Ancient Homo Naledi May Have Walked Alongside Early Humans

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Two years ago, scientists announced a fascinating fossil discovery. Deep inside a cave in South Africa, they found remains of a new human cousin that they named Homo naledi. The space was so hard to get to that they assigned a group of smaller-sized people– they called them underground astronauts– to really squeeze into this chimney-like chamber and get out the fossils. But it did pay off. And now it seems it paid off big, because inside they found a staggering number of remains. 1,500 bones from up to 15 individuals.

Homo naledi had a mix of both primitive and modern features, but there were still lots of big questions, like how old were the fossils? How does this species fit into the evolutionary tree? How did these individuals get into this deep remote cave, and was it intentional?

This week, the age of the bones was announced, and it turns out they are a lot younger than expected. And the team has found more fossils in a second chamber. My next guests are here to take us through what these updates mean. John Hawks is a member of the team that excavated the cave. He’s also a paleoanthropologist at the University of Wisconsin in Madison, and today he joins us from South Africa by Skype, via Skype. Welcome back, John.

JOHN HAWKS: Hi, Ira. Thanks for having me back.

IRA FLATOW: You’re welcome. Susan Anton, who was not involved in these findings, has studied these types of fossils and cave burials. She’s professor of anthropology at New York University. Welcome to Science Friday.

SUSAN ANTON: Hi, Ira. Thanks for having me.

IRA FLATOW: John, you were able to put an age on these bones, so as Johnny Carson used to say, how old is Homo naledi?

JOHN HAWKS: Well, we discovered that they were between 236,000 and 335,000 years ago. It was a really hard job to try to figure out the age of these bones, because that age range is too old for carbon dating, and caves are contexts where it’s often very difficult to figure out exactly the context of the bones. So we in the end employed six different methods. We had 11 different labs around the world involved, some of the best labs in the world for different techniques, and we sent samples to many of those labs double-blind, which means that we sent them samples, didn’t tell them where the samples had come from, including dummy samples that didn’t relate to the bones at all, and two different labs in these cases. So that we waited to see if they would give us independently the same results. And so what we have is the best answer that I think anybody could get right now.

IRA FLATOW: So you went through so much trouble. Why is that so important to pin down the age here?

JOHN HAWKS: We felt, when we discovered these bones, that there was a chance that they were an unexpected age. And we knew that if they turned out to be younger than we expected, it would be a big shock to everybody.

IRA FLATOW: So put that in context for us

JOHN HAWKS: Yeah, these bones look like in many respects, very primitive members of our own genus, Homo. Fossils that lived between 1 and 1/2 million and 2 million years ago. On their morphology, the way they look, a lot of people looked at them and said, well, that’s about the age they should be. 236,000, 335,000 years ago, this is a time frame when Africa has some examples of very large-brained, what we call archaic humans that are actually quite close relatives to ours compared to what naledi looks like. And possibly the immediate ancestors of modern humans themselves.

Modern humans, the first ones we have from Ethiopia, about 196,000 years ago. So we’re really in a frame where our species is originating. And these very ancient-looking, very primitive hominids that are probably distant relatives of ours are there in this landscape in a place that we did not expect.

IRA FLATOW: And could they have been living at the same time as Homo sapiens?

JOHN HAWKS: Yeah, I think that they overlapped with, if not Homo sapiens, modern humans, at least the very close immediate ancestors of them, and other lineages of archaic humans that also existed in Africa. Our view of African evolution has just become massively more complicated in the last few years. Part of that is because we know from genetics, we’ve found the genomes of Neanderthals, and we discovered that hey, some living people have Neanderthal genes. Now Neanderthals were European, Asian.

In Africa, there were also archaic lineages, and we’ve seen in modern people’s genomes that there may be traces of mixture from them. So you’d have multiple lineages of very distantly related humans. And at least now we know these Homo naledi also in Africa somewhere. We don’t know how they interacted, whether they overlapped with each other, when one might have come into an area or left. It is now just an open ground in terms of trying to figure out what was going on in what was really the heartland of human evolution.

IRA FLATOW: Dr. Anton, what are your thoughts on this? It sounds like it’s just an amazing find.

SUSAN ANTON: Well, it is absolutely an amazing find and so that’s the first thing that we should really appreciate is that there is a lot more to be discovered and things that we don’t– we’re not necessarily anticipating. I mean, we could think about it like that game that you used to play as a kid where you had a bunch of dots on a page, all of which had numbers on them, and then you drew lines between them. And it gave you a picture. Except for, let’s take away the numbers and a bunch of the dots and then try to figure out what the picture was. So this has added a few more dots. And then also now with the ages, it’s added some numbers.

And it’s different than we expected. When people first looked at the anatomy of the things that were found, folks suggested that they probably were pretty old, because they looked kind of primitive in some ways. They had tiny brains and certain parts of their bodies looked like some of these older humans.

But then some other parts didn’t. They looked really modern, and so there’s always an idea that you want to look at what these things look like and then say, oh, I know how old they are. But we know that time and time again when we’ve done that, we’ve been absolutely wrong, and this is just one more example of that. So I agree with John. Life’s a lot more complicated than we thought it was a few years ago, and we’ve got a lot of exciting strands to pull together now.

IRA FLATOW: Now there have been other discoveries of early human cousins, like those so-called hobbits that were in an island.

SUSAN ANTON: Yeah, and it hasn’t happened yet. This is the first time within the African continent, and it’s the first time that we’ve got this later overlapping within the African continent. But let’s also be realistic that the fossil record from this period of time is actually pretty sparse. And so we didn’t have a lot to base the idea of one lineage versus multiple lineages. And now this group has provided some of that.

IRA FLATOW: Dr. Hawks, East Africa has been called the cradle of humanity, the birthplace of our species. Does this fine now in southern Africa change this whole idea?

JOHN HAWKS: Realistically, when we look at Africa, which is the second biggest continent, and in human terms, through most of our evolution, was the continent that had most of the space that was really suitable for human-like creatures. If we look at it and think, we’ve got some great evidence of evolutionary history in parts of Ethiopia, in parts of Kenya, parts of Tanzania, parts, very small parts here of South Africa. And the rest of the continent is really largely unknown.

It’s just what Susan’s saying. The record here has been sparse. And we’ve been assuming that we could maybe draw lines between a few fossil discoveries, and that was going to tell us the answer.

One of my colleagues professionally said at one point, every important event happened in this valley in East Africa. And it happened to be a valley where he worked, which works well. But we know now that’s not true. If we explore and find new localities with fossils, we’ve seen that often things are going to turn up that we didn’t expect.

IRA FLATOW: Wow.

JOHN HAWKS: And I wouldn’t say that it’s a message of–

SUSAN ANTON: Great time to be an aspiring scientist. I mean, if you’re that kid looking for really something really exciting to do, go someplace where there aren’t fossils and see what you can find.

IRA FLATOW: And the initial specimens were found in one chamber. You’re also reporting that you found a second chamber. Tell us, Dr. Hawks, about the second place there.

JOHN HAWKS: So the first chamber story is such an incredible adventure, because it is deep inside the cave. It takes a half an hour for our team to get from the surface into this chamber. Incredibly constrained, hard for our team to get down into it, but an incredible number of bones inside that chamber. And thousands still in there. We’ve excavated such a very small area.

As we were excavating there, our explorers were going into other parts of the cave to see if they could understand the system as a whole. There’s more than 2 kilometers of underground passages altogether in the system. And they found another chamber, a second chamber, that also had bones on the surface.

We started investigating that chamber in 2014. Two years, our team leader underground, Marina Elliott, has been excavating there with other members of the team. The place where the bones are most dense is a tiny little side passage that she can fit in only on her hands and knees or her belly and her feet sticking out. So it is really hard to excavate inside of it.

The chamber is likewise difficult for our team to reach. I don’t fit. I can’t get in there. Lee Berger, the team leader, went down to the chamber once, because he could squeeze through, and as he was trying to get out, was stuck. And we had to tie ropes to his arms to pull him out. So it’s dangerous. But inside this chamber are, again, multiple individuals of, as we now know after studying them, Homo naledi.

IRA FLATOW: And you found an intact skull inside that second chamber?

JOHN HAWKS: Yeah. There is a beautiful, nearly complete skull and jaw, a partial skeleton that goes with that skull, so we’re looking at an individual. It’s sort of like the Lucy skeleton now of Homo naledi, because you can see all of the anatomy in different regions of the skeleton and how they go together in one individual. We nicknamed the skull and the skeleton Neo, which is a word that means gift in the Sesotho language here.

IRA FLATOW: Wow, Susan, this just– what–

SUSAN ANTON: Rather astonishing.

IRA FLATOW: It’s leaving me breathless. This must be leaving you breathless. But inside, did you find any evidence of habitation there? Any tools, food, anything that’s fossilized? That they might have left behind?

JOHN HAWKS: In neither one of these chambers is there any artifact or anything that was carried in, other than the bones of the hominids. We have a very, very small number of other animal bones in the Lesedi chamber, the new chamber. In the first chamber, the Dinaledi chamber, nothing there but ancient rodent pieces and a couple of bird bones. So they’re very striking, because in most contexts, we find lots and lots of animal bones for every hominid bone. It was very difficult for a team to try to grapple with.

SUSAN ANTON: So I’m going to jump in there–

IRA FLATOW: Please.

SUSAN ANTON: –on a word. Can I?

IRA FLATOW: Sure, please.

SUSAN ANTON: I’m going to jump in there on a word that John used. There was no other evidence of things that were carried in. Because, John, you guys have made some kind of startling suggestions, or at least provocative suggestions, about how it was that the hominids got into these particular chambers in the cave, suggesting that maybe they’ve even been intentional burials. And I know you’ve gotten a lot of pushback on that, and I’m just wondering, in the new cave, what do you think the evidence is that’s similar to the other cave that this would build on that idea for you or on that conclusion for you?

JOHN HAWKS: Sure. It’s a great question, because in other cave systems in South Africa, we look at the bones, and there’s usually some sign of how they entered the cave. Oftentimes, if they’re carried in by predators, or if predators have collected the bones and they’ve dropped in the cave, you’ll see tooth marks. The bones will be crushed in characteristic ways by the teeth. You’ll have fresh breaks on them that were made by the predators crunching into them.

When bones are carried in by water, they get smoothed around the edges. You have a bunch of grit that comes in, because the bones are being carried from a place that’s closer to the surface. When they fall in directly, of course, there’s an opening from above, but also, that carries with it characteristic sediments because it would have been open, including usually the bones of other animals.

As we had started looking at these two assemblages, we found that they were very similar. There’s no mark on any of the bones from any predator at all. All of the skeletons represented, including very tiny parts, and there are articulated parts of skeletons in both assemblages, so we know that bodies were getting into these. There’s no sign that water was transporting anything. There’s no opening from above.

And so it’s really a process of eliminating the things that work everywhere else. At the end, we thought, well, one reasonable hypothesis is that Homo naledi was responsible for this. They might have been taking bodies, when individuals died, into deeper parts of this cave system.

IRA FLATOW: I have to remind everybody that this is Science Friday from PRI, Public Radio International. Talking with John Hawks and Susan Anton. But that is, Susan, that’s kind of speculative, you’re saying, at this point.

SUSAN ANTON: So I think that any time we come along a site, we have to have as sort of our null hypothesis, if you will, our starting point, that there is some natural reason for this accumulation. And so while I wouldn’t disagree that it’s one feasible hypothesis for how individuals might have come to be in the cave, it seems to me that there could be other reasons for them being in the cave as well. I mean, perhaps they’re using the cave system, and because they’re using the cave system, they’re also dying in the cave system. And that’s why you’re ending up with them.

John and the team have suggested that Homo naledi is using this as an intentional way of either burying or at least getting their remains away from the rest of the group, but if they are co-existing with other humans on the landscape, maybe it’s other humans doing it. Or in fact, maybe if naledi is doing it themselves, maybe they’re piling things up for not ritual kinds of reasons, but simply because they’re piling things up. I mean, my dog makes little piles of things all over the yard, and I don’t think that there’s sort of ritual intention in that. But maybe has to do with the way that they’re using the cave system itself.

So I think there is, having worked in burial caves that were made by recently living humans, there are a number of strategies that you go through to try to figure out why it is that the bones are in the cave and what they mean? And there’s a lot of different reasons, even if you do intentionally inter something in a cave, there’s also a lot of different things that go on for why you might do that. So for example, there’s intentional interment because it’s a ritual and it’s a special place. There’s intentional interment because you’re trying to hide it from an enemy that might desecrate the remains. There’s intentional interment that really is just about getting individuals out of the way because dead individuals are stinky messes. So there are, I think, a vast number of hypotheses that run the gamut of what could be driving this.

IRA FLATOW: This is fascinating. We’re going to extend into the next segment. We’re going to take a break and come back. Talk more with John Hawks and Susan Anton, and then we’re going to bring in another anthropologist. Shelby Putt is going to join us. She’s going to talk about stone tools and stuff like that and brain sizes. We’re going to get granular. I know you like that. So stay with us. We’ll be right back after this break.

This is Science Friday. I’m Ira Flatow. In case you’re just joining us, we’ve been having a really fascinating discussion about Homo naledi, one of the newest additions to the human family tree, with my guest John Hawks, paleoanthropologist at the University of Wisconsin in Madison, Susan Anton, professor of anthropology at New York University. And now we’re going to change gears a little bit and talk about the fossils themselves. Not particularly the ones from naledi, but all fossils, and what they can tell us about a species, and how early ancestors possibly think, from brain size and things like that. How did the brain evolve?

A different group of scientists have studied how our ancient brain evolved by looking how stone tools. You look at stone tools, you can learn about the brain. This week, their results were published in the journal Nature Human Behavior. Shelby Putt is one of the authors on that study. She’s an anthropologist and post-doctoral researcher at the Stone Age Institute in Bloomington, Indiana. Welcome to Science Friday.

SHELBY PUTT: Hi, thank you.

IRA FLATOW: So you try to study how stone tools– brains of normal people– how stone– normal people.

SHELBY PUTT: Quote-unquote “normal.” They are undergraduates.

IRA FLATOW: We know everything we do by 18-year-olds, don’t we? Tell us about how you study the brains and link that to toolmaking.

SHELBY PUTT: So unfortunately, our intelligence doesn’t fossilize. So we have to find a unique way to learn how cognition evolved. And one way to do that is with stone tools, because, really, what stone tools are is cognition in action. Because in order to make them, you have to think about it.

And so what we did was we taught these students how to make stone tools from the past. We had them learn Oldowan stone tool-making techniques and Acheulean stone tool-making techniques. Now the Oldowan we have discovered it first at 2.6 million years ago, but then around 1.8 million years ago, we see a new type of stone tool industry show up in the archaeological record. And that’s the Acheulean. So we go from this simpler method of just making a simple flake to maybe cut something with to actually designing a shape with the core. And this requires, we think, a lot more thought process to do.

IRA FLATOW: And so you ask people to make these stone tools, and then you have a wearable FMRI cap that they’re wearing so you can see what part of the brain is lighting up in there?

SHELBY PUTT: It’s not FMRI, but it’s somewhat similar in that we are measuring oxygenated hemoglobin and where it’s at in different parts of the brain. But the technique that we’re using is called functional near-infrared spectroscopy, which is kind of a mouthful, so we just call it nears.

IRA FLATOW: So what do you learn about the parts of the brain that are engaged in the tool-making?

SHELBY PUTT: So what we actually found is that, maybe what you would expect, that with the Oldowan technique, we see only visual and manual coordination areas of the brain lighting up. But once you get to the Acheulean technology, what we see is a cognitive network that involves a large portion of the cerebral cortex, including working memory areas, planning areas in the frontal cortex, as well as these integrative areas in the temporal cortex. So they are taking visual, auditory, and tactile information, holding it in mind long enough to reach these goals of making this more complex type of tool.

IRA FLATOW: So what does this tell you about evolution of the brain, then?

SHELBY PUTT: So since we have modern people replicating the same exact process that these early hominids were doing, we think what we’re seeing is that the same type of brain network would have been required to make these complex stone tools around 1.8 million years ago. So what that tells us is that we’re seeing a more human-like way of thinking starting quite early in our evolution. And what’s so interesting about this is it coordinates with the fossil record. Because we’re seeing around the same time a much larger brain size and body size. And we see the appearance of Homo erectus, which I think has been mentioned a few times so far.

IRA FLATOW: Let me bring back John Hawks and Susan Anton. And John and Susan, the skull that was found, the Homo naledi skull, could that have been big enough to make them stone toolmakers?

JOHN HAWKS: It’s really a small brain. It’s about a third the size of ours. The range that we have now of the brain sizes of Homo naledi overlaps a bit with Homo erectus, but it’s definitely small. And we have smaller ones than any erectus.

For us, of course, the big question is is size the big issue or is it structure? And looking at what we can see of the inside surface of the skull of naledi, which tells us something about the external surface of the brain, but not as much as you might like, it looks like it is somewhat human-like in some ways. So maybe there’s something structural that triggers the later evolution of larger size in some lineage of hominids. But other lineages like naledi seem to be able to persist for a long time without evolving those big brains.

SUSAN ANTON: And one of the things we’ve been seeing recently, actually, is that there’s actually quite a lot of size variation within Homo erectus. And so there are likely to be some scaling patterns, so that you may have, as John says, you have the structural relationships that are in place, and they may be in place regardless of whether you have large size or small size. But they may be scaling with the size of the individual as well. So I think this is one case in which size itself is really not the main thing that we should be worried about. I hate to say it, but size probably doesn’t matter in this instance, but that the structural underpinnings really do.

And one of the things that I thought was cool and I actually have a question is, in that study where they were teaching undergraduates how to make stone tools, I think I remember that some of the students were instructed with language and some were instructed with just visual cues, right?

SHELBY PUTT: Yeah.

SUSAN ANTON: And there’s been that question as to whether or not language is associated with abilities to make stone tools. And if I’m remembering right, you were only seeing those centers light up when people had been instructed with language. Is that right?

SHELBY PUTT: Right, so previous studies have looked at what’s going on in the brain while making stone tools, and what they found were a lot of language processing areas showing up. But unfortunately, they didn’t actually control for language in their study. And yet, they were still making these larger claims about language evolution. So what we wanted to do in this study was to make sure that we controlled for language. And like you pointed out, what we ended up seeing is that language processing areas of the brain were only lighting up in the group that learned with verbal instructions and not in the other group.

IRA FLATOW: Well, I want to thank you all for taking time to be with us today. It’s fascinating. And I’m sure, John, you’re going to go back and dig up some more caves somewhere?

JOHN HAWKS: We are still exploring in the field. We have made new fossil discoveries and we’re investigating now. Lee Berger and I have a book that’s just come out, Almost Human, that goes through some of those explorations. So it’s an exciting time, just as Susan said.

IRA FLATOW: Wow. People could apply that name to me too. Thank you very much for taking time to be with us, Shelby Putt, anthropologist and post-doctoral researcher at the Stone Age Institute in Bloomington, Indiana, John Hawks, paleoanthropologist, University of Wisconsin in Madison, and Susan Anton, professor of anthropology at NYU. And we have a 3D model of the Homo naledi fossil. You can spin it around and take a closer look up at it at our web site at sciencefriday.com/bones.