Origins of Genus Homo: What Who When Where?; Early Body Form; Life History Patterns

– [Recording] This UCSD-TV program is presented by University of California Television. Like what you learn? Visit our website or follow us on Facebook and Twitter to keep up with the latest programs ♪ [music] ♪ – [Narrator] We are the paradoxical ape, bi-pedal, naked, large brain. Long the master of fire, tools, and language, but still trying to understand ourselves Aware that death is inevitable, yet filled with optimism. We grow up slowly. We hand down knowledge. We empathize and deceive We shape the future from our shared understanding of the past. CARTA brings together experts from diverse disciplines to exchange insights on who we are and how we got here, an exploration made possible by the generosity of humans like you ♪ [music] ♪ – [Bernard] This is a topic that I have been thinking about for some time as you can gauge by the difference in hair color in that picture and now. But what I want to do today is to try and use the experience of those years to see whether it’s taught me anything and also to use some data from some young people. And I’m very grateful to Eve Boyle and to Andrew Du and to David Patterson who are all graduate students in the Home Power Program at the university where I come from. And I’m mentioning Mark Collard here because he and I worked on this now a little time ago and I’m going to say some things that he might or might not agree with and I’m just giving him a warning. So what, what are we looking for? Homo is a genus and when Mark and I started to think about this, we could not find a definition of a genus that was universally supported So we put together, for our own purposes, a working definition of a genus and we suggested that it was “a species or a monophyletic group whose members occupy a single adaptive zone. ” Now let me try and unpack some of that. For a species to be included in a genus, it should belong to the same monophyletic group as the type species of that genus. Now the type species of a genus Homo is Homo sapiens so what we argued was that the different species deserve to belong to Homo then it should be in the same monophyletic group Now a slightly shorter term for monophyletic group is the word clade and how do you define a clade? The definition that we use was “all of the taxa, no more and no less, that are descended from a recent common ancestor. ” Now I like metaphors from the car industry and so as not to let my colleagues down, I got some new ones here. The common ancestor of all Toyotas is a Toyoda, it’s a model which was developed in 1935 by a company, the company originally made machinery to made textiles. So it did not start as a car company, but they decided that they wanted to make cars and they went to America to learn how to make cars then they went back to Japan and they made a car, and it was the A1. So that’s the common ancestor of

all the models of Toyota that are and have ever been. So that’s what we’re looking for. The notion of the second criterion was that for a species to be included in Homo its adaptive strategy should be closer to the one of the type species, i.e.modern humans, than to the type species of any other genus. So the candidate species that we are thinking about including in the genus Homo, that and the type species should be part of the same grade. So, what is a grade? It’s just a series of questions that I keep… So a grade is “a group of taxa that shares a suite of what we call adaptive features. ” So we would suggest that if you do share those features you are in the same adaptive zone So back to the cars. So the Toyota Motor Company decided that it should make a jeep. It saw the success of the Willys Jeep, it was a four wheel drive car. So it decided to make its own four wheel drive car. My suggestion is that as soon as you make a four wheel drive car, you are in a new adaptive zone. You are in a different adaptive zone and this is the one that they made. And so my contention is that in the Toyota clade, that the BJ which is what this is, marked the beginning of a new adaptive zone of four wheel drive vehicles. Now you could argue that hybrid cars might be a new adaptive zone as well You could argue that the design of a minivan which was introduced by the Toyota Motor Company and it was called very imaginatively the first one, it was called a van. Okay. And then the next model was called the Previa, and the model that exceeded that was the one that you see now called the Sienna. My contention and my suggestion is that the notion of a minivan is a new adaptive zone. There are levels of sophistication. Now the doors open electronically and you can argue that, you know, does the addition of electronic opening doors make it a new adaptive zone? That’s up to you. My sense is that it’s not much different as to whether you open the door yourself or whether they open electrically and so I wouldn’t call that a different adaptive zone. So here, there are people who are interested in the evolution of the four wheel drive vehicles made by Toyota. And here is an image that was very kindly found for me by another graduate student who is called Alexander Pruca [SP], and you can see that there are people who are interested in the evolutionary history of the Land Cruiser. And so, they are interested in what we are interested in But the problem is but if all the evidence you had for the evolutionary history of the Toyota was a few fragments, maybe part of the windshield, a little bit of the wheel, something from the grill, a little bit of the fender, or something from the hood. And the problem is you didn’t even have the same parts for the different models that you’re trying to link. That gives you a sense of what we are trying to do. We do not have the equivalent of the luxury of all this information about the models and the developments within the evolutionary history of the Toyota Land Cruiser. So the second question, what about the who? The genus Homo was established by Linnaeus way back in the 18th century. And as the years have gone by, more and more taxa have been added and they have been included in the genus. So initially, the neanderthals were included and then the taxon called Homo heidelbergensis and then the taxon called Homo rhodesiensis and then a taxon called Homo soloensis. And maybe the biggest addition was made by Ernst Mayr during the second World War when he suggested that the taxa that had been in the genus of the genera, tymantrabus and the genus phyticantrobus, should be included in Homo. So as the years went by, the genus Homo became more and more inclusive The criteria for admission were relaxed The initial criterion was you had to have

a brain as large as ours. So admitting Homo neanderthalensis, that wasn’t a big, that wasn’t a huge deal because they had large brains, too. But by the time you get to including Homo erectus in Homo you are admitting that this is a genus that can have individuals that can have brains half the size of the average modern human. Then in 1964, Louis Leakey and the person of the Leakeys had recruited to help them interpret the anatomy of their fossils, Phillip Tobias and John Napier, they published a paper in Nature suggesting that some fossil that had been found at Olduvai should be included in a new species and that species name was habilis But maybe more controversially, they suggested that that species should be included in Homo. Now that meant relaxing the criteria even more and the question is, was that process of relaxation, that last process of relaxation, to what extent did that stay within the definition of a genus that Mark and I suggested? In other words, is Homo habilis part of the same clade and is Homo habilis part of the same grade? What we argued in a paper in Science way back was that we didn’t think the evidence was all that strong, but let’s get back to that. So how has this process of progressive inclusivity affected the grade definition of Homo? This is an extremely speciose interpretation of the Hominin fossil record. Modern humans are in the top left What I call a gray…which I call pre-modern Homo which includes neanderthals and the heidelbergensis and Homo erectus is in the blue And then the hominids that Bill Kimble is going to be talking about, the mustard colored ones are down in the bottom right And then there are some rather brownish ones which are rather like the mustard colored ones except they have extremely large molars and pre-molars. These are animals with very large mandibles and very large post canine teeth. So the inclusion of Homo habilis in Homo meant that the genus Homo would include what I’ve called pre-modern Homo plus the taxa that have called transitional homonins on the basis of the findings that Mark and I published way back in 1999. Now I think that paper was superbly well argued and was extremely clearly written, but it made hardly any impression on my colleagues. And it’s fair to say that apart from a few discerning and discriminating scientists, most people still include the taxa Homo habilis and Homo rhodesiensis within the genus Homo So that’s one way of interepreting the genus Homo. So the origin of the genus Homo would be how do you explain the appearance of Homo habilis? That’s another way of asking the same question. In which case, you would include Homo habilis and Homo rhodesiensis which is some people think might be distinct from Homo habilis but it’s a similar sort of organism. You would include them in the dark blue category, in the dark blue grade. If Mark and I are correct then you would extend the genus Homo down that far. You would stop at the beginning of Homo erectus. In which case you would regard Homo habilis and Homo rhodesiensis as not the same species as the other australopiths but nonetheless, within the same adaptive zone as the other australopiths So what has happened since the publication of the paper in Science that nobody took any notice of in 1999? More fossil evidence has been found and not only has more fossil evidence…more fossils been found that the existing fossils have been reanalyzed and reconstructed and so on. So that’s one development. The other development is that we have new data and there people who are reassessing the existing data which relate to what I call the functional capacities of these animals. What can we infer about how dextrous they were? What can we infer about how smart they were? What can we infer about what they were eating? These are just a few of the publications that are relevant to this, but I want to talk about the categories of the data that speak to cognition and some new data that speak to diet. Now in relation to cognition, these are not new data. Most of the data that were analyzed were the specimens which were used by Leslie Aiello

who’s in the audience and she will be speaking later. And this was a plot which was published in a paper and this was a paper which looked at the relationship between brain size and other revolutionary trends. And it was this plot which gave rise to this notion that there was a burst, there was a period of relatively sudden increase in brain size of the origin of the genus Homo and then there was another burst of increase in brain size at the origin of the species Homo sapiens. But these data, the plot looks as if it is consistent with that interpretation, but the plot represents each value as one point. And the problem with the plot is that the data are subject to error. In other words, there is error in the estimation of the endocranial volume and there is error in the estimation of the age So what a bunch of graduate students did led by Andrew Du was to look at these data again. And so these are the data and it’s the other way around, in other words, the older data are to the left and the younger data on to the right. So theirs are also point there. But then if you add the error, the error of the age and the error of the estimation of the endocranial volume, you see that the data look rather different. Then when you do some very fancy statistics, which I was very tempted to pretend that I knew what they were but I decided that I wasn’t going to pretend that I knew what they were. And then they tested the data against various modes of change, random walk, or gradualism, or stasis, or punctuated equilibrium which was the hypothesis of the relatively sudden increase in brain size, and so on and so forth. They found that the mode which had much the greatest amount of support was gradualism. So in other words, the data if you account for the error of the age and the estimate of the endocranial volume, there is no evidence of a punctuated event. So how about diet? Well, this is work of David Pattison. And you can see here that there are three color bands. The australopiths that Bill is going to be talking about. So you can see they are in the light green band and then the first of the red columns represents the early evidence for Homo in the Turkana Basin which is either Homo habilis or it’s Homo rhodesiensis. And then the second of the red columns is the evidence for Homo in the Turkana Basin which is Homo erectus or Homo ergaster. So if the major grade shift was between the australopiths and the first red column, you wouldn’t expect the first red column to be where it is because these are carbon isotope values. So there is a shift between the first red column, in other words, Homo habilis and the second red column which is Homo erectus Here is David and he’s the one who’s collected these data. So if you look at this plot, you can see the blue squares are Paranthropus boisei who are living in exactly the same lake basin as what is alleged to be Homo habilis and widely accepted to be Homo erectus. And there is no change in isotopic signal or the Paranthropus boisei individuals, but there is a change in isotopic signal for Homo So there is a more C3 signal for Homo habilis and then there is a significantly different, more C4 signal for Homo erectus. You might say, “Well, that’s just because the environment was changing and everything was changing and Paranthropus boisei was the only large mammal that wasn’t changing.” Well, that’s not true If you look at all the other large mammals, they don’t change and Paranthropus boisei doesn’t change, it’s just Homo that does. So there is a dietary shift from Homo habilis to Homo erectus and the isotopic signal for the diet of Homo habilis is no different from the isotopic signals of the creatures that proceeded it and we call australopiths. So my suggestion is that we just should not assume that the interesting things were happening around the appearance of Homo habilis. My suggestion is no different from the suggestion we made in the paper in 1999, that most of the action is around the appearance of Homo erectus and it’s not around the appearance of Homo habilis Thank you very much ♪ [music] ♪ – [Carol] What I’m going to do is either it can be considered as a sobriety checkpoint or something completely crazy, but I’ve been given some might consider the enviable task of talking about the evolution of early human body form and

particularly in the context of understanding shapes of everything from the neck down associated with the origins of genus Homo. Now we have this idea about the transition from australopithecus to Homo. When we look at australopith skeletons we see they’re different from ours. They tend to be smaller in body size, males are much, much larger than females. We tend to see that they seemed to have shorter lower limbs, longer upper limbs. They have longer, more curved fingers and toes. They look pretty different in body form and we have the idea that to go from something like an australopith to something like us involved a series of changes that we see when we make a comparison like this. And sure enough, when we look at some of the early Homo erectus fossils like this beautiful Turkana boy from Kenya, he’s about 1.6 million years old. We see that he also seems to share some of those features of the post cranial skeleton that we see in humans and that he seems to have more human-like limb proportions with longer stronger legs, bigger lower limb joints, smaller upper limbs, thinner body form. So this transition has shaped our ideas about what the adaptive changes would have been to go from point A to point B. Because after all, if we’re trying to understand why and how our genus evolved, we need to know what changes happened. Did they happen together? Did they happen as a package, were some of the features evolving at different times in different places? Those are the data that we have to come up with our ideas about why it all happened. So when we look at something like this, we see australopiths here. They sort of had the stocky ape shape. They’re maybe living partly in the trees. And then we have these more savanna-dwelling, animals that may have been doing long distance walking and running, using fancy pants stone tools, all kinds of things But in terms of the post cranial skeleton, some of the features that we think of with this transition that fuels our adaptive ideas is have to do with changes in limb proportions, changes in lower limb joint size, changes in the shape of the torso, changes in body size and dimorphism or difference between males and females So what I’d like to do today is take you through a little bit of the evidence we have and there’s only a little bit to talk about so I won’t be up here very long, to see first of all was australopithecus different from what we think of as Homo as we thought. And I’m also going to talk a little bit about what we have from the earliest part of the Homo fossil record in the way of post cranial bones that may tell us something about what was happening. So we’ll start with australopiths because that’s the easy part, we have more fossils. If you open up any human evolution textbook you’ll see a picture something like this where you look at the body shape of the torso of australopithecus and you see this reconstruction. This is based on fossils done 35 or 40 years ago. There are more fossils that have come in to change our ideas a little bit. But you see, the stocky anamode with this cone shaped rib cage. If you connect the dots there and imagine the belly of this. Big belly, very stiff and immovable and this would shape our ideas of locomotion and how these things moved around and maybe even digestive biology and so forth. Well, we know from a whole lot of fossils that this probably is no longer really an accurate way to look at things. We have a number of different vertebral columns that show that the characteristic curvatures in the human vertebral column that holds us upright were present in early australopithecus There are lots of vertebrae in the lower back so they can stand up fully upright So they’re not that ape-like that way. And there are new fossils that are bringing new bits of data and I’ll show you one of those bits of data. This is a skeleton called Kadanuumu, it means big man. It’s an australopithecus male and he’s nice and big. And we’re very excited, those of us who care about ribs are very excited because it actually has some ribs. And you can measure the curvature of those ribs to say something about what maybe the rib cage would have been like. And you see, apes have this cone shaped rib cage of very sort of straight ribs. Humans’ curve around, give you this more slender barrel shape rib cage. You can measure this in Kadanuumu and you can see it’s right down here with humans and gibbons who also have this rib cage shape. Very different from something we see in great apes and data like these are giving us the picture that in fact the body shape of australopithecus may not have been so different from our own as we had long thought We also can take a look at limb length. We have this idea that australophitecus has more ape-like limb proportions, longer upper limbs, smaller lower limbs. Based partly on good old Lucy here, Lucy is teeny tiny so this is lower limb to upper limb. You can pretty much pick your favorite measure, it doesn’t much matter And you can see that chimps and gorillas here have bigger upper limbs than humans for their lower limb size and Lucy seemed to fit that picture. But new data like these ones showed here again from Kadanuumu show that once you get larger and fat, australopithecus don’t really have very short legs. They maybe have longer arms, but they don’t really have short legs. And Trent Holiday and other people have done similar analyses to suggest that maybe the lower limbs weren’t that much shorter than australopiths, they’re just littler animals. So they may not be as big a change in limb length from australopiths to Homo as we have thought Another thing we’ve learned recently comes

from the foot. An ape has a foot with not just a grasping big toe, but the whole thing is flexible, so it can wrap around branches and hang on in the trees. Whereas our feet are very stiff and they form a nice propulsive lever to move us forward when we walk on the ground on two feet, and that propulsive lever is supported by arches that go from front to back and side to side that are built into the structure of the bones of our foot. So one we lift our heels off the ground, they stiffen up and they let us work well. We’ve known for a long time from fossil footprints that australopithecus did not have a grasping big toe. But recently, Bill Kimble and his colleagues found this bone from the middle part of the foot, it’s called a metatarsal and it shows us that the australopith foot, just like what we see with maybe Homo habilis or Homo erectus, had nicely developed arches from front to back and side to side, a fully modern human foot really well adapted for long distance travel on the ground. So this isn’t really maybe as different as we would have thought a long time…or a number of years ago as a difference between australopithecus and human And if you blow up an australopith to be about the same size you see this really fairly human-like lower limb, fairly human like body shape, and some of the other differences maybe a little bit less dramatic than we thought. So maybe this transition isn’t as dramatic as we thought from the australopith side. What can we now say about early Homo? We have now 2.8 million years ago we see the genus Homo appear based on this jaw. That’s only a couple of hundred thousand years after Lucy was roaming Ethiopia and it’s a long time ago, but it’s just a jaw. I’m going to talk about the post cranial fossils associated with the origin of Homo. Right, I’m done now. Thank you, have a nice day I’m out. So let’s take a look at what we actually have. We have quite a number starting around two million years ago There are a whole lot of isolated post cranial bones, bits of thigh and arm and this and that and they’re great. But without heads and teeth we can’t tell what species they belong to. So they’re not as useful to us as we’d like. What about Homo erectus? Well, when we find bones that are associated with the heads and teeth we can tell what species they belong to. These are three skeletons and as you see as you move over this way, I’m using the term pretty liberally, associated bones of Homo erectus from the beautiful Turkana boy 1808, 803 from Koobi Fora. But these are all about a million and a half years ago That’s over a million years after the origins of the genus. The Dmanisi fossils are a little bit older, 1.8, but that’s still a million years after the origin of the genus Homo. Well, what about the other early Homo species, habilis and rudolfensis? These are the associated skeletons we have for habilis. Looks a bit like they were hit with an artillery barrage, somewhat underwhelming but they’re a little bit older. Koobi 42.0, Olduvai Gorge 1.8. There are some post crania from the type side of Homo habilis The association with actual habilis has been questioned by some people so they’re a little bit less certain in terms of their taxonomic assignments but they are there too, so we have some of those What about Homo rudolfensis post crania? That’s all we’ve got, right? We know absolutely nothing about its skeleton which is unfortunate. And so this whole exercise is a bit like trying to squeeze blood from turnips which either means it’s really, really hard or it means I can make anything up and there’s no data to falsify it. That’s all fine, too. But what can we actually say about that supposed set of characters that may seem to have gone together with the origin of Homo. Well, we can take a look at maybe body size and Mark Rabowski and colleagues published some new body size estimates and is there really a difference between australopiths and Homo? Well, when we look at australopithecuses we see there’s a pretty good range in body size. They’re not particularly large, they’re all fairly similar. And when we look at Homo habilis just a little bit more recent in time, we only have a couple of specimens but they fall right in that australopith range; not particularly large. When we look at some of these Homo erectus fossils that we know are Homo erectus, even the Dmanisi sample’s really about similar to australopithecus, you start to get a little bit larger individuals but remember again this is 1.5 million years ago. This isn’t very early in the evolution of the genus. And so maybe we’re saying, “Ah, here’s one that’s trended increasing body size happens.” But we can look at the size of some of these isolated fossils and here’s a fossil I’m going to talk about a bit. It’s a partial pelvis called 3228. It was from somebody who is about as big as the Turkana boy and it was 1.9 million years ago. So what can we say about this? There doesn’t seem to be a great trend in early evolution of Homo in either range of body sizes or absolute body sizes. So we’re not seeing anything really dramatic happening early in the origin of the genus with body size and dimorphism Well, what about limb proportions and body build? Well, when you’re looking at the oldest things like habilis it’s a little hard to do limb proportions when they’re pretty fragmentary. But what Chris Russell was able to do is instead of looking at bone length he was able to look at the bone strength

And if you compare it to chimp, you take the leg to the arm here and you see they’re pretty similar in strength. They plot out about like this. Humans, the lower limbs are stronger than the upper limbs so they plot out up here. And he was able to take these measurements for at least the OH 62, the one in black here, and put them on the graph with some Homo erectuses and what you see is these two Homo erectus skeletons are very human-like in their strength proportions, but Homo habilis is not. Homo habilis seems to have a different build. And actually when you take the very few measurements you could take on this scrappy specimen, it also seems to have a little bit larger upper limbs relative to lower limbs than we tend to see in humans and maybe in these Homo erectus. The Dmanisi sample, interestingly, doesn’t seem to have the sort of proportions. It seems to be more like the erectus although the same studies haven’t been done. So there seems to be some sort of a difference here between habilis and erectus perhaps in body proportion, given how fragmentary the fossil evidence is. This is an interesting fossil I want to mention because Meave Leakey and her colleagues found this in 2009, actually fit on this bit was found in 1980 which is kind of cool. And it’s associated piece of pelvis and femur, but this captures the hip joint. And the hip joint is interesting partly because we have a bunch of them in the fossil record but partly because the hip joint seems to be a place that there isn’t a lot of difference among these early Homo species as best we can say. Here’s athe3228 pelvis again. In this pelvis shows a series of features that we only see in humans, we never see in australopithecus, so it’s not a bad hypothesis for a Homo. These two are almost dead ringers for one another but this one is just much smaller. So either these are a male and female of a really dimorphic species or they’re two species that happen to look the same. But they’re both 1.9 million years old so they’re nice and early. Well, when we look at those Homo-like features, we see them in this 5881, pardon me, this new specimen here So here’s Lucy and you look at the front border of the ileum, part of the pelvis it’s straight and every australopith we have is bent in every Homo that we have and it’s bent in 5881. When we look at the ileum from the side you could see this buttress called the iliac pillar here is more vertical and set back from the edge of the bone and it’s big. In the Homo pelvises, it’s very weak in every australopith and angled right into the front of the bone. In 5881 here is looking like Homo. So this looks kind of like a Homo sort of a creature. When we look at the other side of the hip joint at the proximal femur, every time you see an australopith that has a relatively small femural head. So relatively small hip joint. You see that in the pelvis too, where Homo, including modern humans, have a much a larger femural head. 5881 needs a little bit of digital reconstruction which you can do actually for quite accurately using CAD software, it also would have had a large femural head, and we can see them in the pelvis too. And it’s interesting that every femur we have that seems to be Homo, attributed or not, has a big femural head. In every australopithecus we have which is associated with post cranials has a small one. So this seems to be a feature that characterize all Homo, not related perhaps to body proportions. So changes in body proportion, change in hip joint size don’t seem to co-occur in early Homo Well, again, squeezing blood out of more turnips here, we can come back to our bone cross sectional shape. And this is more work by Chris Ruff Mosley, so you can take a femur, you can slice it open in the middle and you can look at these sections And everything we have that we know or suspect is Home erectus, actual Homo erectus that we have data for has this mid shaft femur is very wide from side to side and short from front to back. And it has a really indistinct marking on the back of the femur for attachment of muscles. When you put Homo habilis on there, it’s a very different shape; rounder and it’s longer from front to back. 5881 is a dead ringer for OH 62 in this feature and they both also have this big, thick attachment here for those thigh muscles So, ah, you say, maybe this is Homo habilis, maybe 5881 is habilis, that’s great. But if you put data that Phil Whitemyer kindly lent me from the Dmanisi skeletons, they are actually shaped like the habilis also. Now either this says that Dmanisi is not Homo erectus which I really wouldn’t want to say based on one character here, or something else is going on. Chris Roth’s idea about the explanation for these differences is that in Homo erectus, when the pelvis gets bigger to accommodate larger brains, the whole body gets wider and that puts more medialateral bending stresses on the bone and so they’re wider to accommodate that So that this shape would indicate a narrower body form than this shape. Well, we can look at little bit of pelvic shape and turn 5881. You can take this curvature here which gives you a little bit of an idea of the inlet. You could see australopithecus very wide, a little wider in Homo erectus and then these are later Homo things, but 5881 it seems to be narrower, which seems to fit with Chris’ hypothesis about the explanation for the

femural bone shapes. In which case, perhaps then, Dmanisi may have had a narrower shape than we see in East African Homo erectus. Does this mean it’s not Homo erectus? It’s hard to say. Remember that Dmanisi individuals are 300,000 years older than the Homo erectus individuals I have on this graph. That’s a long time Think about what happened in the neanderthals and humans in the last 50,000 or 100,000 years. So this could be something happening through time. It could be species related. It’s very hard to say given how scrappy the fossil evidence is But it does say that some of these characters aren’t necessarily co-varying and there seem to be different morphotypes within the genus Homo. All Homo doesn’t look like all the other Homo from the neck down. And that’s an important factor to think about when we then constructing our adaptive explanations for what’s going on in this transition from australopithecus to Homo. So we have these creatures that may be not quite as stocky as we thought The lower limbs may have been much better adapted for decent amounts or quality of travel while on the ground, and they may not have been as ape like as we’ve previously thought with australopithecus. When we look at the earliest Homo, we may see at least some that may have even more apey limb proportions than we see in australopithecus. We see that the combination of features of having larger lower limb joints, of having larger limb joints, longer lower limbs don’t necessarily co-vary. Limbs were already long, hip joints may have been gotten big at the beginning of Homo, it’s hard to say. Body form may have evolved differently in different species and/or at different times. But we no longer have this idea of one change associated with the origin of the genus. And these well adapted features that we see here that make this complex, that make Homo erectus great that do things like hunting and tool using and everything later, may be something that weren’t associated with the origin of the genus but came in much later. So in fact, if we compare australopithecus to earliest Homo, this might be a more reasonable picture to have in our mind. Animals that weren’t really very different especially from the neck down, weren’t really different in locomotor capabilities. If I had more reconstructions of different Homo species you might have seen them look a little bit different from one another. But basically, the picture is that there’s not a dramatic change here in the origin of Homo that has anything to do with the post cranial skeleton. Perhaps the adaptive changes associated with the origin of the genus had to do more with diet, other behaviors or something else. And that’s what we need to be thinking that what happened to the origin of Homo to give rise to all the other great things that we’ve been hearing about today. I say thank you ♪ [music] ♪ – [Leslie] So, one thing that I sort of noticed this afternoon is the number of times some of my earlier workers have been criticized and that’s good, that’s normal It shows how the field is growing and developing and building. And I’ve been asked to talk about the evolution of human life history patterns. And this is also a reasonably new approach to study in human evolution and we can understand a lot about the evolution of the genus Homo by looking at life history and by looking at modern people. So basically, life history is more than just looking at the evolution of the physical body form. What it is is looking at how we got to this body form Life history is your tempo and mode of growth and development. And if you look across the primates, you’ll find a variety of different patterns. And if we delve a little bit into life history, as I said, we can learn a tremendous amount about ourselves. And it starts out in childhood You have a difference in the growth and development pattern that’s very obvious For example, chimpanzees all mature by the time they’re about 12 years old. For humans it takes up until your late teens, 17, 18 years old. And our colleague, Barry Bogan, has been very clear about the tempo differences that you have if you compare a chimpanzee with a human. The chimpanzee graph there shows that you have a rapid decline in the velocity of growth. A relatively small plateau period, that’s the juvenile period. And then another relatively rapid decline in how fast you’re growing. Humans are very different in the corner. We have that same decline in the velocity of growth but we have a much longer plateau period where our children are not growing very rapidly. And this is followed by the adolescent growth spurt and then it falls off again. This pattern is very unique and it’s very important to our evolution

The last graph is from the work of Kristin Hawkes who’s here in the audience. It shows you not only do you have the difference in the pattern of the growth but we also have a very much longer longevity or life span. Now what I find fascinating particularly about the early childhood growth is that it has a lot to do with the brain. We know that humans have brain sizes about three times the size of a chimpanzee and that brain grows and develops at different paces in the two species. Now in humans, as a child is growing, a very young child with a huge head uses about 60% of the energy budget just to support that brain size. And as we grow and our body begins to grow, the brain growth slows down and the energy balance tips. One of our colleagues, Chris Kozawa, has come up with I think is a brilliant look at the relationship between this brain growth and body growth. In these graphs, the red line, one for males, the second graph for females. The red shows the energy that the brain takes as you move from birth up through five years of age that is one of the most energy expensive periods of brain growth in childhood because of all the mileazation that’s going on and then it drops off. The blue line is the velocity of your somatic growth, your body growth. So basically there’s almost a perfect play off between brain growth and somatic growth. And this goes terribly long ways to explaining why we have this extended period of childhood that basically correlates and is a necessary correlate in energetic terms with the growth and development of the large human brain cells Now we all may think this is fine and good but it’s actually not. So some of our other colleagues from Switzerland, Karin Isler and Carel van Schaik have developed something they called the gray ceiling And what the importance of this is you can just take so long in your growth and development or you aren’t going to be able to replace your population size. Now think in terms of dependent childhood and if a child is dependent on a mother for five years, six years, seven years, she’s going to come back into fertility. You’re going to extend that inter birth interval. You aren’t going to be able to have enough surviving children to replace your population from one generation to another generation. Okay, this is what they call the gray ceiling. And if you look at the graph here, there is a lot of primates The red dots are the apes with the increasing brain size. And what this shows is that with some of our apes like the orangutans, the gorillas and all, what they’re arguing is they’re hitting the gray ceiling and the only way to avoid that gray ceiling is to somehow increase your reproductive output. Now if we go back to that same little chart I chose earlier, at the bottom is the period of infancy. And in chimpanzees, infants are dependent on their mother, they’re still nursing. They are four to four and a half years old before they’re weaned. In humans, it’s of course very much shorter and this particular graph shows about two years, it varies. But what the take home message of this is is you can have twice as many kids if you shorten that period of infancy And if you then shorten your interval between birth. Now again you may think this is fine, this is a good trick, we’ve all developed it, but it has tremendous problems. And I’ve got this picture hanging in my office and whenever I think I’m having a hard day I think of her Because what you have once you start to double up this is you have a woman who may be pregnant. The infant that she’s probably in the last stage of nursing and a dependent kid. And she has to get the food to support her own large body weight, her own large brain size, and to provide all of the calories for the kids she’s nursing. She has to provide the food for the young infant. Now this is very different from what we see in the

chimpanzees or other apes where mothers focus on one infant. And once the infant has stopped nursing they will gather their own food. There’s very little energetic involvement with the mother. Now this is a huge paradox and this is where the evolution of sharing and cooperation comes in. And of course this is where we have the grandmother hypothesis and the argument that a lot of the extra resources for the grandkids come from the grandmother by provisioning the mother and the kids. Now there’s a number of other arguments also that involved greater cooperation among all individuals in the society, males as well as sibling care and sibling cooperation. The take home message is that once you begin to develop a large brain size, you have growth and development implications And these growth and development implications have implications for the evolution of what we would recognize as a human type of cooperative social organization. Okay, the big question is, can we tell when this all happened in human evolution? And we’d like to think, oh, this is a characteristic of the root of the genus Homo, that’s a hypothesis Now if we go back to the evolutionary tree, we have one way into this in terms of cooperation. And if we go back to the gray ceiling and I know Burden isn’t going to like my brain size against a million year graph. But if we put the gray ceiling onto this and again what Isler and van Schaik argue is that gray ceiling is about 700 milliliters. Now of course there is, you know, big ranges of variation around this, but what’s interesting about this is this just about divides our Homo erectus from the earlier hominids. And if we put it on our evolutionary tree here, it comes at this very interesting time between two million and one million years ago where you have a proliferation of hominids, a variety of different species, and you have this big variation in the brain sizes that we have. Now as we’ve also heard, this time period correlates with the radical change in human adaptation. And particularly in evidence for the precedence of animal based tissues in the diet, it also correlates again with our Turkana boy here and this general time period where you have the evolution of what we call Homo erectus. Now what’s interesting about this also is it also correlates with the time period where hominids begin to move out of Africa So our question here is how much does this cooperative behavior that we can infer from the brain size and we can refer from the life history really affect the hominid’s ability to adapt to a variety of different habitats not only in Africa but also throughout the world? Now the only direct evidence we have for any type of cooperation comes from the side of Dmanisi and our friend here with no teeth. And I’m sure it feels very familiar with the argument that this individual must have whatever you want to argue, been taken care of. The message from this is we don’t really know how to recognize this cooperation in the fossil record. It would be very nice if we could. Now if we come back to the fossils, is there any way from the fossils we could tell what their tempo of growth is? And in this case, one of our colleagues, Chris Dean, has been working on how to infer growth and development from the formation of the teeth. I’ve been very impressed by some recent work by Chris and his colleague, Helen Livesidge in London. Not on teeth this time in particular, but on body size because what Chris has done is sort of bracketed the age of our Turkana boy at death to somewhere between seven and eight years old. Now what these graph show were really startling to me because the green one is stature. And the histogram is the stature of modern human kids who are between about 7 and 10 years old. The red line there is the estimate for the Turkana boy. It’s way in excess of the stature that you would expect. The blue is body mass or body weight. Again way outside of what you would expect in modern human kids

Now what does this tell you about the growth and development of the Turkana boy? If we go back to Barry Bogan’s figures, what it’s telling you is that the Turkana boy was growing on a trend very much more similar to the apes than to modern humans And if you look on the chart, in fact just above age there on the chimp chart is eight years old. And you’ve come out of that plateau of slow growth velocity, the individual would be then growing towards his adult weight. In humans, it would be still well within that plateau before that growth explosion, that’s the adolescent growth spurt. Now this, to me, is very convincing evidence that the Turkana boy was not growing and developing on the human pattern. Now what that would mean is that it would reach maturity much more rapidly than if it was growing on the modern human sort of tempo and mode. Now is there anything more we can tell? Your eruption of teeth tends to still also measure how long your growth period is And what’s become very clear recently is there’s a tremendous amount of overlap not only between living human tooth eruption and tooth formation patterns and apes, but also overlap in the fossil hominids. And when it comes down to it, if you’re looking at tooth formation, your best tooth in terms of distinguishing us between the chimps and humans is your third molar. But again the take home message from this comes in the bottom graph. And the blue line there is the tooth development for your second premolar and that’s in the chimps, the red one is in humans The vertical lines are your early Homo fossils. The green one is the Turkana boy And although the teeth are developing at the very, very fast end of modern humans and there’s a tremendous amount of variation, it’s squarely within the ape pattern as well. And if we’re going to argue about what the life history patterns of some of these early Homo are, basically we’re talking about a much more ape-like growth and development pattern than a human-like growth and development pattern Okay, the next questions comes in is when did we start to grow and develop as humans? And the first indication is with Homo antecessor which is about a million, not .9 million years old. The teeth are still developing more rapidly than ours, meaning they’re developing more rapidly But the argument is made that the first ones that are closer to modern humans than to the early Homo, the early australopithecine pattern. And then as we move up to the top at about a 160,000 years ago at the Moroccan side of Jebel Irhoud and this is some of some John Jack Hublin’s and his group right there in the fourth row, where you have a very modern human growth and development pattern. Now what I want to do is sort of finish with what is probably everybody’s favorite fossil and that’s the neanderthals. And they’re a long way up the record from what we’re talking about in the evolution of the genus Homo. But I think the lessons we can learn from the neanderthal growth and development, we can usefully bring down the record and apply to some of the australopithecines Now neanderthals of course are the alternatives to modern humans. They have brain sizes that overlap with ours. They are in the blue series of Xes there. They lived in Europe during the last ice age while anatomically modern humans were evolving elsewhere in Africa. What, again, another piece of evidence that struck me that comes out of Martin Gonzales and some of his colleagues’ work from Spain is the growth and development of the little neanderthal kids. So the blue lines here are your growth from not years, up to 70 months. The horizontal lines are the equivalently aged neanderthals in relation to that modern human growth pattern. So

here you can say the little neanderthals are basically plateauing much earlier than you would see in the human growth curve Now think about being a neanderthal. I’m often happy I wasn’t born a neanderthal because, you know, what the authors are arguing here is not only do they have the energetic stress of growing and developing that large human-like brain size, they also have a serious thermoregulatory problem. Because in fact with Steve Churchlin I’ve done some modeling on the energetic requirements in neanderthals and it’s about the same as to say somebody riding the Tour de France in the Alps It’s about 500 kilocalories a day. And you think of these poor little neanderthals trying to support that brain and also keep warm. Now there is a second piece also that comes from other research This is from Smith et al in 2010. And the green lines here are your expected and predicted ages for human teeth and the blue lines are the neanderthals. The take home message is their teeth are developing more rapidly so they have a more attenuated growth and development process Now coming back to this and where you would expect to say a modern human populations to have more rapid growth and development. It’s in situations where you have a higher mortality rate. Now think about these poor neanderthals, they have a very high mortality rate, every three calistosis. It’s the same as rodeo riders in the southwest. And you have these poor little stressed neanderthals with a shorter body size. Now if we come back to all of our, you know, fossil species, our australopithecines and early Homo, living in a period of very fluctuating climate in Africa, and this little zig-zag chart is just from East Africa, but also experiencing all of these environments around the world. What we really want to know is what their growth and development patterns are and how these reflect what’s happening in their lifestyle. And what I tend to think is that the same processes that affect us today were also affecting them. And this is a huge challenge, it’s very exciting research and I think as soon as we’re able to screw down into it, we’re going to find similar neanderthal-like patterns among the hominids that are living different types of lifestyles. To end, I’d like to thank CARTA We were all having a great time here. And I’d particularly like to thank all of the attendees of a Wandergrand conference, some of you are sitting in the audience here, that we held on human biology and the origins of Homo. And a lot of these life history ideas were developed in a week-long meeting in Portugal. So thank you very much ♪ [music] ♪