For word. If it happens here or here or here or anywhere that matters america is watching on cspan, powered by cable. Jeremy desilva is an f apologist and editor of and is the editor of a most interesting problem what darling darwins descent of man got right and wrong about Human Evolution hes part of the Research Team that discovered two ancient members of the human family tree , he studied wild bees in western uganda early human fossils in museums throughout eastern in south africa from 1998 to 2003. He worked as an educator at the Boston Museum of science. Kate longest Senior Editor at scientific american, writing about the evolution of humans and other organisms for the magazine since 1997. She is coauthor with Donald Johansson of the quest for human origin. Tonight theyll be discussing jeremy desilvas new book first steps how upright walking made us human. In it desilva explores the history of bipedalism, the ability that makes unique humans unique among other animals to walk on two legs and he makes the case that it allowed for the evolution of humans despite the difficulties imposed on the genome ever after. Publishers weekly praises desilvas love of fossil discovery and collaborating with colleagues come through in the wonderful experiences that examiningbones first had. His ability to turn anatomical evidence into a tale of Human Evolution and his enthusiasm for research would leave readers informed and uplifted. Im going to turn things over to our speaker jeremy and kate. Thank you, i appreciate the introduction. Locate. Great to see you, thanks so much and to the Harvard Bookstore im delighted to have the opportunity to pepper jerry with questions about his new book which is about all the things that i get most excited to write about. Its really a pleasure to be here and i thought maybe jeremy we could sort of take off the conversation by having you tell us why, i mean, humans have a number of traits that separate us from other mammals, other primates. We have naked bodies, large brains and language so white focus on bipedalism . Is a great question. Like you said, we have these differences. We have lots of similarities to our mammalian cousins and our primate cousins but we have these differences as well. Upright walking is one of those. Mammals fly and swim and sprints andleap. Monkeys walk and climb. Your typical mammal moves around on all fours, think about a dog, cat, squirrel moves around on all fours but only humans will navigate the world on their extended hind limbs all the time. Its our very strange way to move and went another mammal does it, we kind of lose our minds. We take out our cameras and videotape and posted to youtube and it gets millions of hits. I was in researching this book i found examples of bears moving on two legs in newjersey. And there have been almost 5 million views of a bear walking on two legs through ov this new jersey suburb. A gorilla in thephiladelphia zoo , lewis and walking on two legs occasionally, not frequently and someone got a video of it and it ended up on the cbs news. So something that we do all the time, we even use the word pedestrian to describe something ordinary went another animal does it its remarkable. But not only that, but fossil record which is what i work on, imkapparently all oncologists. I study fossils. And what we can tell by going back in time to the common ancestor that we shared with our cousins, the further back we go we start to lose some of these unique characteristics, the large brain, evidence of language, those things happen more recently, stone tools whats the most ancient characteristic we think on our lineage is this ability to move on two legs, so not only is it strange as a metal but its the most ancient thing that we evolved. Its sort of set our lineage off and what i argue in the book is that its was the key innovation that led to many of those other anatomical and Behavioral Changes that made us human. Thats a really interesting lens through which to view the entire 80 of Human Evolution in a sense. This might sound like a weird question but thinking about this from a biomechanics standpoint, upright walking we do it all the time. We take it forgranted. And we dont really think about it. So what is special about it from the standpoint of biomechanics, can you describe the act of walking on two legs and whats unique about it, how do you sort of conveythat . Its a balancing act moving on two legs. Think about when i talk to my students about, imagine if i give you an assignment to design me a chair, youd probably design it with four legs. And there might be some clever students that make a barstool and make it out of three legs but if you make a chair out of two legs its probably not going to work and im going to sit in it and go all over the student will fail the assignment. To lead locomotion is pretty unusual way than for a metal to move around the world today. We can get into bird locomotion at some point and then deep in the past we find evidence of bipedal is an in dinosaurs and even in an ancient crocodilians lineage which is fun to think about. But from a biomechanical standpoint this is about p balance. And what we can see and one of the ways we can identify fossils as coming from things that are adapted move on two legs is because they have these specific shapes to them , these individual loans that would align the joints in a way that would prevent us from tipping over or would change the action of certain muscles so that those muscles would d act in a way to again prevent you from tipping over , one of the classic examples is a hit joint that when you take a step and lift her other leg you fall over. And when a chimpanzee walks on two legs its exactly what they do, they wobble from side to side. But in humans we evolved our pelvis so heres a human pelvis. Lv weve evolved of pelvis where the muscle attachments here have wrapped around the side of the body and binding on the side they then it will interact that every time you take a step. So if you find this part of the body and it looks like this you can tell you have something moving on two legs so kate, you know lucy very well, years lucys pelvis and sure enough shes got those hip joints arranged in a very humanlike way. So even if this was the e only part of her we found we y. Would be able to tell that she was able to balance on a single leg and what else do that unless youre moving around on twolegs. But from a biomechanical standpoint, and really connecting it to Natural Selection, its not a great way to move around your world. We are incredibly unstable on our two legs, we fall a lot. And that can bequite dangerous, theres 30,000 americans who die every year from falling. And in addition to that we are stunningly slow. For a mammal. The fastest human who as far as we know has ever lived, the fastest he ever ran was 28 miles an hour in his hundred meter dash in 2009, his world record 28 miles an hour is impressive and it is, i couldnt come close to that but its half the speed of a galloping zebra. After speed of a galloping antelope and perhaps more importantly half the speed of a lion and leopard so evolving this form of locomotion made us slow and so it raises some interesting questions of in what ways was this beneficial . And allowed us to overcome some of those maladaptations i suppose you can even frame it as just lack of speed. You anticipated my next question which is why evolved this, what seems on the surface to be a subpar way of getting around and so i know theres been a lot of scholarship over many decades and with people coming up with all kinds of ideas about why we could come to how this unusual kind of locomotion and theres some really interesting ideas going back as far as lamarck and darwin and icon it would be fun to take a nickel tour through some ofthose ideas if you wouldnt mind indulging us. Its one of those things where if it was another mammal that moved on two legs regularly, we be able to test this more effectively, we be able to do science and say what does this other mammal do, what does it eat or whatever its mating patterns or what ecology does it live in that in which this form of locomotion is beneficial. So as a scientist when youre trying to figure out something by yourself you always want to out into the Natural World and say where else do we see examples like this and the fact that we dont have other mammals that have actually walk around on two legs makes us a really difficult scientific problems to solve and its one of the reasons we have insulted in that you can go to lamarck and take it right edup until 2021 people are still hypothesizing why bipedalism was selectively advantageous for our ancestors. Youve got ideas of crafts and this goes back to lamarck, he was interested in humans being able to stand and see off into the distance. And with that one, if you look off into the distance and you see a predator the worst way to get away from it would be bipedal he, youd want to be down on all fours and gallop away because you be muchfaster. So that one hasnever made any sense to me. There are ideas about of course darwin saw this connection between our small canine, are bipedalism and tools. This was about freeing the hands for tools and that becomes somewhat problematic although i think its an interesting idea of worth revisiting but because problematic because of the timing that we have evidence for bipedalism in homonyms that are 7 million years old, terrestrial bipedalism and we dont have evidence for stone tools until 3. 3 billion years as reported evidence for stone tools and then why wild ideas about displaying genitalia, some sort of showing off of your body for selection, there are ideas that are a little more reasonable and testable having to do with food sharing and if you can free them and not to make weapons or tools but to gather food, there is some ideas that have been promoted where the females are gathering food and sharing it with others, thats nancy cantors idea and on lovejoy that argued its the males that were collecting the sharing it with potential mates. An idea that has had a little maybe more lasting power is energetics, moving on two legs yes were slow but we are energetically very efficient tand one of the best ways to explain this is herman ponce are and i talked about these ideas and he said that in order to lose a pound of weight you have to walk about 30 miles. Because were too good at it. Where to energetically efficient. So now you dont want to lose weight if youre early homonym if you need to get enough food to survive and maybe theres not a lot on the landscape, those individuals who are moving away energetically efficient might survive a little better. So thats possible idea as well. There are lots and lots of offices. We still dont have a handle on it and thats okay. There are going to be plenty ndof things that new discoveries, new fossil discoveries will allow us to go back and revisit some of these ideas. And really the issue for me is not s. Figuring out which one is right, its beginning to narrow hethe list down to the onesthat are clearly wrong. Thats how science works im refuting ideas rather than proving them. So we dont know yet why bipedalism evil but we do have a lot more information than we used to about the timeframe in which he falls. So maybe we could talk about some of the fossil discoveries that have really kind of allows you and your colleagues to start to piece together when this all happened. And you know, what it might have evolved from and where it took us. A lot of folks listening will probably know about lucy discovered in 1970s and lucy is just a magnificent partial skeleton. Ive got the cast of her, the original is in ethiopia of course and not long after lucy was discovered there were footprints found at the site in tanzania where i do some of my research as well. And that pushed idealism back to about 3 and a half million years ago. Those were remarkably important discoveries showing humanlike bipedalism existed 3 and a half million and yet the genetics would point point towards a common ancestor we shared with chimpanzees at about six or 7 million that the split between the two lineages is probably complete by 6 million years, thats a big gap 3 and a half million to 6 million whats going on in that timeframe and in the last 20 years there have been easily remarkable and wonderful and important discoveries that have been made and beginto piece that story together. One is a partial skeleton like lucy from ethiopia thats four and half million years old and its orthopedic s and article because of some of the key morphologies of the pelvis and the foot. That would indicate that at least and was occasionally able to move around on two legs when it was on the ground that it also has a big grasping tow in the foot so this is an excellent tree climber, long fingers and its a really good tree climber when it came down to the ground that it not call walk, no, it appears that didnt and it could actually move on two legs thats 4 and a half million now we get something thats bipedal and as you go further back than that the evidence becomes much more controversial and a little more difficult to interpret. This is toga from a 5 and a half millionyearold homonym from ethiopia and it matches the shape especially the end of the bone of the human tell what was off the ground when youre walking whereas the chimpanzee until actually curves in the ofother direction this has on furniture to it definitely had some time on the trees but it hasnt angulation to it like yours and mine meaning it would probably have been able to push off the ground so this is a cool fossil isjust so , it would be nice to have more. Heres a beautiful fever from kenya thats 6 million years old and whats unique about this one if you compare it to the chimpanzee, heres the chimpanzee. They had or the ball part of a joint is very similar but look how short the net is on the chin and how long that neck is on this fossil. What that would do its similar to what i was talking about earlier ourepositioning those muscles so you can balance on a single leg bite on those muscles farther from the youre making them more efficient. And we think that anatomy is evidence for bipedal locomotion in what we call fossil from lauren and if we go farther than that 7 million years theres this remarkable soul discovered in chat and its very controversial, the researchers who founded and first interpreted it argued that the whole base of the skull abor the spinal cord with a brain was in a very humanlike position and therefore e this creature would have been able to hold itself upright and maybe even walk on two legs. We dont walk with our heads and went to see fossils from other parts of the body and there is a femur now that has been published by one team and another team has a free printout and they come to completely print conclusions on whether this is an upright walker or not. And to me e , as you converge o a common ancestor of humans and chimpanzees youre going to get something that is not quite like any of those living ace and is a fabulous commendation and maybe frustrating commendation of anatomy that is difficult to rinterpret. Its kind of what you might expect in a common ancestor. Do you think this femur looks like that of a biped or no . Ive not been able to. I like to talk about fossils ive been able to see this is not a fossil ive been able to see myself. And however, there are even older fossils now that are, we dont have much from 8 million, 9 million, 10 million but theres this New Discovery from a site in germany and germany sort of like might sound surprising to some of the folks listening because weve been talking about africa but in the late miocene dates expanded all around the mediterranean. What is today the mediterranean and were living in forests of europe so we find a fossils and pain and france and germany, turkey and hungary. This new fossil from a creature called the new bs from 11 and a half millionyearold deposit in germany looks like its very upright. And to me thats a really interesting find because could imply and were still trying to figure this out. Its one of the hottest topics in our field right now of what is the body form from which bipedalism evolved, there are a lot of tshirts and coffee cups and bumper stickers that would suggest agent turned into a human. And chimpanzees are not our ancestors, they are our cousins. The common ancestor is a that we branch from but so did chimps and chimps have evolved to is not a given that common ancestor was a knuckle walker and some of the fossils that were finding in those deposits might indicate that the common ancestor was actually more upright in the trees that knuckle walking could be more derived form of locomotion. There are plenty of researchers, many of my colleagues disagree and think knuckle walking is the form from which bipedalism evolved and they have made compelling cases we need more fossils to figure this out. Is a revolutionary idea so its fun to think about that. If bipedalism is a uniquely homonym traits and the new bs at 10 million years old is biped, is he potentially a homonym . I dont think so i dont think the timing is right and i think the genetic data showed very clearly when these ages were writing. Having said that there are big air marks around these divergent states but i think you raise an important point that our field has always operated on the assumption that if you find anything that shows characteristics of upright locomotion that it is automatically by definition a homonym meeting its an ancestor or a relative of us and it would be more closely related to us than any other of the apes. And i think that assumption is on the table. As maybe not being 100 percent correct because if you had in the late miocene apes experimenting with different forms of locomotion including upright asymmetries navigating in the trees they might have some anatomies that look a little more humanlike. For instance the tibia in some ways looks very much like lucys. And that is telling us about leg positioning not necessarily weightbearing on a terrestrial bipedal leg but an animal thats moving with hand assisted bipedalism like orangutans sometimes do, gibbons will do this. Spider monkeys will do this. But right, it would mean finding evidence of bipedalism may not be enough anymore to claim hominem status. As we find more fossils from that five, six, seven, eight, 9 million year period were going to see lots of experiments going on with locomotion and lots of false starts, lots of places where bipedalism may have been attempted i say but may have evolved and then that animal died out. It just was not a selectively advantageous form of locomotion at but as the habitat changed so we will see, it will be fun. We talked a little bit about what the fossil record shows us about the origin of bipedalism but you mention this briefly, there are other r kinds of theories we can look at to sort of study the emergence of this kind locomotion and you mentioned like totally which is a place ive always wanted to visit. It seems like the most iconic site even just thinking abou