very remote. you can't risk it. yes, it is entirely possible that avery could have another shot but she is no guarantee and the desperation that follows that is something i felt, that when i finished law school and my family, we were very economically precarious i was the first one with real money, and i could make -- couldn't make mistakes. i couldn't stumble and cost us this one opportunity. amazing siblings would all do well eventually but you don't know it for sure. the sense of responsibility i think is one part of what i wanted to imbue in my character but also want to create space for anyone else who's thinking about do i take risks? like what is at stake and what am i willing to jeopardize to do what i think is right? >> to watch the rest of this program visit our website booktv.org, use the search box

to all of her c-span appearances. >> jeremy desilva is an apologist at dartmouth college and editor of a most come rather a most interesting problem, what darwin's descent of man got right and wrong about human evolution. he is part of the research team that discovered and describes to make engine numbers of the human family tree. he studied wild champ these in western uganda and early human fossils in museums throughout eastern and south africa from 1998-2003. 1998-2003. he worked as an educator at the museum of science. kate wong is senior editor at "scientific american." she has been writing about the evolution of humans and other organisms for the magazine since 1997. she's also co-author with donald johansson of loose his legacy, the quest for human origin. tonight they will be discussing

"first steps: how upright walking made us human." in it he explores the history of the ability unique to humans among living mammals to walk on two like speaking makes the case bipedalism was the crucial change that allowed for the evolution of humans despite the difficultieses imposed. publishers weekly prices his love of fossil discovery and a collaborating with colleagues come through in the one expenses and examining bones firsthand. his ability to turn anatomical evidence into a focused tale of human evolution and his enthusiasm for research will leave readers both informed and uplifted. i am so pleased to turn things over to our speakers. the digital podium is yours, jeremy and kate. >> thank you. i really appreciate the introduction. y thanks for doing this. >> great to see.

thanks so much and to the harper bookstore and alike have an opportunity to pepper jerry with questions about establishing new book, which is about all things that i get most excited to write about. it's really a pleasure to be here. i thought maybe, jerry, , we can sort of kickoff of the conversation by having you tell us why, humans have a number of traits that set us apart from other mammals, from other primates. we have naked bodies. we have larger brains and language. why focus on bipedalism? >> is a great question. like you said we have these differences. we have lots of similarities to our mammalian cousins and primate cousins and eight cousins but we have these differences as well. upright walking is one of those. mammals fly in swim in sprint

and delete. mammals walk and climb. your typical mammal moves around on all fours. think about a cow or goat, sheep, dog, cat, squirrel. but only humans will navigate the world on their extended hind limbs all the time. if it really strange way to move. when another mammal does it, we kind of lose our minds. we take out our chemistry with ukip was having. we posted to youtube and gives millions of hits. .. the world on their extended hind limbs all the time. it's a strange way to move. one another mammal does it we lose our mind we take out are calm on - - camera and posted and he gets millions of hits. is researching this book and found examples of bears moving on to legs in new jersey. almost 5 million views through the spare walking through this new jersey suburb. gorilla in the zoo occasionally walking on two legs and someone got a video of >> things that we do all the

time and we also use the word pedestrian to describe something extraordinary. when another animal does it it's remarkable. but not only that the fossil record which i work on, i'm a paleontologist, i study fossils. what we can tell by going back in time for the common ancestor that we shared with our ape 'causes, the further back we go, we start to lose some of those unique characteristics, the large brain, language, art. and those happened recently-- stone tools. what's the most ancient characteristic on our lineage is this ability to move on two legs, not only strange as a mammal, but it's the most ancient thing and set of set our lineage off. what i argue in the book, it was the key innovation that led to many of those other

anatomical and behavioral changes that make us human. >> that's great, that's a really interesting lens through which to view the entirety of human evolution in a sense. this might sound like a weird question, but, you know, thinking about this from a biomechanics standpoint, upright walking, we do it all the time and we kind of take it for granted and don't think about it. what is special about it from the standpoint of biomechanics? will you describe the act of walking on two legs and what is unique about it? how do you sort of convey that? >> so, it's a balancing act, moving on two legs. think what i talk to my students about, imagine if i gave you assignment to design me a chair. you'd probably design it with four legs and there might be

clever students who make a bar stool with three legs, but it's know the going to work with two legs, if i sit in it and i fall over, they fail the assignment. the two legged motion for a mammal to move around the world today. we can get into bird locomotion at some point and deep in the past we find evidence of bipedalism in crocodiles. and this is about balance. what we can see and within of the ways we can identify fossils coming from things that are adapted that move on two legs is that they have the specific shapes to them, these individual bones 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 act in a way to, again, prevent you from tipping over. one of the classic examples is the hip joint. when you take a step and left your other leg, you fall over. and when a chimpanzee walks on two legs, that's what they do, they wobble from side to side. but in humans we've evolved, pelvis, here is a human pelvis. the muscle attachments have wrapped around the side of the body. by being on the side, they will counter act that tilt 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, you know, you know lucy well, here is lucy's pelvis and sure enough, she's not the ilia or the hip joints moved in this way and if this was the only part we found, she was able to

balance on a single leg and why else do that unless you're moving around and two legs. from a biomechanical standpoint and really, you know, connecting it to natural selection, it's not a great way to move around your world. >> right. >> we are incredibly unstable on our two legs and that's dangerous. 30,000 americans die every year falling and in addition to that we're stunningly slow for a mammal. usain bolt the fastest human we know has ever lived the fastest he ran was 28 miles an hour in his 100 meter dash, world record 100 meter dash, 28 miles per hour, sounds impressive, it is. i couldn't. but half the speed of a

galloping zebra or a galloping antelope and most importantly half the speed of a lion and a leopard. so evolving this form of locomotion made us slow and so, it raises some really interesting questions of in what ways was this beneficial and allowed us to overcome some of those -- some of those, you know, mal adaptations you can even frame it as, this lack of speed. >> yeah, yes, and you anticipated my next question, which is, you know, why evolve this kind of -- what seems to be a subpar way of getting around. so i know there's been a lot of scholarship over many decades and, you know, with people coming up with all kinds of ideas about why we did come to have this unusual kind of

locomotion and you know, there are some really interesting ideas going back as far as mamark and darwin and i thought we could take a nickel tour through that if you don't mind indulging that. if there was another mammal that went on two legs consistently, what does the other mammal do or eat or mating patterns or ecology in which this form is beneficial. as a scientist when you try to figure out science for yourself, you want to look at the natural world and where else do we see can examples like this? the fact that we don't have other mammals that walk around on two legs makes it a different problem to solve and one of the reasons that we haven't solved it and you can go back and take it right up

until, you know, 2021. people are still hypothesizing boy why bipedalism, and over tall grass and that goes to humans seeing off into the distance. with that one, if you look off to see a predator, the worst way to get away is bipedalling, instead of on all fours. darwin saw a connection between our small canine teeth and bipedalism and tools to free up our hands for tools. that's an interesting idea, worth revisiting, problematic

because of the timing. that we have evidence for bipedalism in those 6, 7 million years old and we don't have evidence for tools for 3.3 million years for evidence of stone tools and wild ideas about explaining again tail genitalia showing off your body, and others for food sharing, if you can free the hand not to make weapons, but to gather food. there are some to promote female are sharing food with others and adrian zilmer's and lovejoy. and others said sharing with potential mates.

an idea that has had had a little, maybe more lasting power has been about energetics. two legs, we're slow, but energetically efficient and one of the ways to explain this. herman poncer and i talked about the ideas and he said in order to lose a pound of weight you'd have to walk about 70 miles. because we're too good at it. we're too energetically efficient and so now, you know, you don't want to lose weight if you're early, but if you need enough food to survive and maybe there's not a lot on the landscape. those individuals are moving in a way that are energetically efficient and might survive better. so that's a possible idea as well. yeah, there are lots and lots of hypothesis and we don't have

a handle on it and that's okayment and there will be plenty of things, new fossil discovery will allow us to revisit some of the ideas and retest some of the ideas and really the issue for me is not figuring out which is right. it's beginning to narrow that list down and clear the ones that are wrong. that's how science works, by refuting the ideas rather than by proving them. >> right, right. so we don't know yet why bipedalism, but we have a lot more information than we used to about the time frame which it evolved. maybe we could talk about the fossil discoveries that allowed you and your colleagues to

piece this together when it happened and what bipedalism might have evolved from and where it took us? >> a lot of folks listening will probably know about lucy discovered in the 1970's and lucy is a magnificent partial skeleton, got her back here and the original is in ethiopia. and not long after lucy was discovered, there were footprints found in tanzania where i work, and this pushes it back, and that human bipedalism existed three and a half million and yet the genetics would share the come on ancestry with chimpanzees,

that split at six million, and that's a long time, three and a half to six million. there have been remarkable and important discoveries made that begin to piece at that together. one is a partial skeleton like lucy four and a half million years old known as artie, or artpithigus. it has the pelvis and foot that occasionally was able to move around on two legs, but a big toe, a good tree climber, but when it came down to the ground, did it knuckle walk? no, it could actually work on two legs.

that's four and a half million bipedal and if you go further back much more controversial and a little more difficult to interpret. so, this is a toe bone from a five and a half million-year-old from eat oem -- ethiopia and matches the shape and especially the bone of a human toe that would push off the ground. the chimpanzee, the toe curves in the other direction for grabbing. it is more like an ape in the trees, but angulation like yours and mind, it probably could have pushed off the ground. it's a cool fossil, but it's just a toe. it would have been nice. this is a beautiful femur from

kenya, and if you compare it to a chimpanzee, the look how short the neck is on this fossil. and what that would do, it would talk about what i said earlier, the hip muscles, drawing the muscles farther on the hip and makes it more efficient and we think that that anatomy is evidence for bipedal locomotion. if you go farther back to 7 million years there's this remarkable skull that was discovered in chad and is very controversial. the researchers who found it and researched it argued the hole at the base of the skull where the spinal cord would exit the brain was in a

human-like position and this creature would have been able to hold itself upright. we don't walk with our heads so i'd like to see fossils from the other part of the body and there's a femur now that has been published by one team and another team has a print out and they come to different conclusions whether this is an upright walker or not and to me, if you converge on the common ancestor of humans and chimpanzees, you'll get something that's a fabulous combination and maybe frustrating combination of anatomies that are difficult to interpret. it's kind of what you might expect in a common ancestor. >> do you think that this femur looks like that of a bi-ped or

not? >> i like to talk about fossils i'm able to see and this is not a fossil that i've been able to see myself. and, however, there are even older fossils now that are-- we don't have much from 8 million, 9 million, 10 million, but there's a new discovery from a site in germany and germany sort of might sound surprising so some of the folks listening because we've been talking about africa, but it expanded around the mediterranean, is what is now the mediterranean so we've found fossils in greece, turkey-- and this fossil from 11,

11 1/2-year-old fossils from germany looks upright and to me that's an interesting find because it could imply and we're is it trying to figure it out. one of the hottest topics in our field right now, what is the body form from which bi-pedalism evolved. there are some coffee mugs and stickers suggest a chimp into a human. >> chimpanzees are not our ancestors, they're cousins. chimps evolved, too and some of what we found might indicate that the common ancestor was more upright in the trees and that knuckle walking could be a

more derived form of localmation. there are plenty of colleagues that disagree with that, that knuckle walking is the form by which bipedalism evolved. we need more to figure this out. >> it's a revolutionary idea and fun to think about that. now, if bipedalism is a uniquely trait and denuvious-- >> i don't think so. it shows when they were branching. having said that, there are big error marks around these divergent states, but i think you raise an important point

that our fields have operated under the assumption that if you find anything with characteristics of upright locomotion that it's automatically by definition an ancestor or extinct relative of us and would be more closely related to us than to any other of the apes. and i think that that assumption is on the table. as maybe not being 100% correct because if you had apes experimenting with different locomotion, including upright apes in the trees, navigating in the trees, they might have anatomies that look more human-like. and the tibia not in all ways, but in some ways looks very much like lucy's and i think

that's telling us about leg positioning, not necessarily weight bearing on a terrestrial bi-pedal leg, but in the trees and movements with hands assistance. gibbons will do this, spider monkeys will do this, but it might not be enough. this is going to be fun as we find more fossils from that, 5, 6, 7, 8, 9, 10 million time period i think we'll see lots of experiments going on with locomotion and lots of false starts, where bipedalism, i say attempted, but may have evolved and then that animal died out. it just was not a selectively

advantageous of locomotion as the habitat changed. so, yeah, it will be fun. >> definitely. i mean, we've talked a little about, you know, what the fossil record shows us about the origin of bipedalism, but you mentioned this very briefly. there are other kinds of data that we can look at to sort of study the emergence of this kind of locomotion, and so you mentioned litoly, where i always wanted to visit sort of one of the most iconic sites even just thinking about it kind of gives me chills. so there is a famous set of tracks and so you're seeing behavior, right of an animal. and what does that trackway

tell us about the evolution of bipedalism at that point in time, which is what, 3.6 million, compared to what you know about it going back, and aurora or-- >> it's bipedalism 2.0. it's a really good bi-ped. those footprints, i was there in 2019 and that place is magical. that place is just amazing. and there are footprints in all of those ash deposits that are eroding out of the hill sides and right, like you said, bones fossilized bones are-- i love fossils and these are wonderful and we can squeeze information out of them and tell what our stories like from the bones, but footprints are

alive. they're telling about this moment in time in the life of a leaving, breathing, thinking individual who was a lot like us and a lot of the recent biomechanical work that's done on the footprints is telling a story of a human-like bi-ped. it's moving like us. not hunched over like groucho marx walk or like a chimpanzee, from a distance it would look like you and i walking. if you put it on a treadmill, you'd pick up subtle differences and that's a fun thing because you can't ever put it on the treadmill, but from the footprints and from the bones, it looks like they're not pushing off the big toe as much as we do, our arches are flatter than ours,

their legs are shorter and maybe not extending at the hip quite as much as we do when we walk, but those distances are subtle. one of the really, i think, amazing discoveries of the last 10 years is that we often will think of bipedal evolution in a linear way and i did it by talking 2.0. and what we see are dinner forms of bipedalism in different speices and so at the same time lucy and her species were around and her species were making the human-like footprints, there was another species that had a divergent big toe, in ethiopia not far from where lucy was found, climbing trees and walking in a biomechanically very different kind of way.

and this was a fabulous discover made in ethiopia in 2009 and showed there were different forms of walking, co-existingment and behind me, this skeleton here was discovered by lee burger and also the first by his nine-year-old son in south africa, also in 2009. they were published 2008 was the discovery and i've worked on the foot and the leg of this skeleton and when i first started working on it, to me it was a-- i finished my ph.d. and studied the homnoids and there was no functional variation except this thing. it was so different with its heel and ankle and knee and aspects of the hip and the lower back that we've

hypoth-sized that about it like lucy and even on the doorstep of homosapiens, you have in europe and asian, indonesian islands, you have these and in south africa, brand new species. and there are all the different species and populations co-existing. some of them we interbred with. some of them i don't think we probably did, but from the bones and the leg bones, it looks to me like many of them walked in these biomechanically slightly different ways or different flavors of walking. so i like to sort of think about jumping in a time machine

and going back to any of the time periods and you'd see these different kinds of us, different species of our ancestors and they wouldn't-- they'd not only look different and maybe eating slightly different things, but they'd be walking in slightly different ways. >> yeah, it's really wild to think about that degree of experimentation occurring for the vast majority of human evolution, not just something that happened in when it was planet of the apes or first appearing, but right up until virtually yesterday in geological terms. >> it's amazing and when i was in grad school at university of michigan, the story very much was hemoerectus right up to homosapiens, and neanderthals,

and then it wasn't interesting, we had evolved to bipedalism so let's go back. and now this is interesting, there's a lot going on there. >> yeah. if we go back to licoli and the sort of earliest evidence we have of walking more or less like we do, you know, it's interesting that the first -- that the oldest known stone tools are just a few hundred thousand years younger than those foot prints. so, we're getting a little closer to what darwin was talking about potentially, right? and i'm just wondering sort of how you see that -- how you see things aligning there? could it be that this bipedalism 2.0 is what, you

know, frees the hands to start doing stuff like making stone tools? >> i think that possibility, again, is back on the table and this was, you know, darwin's idea of bipedal origins and he also incorporated brain size enlargement which we know is not part of the story that does indeed happen later and, but you're absolutely right that if you go back to the 1970's, 1980's, we have the footprints at 3.6 and the oldest stone tools at 1.8. and it looked like darwin was wrong and it looks like the two are chronologically not aligning and then they were stone tools, that are 2.6, okay, 3.6, 2.6, we're getting closer. human-like bipedalism did get pushed back thanks to a tibia

discovered, it's about 4.2 million years old and it's very human-like. i'd love to see what the rest of that creature looks like. and my-- honestly, i was going to say my hopes, but my expectation different how remarkable my colleagues are at finding these fossils, i love being out there looking for them, but, you know, they're much better at finding them. you know, i think about johannas who has made discoveries in east africa the last decade or so, or last two decades, knowing more about the creature is very important. back to your point, we have at least reports of stone tools at 3.3 million and they're controversial. but at that same time, 3.3 million, there were

behaviorally, i don't see any reason why they wouldn't be making stone tools. they're walking like us. and there's about a 20% increase in brain size and there's that new discovery on the basis of the child, a juvenile skeleton that shows that they had slowed down brain growth and slowed down brain growth is tied in mammals to learning and relying very heavily on learning, and this is a horrible idea for in i slow bi-ped, but something heavily predated on. you'd want to speed it up and not slow it down. and there were plenty that wanted to eat them. and the fact that it was slowed brain growth to me tells a heavy reliance on learning, learning what? learning how to make stone

tools, it might have involved, and also a story of cull turing buffering and social buffering, how do you ward off-- you know, how do you survive on a landscape like that when you're slow, how do you avoid picking off the leopard all the time, you look out for each other, you have each other's backs. ng our socialalty is built into the bipedal locomotion. it's not going to be an evolutionary success unless it happens in something that's either super fast like an ostrich or is super social. and even compassionate and empathetic like we are. >> yeah, i mean, i thought that was a fascinating point you made in the book where you start out by talking about early idea liking bipedalism to violent behavior to now you

making the argument that actually it could never have worked if our ancestors didn't have the capacity for empathy and cooperation. >> i think so. you know, there are -- i think that idea of uprightness, freeing the hands not just for tools, but for weapons, is still part of the popular culture. we've all seen 2001 a space odyssey, right? the beginning there with the wielding of the weapons and that has its intellectuals roots back to raymond -- and discovered, this over my shoulder the little fossil. but later in his career, 1940's, post world war ii, he

worked in a site where bones that had been smashed and formulated the hypothesis that they had been doing that, that we were blood thirsty killer apes and that idea has had roots and is still sort of the popular culture even though we know now at the site, the bones were smashed up because of hyenas. so science was refuted the idea and that's part of how we think of ourselves. instead i draw attention to a fossil like this, discovered in the 1907's discovered in kenya. this is an upper leg bone, about 2 million years old, short of 2 million years. a long femoral leg and that's how we can tell it's from an upright walker. the amazing thing about the fossil, it has a heel fracture.

this bulge of bone sticking out of the medial side of the inside of the femur, that's a healed fracture. think about breaking your femur 2 million years ago, no hospitals, no doctors, no fire, no shelter, and you break your leg, but you heal, you survive? that can't happen unless other individuals are helping you out. and it's not just 2 million, that -- back to lucy's species, there's a skeleton, a second skeleton known as cattanumu. 3 1/2 million years old, we think it's a large male. and he has a healed ankle fracture. again, he accepted in-- stepped in a hole and fell out after tree and broke the ankle. if you're a zebra, it's not a good situation, you can get

point a to point b on three legs. if you're a bi-ped and you're slow and hopping around your landscape, i don't see how you survive and yet, it's a healed fracture and so that individual did survive and again, it connected to bipedalism, that the vulnerabilities that we have as bi-ped, but then the fact that we have injuries that make us particularly feeble as bi-pedes is explainable only if we were and continue to be empathetic and compassionate and generous and pro social with one another. >> fascinating. and i now have some questions from the audience that she wants to put to you. we'll turn it over. i nt had--

i hadn't heard that about the healed ankle, amazing, i had no idea it went that far back. >> that was a discovery-- it was a discovery in 2010. >> okay. >> and you know, which it's 11 years ago now, but still, it's an indication of how rapidly by colleagues are finding these fossils and, you know, putting them out there and each of those fossils has this amazing story to tell about why we are the way we are today. so it's easy if someone gets-- for one to get overlooked and that one, that's a cool fossil and that one definitely didn't get the attention it deserved. >> that's amazing, because i -- while i'm looking through the questions, yeah, i do like the memory that i have of it sort of that the last i heard there wasn't evidence of that until -- and anyway, sorry, that's

awesome. that's nice to know that we can be nicer than we think and that goes back longer and that's reassuring. we have a question, let's see, if you were able to change u of m hoo anatomy that make bipedalism easier on us, what would you adjust? >> oh, the foot. the foot is a disaster. i mean, i study feet and, you know, the foot is sort of like, you know, evolution's example of a good try. [laughter] >> you did your best, but what happened here is you converted a grasping ape foot into something that needs to be rigid and to, yes, have moments of flexibility, but also push off the ground in a rigid wayment so we have the same 26

bones in our foot that chimpanzees do. so emergency you're trying to create something from scratch and it needs to be able to contact the ground, absorb elastic energy and kick off the ground for your next step and you make it out of 26 parts? you'd fail that engineering course, it wouldn't happen. look at this. now there you go. >> yesments so here is a foot from an ostrich and what's happened over the course of avian evolution, bird evolution is that the bones that make up their ankle and foot have fused together into a single rigid structure, composed of instead of 26 bones, it's eight or so in the foot of an ostrich and this ends up looking a lot like the blade prosthetic that a lot of para olympians will use and

use with great effect and can run very fast. and so, oh, yeah, i would totally change the foot. now, the back is a bit of a mess as well. but, you know, i work more on the foot so that's the first place i'd go. oh and the knee is a disaster as well, but let's stick with the foot. branching off of that, we have another question, do you think that like -- so the question is kind of is it possible for bipedalism in humans or anywhere else to evolve and improve any more to sort of like do we represent the zenith of what this is going to be? is that possible to speculate on? >> it's a great question, what i love to talk to my students

and speculate about. i don't think so. if you look at the different body forms that existed i don't see the human body today, homosapiens as having an advantage over others, hemoerectus. and with others it maybe isn't as large, but i don't think that we've reached some pinnacle of bipedal locomotion. again, i'd much rather have the skeleton of an as ostrich if i want today get to point a to point b fast or even a t-rex. when you look at the past, one of the fun things to look at bipedal animals that went extinct. there's a crocodile discovered in north carolina by lindsey

zano, a vertebrate paleontologist at north carolina state and she at the museum, sorry, the museum in north carolina. and she reconstructed the gait of this ancient crocodilion up on two legs. imagine a nine-foot crocodile that could be up on two legs and sprint? horrifying. i find fascinating, that didn't have evolutionary legs. what happened to crocodiles? they're on all fours, and they're stealth hunters, ambushers, and being pi bipedal, they weren't successful. and the first dinosaurs were bipedal, and the stegosaurus, and triceratops, those are were

bipedalism. and they crop up and honestly failed and either convert to quad dra-pedalism or be a deadli deadline -- dead lineage. >> and you brought this up, bipedalism, what is the time span? how many millions of years? what's the time span generally? >> we don't know. it depend on what the body form of that common ancestor looks like. if it was a knuckle walker, if knuckle walking is the ancestral trait and chimpanzees have retained it on their lineage and gorillas on their lineage, then you would have to have intense rapid natural selection to go from a knuckle

walking common ancestor to something that is not just getting picked off by leopards because it's hunched over and can't move. it would have in that circumstance, i forsee this happening incredibly fast, or it happens incredibly slowly, if the common ancestor is something that's imagined more like a large gibbon with shorter arms, or up in the trees moving on two legs and if there's environmental change and you begin to get patchier forests, it has to move across on the two legs and it already has a body form to do that. so it's not a new locomotion, it's a new locomotion in a new setting. in that case it would be very gradual and what we'd be looking for, i think, are

anatomies, from something that's a terrestrial bi-ped. we haven't thought what that would be, how do you distinguish from something moving on two legs on the ground, very different forces, or in the trees where the trees are more compliant. and the forces are different. you probably want have the hip mechanics because you're holding your body with your hand and you're not going to have the pelvic tilt problem and that's something that we as a field haven't grappled with. >> it must be hard, i would think in contemplating these scenarios to fall into a lamarkion trap. maybe know the in your position, but for the layman, it would be a pretty easy trap

to fall into. >> i'm a darwinian graduate and i think it probably happens gradually and i think there's probably not one explanation why bipedalism was advantageous, but a most -- host of things to search for the answer is probably wrong-headed, but, so, yes, you've got population and certain individuals that move more than others and they end up having more food and more reproductive students and off you go and we're trying to figure out what it is that allows the individuals to have more. but there are some that think that bipedalism emerged as a meme, that it was just a cool

thing to do and that, you know, chimpanzees, gorillas occasionally move on two legs if that became sort of the fad in that population then you could have more and more individuals aping each other, which is what we do, right? and because bone is elastic to an extent, you might get some of the anatomies that have been key to bipedal locomotion not because you inherited them, but acquired them through the knife. the best example at the knee. when you're born your femur is straight, but as you toddle around, your femur angles in and you're knock-kneed. and when you see an angle to

it, this individual had to have walked on two legs there's no other way to get that anglement so there's a cool combination of anatomies that you're born with and what you acquire that allow you to move on two legs. >> well, thank you. [laughter] >> we have matthew st. ang asking what circumstances are making it easier to find more fossils today? >> oh, great question, matthew. great question. so like any science, you know, you build on the work of previous generations and there are are lots of, you know, false starts that happened and mistakes made and you learn from the mistakes of predecessors. but having said that, there's also a lot of technological advances that are happening. for instance, in south africa, one of the reasons that my colleague, lee burger, has been

able to find as many fossil sites as he has is bye using satellite imagery and looking at the clusters of trees that grow out of gates. when you're on the landscape walking, it's really hard to see those caves, but from the top down, you can see them, you can see them much better. and so that's one of the things that's happening. i also would argue that the key colonization of the science especially in eastern africa has played a huge role in this. instead of parachuting science and dropping into the places and spending a couple of weeks and going back to the united states or eastern europe, a lot of incredible fossil discovery is being done from individuals from those countries, in ethiopia, and charles in tanzania and charles in kenya and many, many other folks.

>> kate, i'm curious, why do you think we're getting this, the discoveries? >> the reasons you described, maybe a snowball effect, oh, lee burger went into the cradle of human kind which was already supposedly really well-explored and found these amazing things and so we maybe start to go back to places that we thought didn't have any more fossils for us or that we haven't looked at yet and, you know, kind of go there with fresh eye and fresh outlook? >> yeah, i agree, i think that's true and, yeah, that assumption that we'd already -- that many of the great discoveries had already been made, you know, again, this

last 10 years, i've just been astounded by the number of fossils and not just the number, it's not like we're getting more of what we already knew about. that's happening to some degree, but we're also finding -- or my colleagues are finding things, i don't think that any of us could have predicted. you know, i certainly wouldn't have predicted any of them, so, it's been this really wonderful awakening in our field and a dose of humility that there's out there for us to discover and a lot of our ideas are going to end up being wrong. that's okay as long as we're following the evidence, then it's okay to have an idea based on the evidence you have and oh, look at this new fossil, shows i was wrong. oh, well, great new fossil. >> i think we can leave it

there. i think we're out of time. thanks to both of you so much. jeremy and kate, thank you, this is fantastic and thanks to you for joining us. and please, learn more about this incredible book at -- i've posted the link in the chat harvard.com/book under score, and there's a place to donate and thanks for tuning in. stay safe, have a lovely night and thanks again to both of you. >> weekend on c-span2 are an intellectual feast. documenting america's stories and book tv brings you the latest nonfiction books and authors. funding for c-span2 comes from these companies and more. including midco. ♪♪

♪♪ >> midco, along with these television companies support c-span2 as a public service. >> the bookstore in nashville hosted, sebastian who talked about his walk along the train track from washington to philadelphia. >> we and buddies walked from washington d.c. to the rail lines to philadelphia and we were headed to new york and then decided to go west to pittsburgh. we picked the railroad lines, it's a weird no man's land. there's really not know police on there. there aren't that many people. marginal people out there, but it's a weird sort of world that

you can exist in. we slept under bridges and in abandoned buildings and got our water out of creeks and cooked over fires in the woods or whatever and the railroad lines also, they're interesting because they go through the middle of everything. you see the backs of the factories, the junkyards, the ghettos, the corn fields and the farms and the woods. when we hit pennsylvania, it got very rural and wild. a lot of the trip through pennsylvania was along the juniata river that i later found out was sort of the gateway, the only east-west trending river in pennsylvania. the gateway to western pennsylvania and ohio territory in the 1700's when settlers were pouring through a mountain gap west of harrisburg and headed into the unknown. so we did the trip over the course of a year and we walked 50 or 100 miles at a time and

as i write in the book, over 400 miles and most nights, we were the only people who knew where we were. >> sure. >> and there are many definitions of freedom, but surely that's one of them and that's one that i particularly enjoyed. >> to watch the rest of this program, visit bock tv.org. and search for sebastian younger using the search box at the top of the page. >> after obtaining a ph.d. in oxford, that aging is the most important scientific challenge of our time and switch fields and competitional biology and he worked at the institute and predicted heart attacks and records. >> he's appeared on discovery and the bbc. he will be guiding us on a journey on the work being done to combat the causes of death