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How Homo Naledi is Changing Human Origins

Welcome, everyone, to Wednesday Nite @ the Lab. I’m Tom Zinnen. I work here at the UW-Madison Biotechnology Center. I also work for UW-Extension Cooperative Extension, and on behalf of those folks and our other co-organizers, Wisconsin Public Television, the Wisconsin Alumni Association, and the UW-Madison Science Alliance, thanks again for coming to Wednesday Nite @ the Lab. We do this every Wednesday night, 50 times a year. Tonight it’s my great pleasure to welcome back to Wednesday Nite @ the Lab, John Hawks, professor of anthropology here at UW-Madison. He was born in Norton, Kansas, graduated from Norton Community High School, then he went to Kansas State University where he studied English, French, and anthropologie. Then he went to Michigan, got his Ph.D. in anthropology, did a postdoc at the University of Utah, and then came to UW-Madison in 2002. As a testimony to what an extraordinary presenter John is and what a great story he has to tell. In the back, your name is? Sandy, what’s your friend’s name? – Me? – You, yeah.

[laughter] Say again. – Paul. – Paul. Paul just told me this is the first time he’s been in a lecture hall at the University of Wisconsin Madison since 1968. [laughter] And I think that’s a great testimony to… [laughter] To what you can do. I was here last night. [laughter] If there’s a better storyteller, let me know. If there’s better stories, let me know, than what John Hawks is going to share with us.

I think in future years people will look back at this recording and think, man, I wish I was there to see it in person. And you are all lucky enough to see and hear John Hawks tell us about his latest update on Homo naledi. Please join me in welcoming John Hawks back to Wednesday Nite @ the Lab. [applause] – Thank you, Tom. Thank you, everyone, for coming out. I’ve been in the US now for four days, and a week ago at this time I was in the field working underground with Homo naledi. And I will tell you that we have some remarkable new findings from the cave system. A lot of you have come out for previous talks that I’ve sort of presented our initial findings on Homo naledi, our discoveries in 2013, our publications in 2015. We’ve had some incredible things, but we’ve also had some incredible mysteries that have arisen. How did all these bones get into this remote cave chamber? What are they doing there? When did Homo naledi live? How was it connected to our species? These are the things that we’ve been investigating for the last four years now, and I can tell you that we can answer some of those questions and many of the questions have become more intricate and fascinating for us.

I know that some of you haven’t heard all of this story before, and so I have to present sort of how the cave was found and where I come into the story and what the excavation was and why this was news in the first place. And I’ll do that in the first part of tonight’s lecture. And then I’ll talk about the publications that we had earlier this year, where we uncovered a second cave chamber in the Rising Star Cave, the Lesedi Chamber. A second cave chamber with more remains of Homo naledi, with a wonderfully complete skeleton that we’ve named Neo. And here’s Neo’s skull here on the first slide. At the same time, we determined the age of the fossils, and the age surprised many people in the world who did not expect them to be the age that they are. So it was a wonderful discovery. But in the last third of the lecture I want to focus on what we’re doing now and what our most recent field excavation has uncovered. This is the newest stuff.

This is stuff that I didn’t know last week at this time, right? So I will give it to you unfiltered, and some of it may be stuff for the history books and some of it I may change my mind about two weeks from now. But it’ll certainly give you the freshest take on it. And you guys are the first people outside of South Africa to know any of this, except for the people at the University of Alabama because Lee beat me at this for one day. One day. [laughter] So let me– It’s a wonderful privilege. I say this whenever I present on this stuff, that we have the involvement of National Geographic in the project and also of the University of Wisconsin, who both have enabled us to film a lot of the original research as it happened. And we have footage from the initial discovery of the fossils in 2013, we have footage through the analysis of the fossils, through the first field expedition, through this field expedition. I’ll be showing you video later that I took just this month and that our team took underground this month. So it’s wonderful because I get to show you some of this stuff and allow people to tell their own story in their own words.

And one of the most important parts of that is the discovery of the fossils. So I’m going to show you here Steven Tucker, who was the first person to enter the Dinaledi Chamber. – Caving has always been great. Caving, you want to answer that question of what’s around the next corner. That’s, like, always the question you want to know. It’s mostly fueled by curiosity. But as you get into caving more and more, the scientific side of it comes into it. You want to know how did these places form? What happened here millions of years ago? What happened here billions of years ago? Basically, it creates a fascination with this whole environment. In my wildest dreams I would never have thought that caving would take me to what’s happening here.

You can almost call this a bit of an accident. So my caving buddy and me, Rick, we were out exploring this cave on a Friday night. We’d gone into a very remote section of the cave, a part that I’ve never been in before, and in that section we stumbled upon fossils. Yeah, at first we didn’t exactly know what fossils yet. We started looking around a bit more until we found a mandible, and that was when we knew this was probably Homo naledi. That was when we got excited about it. And since this discovery, it’s crazy what’s happening here. – So that was the discovery of the fossils. It occurred September 13, 2013.

So that’s four years ago. We celebrated the fourth anniversary last month. Steve, at the time, was studying to be an accountant, and Rick was unemployed and basically a super, super clever guy who loved to cave on the weekends. And these two guys were exploring for fossils. They were working with my friend Lee Berger, who is a National Geographic Explorer-in-Residence and also a professor at the University of Witwatersrand. Lee is famous for having discovered Australopithecus sediba in 2008. And the story of sediba goes that his son found the fossil. The story of naledi goes that these cavers found the fossil. They were looking for fossils, and in this cave, which is less than 800 meters away from one of the most famous fossil sites in the world, Swartkrans, less than one-and-a-half kilometers from Sterkfontein, the largest fossil hominin assemblage in Africa at the time.

This area that within two kilometers are five famous hominin fossil sites, no one had ever located any fossils in this cave. They’re there and these guys found, on that first trip, not only the Dinaledi Chamber but also they went through a second chamber, the Lesedi Chamber. And I’ll show you that chamber later. They didn’t recognize at the time what it was. Only after we began working in the Dinaledi Chamber did they realize, hey, we’ve seen something else like this, maybe you guys would be interested. Steven no longer is an accountant. He now is a full-time explorer for our exploration team, as is Rick. And we have an exploration team that’s in the field every day, professional explorers, and they are, at this point, some of the most experienced cave explorers in the world. Steven, however, can be trusted to review a budget.

[laughter] The Dinaledi Chamber is in an excruciatingly difficult to access part of the cave system. The entrance that we use, the closest entrance to this, in order to reach the Dinaledi Chamber you have to go through some very serious vertical climbs. This is about 40 meters underground. This is about a 30-meter climb down to the Superman’s Crawl. The Superman’s Crawl is a narrow squeeze with a height of about 10.5 inches. That’s called this– And I’ll show you footage of people going through it in a while– It’s called this because if you have any size at all, you have to go one arm first and squeeze through it this way. It’s all horizontal. But, more seriously, after climbing a very rugged sort of rockfall called the Dragon’s Back, you can only access this chamber through a vertical passage that is a width at a minimum of 7.5 inches and a height of 12 meters. So it’s a 40-foot vertical climb.

That’s the only way in or out. I cannot enter this chamber. Lee can’t enter this chamber. In fact, only a very committed group of people with the right skills and talents can enter this chamber. Lee, initially, upon the discovery of this, didn’t know how he was going to get people to recover these fossils. He put out an ad on Facebook, which later became famous. “I need people with excavation paleontological skills, “who can pitch up here next month for no pay, “and you must be skinny.” [laughter] “And not claustrophobic.” [laughter] He recruited these incredible six cavers, explorers, archaeologists. All of them, master’s, Ph.D. students in archaeology, including Alia Gurtov from the University of Wisconsin, but others from the US, Canada, Australia.

Marina Elliott you’re going to see a lot tonight. She is now full-time head of the exploration team at the University of Witwatersrand. Just this last month we had Becca, Elen, Hannah, all out with Marina for our last field expedition. So the archaeologists who are initially involved remained committed with us. Rick Hunter, who you saw in the video, is married now to Lindsay Hunter. Don’t giggle. This is the sort of thing that camp people like me are supposed to prevent from happening. [laughter] I can’t. I’m not a good chaperone, sorry. [laughter] I’ve got three teenage daughters.

I have my priorities. [laughter] This is the opening to the chute. I want to show you some video. We have, on this trip, managed to get some extraordinary video of some of these passageways through the cave that we haven’t been able to get video in before. Now we can use a steady cam set up with the GoPro that, with the right lighting situation, can actually see into some of these chambers. So I’m going to show you what it’s like to go down this chute. This is the first time I’ve shown this video anywhere, so we’ll see if it comes out all right. – Can you go into that crack? – Sure, I can go into this crack, here. Does that make sense? – Yeah. – This is Becca.

Becca can– She’s just about 4’10”, and she can fit into things that no one else on the team can. And you’re going to see her squeeze into this crack that none of the rest of the team knew was there. And we’re going to have a camera switch now. – I’ll give this back to you. And then I’ll get higher. – And there goes Marina up this next section of the chute. – I’m not going anywhere. – Ok. – That’s a pretty awesome shot right there. – And once she gets up to the top here, which is just another second, we’re going to see Elen coming up the rest of the way out of the chute.

So you’ll see part of that. This part of the cave is actually a dotted line. You saw the map that I showed you earlier had, it’s laser scan data through the entire cave. We have three-dimensional point cloud data from lasers, and this is the one part of the cave that we can’t actually get the laser into. This is what our team goes through every day to get down to where the fossils are. – How long does it take? – Well, the most skilled members of the team can do this climb in about three or four minutes. Most people take five to 10. It depends on how much gear you have to also haul up. To get from the cave entrance to this point to do the descent or from here to the cave entrance is about 20 minutes to 25 minutes through the cave system.

Now, this distance through the cave is about 170 meters. So if you guys can imagine moving something like the length of this building, right? Through the Biotech Center and genetics building, right? That’s 170 meters, more or less. Imagine taking a half an hour to do that, and you get some idea of how difficult it is to move through these places. And these people are all now professionals. I’m talking about people who cave now for a living, who are doing it in that time period. People without these sorts of skills, you’re talking about much longer. Well, the story of our 2013 expedition. We all assembled in November of 2013. Our team went underground.

We were there for 21 days underground. The team in that time span recovered more than 1500 fossil specimens. Almost every single one of them was a hominin fossil specimen. And it was immediately the largest fossil hominin assemblage ever discovered in Africa. It is the second largest fossil hominin assemblage in the world. It’s an amazing, amazing discovery, and nobody had ever seen anything like it. It represents every part of the skeleton, multiple times in most cases. We have the remains of at least 15 different individuals in this chamber. What a lot of people didn’t appreciate at the time was that aside from a surface collection, you saw their bones on the surface, and we collected the bones from the surface of the entire chamber.

There were around 300 bones and bone pieces from the surface of the chamber. The rest of those bones all come from an excavation area that is less than one meter square. It’s about 80 centimeters on a side. And the depth of deposit with these fossil hominins is around 15 to 20 centimeters. So this is a bone bed that is totally composed of hominin bone. Under the hominin bone is sterile sediment, down at least 50 centimeters. At the base of that sterile sediment, in the area that we dug, we found a single tooth of a baboon. We don’t know what that relates to, but we know quite a lot about its provenience right now because we were able to estimate the date of this and the date of the fossil hominins. So we know quite a lot about these.

At the time, this discovery was unprecedented, and it was up to us to figure out how to study it. We recruited a team of specialists who had been involved in some work in South Africa before, people who’d been involved in the description of Australopithecus sediba. And we recruited a team of 35 early career scientists to join us in describing these fossils for the first time. That workshop occurred in May of 2014. We did our work. We had different anatomical specialists. It was a tremendous, tremendous experience. Experts coming in who had done their dissertations on the vertebral column. People who’d done their dissertations on the lower limb.

My student, Zach Throckmorton, who had finished here, was an anatomy professor at Lincoln Memorial University in Tennessee, had done his dissertation on the foot. And we had all these specialists come and describe every element of this hominin and, in the course of that, discovered that this represents a previously unknown species. We compared it to every other kind of fossil hominin that had ever been discovered. We had cast materials over the originals, in many cases, available to us to inspect and study. These are some of them. Homo erectus, on the left here. Australopithecus afarensis, this Lucy skeleton here, and another male afarensis partial skeleton. Australopithecus africanus from South Africa. Australopithecus sediba, represented by two partial skeletons.

I’m showing you here the partial skeletons of the hominin fossil record. Before Neanderthals, this is what there is. And so when we have a collection of fossils that is an array, representing multiple, multiple individuals. It’s really, really powerful evidence. We identified this as a new species previously undiscovered. We named it Homo naledi. Naledi means star in the local Sesotho language, which is one of the major languages of South Africa. So naledi is very interesting because it’s different from other fossil hominins in ways that we did not expect fossil hominins would be. Now, you guys who know something about evolution know that evolution is not a straight line.

It doesn’t occur in the famous illustration of a hunched ape-like thing becoming slowly human-like. [laughter] Step by step, right? [laughter] It doesn’t happen that way. Our ancestry was complicated. There were multiple branches that formed a tree. And these species are related to each other sometimes in ways that we don’t fully understand because their fragmentary fossils and it’s very hard for us to compare. You saw the whole skeletons, right? That was what there was. Every other piece of thing that we have is a fragment of one kind or another. And we have some extraordinary samples of fossil hominin teeth and jaws and, in some cases, skulls, but we don’t know a lot about how the rest of the body goes together except from skeletons that actually put those parts together from one individual. What we have increasingly discovered over the last 10 to 15 years is that when we have more complete remains, skeletons like naledi, like sediba, like Homo floresiensis, you start to discover that the parts don’t always go together in the ways that you might have anticipated.

You might think that even though things are a tree and they’re more complicated than a straight line, nonetheless there’s a main branch, and when things branch off of it, they inherit the characters of the main branch. And so there’s some sort of order to it. In fact, for the most part, there’s so much parallel evolution and convergence among the branches of our hominin tree that it’s very difficult to trace what the main branch might be. So when we look at naledi’s skeleton, it puts together characteristics that we didn’t expect would go together. The most obvious of these is its brain. Naledi has a very small brain compared to humans. It’s about 450 to 600 cubic centimeters in size. That’s about a third the size of a human brain. It’s the size of a large orange.

That small brain is in a skull that has a number of characteristics. It’s got a torus, an angular thickening of bone here called the angular torus. It’s got a brow ridge with a groove behind it called the sulcus. It’s got a relatively low, not very high forehead. It’s got a bar here at the back of the skull called a nuchal torus]. It’s got no chin but a relatively vertical front of the mandible. It’s got a flat face. These are features that we associate with other species that we attribute to early Homo, members of our genus but early in the evolution of our genus. Fossils that we found that are two million years old.

They’re one-and-a-half million years old. Fossils like Homo erectus and Homo habilis. So, looking at its features, it looks like those early human species. Its brain size is too small. It’s smaller than those early human species. So there’s a bit of a puzzle. My friend John Gurche is a tremendously talented Paleoartist. He’s one of the best reconstructors of what fossils may have looked like in life. This is his reconstruction of naledi.

And I think it’s a very good one. Obviously, some aspects, like skin tone, like the hair pattern, have to be speculative in some ways, but by studying the distribution of these in human populations, other primates, John has an educated guess about what they would look like. But the overall facial profile and everything is basically this. This is a nice portrait of naledi. In this deposit, we have the remains of at least 15 different individuals. They are of all ages, from newborn, or what we would call a perinate, possibly not yet born, to old adult and every age group in between. This is a series of six different dentitions that represent individuals, and they’re all of different ages. This is a toddler, maybe one-and-a-half to two years old. This is a young child of maybe six or seven.

This is an older child of nine or 10. Here’s an adolescent, a teenager. Here’s a young adult. Here’s an old adult. This is a sample which, for the first time, we can study development in an entire series of individuals from one place. One of the things that we’ve learned by studying this particular dentition, this older child’s dentition, is that its development is strikingly human-like. The human-like detail that’s maybe the most telling is that the permanent canine teeth are in. Those are the canine teeth. They’re all the way in, and the second molar is not yet erupted.

This is a very human-like trait. Our canines erupt early. Our molars erupt late. In chimpanzees and gorillas and other primates and in all earlier hominins that we know about, the second molar erupts first and the canine is delayed because the canine is a social signal. When you erupt your canines, if you’re in a primate society, what you’re saying is you’re ready for a fight because that’s what you fight with and that’s what you threaten with. And delaying the eruption of the canines is something that prevents you from getting into fights before you’re ready. In Homo naledi, they have a very human-like developmental profile. We can’t say what that means socially, but it is very interesting because they’re so primitive in their brain size, you might imagine that their development would be very primitive. But, actually, it’s very human-like.

This is a new discovery that I haven’t been able to talk about before. If we looked at other parts of naledi’s skeleton, it is actually strikingly human-like. It’s feet, for example, are your feet, if you’re a size four women’s shoe size. [laughter] Anybody a size four? Any size fours in the room? Any size fives? You’re just a little bigger than naledi. This is naledi’s feet. This is a very human foot. You can see the arch in this foot longitudinal, the arch medially, mediolaterally. This is a human foot. It’s got a big toe that’s actually a big toe.

It’s in line with the other toes. The other tiny toe bones here are not reconstructed with this because our foot team actually, you can’t tell those apart. You might imagine, well you can tell them, you know, second toe from the fourth toe. Actually, you can’t. So we don’t put them on because we’re not confident about the placement, but we have all of them. The hands of naledi are a mixture of human-like and primitive characteristics. This is a complete hand. It was found in articulation in the site. Here it is. Folded over fingers, the thumb here.

It’s a right hand. There it is. And I was going to show you, it’s got big, broad fingertips, as humans do, which are made for gripping hard objects like stone tools. It’s got wrist bones that are arranged in a human-like pattern, including the crucial difference between the thumb and the first finger, which helps to buttress against hard grip forces, again tool use, but it has tremendously curved finger bones. The finger bones are curved in a way that suggests it was grasping onto branches, or grasping onto something, climbing. Naledi’s shoulder is also really well suited to climbing. Its shoulders are canted upwards like this and really well made for reaching over head. So it’s go this interesting combination of traits. Its lower limb, its feet, very human-like.

Its skull like an early species of Homo, something like Homo erectus, Homo habilis, but with a smaller brain. Hands that are really well made for tool making but also well made for climbing and shoulders made for climbing. Hips that are really widely flared, which are very primitive for hominins. It’s like Lucy’s hips. It’s not like our hips at all. It is a weird combination of traits. We’ve never seen it before. It has features that we’ve never seen before in any hominin species. So for all those reasons, we’re really confident this is something new that we hadn’t seen before.

What we, and this is John’s, again, reconstruction of what naledi would have looked like standing here. This is Lucy, Australopithecus afarensis. And the Turkana Boy, Homo erectus. And you can see that they’re really visually different. If you were looking at erectus and naledi from a long ways away, from a hundred meters away, you might think, well, they’re not so different. But as you get closer, you start to notice that these people don’t look like the others. They don’t look like us. Their heads are wrong. They’re standing at sort of an odd posture.

They walk like humans do, but there’s something different about them. And as you get closer and closer you start to notice those primitive features. This is a really different species. So after our publication of the species Homo naledi, we began to work in earnest on our second discovery in the Rising Start Cave system, the Lesedi Chamber. This is a layout of the cave as a whole. This is our cave map. Our entrance is here. And the Dinaledi Chamber, I’ve described the pathway to it. It’s over here.

It’s around a hundred meters linear distance from the entrance, but around 160 meters through the cave to get there. In linear distance in a totally different direction, is a second chamber, the Lesedi Chamber. The Lesedi Chamber is not as difficult to access as the Dinaledi Chamber. Nonetheless, it’s difficult, there are multiple squeezes between the entrance and the Lesedi Chamber. I’ll show you from the main surface entrance there is a big squeeze, or I should say a small squeeze, that we’ve come to call the Berger Box. The reason why is that Lee went to the Lesedi Chamber one time and didn’t get back out. He was stuck at this place. And the reason why, as you can see, it’s an uphill climb, and, actually, it’s easy to go down through it, relatively speaking. It’s about 10.5, no, it’s not 10.5 inches.

It’s about a nine-inch squeeze. So Lee can fit through it that way. I felt that I couldn’t so I didn’t go that time. But you have to get purchase against the ground in order to get back up through it, and that takes different muscles than it does going up. And people with long legs have a disadvantage, and he was stuck there for 45 minutes. It was crazy. We had to pull him out like the Winnie the Pooh out of a stump. [laughter] So Lee has never been to the Lesedi Chamber again. [laughter] And I’ve never been at all.

There are a number of climbs through this and then a vertical drop into the chamber. In this chamber were bones, again, exposed on the surface. During 2014 and 2015 into 2016, our team, led by Marina Elliott, excavated in the Lesedi Chamber and recovered the bones of Neo, in addition to at least two other individuals of Homo naledi, one juvenile, one young child, and one other adult, Neo. Neo means gift in Tswana, which is another one of the local languages. Neo is one of the most incredible– Here’s Marina working in the Lesedi Chamber with Ashley Kruger, our specialist of 3D. All of these images that we have from the caves and the maps and everything involve Ashley creating these from the 3D data. Before I leave this, because it might not be easy for me to get back to it, I want to point you to this little area in the chamber is where we found Neo. His skeleton was mostly in this blind tunnel, which is off the main part of the chamber. The main part of the chamber has clearly had a huge amount of sediment removal.

And where sediment remains there is fossil material exposed, including up here in the north/south fracture passage, down here in this part of the chamber, and here in the side. We speculate that this was once a formation very much like the Dinaledi Chamber, full of bones, and parts of that have been removed over time by erosion. So we’ve lost bones. We do have some ideas of where bones go to after they leave this chamber. And our current excavations last month were focused right here, next to Neo. And we found a couple of additional small pieces of Neo’s skeleton. We haven’t got down past the level that we found Neo at, however, so there may be more yet to be found. The Neo’s skeleton is one of the most complete fossil hominin skeletons every discovered. It is amazing.

I was privileged to be able to lead the description of it that we published earlier this year. Here’s Neo’s mandible. Here is the most complete mandible from the Dinaledi Chamber. You can see that they are nearly identical to each other. The form of the teeth, the proportions of the different teeth. This is a bit more warn. It’s an older adult than this individual. Cranially, you can see that Neo is a more complete version of the cranial material we have from the Dinaledi Chamber. The Dinaledi Chamber hominins are almost morphologically identical to each other.

They’re really, really similar. They are more similar in things we can measure than humans from small populations today are similar. So we’re looking at something that’s like a population in terms of its variability. This is also true when you add Neo and the other Lesedi material. You don’t add more variation. They look like they’re parts of this same population. Neo’s skull from many angles. It’s a beautiful thing. Neo also has a relatively complete femur.

And from this we know quite a lot about his size. This is the best femur we have. This one. And we’ve estimated the total length of it from these. And we have a relatively complete endocast, about 600 cubic centimeters. It’s a bit bigger than any of the ones we have from the Dinaledi Chamber. Okay, so I don’t want to go into super detail about biology, although I get really, really excited about biology. I do want to say that this is all published in Open Access, and you guys can download it and read it and all these charts are there and it’s wonderful. But I wanted to show you a few things. The brain of naledi, its size, as you can see is smaller on average than any other species of early Homo.

It is a bit bigger than Homo floresiensis, the very late surviving hominin species on the island of Flores. So it’s not by any means outside the range of what we see in things we attribute to Homo, but it is very much on the small end. It overlaps with Australopithecus species. So, small brain. Its femura are very human-like in their length. These are erectus femura, and this is naledi’s adult. This is Neo’s femur. This is a juvenile femur of naledi. This is Lucy’s femur, so you can see that, in terms of height, they’re human-like.

Small human, but human-like. In terms of their teeth, I get really excited about teeth. Unnaturally so, maybe. [laughter] And especially when you’ve got so many teeth of naledi. But one of the impressive things about their teeth, this is a human all the way at the far right, these are all erectus teeth in between the human here and naledi, and this is a habilis dentition and these are Australopithecus. This is africanus and afarensis, right? So these are all hominin species. And what you can see is that when you look at naledi’s teeth, they are smaller than the habilis teeth, they’re smaller than erectus teeth, they’re more human-sized, but these molars, the first molar is smaller, the second molar is bigger, the third molar is biggest. That’s the opposite pattern from what you see in humans. It’s the primitive pattern that you see in Australopithecus.

And when you look at the front teeth, I’ll tell you that these pre-molars, this one in particular and this third pre-molar, looks nothing like these third pre-molars of any of these other hominins. It is really unique. I say naledi tells us things by the way it looks. We don’t know that these traits that are unique have functional importance. I can’t tell you that these pre-molars function differently. I can tell you they’re probably a reflection of the species history. They’re pointing to something strange about it. Naledi had some interesting history. But, functionally, its teeth are working a lot like human teeth.

More so than these other early species of Homo. Yeah, this is two sides, and I love this. Here’s naledi. Here are these habilis erectus things. Two big teeth. And we think of humans as having relatively small teeth, and Homo having small teeth because of a high-quality diet. They’re hunting, they’re using tools, etc. Naledi is using more tools. It’s hunting better, or something. Naledi compared to other species.

And I want to show you the contrast. Here’s naledi, and you can see that in general terms it looks a lot like something like habilis or something like a small erectus skull, like this one from the Republic of Georgia. This is a big erectus skull. That next to naledi, whoa, they look really different, right? Very different in size. Here’s a modern human skull, one of the earliest modern humans. And you can see that this is, I’m going to show you this right next to each other in just a second. All right. Naledi, we worked really hard to figure out how old these fossils were. Last time I updated you guys about naledi I said we don’t know how old they are.

And we really didn’t. The fossils are preserved extraordinarily well. They feel like Neanderthals fossils to me. They don’t, they’re not highly mineralized. This isn’t like a dinosaur bone where it’s super heavy because it’s turned to rock. This is bone that’s lost most of its organic content and has some slight degree of replacement with calcite but not a lot of replacement. And that tells us something but not as much as you might expect. I have studied bones that are two million years old that are like this. But I’ve studied bones that are Bronze Age that are like this as well.

So it’s very difficult to tell from the preservation, but these bones were in a soft sediment. It seemed like very strange that they might have been preserved for millions of years in that context. It would be very exceptional. So we looked at that and said, well, okay, we can’t say how old these are but there’s something very interesting and strange about the context we found them. Morphologically, looking at what they look like, everybody said they looked like fossils that are two million years old. That’s how old they should be. We had colleagues publish papers saying we believe these fossils will be two million years old. Boy, that is the dumbest thing in the world. [laughter] To say the evidence points to them being two million years old but I’ll have to wait and see what the geologists say.

This is like setting yourself up for a fall. So our geology team, here you can see them taking samples. Here are some of the flowstone samples that they’ve taken out of the chamber, including this one, which is super cool because it’s got Homo naledi bone embedded in it, right? We can figure out the ages of flowstones because they contain uranium from groundwater, and that uranium decays part of it over time into thorium and lead. And so we get an estimate of how old the flowstone is when it formed. That doesn’t tell us perfectly how old the fossils are, but we can also look at the teeth of these fossils themselves and… with the aid of a laser, take tiny, tiny samples across them to determine the concentration of uranium and thorium in the teeth. And we can also take somewhat larger samples and assess the amount of electron traps that have been created in the crystalline structure of the teeth by ionizing radiation over time. That technique, called ESR, electron spin resonance, gives us a direct date on the teeth. The absorption of uranium by the teeth from the groundwater gives us a minimum date on the teeth.

The uranium and thorium in the flowstones gives us an absolute age for the flowstone formation. We also looked at the tiny quartz grains that are in some parts of the deposit, which will absorb– Which will also give a sign of the ionizing radiation over time since they were last exposed to light. That method is called optically stimulated luminescence. We also looked at the changes in magnetism over time in the formation of the flowstones in which we can confirm that all the flowstones in the chamber were formed during the last 780,000 years since the last major magnetic, paleomagnetic reversal of Earth’s magnetic poles. I’m listing these because we use six different techniques from 11 different laboratories, and we sent samples to these laboratories blind. We sent them samples and said you tell us what you’re looking at. And we sent them fake samples. And we sent the same samples to different labs to see if they gave us the same answer without corresponding with each other about their methods. We, for the first time, did double-blind date testing on hominin fossil assemblage.

We have what I think is the most rigorous evidence about the age of this fossil assemblage that’s ever been developed. And all of these methods come together, all of the different methods. This chart is too complicated to even read. But what I was going to say is all the different methods tell us that these bones were laid down some time after 335,000 years ago and before 236,000 years ago. That flowstone that has a bit of naledi in it is 236,000 years old at a maximum. The ESR from the crystal structure of those teeth tells us at 95% probability the teeth are younger than 335,000 years. So those two bracket the age of the fossils. Those fossils were put there in the late middle Pleistocene. This was shocking to everybody, because in the late middle Pleistocene this is what everyone thought was in Africa.

This is the earliest modern human cranium. It’s about 200,000 years old from Ethiopia. And here is Homo naledi, around 250,000 years old, from South Africa. Naledi lived there at the time our ancestors were evolving. Our modern human ancestors. This skull from Zambia is thought to be around 300,000 years old. It might be older, it might be younger, but this skull represents an archaic form of human. Big brain, more than double the size of naledi’s brain. Big brow ridge. Massive face. Big hominin.

And naledi is there, less than 1,000 kilometers away, at the same time. Naledi did evolve two million years ago. It did branch from out ancestry some time that antiquity. And it survived alongside of all of these other kinds of hominins until at least 300,000 year ago. Naledi was there in the human story and we didn’t notice it. This is shocking. How is naledi related to us? I can tell you we don’t really know. I don’t know. I like to put question marks on the tree.

I’ve got naledi here in its proper age, right? Here it is, 250,000 years ago, just before modern humans, at the same time than Neanderthals are evolving in Europe, at the same time that archaic forms of humans are evolving in Africa, well after Homo erectus existed but the hobbits hang on. But how these are related we don’t know. The reason why we don’t know is when we look at one set of characters in one way, these are all from the skull and the teeth, these features that we looked at, when we look at one set of characters in one way, naledi looks like it belongs to the earliest branches of our genus. It comes from way deep. And sapiens, Neanderthals, erectus, these primitive habilis, all those forms are closer to each other. But if you look at the same data in a different way, naledi looks like it’s connected to archaic humans and sapiens and Neanderthals, and erectus and habilis and all these other forms are out. We don’t know how they’re connected to us. For those of you who do biology, this is a Bayesian tree, right? If you walk down the hallway to the genetics department and ask them, how should we build a tree of these, they’ll say use this method, and it puts naledi as a closer ancestor to humans than erectus is. But if you ask a paleontologist, how should is study this, they’ll give you this tree, and it puts naledi farther from any other hominin.

I don’t know the answer because none of these actually involve any of the features of the rest of the skeleton because most of these other species have no skeletons. So we can’t actually compare them. We’ve come to a point where the data that we’re acquiring from this evolutionary story are more for naledi than they are for any other species in our ancestry other than Neanderthals. It’s a cool situation to be in. It’s an exciting situation to be in. I like it. Don’t get me wrong. I like it so much that last month we went back to the cave to dig up more of them. We had some hypotheses to test about the Dinaledi Chamber.

How did the bones get in there? Oh yeah, this is the one I want. This is where we enter the chamber. This is a map of the chamber surface. These colors are the elevation. It’s high here where we enter the chamber at the chute. It rapidly descends, and most of the chamber is lower in its floor elevation. Where we dug is here. Where we dug is 15 meters from where we enter the chamber. Our best hypothesis for how the bones entered the chamber was that somebody put them down the chute, the same one that we used that seems to be geologically stable for the last 250,000 years, somebody put the bones down the chute and they formed as a pile here at the base of the chute and spilled off and some of them end up here.

But it’s not a very satisfying hypothesis, I’ll be honest with you. And the reason why is that this is where that articulated hand comes from and an articulated foot and an articulated leg of a juvenile and a huge concentration of bone. How did all those bones get over here, 15 meters away, right? That’s the back of the room, right? From where they apparently entered, going through two tiny channels? It’s puzzling. It’s a real puzzle. We can rule out– those of you who don’t know the story– we can rule out lots of ways that the bones could have entered the chamber. There’s no mark on them from any kind of carnivore or anything. The bones haven’t been eaten. They haven’t been crunched. They haven’t flowed in water. The sediment that they’re deposited in is endogenous to this chamber.

It hasn’t come from nearby chambers. There’s no wash of gravel and stuff that would come in from outside. They entered the way that we enter. Whether they go through the rest of the cave the way we do is uncertain because the rest of the cave may well have changed quite a lot. But the Dinaledi Chamber was very much the way it is. So we went back this month to dig here to test whether there’s actually bones at the base of the chute because there’s a logical hypothesis. If the bones entered this way, that should be where the maximum concentration of them should be. If naledi was putting the bones there, there’s some chance that that’s where an artifact might be. If they were depositing any kind of artifacts with them, where they enter is probably the most likely spot.

So let me give you just a quick clip. Here’s our excavation in process. – Now, we are not going to do any [inaudible]. That will not be. – [inaudible] – Yeah. – [inaudible] – Okay. – [inaudible] – Yeah. – This is the cave entrance, where we have our command center set up during excavations. – [inaudible] – So, where was this? – Down that. -[inaudible] – Okay.

– The pathway to the Dinaledi Chamber is back in the back there. Here is Becca Peixotto working at the base of the chute. Within a very short time of opening an excavation unit here, which is 50 centimeters on a side, Becca uncovered parts of a white, chalky flowstone area with some pieces of bone. And, as they began to work this unit to uncover the edges of this thing– This is Montebella coming through Superman’s Crawl. Montebella Sequani is one of our exploration team. – [inaudible] – There we go. Look, it’s Marina. Help! [laughing] – Almost. – I think I can see you. – I’m going to show you this last clip because as they were working the edge of that whitened area and determining its extent, it wasn’t clear exactly what we were looking at.

It was clear that there were bone shards in it and flowstone pieces. As they began to work, they uncovered a set of maxillary teeth in position. So it was clear that what we’re looking at is a skull that is crushed there, mostly gone. The skull fragments are basically down to nothing. But they continued to expand that unit and dig down– at the end about 20 centimeters down– they found that the lower edge of this, downslope from the chute and we’re literally talking about a distance like this, downslope from the chute had a number of much better preserved bones, including articulated parts of a hand, including what appears to be an articulated part of a rib cage, a shoulder. We’re looking in that area at the base of the chute at a partial hominin skeleton there. That partial hominin skeleton remains there. We exposed the outline of it down to where our excavation unit ended, and we left it in place because we will have to recover this from the cave whole in order to study it in the laboratory. We’re going to have to consolidate it, which is going to be a serious task because these sediments are wet.

And those of you who know archaeological preservation, you know that wet things are terrible. We’re going to have to replace some of that moisture with a hardened plastic consolidant so that we can take this out of the cave as a whole element, through the chute, out and study it by preparing it in laboratory, get the information that’s there to be had in the arrangement of this skeleton. But, at the same time, we put some of our best cavers deep into the Dinaledi Chamber’s most difficult to access recesses in order to try to understand that part of the system. This is Marina in one of those places, which we’ve come to call Hades. [laughter] Yeah, I’m going to skip this a second and talk about… Yeah, okay. The Dinaledi area where we excavated is here. There is a tremendous jumble of fallen rock and all kinds of things back in this part of the cave system that we call Chaos, and behind that there are passageways that we’ve begun to name. And, as you can tell, with names like Hades, Purgatory, and Limbo– [laughter] These are places that are team has a real problem getting into.

In fact, only the best, smallest cavers can get into these places. I’m going to show you a little bit of video of what it’s like to get into this stuff. So here’s Steve Tucker, and you’re going to see him squeeze through this. And as you’re about to see, his helmet isn’t going to fit, and so he’s going to take it off to squeeze his head through this. And what I want to do just is– Hopefully the video will cooperate, zoom to the back of this, and you’re going to see Marina at the same passage. This is all one contiguous clip. But I just want to show you this is what these are like. These passageways that are leading off are blind tunnels that eventually lead nowhere. But you can see they’re tremendously, tremendously narrow.

The temperature in the cave is 19 degrees. Celsius, sorry. It’s 19 degrees Celsius. I wanted to show you this because this is Purgatory. In Purgatory, in Hades, in Limbo, and in Pandemonium, the named places… we have hominin fossil remains on the floor. And this is how our team has to work to get to them. – [audience] How do they turn around to get out? [John Hawks laughs] – I think that that’s something you don’t ask a lady. [laughter] Don’t ask me how they turn around to get out.

I don’t understand how they do some of the things that they do, but you can see exactly what’s necessary to get there. There are places back here that Becca cannot get to because it depends exactly what your height is whether the narrow parts of your body correspond to the narrow parts of the rock. It is crazy what’s going on back in these passages. And the fact that we have hominin remains on the floor of some of these very remote passages is very interesting. I can’t explain it. There they are. So, in terms of testing our hypothesis about is there bone at the base of the chute: there’s bone in abundance at the base of the chute. There’s articulated bone at the base of the chute. There’s a skeleton there. We’ve opened a second unit that downslopes slightly that has additional skull parts that may represent the same individual or may represent a second individual in that area of the cave.

That’s not really what we expect for a pile of bodies, actually. It’s too good. We also don’t expect these places, which are more than 30 meters from the entrance that we use to enter this chamber, to have fossil remains in them. There’s a puzzle there, and we don’t fully understand the dimensions of this puzzle. Okay, I want to quickly say, at the same time, we were carrying out excavations in the Lesedi Chamber. And I just don’t want to forget that we’ve done that. In the Lesedi Chamber, there was also an incredibly constrained area that we’re working in. This is Elen Feuerriegel, who is working in the excavation unit. And you can see that she’s enclosed by chert blocks coming out from the wall of this and is working a few centimeters below where she’s able to be.

To excavate there, we had to erect a ladder and put up a horizontal one for our team to lie on and excavate in this very narrow spot. So we’re reducing the level of sediment in this area, and hopefully we’ll open up part of the sediments where Neo’s body was arrayed. We’re hoping to find additional parts of him, and we have found a couple of pieces in this that might be part of Neo. So we haven’t gotten there to where we’d like to be yet. Okay, so that’s the update that we have for this month. I have written about it online, so you can read the summary of this. Just to close, we have, throughout the entire course of the project, really worked hard to get material out to the public as it’s happening, as fast as we can to put people virtually into the cave while we’re there, and to put material out so that we can access it. And, of course, for me working at the University of Wisconsin, this is really part of the Wisconsin Idea. We can do no better to bring people into the science of human origins than to enable them to participate in the excavation to the degree that is possible.

And, of course, we’re working in a World Heritage site in one of the most difficult to access places on Earth, with some of the rarest, most precious things. We can’t bring people into the chamber physically, but we can use our technology to bring people there virtually. And I just want to emphasize that during this expedition we were able to put Internet down into the Lesedi and Dinaledi Chambers, and we brought schoolkids in through National Geographic Explorer Classroom, through Skype, and through other mechanisms. Here’s our team explaining how they’re doing the excavations to a school in South Africa. We’re bringing schoolkids in. Those sessions are on YouTube. Other schools can watch those. They’re all there. We were able to bring the public in through Facebook Live using National Geographic’s portal. And on that we had, at the excavation watching us, 50,000 people interacting with us online. And we continue to do as much of that as we can.

We’ve published the research in Open Access journals so that people can download and read them. Our publications describing naledi have been downloaded and read more than 400,000 times around the world. This is the Deputy President of South Africa, Cyril Ramaphosa. I don’t dare say anything about their political situation, but he could be the next president. We’ll see. But in addition to having the government engaged at every level, through science and technology, through tourism, through the World Heritage authority, we have, the World Heritage site itself has put the fossils of naledi on exhibit. They are on exhibit now. The largest exhibit of fossil hominins ever put on for the public. And they’re there for people to see and people are seeing them in huge numbers, unprecedented numbers.

It is an amazing thing to stand there and have schoolkids come through from all parts of South Africa to see the fossils for themselves, to repeat, in whatever language they’re speaking when they come in, naledi, Homo naledi. And it’s an amazing story that’s told in the exhibition. So I’m really proud of that. We started that in May, and that will be there at least through the year. So it’s been an amazing experience. It’s been an amazing public profile for the research. It’s been some of the most voluminous research. We have, in the last two years, since our first publication, published more than 550 peer-reviewed pages of research on Homo naledi alone. Our team involves more than 100 scientists around the world in all aspects of biology.

We are now publishing second round science, what we call the more complicated analyses done in the laboratory. Things like the developmental work that you saw on the teeth. Things like studying the actual wear chipping on the teeth to compare them to other populations of humans and other primates. We’re now studying the isotopic signatures in the teeth. We have not had success in getting DNA evidence out of the teeth. We have tried very hard, so far without success. But we’re very hopeful that we will have evidence from proteins out of the teeth. So we’re going to have some tremendous evidence coming out about naledi as we move forward, but what we’ve learned so far has really transformed the way that we think about human origins. It’s an amazing project.

It continues and I hope that you’ll all continue to follow along because, certainly from the Wisconsin point of view, we’re going to be there working as long as we can. All right, thank you, everyone. [applause]