- 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   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. Hom  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 the