledi remains.

Lee - What’s also fascinating is that the Lesedi chamber which, by the way, means 'chamber of light', is almost as difficult to get to as the Dinaledi chamber, the original chamber. It’s not quite as difficult, the squeeze is only about 25cms instead of a terrible 18cms, and I can attest to the difficult because I’ve been in it once and almost didn’t get out of it. I was stuck for almost an hour before they had to pull me out. But there it’s clear that Homo naledi was choosing to go into these very similar, very difficult to access chambers, generally 30 metres or so underground. That is a really remarkable to think the journey that they would have taken to get to these two places and why they would have done that?

Tom - That is my next question then, why do we think they may have been going into these chambers?

John - We know that we find their bodies, and bodies of individuals of all ages. In the Dinaledi chamber, at least 15 individual, newborns to old adults. In the Lesedi chamber we have at least three individuals, two adults and one juvenile, potentially more. So we know they’re leaving their bodies there.

What we don’t know is how they may have been using other parts of the cave system. We are now turning to investigate that by excavating probably nearer to the surface where we use and also by looking systematically for other evidence of naledi behaviour inside the cave. In particular, we’re super interested in the possibility that there will be evidence of fire somewhere in the cave.

Lee - So we went to initially a great deal of effort to try and explain any other reason that Homo naledi might be using these chambers except for ritualised, deliberate body disposal, which a lot of people just didn’t like. Several scientists wrote a couple of articles, which we responded to, and say a small-brained hominid can’t do it, but that’s about the only argument there is against that idea - just not liking it. That one of things we see as precious has been intruded on by a hominid with the brain the size of an orange.

Finding a second Lasedi chamber that is practically identical in its formation, its location, its position, and contents to the first chamber I personally think adds quite a lot of evidence to the idea that Homo naledi really was ritually disposing of its dead.