weekend on book tv. tonight on our weekly author interview program "after words", wall street journal columnist jason riley discusses the work of economist thomas soul for then tomorrow best selling author michael lewis looks at the early warning signs of the covenant teen pandemic and the trump administration's response. and on monday it's an extra day of book tv. featured programs and article presentation of our in-depth interview with historian and ronald reagan biographer craig shirley. "after words" with neuroscientist lisa on how memory works and author discussions on military history with malcolm gladwell and margaret mcmillan. fine. information online epic tv.org or consult your program guide. >> jeremy da silva is anthropologist at dartmouth college editor of a is the editor of a most interesting problem, what darwin's dissent

of man got right and wrong about humans evolution. he is part of the research teams that discovered two ancient members of a human family tree. and home on the lady. he studied wild chimpanzees in western uganda in early human fossils and museums throughout eastern and south africa from 1998 to 2003 he worked as an educator at the museum of science. kate is senior editor at scientific america purchase been writing about the evolution of humans and other organisms for the magazine since 1997. she also co-authored with donald johansen of lucy's legacy the quest for human origins. tonight though be discussing jeremy dasilva's new book first steps held upright walking made of human. and it dasilva explains the history of bipedalism the ability unique to humans among living mammals to walk on two legs he makes the case

bipedalism is a crucial change 11 the evolution of humans despite the difficulties to the promo ever after. publisher weekly praises desilva's love for fossil discovery and colleagues in the wonders he experience examining's 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'm so pleased to turn things over to our speaker the digital podium is yours, jeremy and kate. >> thank you. now i really depression at the introduction. hi kate thanks her being here in doing this. that great to see you thanks so much. and to the bookstore i'm delighted to have the opportunity to pepper jury with questions about his fabulous new book which is about all the things that i get most excited to write about. it is really a pleasure to be

here. i thought maybe if you are up for it we could kind of kick off the conversation by having you tell us why, humans have a number of traits apart from some other mammals some other primates. we have naked body we have large brains and language. why focus on? >> it is a great question. like you said, we have these differences but we have a lot of similarities to our primate cousins but we have differences as well. up right walking is one of those. mammals cry, swim, sprint, leap, mammals walk and climb. your typical mammal moves run on all four think about a cow, goat, sheep, dog, cat, squirrel. ms. run on all fours. only humans will navigate

the world on their extended hind limbs all of the time. this is really strange way to move. and when another mammal does it we lose our mind in researching this book bears but almost 5 million views of a gorilla in the philadelphia zoo lewis started walking occasionally. someone got a video of it and ended up on the cbs news. and so something that we do all of the time. we even use the word pedestrian, w right to describe something ordinary. when another animal does it is remarkable. but not only that, the fossil record is what i work on i met paleo intelligence.

i study fossils. but we can tell by going back in time to the common ancestor that we shared with our ape cousins, the further back we go we start to lose some of those unique characteristics. the large brain, evidence for a language this is happened more recently. what is the most ancient characteristic we think on her lineage is this ability to move on two legs. not only is it really strange as a mammal, it is the most ancient thing we have evolved. it sort of set our lineage off. what i argue in the book is it was the key innovation that led to many of those other anatomical and behavioral changes that make us human. >> that is great that's a really interesting lens through which to view the

entirety of human evolution and a sense. this might sound like a weird question but think about this mobile mechanic standpoint. upright walking we do it all the time we take it for granted. and we don't really think about it. what is special about it from the standpoint of biomechanics? can you describe the act of walking on two legs and what is unique about it? how do you conveyeg that? >> it is a balancing act moving on two legs. think about what i talk to my students about his imagine if i give you an assignment to design the a chair. you probably design with four legs. there might be some clever students to make a barstool negative three legs. if you make a chair out of two legs it's probably not going to work. i'm going to sit in it, fall over in the student will fail the assignment.

two legged locomotion is unusually for mammal to move around the world today. we can get into bird locomotion at some point. even the pacified evidence and dinosaurs and even in an ancient crocodile lineage which is think about. from a biomechanical standpoint this is about balance. what we can see one of the ways we can identify fossils is coming from things that are adapted to move on two legs is because they have these specific shapes to them. these individual bones that would align the joints in a way that would prevent them from tipping over. or would change the action of certain muscleses so that those muscles would act in a way to again prevent you from tippingng over. or the classics example does a hip joint. when you take a step and lift the other leg you fall over.

i went a chimpanzee walks on two legs that's exactly what they do. they wubble from side to mside. in humans we evolved a pelvis. we evolved a pelvis or the muscle attachments have wrapped around the side of the body. by being on the side to counteract the tilt every time you take a step. so if you find this part of the body and it looks like this can tell you something moving on two legs. so you know lucy very well here's lucy pelvis. sure enough she's got the hip joints arranged in a very humanlikeoi way. so even if this is the only part of her we found will be able to tell she was able to balance on a single leg and why else do that unless you're moving around on two legs. from a standpoint and really connecting to natural selection it's not a great way

to move around your world. we are incredibly unstable and her two legs. we fall a lot. that can be quite dangerous there 30 million americans falling. and in addition to that we are stunningly slow for a mammal. fastest human as we know ever lived, the fast is he ever ran was 28 miles per hour in this 100-meter -- in 2009 this world record 100-meter. it sounds impressive and it is i could not come close to that. it is halff the speed of a galloping zebra, half the speed of a galloping antelope. perhaps more importantly half the speed of a lion and a leopard. so involving this form of locomotion made us slow.

it raises some really interesting questions of in what ways was this beneficial and allowed to overcome some of those adaptations you could frame it as this lack of speed. >> to zepeda my next question which is why of all this? click on the surfaces being a subpar way of getting around. i know there has been a lot of scholarship over many decades coming up with all kinds of ideas about why we come to have this unusual kind of locomotion. there's some really interesting ideas going back as far as lamarck and darwin. federally funded take a nickel tour through some of those ideas that unite mind indulging us.

>> it's one of those things where if it was a another mammal that moved on legs regular will be able to catch us more effectively we be able to do some science and say what is this other memo do? what is it eat literate mating patterns in which this form of locomotion is beneficial? and so as a scientist when you're trying to figure outut something about your selfie was want to look out into the natural world and say where else do we see examples like this? the fact that we don't have other mammals that habitually walk on two legs make this a really, really difficult scientific problem to solve. it's one ofro the reasons we haven't solved it. you can go back and take it right up until 2021 people are still hypothesizing why it was selectively advantageous for our ancestors got ideas about seeing over tall grass, that

was back to lamarck. very interested in humans being able to stand c 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 is bipedal he. you want to be on all fours and galloped away and be much faster. that one is never made any sense to me. there are ideas about the course darwin saw this connection between our small canine teeth are bipedal -ism and tools. this is about freeing the tools.or that becomes somewhat problematic. even nothing interesting idea worth revisiting. problematic because of the timing. evidence for bipedal nihilism six and 7 million years old. do not have evidence ofe tools until about three —-dash

3.3 million years is the oldest reported evidence for self hull. wild ideas about splaying tell youyi, this was some sort of showing off your body for selection. the ideas are little more reasonable and testable having to do with food sharing is you can free the hand not to make weapons for school together food. there are some ideas fortoat having promoted while the females are gathering food with others and sharing with others. then owen lovejoy look that and argued that it was the mail collective food and sharing it with potential sexual meet. an idea that has a little more lasting power is about energetic moving on two legs yes we are slow. we are energetically very efficient. one of the best ways to

explainrg the urban and i talked about these ideas and he said that in order to lose a pound of weight you have to walk about 70 miles. because we are too good at it. we are two energeticallyen efficient. now you don't lose weight. early but if you need to get enough food to survive and maybe there's not a lot on the landscape those individuals are moving away energeticallyly efficient. they might survive a little better. and that is ar. possible idea as well. there are lots and lots of hypotheses. we still dond not have a handle on it. and that is okay. there will be plenty of things you fossil discoveries are going to allow us to revisit some of these ideas and retestal

some of these ideas. clearly the issue for me is not figuring out which one is right, beginning to narrow that down to make the ones that are clearly wrong. that is how science works by refuting rather than improving them. right right. so we do not know why it evolved. you have a lot more information than we about timeframe in which it evolved. so, about some of the fossil discoveries that have really kind of allowed viewing your colleagues start to peace together on this all happened? and, what it might have evolved from and where it took us? >> a lot of folks listening probably know about lucy, discovered in the 1970s.

lucy is a magnificent skeleton pretty got her back here the originals in ethiopia course. not long after lucy was discovered their footprint found in tanzania when i some of my research as well. that pushed bipedalism back through and half million years ago. those remarkably important discoveries showing human like existed three to half million. and yetsm t the genetics point towards a common ancestry share the chimpanzees at about six or 7 million. split probably complete by 6 million years that's a big gap. what's going on that timeframe? the mint really remarkable important discoveries that have been made to begin to peace the story together.

one is a partial skeleton like lucy from ethiopia with the fort half-million no snoring known as already. have some of the key elegies of the pelvis and the foot that would indicate that was at least occasionally able to move around on two legs and it was on the ground. also a big tobin the foot. this is an excellent tree climber long curved fingers. when it came to the ground, local law? no it appears it could actually move on two legs. foreign half-million now we've got something bipedal. if you go further back than that the evidence becomes a little much more controversial. a little more difficult to interpret. this is from a five and half-million-year-old from

ethiopia. that matches the shape especially the end of the bone of a human to push off the ground are walking. oregon pension with total curves in the other direction for grabbing. this has a curvature like it that's more like an eight. it had some time in the trees but hasn't angulation to a case like yours and mine. it probably would amanda push off the ground for this is also but it's just a toe. it would be nice to have more. here's a beautiful femur from kenya venice 6 million years old. what's unique about this one few compared to a chimpanzee, the head or the ball part of the hip joint is very similar. looklp how short the neck is from the chimp and how long that neck is similar to what i

said earlier repositioning those head muscles become balance on a single leg by drawing most muscles further from the heck you're making them more efficient. and we think that anatomy is evidence for bipedal locomotion this is the fossil. in the back even further that the 7 million years there is this remarkable school that was discovered in chad. the very controversial. the researchers who found it in first interpreted it argued that the whole of the base of the skull where the spinal cord would ask exit the brain was inhe a humanlike position and therefore this creature would have been old hold itself upright. i maybe even walk on two legs. we do not walk with her head so i would like to see fossils from other parts of the body. there is a femur now that has

been published by one team. another team has a pre-print out and they come to completely different conclusions.t on what is right walk or not. as you converge on the common ancestor you are going to get something that is not quite like any of the living apes. it is a fabulous, combination and maybe a frustrating combination of anatomies that are difficult to interpret. it's kind of like you might extract any common ancestor. the next so do you this femur looks like that of a biped? or no? unit i have not able to estimate like this talk about fossils and unable to see this is not a fossil that i have been able to see myself.

however there are even older fossils no, we do have much of a million, 9,000,010,000,000 new discovery from a site a in germany folks listening because we went on site apes expanded all around the mediterraneanra what is today the mediterranean and were living in force in southern europe we find eight fossils in spain, france, turkey and hungary. fossil from 11 half-million-year-old deposits in germany looks like it is very upright. he that's a really interesting find because it could imply, we're still trying to figure this out some of the hottest

topic centerfield right now of what body form to the ball? there a lot of t-shirts, coffee cups and bumper stickers would suggest the children human rights customer tendencies are not our ancestors there are cousins. the common ancestor is an eight week branch from and so have chimps and chimps have evolved two. so it's not a given that common ancestor was a knuckle walker. some of the false fossils were finding in those deposits might indicate the common ancestor was actually more upright in the trees and knuckle walking could be a more arrived form of locomotion. there are plenty of researchers played my colleagues would disagree with that and say knuckle walking was the form from which bipedalism involved in compelling cases for that. we need more fossils to figure this out.

it is really revolutionary idea it's fun to think about that. now it bipedalism is a uniquely trade and at 10 million years old is a biped, visit the country home and in? >> i do not think so. don't think the timing is right. i think the genetic data show very clearly when these lineages were branching. having said that, there are big aero bars around these divergent states. but, i think you raise an important point. our field is always operated under the assumption that if you find anything that is characteristic of straight locomotionte that it is automatically, by definition a homonym.

meaning ancestor or extinct relative of us and would be more closely related to us any of the other apes. and i think that assumption is on thehe table. as maybe not being one 100% correct. because if you have apes experimenting with different forms of locomotion including upright apes in the trees, navigating in the trees they might have some anatomies that looked a little more humanlike. perhaps the tibia in some ways not always someways looked very much like lucy's. i think that is telling us about leg positioning not necessarily weight bearing on a thrill bipedal leg. but an animal that is in the trees and living with hands assisted bipedal is in.

given the hold, see monks will do this, spider monkeys will do this. but right it would mean finding evidence for bipedal is him may not be enough anymore. this is going to be fun as we find more fossils from the five, six, seven, eight time. things are going to see lots of experiments going on with locomotion and lots of phone starts lots of places were bipedal is a might have been i would say attempted may have evolved in the net animal died out. it was not selectively in each cup. can be found respect definitely.

origin of bipedalism mentioned this very briefly data that we can look at to sort of study the emergence of this kind of locomotion. you mentioned place of always wanted to visit. it's one of the most iconic sites, even just thinking about it gives me chills. so, they are the very famous set. you are seeing behavior of an animal. point is that track wave tell us about the evolution of bipedalism at that point time which is 3.6 million compared to what you know about it going back to previous for

aurora? bipedalism 2.0. it's a really good biped. those footprints, yes that place is magical. that place is just amazing. there are footprints in all of these, ash deposits that are eroding out of the hillsides. and like you said, fossilized bones, i love fossils. these are wonderful we can squeeze information out of them and tell stories about what her ancestors were like from these bones. footprints are live. they're telling you about this moment in time and the life of a living, breathing, thinking individual who was a lot like us.

a lot of the recent biomechanical work that has been done on the footprints, telling a story of a very human like a biped is something moving a lot like us. it's not hunched over, crouched. down, not a hip need for a chimpanzee moving on two legs. this is something that from a distance it would look like you and i walking. now if you could put a treadmill you would pick up some subtle differences probably. that is a fun thing think about you not put it from the footprints and from the bones it looks like they are not pushing off his big toe quite as much as we do. arches are a little flyer than we are, their legs are little shorter. there may be not extending at the hip quite as much as we do when we walk. those differences are subtle. one of the really i think

amazing discoveries of the last ten years is that often think of bipedal revolutions in a linear way. talked about bipedalism 2.0. what we see instead are different forms of bipedalism evolving in different species. so at the same time lucy and her species were around in her species were making this human like life footprints there was a another species that had a divergent big toe that was in the field via her lucy found, climbing trees and walking in the file mechanically very different. kind of way. this is a fabulous discovery made in ethiopia in 2009. and showed the release of walking and coexisting. behind me the skeleton here was discovered by first peace

was by his 9-year-old son in south africa. also in 2009 is when they're published 2008 with the discovery. i've worked on foot and leg of the skeleton. i first started working on it, he finished the 30-foot, ankle, leg and i'd seen all of these fossils. to me there were variation but not functionally meaningful variation until vesting. this thing was so different than anything i had ever seen. ankle and knee and hip and lower back. that we have hypothesized that walked in a very different kind of way than lucy and her kind. : : : is right up through the pleistocene. even on the doorstep of homo

sapiens and then right in south africa a brand-new species so they were all the's different species coexisting i don't think we probably did, but from the leg bones looks to me like many of them walked in these biomechanically different ways or these different flavors of walking. so i love to think about jumping in a time machine and going back to any of these time periods and see these different kinds of us, different species of our ancestors, and they wouldn't -- not only look a little different and maybe be eating slightly different things but they'd be walking in slightly different ways.

>> it's wild to think about that degree of experimentation occurring for the vast majority of human evolution, not just something that happen when it the planet of the apes but up until yesterday in geological terms. >> it's amazing. when i was in granddaughter school, at the university of michigan, the -- granddaughter school at the university of michigan it was home hoe rectus and them homosapien monday and then knee andry thats -- knee -- and then studying upright walking walking walking the plasticene wasn't interesting. let's go back to then and now the plasticene.

there was a lot going on there. >> if we go back to early jest evidence we have -- earliest we have of holm notices walking more or less like we do i it's interesting that the first -- the oldest known stone tools just a few hundred thousand years younger than those footprints. so, we're getting a little bit closer to what darwin was talking about potentially, right? and i'm just wondering like how you see that -- do keis buy speedallism 2 .0 stars freeing the hands to do stuff like making stone tools. >> i think that possibility is back on the table. and that's was darwin's of

bipedal origins, but you're absolutely right, that if you go back to the 1970s and 1980s we had the footprints at 3.6 and the oldest stone tools at 1.8. and it looked like darwin was wrong. like the two are just chronologically not aligning, and then there were stone tools found that are 2.6. 3.6, 2.6, getting closer. human-like bipedalism was pushed back thanks to a tibia discovered, 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 -- i was going to say my hopes but my expectation, given

how remarkable my colleagues are at finding fossils, i look being out there looking for them but they're much better at finding them. i think about -- just made extraordinary discoveries in eastern africa in the last decade -- last two decades, and so knowing more about that creature is going to be really important. back to your point weapon now have at -- we now have reports of stone tools at 3.3 million and they're controversial. but at that same time, 3.3 million, -- the behavior -- i don't see any reason why they wouldn't be making stone tools. they're walking like us there. is slight brain enlargement, a 20% increase in brain size and there's that new discovery on the basis of the child, the juvenile skeleton that shows

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 slow biyesterday biped and plenty of carnivores that were more than happy to eat. so the fact that selection was favoring slowed brain growth shows the story of heavy reliance on learning, and learning what? learning how to be -- that might have involved learning how to make stone tools, but it also is a story of cultural buffering and social buffering, that how do you ward off -- how do you survive on a landscape like that when you're slow? avoid just being picked off by

the leopard all the time is that you look out for each other, have each other's backed and so i think our sociality is built into bipedal locomotion and that is not going to be an evolutionary success unless it happens in something that is either super fast, like an ostrich or super social and even compassionate like we are. >> that's a fascinating honest you made the book. you talk about early ideas like bipedalism to violent behavior, to now you making the argument that actually it could not -- could never have worked if our ancestors didn't have the capacity for empathy and

cooperation. >> i think so. there are -- i think that idea of uprightness, bringing the hands not just for tools but for weapons, is still part of the popular culture. we have all seen 2001, a space odyssey, the beginning with the wielding of the weapons and that has its intellectual roots back to raymond dart, who discovered the very first tongue child just over my shoulder here, this wonderful little fossil, but later in his career in the 1940s, post world war ii, he work at a site where he discovered bones that has been a smashed and he form rated a hypothesis that we were blood thirsty killer apes and that

idea has had roots and part of the popular culture even to the we know at that site to the bones were smashed but a because of eye -- eye eye eye even nas i draw attention to a fossil like this, discovered in the 190s by the richard leake and his team in kenya and this is an upper leg bone of an early homoinin. that long femoral neck, so we can tell it's from an upright walking but the amazing thing it has a heel fracture. so, this bulge of bone sticking out of the medial side of the -- inside of the femur and that's a healed fracture. and think of that no doctors no fire, no shelter, and you break

your leg but you heal? you survive? that can't happen unless other individual are helping you out and it's not just two million. that -- back to lucy's species, there's skeleton, a second skeleton, and he is about three and a half million years old, large -- we think it's a large male and he has a healed ankle fracture. so again, he stepped in a hole or fell out of tree, something happened, and he broke his ankle. now if you're a zebra and you break your ankle, that is not a good situation, but you're still able to get from point a to point b on three legses. you're a biped and you break your ankle, you're already slow and now you're hoping, i don't see how you survive and yet this is a healed fracture and it's connected to bipedalism, these

vulnerabilities we have as bipeds but then the fact we have injuries that make it particularly feeble as bipeds is i think explainable only if we were and continue to be empathetic and compassionate and generous and pro social with one another. >> fascinating. i know now has some questions from the audience she wants to put to you so we'll turn it over to you. >> thank you. i hadn't heard that about the healed ankle. that's amazing. no idea it went that far back. sorry. that -- >> well, no -- that it was a discovers in 2010. >> okay. >> it's di -- it's 11 years ago

now but still it's is an indication of just how rapidly my colleagues are finding these fossils and putting them out there and each of these fossils has this amazing story, to tell about why we are the way we are today. so, it's easy if one -- for one to be over looked and that one is a cool fossil and that one didn't get the attention it deserved. >> that's amazing. i feel like the memory i have are that you don't -- the last i heard there wasn't evidence of that until -- so the idea that -- anyway, sorry. that's awesome. that's nice to know that we can be nicer than we think and that goes back longer. that's very reassuring. we have a question from -- if you were able to change human

anatomy to pick bipedalism easier on us, what would you adjust? >> oh, the foot. the foot is a disaster. i mean, i study feet, and the foot is sort of like evolution's example of a good try. you did your best. but what happened here is you converted a granting ape foot into something that needs to be rigid and have moments of flexibility and then push off the ground in a rigid way. so we have the same 26 bones in our foot that chimpanzees do. so imagine year trying to create something from scratch and needs to be able to contact the ground, aso-elastic energy and then kick off the ground into your next step and you make it

out of 26 parts? you'll fail that engineering court. just want happen. so, look at this. now there you go. here's a foot from ostrich and what happens over bird evolution the bones that make up their ankle and foot have fused together into a single rigid structure that is compose of eight or so bones in the foot of an ostrich, and this ends up looking a lot like the blade prosthetic that a lot of par paraolympians will use and can run very fast. i'd change the foot. the back is a bit of a mess as well. but i work more on the foot and

that's the first place i'd go. the knee is a disaster as well, but that's -- we'll stick with the foot. >> kind of branching off of that another question. do you think -- the question is kind of -- is it possible for bipedalism in humans or anywhere else to evolve and improve anymore to sort of like -- do we represent the zenith of what this is going to be? is that possible to speculate on? >> that's a great greatquestion. the think i love to talk to students about and speculate about. i don't think so. if you look in the plasticene all these different body forms that existed i don't see the human body today, home run -- homosapiens having an advantage.

with one looks like the joints were smaller and the home range wasn't as large, but i don't think we have reached some pinnacle of bipedal locomotion, and i'd much rather have the skeleton of an ostrich if i wanted to get from point a to point b on two legs. or a t-rex for that matter. and even if you look back in the past, one of the really fun things i got research writing this book were bipedal animals that have long gone ex-stink. there's a crock tile known as -- discovered in north carolina, by a vertebrate paleontologist at north carolina state -- at the museum in north carolina -- and she reconstructed the gait as being up on two legs, at least

occasionally. so imagine a nine-foot tall crocodile that could sprint on two legs. horrifying. and yet, what is -- i find fascinating is that didn't have evolutionary legs. what happened to crocodiles? they're on all fours and they're stealth hunters, ambush hunters, so being bipedal was not evolutionarily successful ultimately, being quoted trispeedal was and you see nat dinosaurs, the earlier dinosaurs were bipedal and then a bron to the sore russ and triceratops -- bipedalism seems to pop up occasionally and honestly fail. and either con verdict to quadrupedallism or being a dead-end lineage.

>> could you -- you brought this up in the conversation but maybe just as a kind of a reminder but what -- bipedalism arose gradually. what's the time span, how many millions of years? what's the time span generally? >> we don't know. it's really interesting. depresseds entirely on what the body form of that common ancestor look like. if it was a knuckle walker, it's they an stress central traits and chimpanzees retained. gorillas on their lineage, you have to have intense rapid natural selection go from a number-walking common ancestor to something that is not just getting picked off by leopards because it's hunched over and can't move quickly or efficiently. i foresee this happening

incredibly fast, or it happens incredibly slowly. if the common ancestor is something that is imagined more of -- like a large gibbon with sorter original originals or an orangutan thing and you get to get patchier forests of hates to mo mon 0 two legs legs and alrey has a body form to do that. it's not a new locomotion, it's an old locomotion in a new setting and would be very gradual, and what we would be looking for i think are anatomies that are not from an an arboreal biped but from a terese central biped and we have not thought would that be would how to distinguish something walking on two legs on the ground versus something moving on two legs hand assisted by

pedallism in trees where the trees are more compliant. and the forcees would be really different. wouldn't have to have that -- those hip mechanics because you're holding your body with your hands and won't have that pelvic tilt problem. and that's something we as a field haven't really grappled with. >> i would think that just in contemplating these different scenarios it would be easy to fall into the la markan trip about these. the way that -- i don't know. maybe by the time you're in your position not but i don't know, for the layman that we about a pretty easy trap to fall into. >> so, i'm a darwin union -- darwinian graduate and i think it's probably happened gradually, and i think there's probably not one explanation for why bipedalism assed a invokous

but was- -- advantageous and search north answer is wrong-headed. so, you have a population and variation and there's certain individuals that move bipedally more than others and they have more food and more reproductive opportunities and offow go. we're trying to figure out what allows to the individuals to have more food and more reproductive opportunities there oar scholars that think was more la markan, this was -- richard dawkins has written but that. things biteedallism emerged as a meme, cool thing to do, and that chimpanzees, gorilla's occasionally move two-legs and if that became the fad in that population you could have more and more individuals aping each

other, which is what we do, right? and because bone is plastic to an extent, you might get some of the anatomies that are really key to bipedal locomotion because you acquired them through your life, and the best example is at the knee. when you're born the femur is perfectly straight and as you toddle around your femur angles in and you become knock-kneed but we're not born that way. so when you find a femur and it has an angle to it tells us this individual had to have walked an two legs because there's no other way to get that angle. so there is this really cool combination of anatomies you're born with and anatomies you acquire that blend together in your musculoskeletal system that

allow you to move on two legs. >> man, okay. thank you. we have matthew asking, what circumstances are making it easier to find more fossils today? >> oh, great question, matthew. so, like any science, you build on the work of previous generations, and there are lot of false starts that happened and mistakes made, and you learn from the mistakes of predecessors but there's also a lot of technological advances happening, and so, for instance, the south africa, one reason that my colleague lee burger has been able to find as many fossil sites as he has is by using satellite imagery, and looking at clusters of trees that grow out of caves. when you're on the landscape walking it's really hard to see the caves, but from the top down

you can see them much better. so that's one of the things that's happening if also would argue that the declinization of the -- decolonization -- instead of dropping into spaces and spending a couple of weeks and then going back to the united states or western europe, a lot of this work now -- incredible fossil discovery is being done by individuals that are from those countries. so, charles in tanzania, charlie in kenya, and many, many other folks.so, kate, i'm curious what you think about that? why do you think we're getting this? >> i mean, i wonder if there's a little bit of a snowball effect.

oh, lee burger went into the cradle of humankind which was already supposedly really well- explored, and found these amazing things, and so maybe we all need to kind of like start going back to places we thought didn't have anymore fossils for us or we hadn't looked at yet, and kind of go in there with a fresh eye and fresh outlook. >> i agree. i think that's true. that assumption we had already -- that many over the great discoveries had already been made, i can't -- this last ten years, i've just been astounded by the number of fossils and not just the number -- it's knock like we're getting more of what we already knew about. that's happening to some degree. but we're also finding -- my colleagues are finding things that i don't think any of accuse

have predicted. certainly wouldn't have predicted -- any of them. so it's been this really wonderful awakening in our field and there's a humility there's a lot to discover and a lot of our ideas will be wrong, and that's okay. as long as we follow the evidence, then it's okay to have an idea based on the evidence you have and then, oh, look at this new fossil. shows i was wrong. oh, well. >> i think we can leave it there, i think we're about at time. thanks to both of you so much. jeremy and kate, thank you. this is fantastic, and thanks to you for joining us. please learn more about this incredible book at -- i posted

the link in the chart, harvard.com/book/first underscore steps and there's a link to donate. thank you so much for tuning in, and stay safe. have a lovely night and thanks again to both of you. >> here's a look at the best selling nonfiction books accord ago elliott bay book company in seattle. topping the list is musician brandy carlisle's memoir, broken horses. followed by 400 souls historians' edit he collection of writings on african-american history from 1619 to today. after that is caleb auto graphical poems in water i won't torch. next is an essayist thoughts on race and identity as an asian-american and wrapping up our look at the best selling books according to the elliott bay book company is braiding sweet grass that we should work with rather than shape the land

we live on. these authors have appeared ton booktv and you can watch their programs anytime at booktv.org. >> during a virtual iven hosts by the as spend institute in wbc, amanda riply discussed the importance of healthy debate and conflict resolution. >> four years ago i felt like as a journalist i had to do something differently. i felt like it is so easy at a journalist to make our political conflicts worse, even if you didn't intend to. some people intend to but most don't, and yet here we are, and it just felt like there was something i wasn't understanding about what was going on in the country and that's a problem; so, i spent a lot of time with people who study conflict of all kinds, personal, political, professional, at scale, individual, and the study of conflict as a system, particularly intractable

conflict, clicked everything else into place. a lot of forces got us where we are but that as an overlay suddenly made everything make sense in a distorted kind of way. so then the question became, all right, what can we learn from people who have been through really ugly conflict and gotten to a better place? i followed a handful of people, including a politician in california, a former gang leader in chicago, and an environmental activist in england, regular frustrated democrats in new york city and regular frustrated republicans in rural michigan, and the whole goal was to see how did they get a from high conflict, which is this really unpleasant, toxic, destructive kind of conflict to good conflict. the problem isn't conflict, turns out. it can feel that way but the problem is the kind of conflict and all those people made the journey which is encouraging and

there were pattern what happened first, second and third. so the book is about how they did that and how more of accuse do the same if we want to. >> watch the rest of the program online at booktv.org. ♪♪ ♪♪ >> starting now comp of the

gaithers burg book festival in maryland. toad today you'll hear author discussions on the trump administration, poetry and activism and how the national basketball association handled the covid-19 pandemic. find more information on program guide or visit booktv.org. the book festival starts now. >> people of the book, hello and welcome to the 2021 -- i'm your host for this morning's presentation. before we get started a quick plug to support today's authors by purchasing their book, not just from anywhere but from our wonderful book seller partners at politic and prose, one of america's premiere independent book stores women have links to the book in the description and i'll note that given all we have been through over the past year it's so important to support local jobs and the local economy. more on that later. i also want to extend a big thank you to your