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Significance of Homo Naledi Limb Proportions

– 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, Wisconsin Public Radio now, 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 pleasure to introduce to you Sarah Traynor. She was born in Colorado Springs, Colorado, and she went to high school at the Air Academy High School at the Air Force Academy there at Colorado Springs. And then she went up to Fort Collins to get her undergrad degree in biology at Colorado State University. She came here to UW-Madison to get her PhD in anthropology, which she finished about three-and-a-half days ago. [laughter] [applause] All right, it was earlier this year, but it’s a lot better to say three-and-a-half days ago. [laughter] She now works for the School of Medicine and Public Health. She’s teaching medical students human anatomy, which is a good thing because it’s good to know.

[laughter] Tonight, she gets to tell us more about the continuing saga of one of the most interesting pieces and projects of research going on at this university in its long history. We’re going to get to hear about the evolutionary significance of the limb ratios of Homo naledi. Please join me in welcoming Sarah Traynor to Wednesday Nite @ the Lab. [applause]

– Thank you, everyone. Can you hear me okay in the back? All right, thanks for the thumbs up. Okay, so I’m sure a lot of you have heard about Homo naledi before. Hands in the air if you have. Wow. Okay. So this is the perfect audience. So because a lot of you are familiar with the research already, I’m briefly going to introduce it just for those who don’t know about it, and then I’m going to discuss kind of my involvement in the project, the more recent developments in the project, and then my research, a little bit of my research that I did for my dissertation, and I finished in May, not three days ago. [laughter] Otherwise I would not be here if I just finished my dissertation.

You need a break, you know? Okay, so today I’m going to talk to you about the evolutionary significance of the limb proportions of Homo naledi. So the relative size of the upper limbs to the lower limbs. That’s what limb proportions mean. All right, so Homo naledi. Way back in August of 2013, a simple plan was enacted, and Professor Lee Berger, at the University of Witwatersrand, was the guy to enact this plan. So let’s set the stage. We’re looking at South Africa in the Cradle of Humankind. This is about like an hour drive west of Johannesburg. And this, the Cradle of Humankind is an incredibly rich area full of hominin fossils.

We’ve been excavating this area for, I don’t know, almost a hundred years now. And, you know, we’ve been really focused on a few very significant sites. There is continuing excavations at a lot of the very famous sites in the Cradle of Humankind. And that’s all well and good, but Professor Lee Berger here, he knew that there were more fossils in the Cradle of Humankind, we just weren’t looking in the right place. So he hired, he basically went to this spelunking, caving club in Johannesburg and he said, listen, I know you’re out here all the time, you’re in the caves, I’m just going to support your efforts in the caves, and if you find bones in the caves, let me know and bring back some pictures and that would be great. And within a month, Steve Tucker and Rick Hunter, they sent Lee these pictures here, and Lee knew that he was looking at hominin bones. And so he enacted this project, this Rising Star project, and we called the cave this Rising Star Cave. So, from these pictures, it was thought that there was maybe one or two individuals at this site. We were looking at a couple long bones here just kind of laying on the surface, and then we had this beautiful brain case here that we wanted to initially kind of get out of the ground.

So he sent out this Facebook message, did a bit of crowdsourcing, and found these incredible women to be the underground astronauts, or the excavators of this site. Okay? So this site is really difficult to get to. It is a couple hundred meters below the surface, and you have to be really not afraid of small spaces and you have to be a fairly small person because some of the areas and the routes are like seven inches wide and I wouldn’t fit in the cave, nor would I want to be in the cave. I’m a little claustrophobic. [laughter] So that’s not my thing. So he found these amazing women, and these were referred to as the underground astronauts. They excavated for a month, and they ended up pulling out over 17,000 fossils from this one chamber. So let’s look at the route. When I was in Johannesburg, I kind of hung out at this entrance here. It’s beautiful.

[laughter] So you have to climb this ladder down here, and then it’s about 20 minutes all the way to the Dinaledi Chamber. So you have to go through a series of really large chambers. I’ve been told there are beautiful stalagmites, stalactites, you know, the perfect kind of cave setting. And then you have to go through Superman’s Crawl. Superman’s Crawl, it’s named that way because you have to crawl through like this, like Superman, and scoot your way through. And then you have Dragon’s Back, very steep climb before you reach the chute here, which is that choke point, the seven inches that you have to kind of wiggle down, and then you’re in the Dinaledi Chamber. Okay, so that was their route; it took about 20 minutes to get in there and 20 minutes to get out. And while they’re in the cave within this chamber, the Dinaledi Chamber, where all of these hominin fossils were discovered, you know, they had to be quite creative with how they were getting the technology down there and also how they were excavating the material. They tread lightly.

They took off their shoes so that they wouldn’t crush any of the bones that were just kind of laying on the surface. And then, after they would scan the area and collect all the bones, then they took this 20-minute route back through the cave and passed on the bones. This is one of our very own, Dr. Alia Gurtov. She was here last year discussing this site. So once the bones were out of the ground, right, they went to the science tent and they started, you know, to be cataloged and all of that stuff. And then, all the while, you know, they’re doing lots of outreach, and that’s kind of what this Rising Star team prides itself on is the amount of outreach that we’ve been doing, kind of public education about Homo naledi, about the excavation process, about the research process, kind of the behind the scenes of anthropological research. So that’s ongoing. This is in 2013, but that, those efforts are ongoing all the way to now. All right, so you have 1700 bones that you need to look at, and it’s best that you don’t just have two people doing it.

It would take years. So Dr. Lee Berger and our very own Dr. John Hawks, who has also been here a couple times talking to you folks, they are the co-leaders of the project, and they sent out this call for early career scientists, early career anthropologists. Early career meaning, you known, finishing up your PhD to before tenure track. So kind of the people that had the most to gain from this experience. So they called in the early career scientists. You had to apply for this position and apply to be a part of the workshop that occurred in Johannesburg. It was about like a five-week long workshop in 2014. This was a really quick turnaround, right? The bones were out of the ground a month later after they were found, eh, a couple months later after they were found. And then 2014, early 2014, we looked for the early career workshop.

So they brought in over 30 people, 30 early career scientists to work on this material. And it was really cool. So, this is where I come into the project. So, at this time, in 2014, I had yet to prelim or come up with, like, a project idea, which is perfect timing that Homo naledi was discovered. [laughter] And so I was there kind of documenting this process of the early career workshop. So I was involved, but I wasn’t one of the early career scientists that were researching this material initially. So it was really, it was amazing to be in this room. There were, you know, like I said, over 30 people in here. This is the crani– The head team. The cranium team.

And they did the skull and the mandible. And you can see all of them working together here. Lots of skulls on the table. They are hard at work. And then we had, like, other teams. So the tooth team, they were in this really small room, and it was called the Tooth Booth. And it was like very, very crowded for them. Uncomfortably so. And we had a lower limb team, and we had a growth and development team. Right? We had all these teams where their focus was on specific parts of the body. And they brought in all of their expertise and to, you know, apply all their expertise to these bones to figure out what are we looking at, right? Are we looking at a species that has already been discovered? Are we looking at a modern human? Right? Is there just, like, an old caver in there that just got lost and couldn’t climb back up that chute? What are we looking at? So it’s kind of amazing to– So this is the whole group here.

So what I was really interested in is kind of like what happens when you have all these fossils, right? You have 1700 fossils and multiple individuals and, like, how do you get to the point where you now are at the point where you’re publishing a new species? Like what happens between, like, just fossils on the table and a publication on a new species? And I don’t think that’s been kind of fully kind of brought to the forefront before. So I was really interested in, like, what happens during this research, what is the process of science behind these really large anthropological sites and these large findings, these large discoveries. So I was kind of documenting this process, and, really, the goal of a lot of this video and footage and photos and interviews is to create more educational material for like K-12, kind of showing them the process of anthropological science, like how we test hypotheses. You know, to teach them, like, when we look, when we have a piece of the skull, this is, these are the next steps. This is what we’re looking at. We’re going to compare it to modern humans and look at the variation to modern humans. Then we’re going to compare it to extant apes. We’re going to compare it to other fossil species that have been discovered before. So it’s really like, it’s all comparative anatomy really.

That’s the name of the game. And it’s, you know, it’s going back to like Sesame Street. Like, is this one similar to this one, or is it different? Like, at the most basic level, this is what we’re doing. You just have to, like, know a little bit about bones in order to get there. So that is the goal of this footage is to just show video, like this kind of setting here, where we have the lower limb team, Chris Walker, Damiano Marchi from– So Chris Walker is from North Carolina. Damiano Marchi is from Italy. And we have Pianpian Wei here from China. And they are all kind of working out these, they’re looking at the bones, they’re kind of working out these issues. And, as you can tell here, we have all the Homo naledi femora kind of laid out in front of them, and then we have all of the fossil femora possible.

These are all of the available fossil femora that we have. And, you know, this is what they’re doing. They’re doing comparative anatomy, and it’s kind of really interesting to kind of hear these conversations and kind of feel out the room. Like the lower limb team, they’re like, oh, yeah, this is really human-like. Like the tibia looks elongated. That’s the shin bone. It’s fairly long. It’s kind of narrow but looks pretty human-like. And then we have the pelvis team that, you know, they now go to the pelvis group, and they’re like, well, let’s, you know, the femur, you know, the thigh bone’s connected to the hip bone.

And so they’re like let’s go over to the pelvis room. And then the pelvis team is like, no, this is the, like, super, super old-looking. This looks like an Australopithecine. This is nothing like a human-like pelvis. And then they’re like, they’re at an impasse, right? So how do you kind of deal with the data? How do you explore these kind of mosaic findings and fossil species, so. It’s kind of the process of science that I am interested in this kind of early career shop. And then we have this, we have this limb head team again. I just loved how they had so many crania at the table. So they are comparing this small little fossil fragment here.

This is a video, but I’m not going to show the video. But they have this small little fossil fragment that they’re trying to place onto the human skull here. And then, of course, they’re comparing, this is chimpanzee, they’re comparing it to other hominin fossils to figure out, like, what is different, how is it different, how is it similar. Because at the end of this, we have a bunch of bones, right? And it turns out as this. It turns out to be this kind of reconstructed hominin where we’ve made a lot of conclusions about its anatomy, about its morphology, about its behavior just from these bones here. I always think that that’s interesting. So what we’ve found was that it was this highly mosaic, it had a highly mosaic species and it had a lot of features that we had never seen before, and so we called it a new species because of that. All right, so since then, there has been ongoing excavations in the Rising Star Cave. So the initial excavation was in 2013.

They brought people back in, some underground astronauts back in, in 2014. And they knew about this Lesedi Chamber way back in 2013, but their primary goal was the Dinaledi Chamber. They knew about this chamber, they knew that there were bones in it, but they needed to kind of complete one task at a time. So they started the major excavation in 2016 and the paper was published in 2017 about the hominin material that was discovered in the Lesedi Chamber. So this is the main surface entrance here in blue. The Lesedi Chamber is closer to the entrance than the Dinaledi Chamber here is in yellow. So the Lesedi Chamber, in order to get down here, you got to take a right instead of a left. It’s all about just traffic control, really. And it takes a little bit less time to get down there, but it’s still a couple hundred meters down.

And there are, of course, like a lot of goofy names for the parts that they’ve been, like, stuck in. And then we get to this point here, which is the Lesedi Chamber down here, and there were three individuals discovered in this Lesedi Chamber. About 118 fossil fragments. You know, way less than the 1700 of the Dinaledi Chamber, but, like, that’s okay, we have a lot of stuff to work with. So 118 fossil fragments is just fine. So three individuals, right? We find this adult, this partial skeleton, which we’ve named Neo, and this adult is right next to an infant skeleton, which is really interesting. These bones, these individuals, are placed up against the walls of the chamber. Kind of, like, stuck in crevices, which is interesting. They found another individual here.

The location of the second adult is here. So not as close as the male adult and the infant are to each other, but still there’s a third individual in this chamber. When we’re looking at Neo, this is the beautiful partial skeleton from the Lesedi Chamber. What’s really cool about this is that we have a bit of the face, which we didn’t have out of the Dinaledi Chamber. Usually, you know, the face around this area is really tough to preserve because you have really small nasal bones and your zygomatics are fairly delicate. Those are your cheekbones. And so usually we just don’t have a lot of the face preserved in a lot of fossil hominins. A lot of it has just been reconstructed over the years. But we have a bit of the face here.

So, obviously, you could mirror image that and basically have a complete face, which is what we are now kind of 3D printing, and that’s the 3D scan that’s up online now, is of this kind of mirrored structure so you could print out an entire skull. We just printed one out in our lab, and it took four days. It’s a big skull, so it takes a little time if you’re printing it off at the public library, which you very well could. All right, so this is Neo. This is a male skull about 600 CCs. So a little bit larger than the cranial capacity from the Dinaledi Chamber. This individual looks a little bit more robust. But, we have this partial skeleton, and anthropologists love partial skeletons. You know, it gives us– They’re important.

It gives us a lot of information about one individual. Okay, like the Dinaledi Chamber, when you have multiple individuals, right? You have like 15 individuals from that site. You have a little bit of information about a lot of individuals. But these partial skeletons give you a lot of information about one individual, so. You can choose which one you like better. If you have a lot of information about one individual, it’s not going to give you the range of variation for the species, but it’s going to tell you what this one individual looked like, which sometimes that’s all we have. All right, so that’s the new, that’s the newest discovery here, this partial skeleton. And then the date came out this year as well. It’s been dated, the bones, the bones themselves have been dated to 230,000 to 330,000 years ago.

When you have thousands of fossil fragments, you can, like, spare one or, like, three for DNA analyses and also for dating. So we dated this with ESR, electron spin resonance. We have not been able to get DNA out of these individuals because… DNA preserves in cold and dry climates. And Homo naledi was discovered in warm and wet climates. So the exact opposite of what you want. But this tells us that Homo naledi is very recent and is a lot more recent than we thought it was. There was a camp that thought that these fossils were about two million years old, one million, and now they’re 300,000. So this tells, you know, these hominins are living at the same time as we see the first modern humans.

It was around 200,000 years ago. We see the very end of Homo erectus. We also, Homo naledi is living at the exact same time as Homo heidelbergensis, which is right here. This cowboy skull So this is Homo heidelbergensis. Really robust. We think of it as the ancestor of the Neanderthals. And I mean huge brain. Very modern, modern brain. Very robust but still big-brained.

And then we have Omo, which is kind of early modern human, and that’s like 200,000 years ago. So Homo naledi is living at the same time as these very large-brained individuals, and that kind of is changing our entire paradigm of the fact that 300,000 years ago, very recent in our human evolutionary history, we thought that all big-brained species were on the landscape surviving. They won, right? From 300,000, really from like 500,000, to now, it’s just big-brained species. And that’s not the case anymore. Right? Homo naledi is living at the exact same time with a 600 CC brain. Chimpanzees are about 400 to 500. So that’s kind of changing the way that we’re thinking about recent modern human evolution. And, of course, right, we have this small-brained species, but we’re wondering kind of is this modern behavior? The intentional deposition of these 15 individuals into the Dinaledi Chamber or the intentional deposition of the three individuals in the Lesedi Chamber. Right? It seems like something’s going on here. They’re expending the energy to do something repeatedly that doesn’t necessarily seem like it needs to be done. And so when that is happening, we tend to think that this is modern behavior because we do things that don’t need to be done.

That’s what we’re known for. So is this behavior expected for a 600 CC brain? I can tell you if this was, if Homo naledi had a larger brain and it was 300,000 years old, we would not question it whatsoever. But it’s because it has a smaller brain that kind of our paradigm is shifting, and we have to not put so much stock into having a large brain, I think. All right, so we have these kind of big questions, right? We have these big questions about the modern behavior, and we have the questions about, like, tool use, right? 600 CCs, are they using tools? Are they responsible for some of the tools on the landscape at that time? We certainly can’t rule them out anymore, right? We find some stone tools, we find any sort of crushed bone, any evidence of butchery 300,000 years ago in South Africa, we can’t rule out Homo naledi. So Homo naledi was not in the chamber themselves. Homo naledi was not discovered with any stone tools. But, really, they were just depositing the bodies, they weren’t depositing anything else. And they weren’t living in there so they weren’t, like, disposing of their trash in the caves, or at least in these chambers. Okay, so we have a big question. Diet, what were they eating? Were they competing with Homo heidelbergensis? Like, were they competing for food? What did that relationship look like on the landscape? What were their growth and development patterns, right? Did they have an extended juvenile period like modern humans? Or did they have a shorter juvenile period and kind of accelerated growth like chimpanzees? What is the variation species? We can determine some of that from the Dinaledi Chamber, and we know that they’re not very variable at all.

They’re fairly– They look very similar to one another. And then, my favorite thing to talk about is locomotion. Like, how were they moving on the landscape? What kind of activity patterns were they doing? How were they moving on the landscape? What was their posture? What was their positional behavior during the day? I think this is interesting. So I study limb proportions because I want to know about the locomotion of Homo naledi. So we define limb proportions as the relative limb length, size, and robusticity of the upper and the lower limbs. And when you’re talking about relative limb proportions, you’re talking about the relative size of the upper limbs to the lower limbs. Right? As humans, we have a smaller upper limb compared to our lower limb because we rely on bipedal locomotion. We rely, all of our weight is kind of resting on our femoral heads, and we rely on our center of gravity to be at the femoral heads as well. So we use our limbs very differently than, let’s say, a gibbon would use their lower limbs. Or their upper limbs, right? Gibbons are brachiators.

They only, like, swing in the trees, and so they have incredibly long arms and shorter limbs. If you were to compare a gibbon femur compared to ours, their femoral head is going to be quite small because they’re not putting of their weight on their femur like we are. So these are kind of the things that we can glean from the limb bones in extants, apes, and also in modern humans. And then we can apply this information back to the fossil records to figure out how these hominins are moving around the landscape. I always loved this picture. It’s very old. It was drawn a long time ago, but I always liked this picture. These are the gibbons here. The body size, the gibbons look huge, but they’re not as big. But it’s just to show there the relative limb lengths of these individuals.

The orangutans, of course, they are highly arboreal. They have really long arms. And then we have the chimpanzees and gorillas. Those are knuckle-walkers. So this means that they’re quadrupedal, but because they’re knuckle-walkers, they have a little bit longer arms compared to their legs but not much. It’s not like a dog that has really equal arms and legs. And then we really have a question mark about these hominins. Are they more arboreal? Are they more terrestrial? What are they doing? All right, so limb proportions. Whenever we are looking at the bones, we are making a lot of assumptions about the musculoskeletal system.

So we’re letting the bones tell us something about the muscles, and then the muscles are going to tell us how they’re moving around the joints, and then we kind of figure out how these hominins are moving on the landscape. So it’s like this building block. So, obviously, if you have this tubercle that muscle is attaching to, and it looks different in us than it does in gorillas, we are assuming that either the muscle is larger or smaller or the muscle is oriented differently around that joint. So we’re allowing the bones to give us a lot of information about the muscles. So the first limb proportion that we can look at is relative limb length. I’ve been talking a lot about that. Like if you’re primarily arboreal, you’re going to rely on your arms a lot more than your legs. If you are bipedal, like us, we have really long legs and shorter arms. So that’s pretty basic.

We have this gorilla femur here next to this human femur, and these are both life-sized. So you can tell that the human femur is a lot longer. So this is kind of going to tell us something about locomotion. And then we have relative joint size. So the more body weight that’s placed on a joint, the larger the joint becomes. This is why we have huge femoral heads compared to, let’s say, a chimpanzee, who’s quite a large individual but still has a smaller femoral head because it’s not relying on the femoral head to carry its weight. Okay, so we can look at relative joint size. We can do this in the arms as well. We can do this in the hands or in the feet depending on, like, what questions we’re asking about locomotion.

And then the last one is relative diameter of the long bone shafts. We can look at the cortical bone and the thickness of the cortical bone on long bone shafts, and we can determine with increased cortical bone thickness we usually let that, we think that that is telling us something about mobility patterns. So you kind of have to be, you have to have, you have to compare individuals that have a similar style of locomotion to then assess how mobile they are or, like, what their different activity patterns are. But if we’re assuming that the hominin is bipedal, then we can assume that they’re walking on two legs just like us, and then we can look at their mobility patterns compared to modern humans, so this is kind of cool. We have this late archaic species. We have a couple, this is a Neanderthal. So we have a couple late archaic humans on the left, screen left, and then we have early modern humans on the right. Fossil species here. So we can look at the distribution of cortical bone and look at the thickness and be able to determine that the early modern humans, because they have thicker cortical bone, especially along this linea aspera of the femur, we can tell that the muscles are pulling on the bone more and you have larger muscle mass that’s pulling on the bone.

It’s remodeling the bone, and we can tell that these individuals, like this individual here is more active and using their legs in different ways than this individual here. Okay? So we can let that cortical thickness, the bone shaft, tell us something about activity patterns. So they do this a lot in, like, comparing humans. Like hunter/gatherers versus agriculturalists. This is a big area of study because as soon as we stop being hunter/gatherers and we rely more on agriculture, then we are not as mobile as a species and then it comes along with a whole host of other health issues because of that. But this is a big thing that we look at in that case. All right, so why do we care about limb proportions? Let’s just review why we care here. We assume hominins, the definition of being a hominin, or a human ancestor, means that you are bipedal. Right? We immediately look for evidence that you were a bipedal hominin. You have evidence that you are walking upright. But this doesn’t mean that all hominins are always terrestrial.

It doesn’t mean that the bipedal hominins aren’t, like, in the trees sometimes or, like, using a little bit of their arboreality. Or they could just be kind of maintaining these arboreal features and just be on the landscape. Like, we don’t know how much arboreal behavior they are doing throughout their lives, but they have to be bipedal. They can be any kind of range of arboreal after that. Okay? So that is just like the definition of hominin. We don’t assume that all of their arboreal behavior just goes out the window once they’re bipedal. So that’s, like, hominins in general, right? That’s the Australopithecines, that genus. But as soon as we get to the origin of Homo, as soon as we get to our genus, we really want the species that are in our genus to be, like, terrestrial. We want to look for evidence that they have lost a lot of their arboreality and they have an increased commitment to terrestrial long-distance walking. This is a hypothesis that we always test when we’re talking about the origin of Homo.

Like, we want to see early Homo species relying on bipedalism and not really relying on any arboreal features, right? They’re becoming more modern and less primitive, in a sense, or less ancestral. Okay, so we don’t, you know, the origin of Homo, we don’t have a lot of evidence of these early Homo species. We have a couple of partial skeletons, and from those partial skeletons we can– I’m only going to show you two graphs during this presentation, so this is one of them. So if we are looking at the humerofemoral index, so this is the length of the humerus to the length of the femur. We’re just looking at relative limb length. Okay? And we have plotted here 1200 Homo sapiens. So we have the mean relative limb length in modern humans. We have this really nice, normal curve around it. So this Nariokotome boy skeleton is down here in Dmanisi. So this first red box is Homo erectus.

So Homo erectus is within modern human range for humerofemoral index. And so we’re thinking, great, they are less arboreal, right? They have the shorter arms, the longer legs. They’re doing things that modern humans are doing because their skeleton looks like us. Okay? And then, if we’re looking at this species here, this AL288-1, this is Lucy. This is Australopithecus afarensis. And look at her. She has these long arms, these shorter legs, right? This is an Australopithecine. This is what we would expect. This is like a clean case for increased arboreality, increased arboreal behaviors, not quite relying on terrestrial bipedality. But then you get to the cases that are kind of up in the air, right? You have Australopithecus garhi here, which kind of falls within the range of modern humans. So, uh-oh, now you have an Australopithecine in the modern human range.

What do you do with that? And then you have here, LB1. This Homo floresiensis. This is the hobbit out of Flores, Indonesia, and they have longer arms than Lucy. So, like, it gets messy when you start to, like, come up with this, like, one rule that makes Homo Homo. So this is what we’re dealing with here. All right, so what do we know about Homo naledi in terms of limbs and in terms of locomotion already? So I kind of came into this like, what do we already know and what do we want to know? So we already know that its shoulder is like that of a gibbon, surprisingly. The shoulder looks like it is a gibbon shoulder. It looks like it has so much rotation, it has so much movement. It does not look like a modern human shoulder.

When Homo naledi is just kind of standing here, its shoulders are hunched. It’s not as, like, they’re not brought down like they are kind of like with the scapula sitting along the back. Homo naledi has a shoulder like that of the gibbon, which is a highly arboreal species. So that’s confusing. And then we have a really ancestral-looking pelvis. This pelvis looks like that of Lucy. So very Australopithecine-like pelvis. It’s very broad and flat rather than bowl-like, which is what modern humans are. And we care about the pelvis.

We care about the shape of the pelvis because that tells us something about how center of gravity is being maintained from this trunk through the lower limb. Okay, and in the hand, the hand proportions, they have small hands, but the proportions are similar to those of modern humans. They have this long thumb, but if they were to extend their hands out, they wouldn’t be able to extend them this way. Their fingers would look like this. Their fingers are curved. And curvature in fingers is interesting because if you’re looking at a chimp baby, like a chimp infant, chimp babies do not have curved fingers. Their curvature in their fingers occurs throughout their life the more arboreal they are. So you look at a chimp baby, straight fingers. And then you look at the juvenile and then the adult, they have really curved fingers because throughout their growing period, they are constantly grasping things.

The tendons, the muscles, they’re going to change what the bone looks like, and it’s more productive for your hands to be curved if you’re grasping things all the time and if you want a really strong grip on those branches. So Homo naledi has curved fingers. So this tells us something about what they’re doing throughout their life. This is happening because of behavior. This isn’t genetic. All right, we also know that the tibia, so the shin bone, we don’t know a lot about the femur but we know that the tibia is elongated. So this is really a long and really narrow bone. It’s more similar to modern humans, but we don’t know if it’s long, relative to the femur, because we don’t have a total femur length. In Neo either, that partial skeleton, we don’t have a total femur length of that individual either.

So elongated tibia, that means maybe it has an elongated lower limb but we’re not sure. Maybe it just has an elongated leg, which is just the tibia. So this is what we know so far. And, oh, and then, sorry, the foot. The foot is incredibly modern. The foot, I had a colleague who studies the feet, and he said that if he was just looking at the foot he would have thought that it was miner that fell into the cave 40 years ago. He thought it was incredibly modern. But the toes are curved. So that means that they’re grasping onto these whatever, they’re grasping onto something with, like, short toes.

So we all know how efficient that is with our toes. So I’m not sure what’s going on. All right, so that’s what we know, and my null hypothesis is that Homo naledi, it’s in the genus Homo, our null hypothesis is usually that Homo naledi is like humans. It has human-like limb proportions. And then we test this null hypothesis, and we can either reject it or we cannot reject it. So this is what I’m going to do. So this is the, so I studied the relative limb size of Homo naledi. So this is what we’re working with. And when I was writing my dissertation, I didn’t have Neo.

So I was working with this, like, commingled assemblage here. So the majority of the fossil material is unassociated, right? You can’t attain direct proportions. You can’t say that this humerus goes with this femur and let’s study this individual, right? Because there are 15 individuals and you can’t actually say which bone belongs with which individual. And you can’t study limb length because we don’t have a lot of complete bones. We have incomplete bones. But what you can study and what I did study is joint size because we have a few joint ends. Those are more likely to preserve than the shafts. And then we do have a few mid-shafts as well. Okay, so this is what I did.

I studied the joint size and the mid-shaft diameter of Homo naledi. And I was able to gather four measurements on the upper limb. So measurement of the humerus, two of the radius, one of a carpal bone, a wrist bone, and then I took four measurements on the lower limb. So femoral, two femoral measurements. So two measurements on the femur. And then a measurement on the tibia, and then also a measurement on the ankle bone, the talus. So I was able to take four measurements to kind of represent this upper limb size, and then four measurements to represent this lower limb size. This is a small sample as it is always in anthropology. So the fieldwork was me basically in South Africa.

I studied the Homo naledi material. That was my second time in South Africa. After that early career workshop, I went there again to study the material for two months. And I measured the distal ends of the long bones. You need to measure the joint sizes in modern humans. So, in South Africa, there’s the Dart Collection, and the Dart Collection is this huge modern human collection at the medical school at University of Witwatersrand. So that’s where I collected my modern human data in South Africa. And then I collected my other modern human data from the Bass Collection in Knoxville, Tennessee. That place is very famous for the Body Farm, as you might know.

That would be a good talk, to talk about the Body Farm. All right, so measure the distal ends of the long bones of these modern humans, measure the diameter of the long bones, just took the diameter of the mid-shaft here, and then tried to figure out the relative size of the upper limb to the lower limb. And so I did these things in Homo naledi, and then you do the things in modern humans, and you’re going to compare what you found in Homo naledi to a sample of modern humans. So these are the measurements. The measurements of the upper limb. They’re going to give you this mean upper limb measurement. And these are the measurements of the lower limbs. You combine all those and you’re going to get a mean lower limb measurement. And then you divide them, and you’re going to get a relative limb size measurement.

And you get one from Homo naledi, right? These measurements, I got one relative limb size measurement. It’s like this is the measurement from, you know, these estimated 15 individuals. So what you do, basically, is you have this, you have a sample of modern humans. And, you know, obviously I’m not going to cherry-pick. Just like the humeri and the radius of these different individuals, we don’t know what individuals go together with the Homo naledi data set. So you just have to figure out, you have to make a modern human data set that mirrors your fossil data set. So if I have seven adult individuals, Homo naledi individuals, and I’ve taken 27 measurements from those individuals, I’m going to take a sample from my modern human collection, like 130 individuals, I’m going to take a sample of seven individuals, and I’m going to collect those 27 measurements, and then I’m going to find that limb index value. Right? So you’re just constantly resampling from your human sample, and you come up with a range of values so that you can ask, what is the statistical likelihood that we would find the given Homo naledi fossil sample in this human sample? Okay, so this is called resampling, and this is very common in anthropology and paleoanthropology. Because we have such small sample sizes, we need to come up with a way to create the most power that we can, so we compare this one value of fossil species and we say, how likely is it that I get this one value in a modern human distribution? So, how likely is it to get this Homo naledi value here, which is this yellow line? And this is the modern human distribution here. And it turns out that it’s likely.

So we, the Homo naledi, this Homo naledi relative limb size value falls within the range of modern humans. So it falls within the possible combinations that you could create out of this sample of 130 humans. So it’s not likely to be human-like. So, basically, what we say if the value, this relative limb size value, falls within the range of modern humans, we say that we cannot reject the null hypothesis that Homo naledi is different than modern humans. This isn’t saying that Homo naledi is modern human limb proportions, it’s saying that we cannot reject the hypothesis that it doesn’t. Okay, let’s just be clear here. But that’s really the best that we can do. We just say that we cannot reject the null hypothesis that Homo naledi has human-like limb proportions, and we’re really happy with that. So we say that Homo naledi is maybe has these relative limb sizes that are similar to modern humans, but they’re combining them with these arboreal features on their shoulder and with their hands.

So they’re doing something that is very different than what modern humans are doing today because we do not have curved fingers and we do not have curved toes, the majority of us probably. [laughter] And we certainly don’t have gibbon-like shoulders. So what we’re seeing is that Homo naledi could have these kind of more human-like proportions, upper limb size, lower limb size proportions, but they are combining them with these really kind of strange arboreal features that we don’t see in modern humans today. So that means something to us, and that tells us that Homo naledi is moving around the landscape in a different way than modern humans are today or modern humans were 200,000 years ago. So they’re different. And there are some people that are now studying, I am not one of them, because I don’t like rock climbing, but some people are studying rock climbing because there’s a thought that these climbing behaviors, they’re not arboreal, they’re not in the trees, but they’re on the rocks. They’re doing what maybe baboons are doing. Climbing up cliff faces, standing away from predators. They are climbing throughout those caves.

I mean, it’s an interesting hypothesis. How are they using these caves, right? What are they grasping on to their entire lives to create these curved fingers? What are they doing, right? And on the landscape there are some trees, not too many, and then there are some, like, rocks. So it’s thought that maybe they are climbing rocks using the rock faces in a different way than we are today. So people are studying baboons, baboon hands, baboon toes. And then, also, some people, my colleague also is studying rock climbers and studying the way that if you are a rock climber your entire life, is that going to change the way that your, like, fingers are positioned. Not necessarily saying the rock climbers are like this, but is it changing the morphology on a bit of your finger. So people are studying rock climbing, and this is where we are right now with figuring out how Homo naledi is moving on the landscape. So that is all I have for you. [applause]