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>> and worked as an educator. kate senior editor at scientific american writing about the organization and its organisms in some magazine also co-authored of lucy's legacy. tonight we will be discussing jeremy's new book exploring the ability unique to humans

of living animals walking on two legs that this was the crucial change that on for the evolution of humans despite the difficulties of the human genome. publishers weekly praises discovery in collaborating with colleagues to come through these experiencing firsthand his ability to turn anatomical evidence into a scale of human evolution and his enthusiasm will leave leaders informed and uplifted the digital podium is yours. >> i appreciate the introduction. >> great to see you. and also to harvard bookstore i'm delighted to ask jeremy about his new book about all the things that i get most excited to write about.

it is a pleasure to be here and i thought if you're up for it we could kick off the conversation by having you tell us why what sets us apart from other primates in mammals. we have large brains. >> we have a lot of similarities to our primate cousins that we have differences as well. upright walking is one of those other mammals fly and swim and delete your typical mammal lives around all fours like a goat dog cat squirrel moves around on all fours. but only humans will navigate

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 it. it ended up on the cbs news. it's something we do all the time. even use the word pedestrian but when another animal does it is remarkable. but the fossil record which is what i work on.

i study fossils and what we can tell they going back in time the common ancestor that we shared with our eight cousins the further back we go we lose those unique characteristics of evidence for language or a large brain. that happened more recently like the stone tools. the most ancient characteristic is the ability to move on to legs. not only strange as a mammal that the most ancient thing that sets off our lineage so i argue in the book it was the key innovation that led to leading to those other changes that's an interesting lens to

view the entirety of evolution. thinking about this from the biomechanics standpoint we take upright walking for granted we don't think about it. so what is special about it from the point of biomechanics when you describe the act of walking on two legs and what is unique about it? >> it is a balancing act. think about when i talk to my students imagine if i give you an assignment to design a chair you're probably design it with four legs there may be some clever students that do a barstool out of three legs but

if it's only two legs it will not work and the student will fail the assignment. to leg of locomotion is pretty unusual for a mammal to move around the world. we could get into bird locomotion then we see bi-pedalism in dinosaurs even ancient crocodilians lineage which is fun to think about. from a biomechanical standpoint it is about balance. one way we can identify fossils coming from things that are adapted to move on to legs because they have the specific shapes. these individual bones to align the joints that prevent us from tipping over or we change the action of certain muscles. so they would act in a way to prevent you from tipping over the classic example if you take a step and lift your other leg you fall over.

when a chimpanzee walks on to legs they waddle from side to side. but in humans we evolved a pelvis where the muscle attachment wraps around to the side of the body and on the side it counters act the tilt every time you take a step. if you find this part of the body and it looks like this you can tell something moves on to legs. here is lucy's pelvis and sure enough she has the hip joint arrange in a very humanlike way. even of this is the only part we found we could tell she could balance on a single leg and why would you do that unless you move around on two legs? from the biomechanical standpoint and connecting it to natural selection, it's not

a great way to move around your world. we are incredibly unstable and we follow a lot. that can be quite dangerous 30000 americans die every year from falling. in addition we are stunningly slow for a mammal. you same bolt the fastest human whoever lived, the fastest he ever ran was 28 miles an hour and his 100-meter dash the world record 28 miles an hour. but that is half the speed of a galloping zebra antelope and perhaps half the speed of a lion and a leopard. so evil thing this form of locomotion made us slow so it

raises interesting questions in what ways was this beneficial and allowed us to overcome some those now adaptations. >> and then you anticipated my next question. why he even all it seems to be a subpar way to get around i understand scholarship over many decades and people coming up with all kinds of ideas why we did come to have this unusual locomotion and there are some interesting ideas going back as far as darwin and i thought it would be fun to take a tour through those ideas if you wouldn't mind

indulging. >> if there was another mammal that moved on to legs regularly we could test this more effectively and say what does it do or eat or meeting patterns that this form of locomotion is beneficial? as a scientist you want to look into the world and say where else do we see examples like this the fact we don't have other animals that habitually walk around on two legs make this a scientific problem to solve. and the reason we haven't solved it that you could go back and take it right up through 2021. people were hypothesizing why bi-pedalism was advantageous for our ancestors. also seeing over tall grass.

interested in humans being able to stand and see off into the distance. if you look off into the distance and to see a predator the worst way to get away is bi-pedalism you could gallop away if you would be much faster. it never made sense to me. there are ideas that darwin saw the connection between the small canine teeth and bi-pedalism and tools about freeing the hands for tools. that becomes somewhat problematic although it is an interesting idea worth visiting the problematic is the timing we have evidence for bi-pedalism may be 7 million years old but we don't have evidence of stone

tools to three.3 million years is the oldest reported evidence for stone tools. then wild ideas about displaying genitalia that showing off your body. the ideas are a little more reasonable having to do with food sharing if you can free the hands to make weapons or tools and gather food than there is an idea that has been promoted the females gather food and share with others and then to flex that and argue the males were collecting the food and sharing it with potential mates. an idea that has may be a little more lasting powers but moving on to legs yes we are slow but we are energetically

very efficient one of the best ways to explain this is the ideas of an order to lose 1 pound of weight you have to walk about 70 miles because we're too good at it we are to energetically efficient. now you don't want to lose weight but if you need to get enough food to survive and maybe there's not a lot on the landscape than those individuals are moving in a way energetically efficient may survive better. that's a possible idea as well. there are lots of hypotheses and we still don't have a handle on it and that's okay. there will be plenty of things new discoveries will allow us to go back to revisit these ideas. really the issue is not

figuring out which one is right but narrowed the list for those that are clearly wrong. that's a science works by refuting ideas rather than proving them. >> so we don't know why bi-pedalism but we do have a lot more information than we used to about the timeframe in which it evolved. maybe we can talk about the fossil discoveries that have allowed you and your colleagues to start to piece together when this all happened and what bi-pedalism may have evolved from and where it took us. >> yes a lot of false listening know about lucy discovered in the seventies.

she is a magnificent partial skeleton the original of her is in ethiopia. not long after there were footprints at the site in tanzania where i do some of my research as well. that pushed bi-pedalism from three and half million years ago a report and discovery that human life bi-pedalism existed at three.5 million but genetics point towards a common ancestor we enjoyed with chimpanzees at six or 7 million the split between the two lineage is complete by 6 million years that's a big gap three.5 million or 6 million what goes on in that time frame? it has been important discoveries that have been

made that teach that story together one is a partial skeleton from ethiopia like lucy look at the pelvis in the foot would indicate at least occasionally was able to move around on two legs and it was on the ground also has a big rasping told so when excellent tree climber with long curved fingers. when it came down to the ground it did not knuckle up and moved on to legs now four.5 million it is bipedal. then the evidence becomes more controversial and a little more difficult to interpret

this is five.5 million from ethiopia it matches the shape of a human toe that would push off the ground when you are walking whereas a chimpanzee the toll curves near the direction for grabbing. this has a curvature more like an eight but has the angulation to the base meaning probably it could push off the ground so this is a cool fossil but it is just a total. [laughter] here is a femur from kenya 6 million years old. compared to a chimpanzee, the head or the ballpoint of the hip joint is very similar but look how the neck is on this

fossil compared to the champ and what that would do to reposition the hip muscles by drawing them farther from the head and making it more efficient and we think that anatomy is evidence for bipedal locomotion and then if you go back even farther at 7 million years with this remarkable school discovered in chad and is very controversial. researchers who found and first interpreted it argued the whole at the base of the school where the spinal cord would exit was in a humanlike position and therefore this creature could hold itself upright and maybe even walk on two legs. we don't walk with our heads i like to see fossils from other

parts of the body and now there is a femur that has been published by one team and another has a printout in it comes to completely different conclusions if this is the upright walker or not. as you converge as a common ancestor you will get something that isn't quite to the living eight or a fabulous combination or may be a frustrating combination that are difficult to interpret. it's maybe what you might expect in a common ancestor. >> do you think that femur looks like that of a bipedal? >> i love to talk about fossils. this is not a fossil that i

have not been able to see myself. however, there are even older fossils now we'll have much room eight or nine or 10 million but there is a new discovery from a site in germany that may sound surprising because we been talking about sites in africa but apes expanded all around the mediterranean what is today and living in forest in southern europe's suites find fossils in turkey greece italy hungary but the new fossil from a new creature from 11.5 million years old in germany looks like it is very upright. to me that is an interesting find because it could imply

were trying to figure this out it is the hottest topic in our field right now of when the body form from which bi-pedalism evolved. a lot of t-shirts and bumper stickers and cost one - - coffee cups suggest a chimp turned into a human but chimpanzees are our cousins not ancestor the common ancestor is in eighth that we come from and so have chimps of they have evolved it's not a given a common ancestor was a knuckle walker and some of the fossils we are finding in those deposits might indicate the common ancestor was more upright in the trees and knuckle walking is a more derived form of local one - - locomotion plenty of colleagues disagree and think

knuckle walking is the form from which bi-pedalism evolved and they make compelling cases for that we need more fossils to figure it out. >> a very revolutionary idea to think about that. actually it is a unique trait and at 10 million years old to be a biped is quick. >> i don't think so i think the genetic data show very clearly when the lineage was branching. having said that, there are big marks around these divergence but you raised an important point they have always operated under the assumption that if you find anything that has characteristics of upright locomotion that it is automatically by definition a

homonym meaning and ancestor or an extinct relative of us more closely related to us than any of the apes. i think that assumption is on the table maybe not being 100 percent correct because in the late miocene you were experimenting different forms of locomotion like apes 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 lucy. i think that tells us about like positioning not necessarily weight-bearing at the terrestrial bipedal way but an animal in the trees

moving with hand assisted bi-pedalism sometimes gibbons will do this. spider monkeys will do this. but it would mean that the evidence for bi-pedalism may not be enough anymore to claim homonym status. this will be fine as we find more fossils from the 10 million your time. we can see a lot of experiments going on with locomotion and lots of false starts where bi-pedalism may have evolved and then the animal died out. that it was just not selectively advantageous form of locomotion in that habitat as those habitat changed it will be fun.

>> definitely. so let the fossil record show that the origin of bi-pedalism but you mentioned briefly that there are other forms of data we can look at to study the emergence of this locomotion and you mentioned a place that it was wanted to visit one of the most iconic sites even just thinking about it gives me chills. so there is the very famous set so you see behavior of an animal. what does that tell us about the evolution of bi-pedalism at that time compared to what you know about going back?

>> it is bi-pedalism two.zero. those footprints, i was there in 2019. yes. the place is magical. it is amazing. there are footprints in all of the's deposits coming out of the hillside and bones i love fossils these are wonderful and tell stories about the bones but the footprints are alive. they tell you about this moment in time in the life of a living breathing thinking individual who was a lot like us.

and a lot of the recent biomechanical work that has been done on the footprints, tells a story it moves a lot like us. it is not hunched over or crouch down like a groucho marx or a chimpanzee but something from a distance would look like you and i walking if you put on a treadmill you would pick up subtle differences and that's a fun thing to think about but from the footprints and from the bones looks like they are not pushing off the big toe quite as much as they do the legs are a little shorter and maybe not extending at the hip quite as much when we walk but those differences are subtle.

one of the amazing discoveries of the last ten years we think of bipedal evolution in a linear way talking about bi-pedalism two.zero but instead we see those evolving in a different species so at the team time on - - same time there was another species and had a divergent big toe and ethiopia climbing trees and walking in a different way. is a fabulous discovery and ethiopia in 2009 to show there was different forms of walking and coexisting and i worked on

the foot and the leg of a skeleton and when i first started to work on it, to me i just finished my phd i finish the foot and ankle and leg of domino aids i saw the biggest fossils it was interesting but not a functional variation until this. it was so different from any i had ever seen and aspects of the hip and the lower back we would've walked in a very different way than lucy and her kind this 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 some of them i don't think we did but from the foot down and the leg bone i think many of them walked in the's different ways or flavors so talk about jumping in a time machine to see the different species of the ancestors not only look a little different but they

would be walking in slightly different ways. host: to think about that degree occurring for the vast majority of human evolution not just in the miocene but when it was first appearing that virtually up until yesterday in geological terms. >> that's right. it is amazing. when i was in school at the university of michigan the story was home or rectus and homo sapiens and then what do we do? a different species or part of the heritage? and now studying upright walking the pleistocene was not that interesting so let's go back to the pliocene. that is interesting there's a lot going on there so the

earliest evidence we have with the evidence that we do it's interesting that just a few hundred thousand years later with those footprints so we are getting closer to what darwin was talking about potentially and i am wondering that could it be that bi-pedalism two.zero is what frees the hands to start doing things like making stone tools? >> i think that possibility is on the table and those bipedal

origins also brain size and management which we know is probably not part of the story but you are absolutely right if you go back and then the oldest stone tools at one.eight. so it looks like darwin was wrong that the two are chronologically not aligning then stone tools that are two.six found at the site of go now. we are getting closer. humanlike bi-pedalism did get pushback things to aid tibia discovered that would be four.2 million and very humanlike. i would like to see what the rest of that creature looks like.

and honestly my expectation given how remarkable my colleagues are looking one - - finding for the on - - finding these fossils. wish i could be out there but they are better. there has been extraordinary discoveries in eastern africa over the last decade or the last two decades. but we now have reports of stone tools three.3 million and it is controversial. i don't know why they would not be making stone tools there is slight black brain and large meant and there is a

new discovery on the basis if they keep a child of a juvenile skeleton it shows they slow down brain growth. that is tied in mammals to rely very heavily on learning edits but also heavily predated upon in the environment you want to speed up your growth rather than slow down and there are plenty of carnivores more than happy to be the early homonym so the fact it slowed brain growth tells the story heavy reliance on learning and that might have evolved but also cultural buffering how do you ward off how do you avoid and do that

all the time you look out for each other and have each other's backs. that is bipedal locomotion it is not an evolutionary success it is either superfast like an ostrich or super social and even compassionate like we are. >> that is a fascinating point you made in the book talk about the early ideas of bipedal is on to now you make the argument that it never could have worked with that

empathy and cooperation. >> i hope so. i think that idea about the upright not just for tools but for weapons is part of the popular culture we have seen in 2001 a space odyssey at the beginning with the weapons. and that has intellectual roots back to the very first the child sitting over my shoulder here but later in his career and he discovered bones that were smashed and he formulated a hypothesis that the homonyms themselves had been doing this that we were the blood thirsty killer apes

and is part of the popular culture even though we know now but those bones were smashed up because of hyenas but it is still part of how we think about ourselves instead i draw attention to a fossil like this and this is an upper leg bone about 2 million years old with that long neck that's how you can tell from the upward walker but what is amazing it has that heal fracture. this bolger bone sticking out of the medial side of the femur and think about breaking your femur 2 million years ago

node doctors or hospitals or fire or shelter and you break your leg and heal and to survive? that cannot happen unless other individuals are helping you out. not just 2 million in fact lucy species there is a second skeleton about three.5 million years old we think is a large male and he has a heal fracture he fell out of a tree or stepped in a hole and broke his ankle. if you are a zebra and break your ankle that's not a good situation but you can still get from point a to point b on your three legs if you are a biped and breaker ankle you are already slow now you are hopping around? i don't know how you survived but it is a healed fracture so he did survive it's connected

intimately to bi-pedalism that then the fact we have injuries that make you particularly feeble that is explainable only if we continue to be to be empathetic and compassionate and prosocial with one another. >> fascinating. we have questions from the audience. >> i have not heard that about that heal the ankle. i had no idea that went that far back. >> it was a discovery in

2010. now it is 11 years ago but it is an indication of how rapidly my colleagues are finding these fossils and to put them out there and each has an amazing story to tell about why vr the way we are today so it's easy to be overlooked and that is a cool fossil to get the attention that it deserved. >> i feel like the memory that i have is there was evidence of that that is awesome and it is nice to know that is just very reassuring. we have a question if you were

able to make bi-pedalism easier on us what would you suggest? >> the foot. it is a disaster. [laughter] i study feet. the foot is evolution's example of a good try. [laughter] it did its best but what happened here is you converted a class being 8-foot into something that needs to be rigid and have moments of flexibility but also push off the ground we have the same 26 bones in our feet so if you try to create something from scratch and you need to contact the ground absorb the

energy and kick off the ground and you make it out of 26 parts? you fail that engineering course. [laughter] look at this. there you go. there is a foot. that is an ostrich. what has happened over bird evolution is the bones that make up the ankle and foot are fused together in a rigid structure composed of instead of 26 bones it is about eight in the foot of an ostrich. this ends up looking a lot like the blade prosthetic that the parent olympians will use with great effect and can run very fast. i would totally change the foot the back is a bit of a

mess as well. but i will look more with the foot in the first place i would go. the knees are a disaster as well but we will stick with the foot. [laughter] >> do you think. >> is it possible for bi-pedalism in humans or anywhere else to eve all for improve anymore? of what this will be? is that even possible? >> that's a great question. if you look at the pleistocene all the different body forms that existed, i don't see the human body today as homo sapiens having an advantage over others like, rectus.

it looks like the joints were smaller in the range was not as large but i certainly don't think we have reached a pinnacle of bipedal locomotion. i would much rather have the skeleton an ostrich getting from point a to point the one - - or point b so if you look back in the past one of the fun things i get to research writing this book were bipedal animals that have gone extinct there is a crocodile discovered in north carolina who is a very good paleontologist at north carolina state i'm sorry at the museum in north carolina. she reconstructed the gate of

the ancient crockett daily and on two legs so imagine a 9-foot tall crocodile up on two legs that could sprint. that is horrifying. [laughter] but yet what i find fascinating that didn't have evolutionary legs. but crocodiles are are on all fours so being bipedal was not successful ultimately but quiet was the earliest dinosaurs were bipedal a pattern stories and brontosaurus tego saurus and triceratops quadrupeds that evolved from the biped. since the pop up occasionally and honestly failed and convert to quadra pedal is a

more it is a lineage. >> you brought this up in the conversation as a reminder but what is the time span generally? >> we don't know. it depends highly on the body form of the ancestor because if it was a knuckle walker if that is the ancestral trait then chimpanzees retained it on their lineage, then you have to have intense natural selection to go from a knuckle walking common ancestor to something that is not just picked off by leopards because it is hunched over and cannot move quickly or efficiently. so in that circumstance it

would have been incredibly fast or incredibly slowly of the common ancestor is something more like a large given or smaller orangutan and the trees and then you get a patch year forest it has to move across the landscape but it already has the body form to do that. it's not a new locomotion but the old locomotion in a new setting. in that case it would be very gradual what we're looking for are the anatomies something from a terrestrial biped.

we haven't even thought what that would be how do you distinguish from something walking on two legs on the ground versus two legs in the trees where the trees are more compliant so the force is different you probably wouldn't have to have the hip mechanics because you hold your body with your hand see you don't have that tall thick tilt problem. >> so to contemplate these different scenarios it would be easy to trap these. it would be pretty easy trap to fall into. >> and there's probably not

one explanation why it was advantageous but a host of things so however, you have a population and the variation in certain individuals that move more than others and they end up having more food and reproductive opportunities. offer you go. we try to figure out what has those individuals to have more food. there are other scholars and richard docs it on - - dawkins has written about this he thinks bipedal is a merged that it was a cool thing to do. and chimpanzees and gorillas occasionally move on two legs

but if for some reason that was the fat in that population then you could have more and more individuals aping each other. and bonus to the extent you might get some of those anatomies that are key to bipedal locomotion not because you inherited them genetically but acquired them three or life. the best example is when you are born your femur is perfectly straight but as you start to toddle around your femur begins to angle in. you become not need but we are not born that way. some you find that femur with an angle it tells us this individual had to have walked on two legs because there is no other way to get the angle so there is a cool combination

of anatomy you are born with an anatomy that you acquire that land together in your musculoskeletal systems to allow you to move on two legs. >> thank you. >> what circumstances make it easier to find more fossils today? >> great question. like any science you build on the work of previous generations. there are a lot of false starts and mistakes made. you learn from the mistakes of predecessors. having said that technological advances are happening. in south africa one of the reasons why my colleague could find as many fossil sites as he has come is by using satellite imagery and looking

at the clusters of trees that grow. on the landscape walking it is really hard to see. but from the top down you can see them much better. that's one of the things that is happening. also the decolonization of east africa has played a huge role instead of dropping into the places spending a couple of weeks then go back to the united states or western europe, now we work incredible fossil discovery is being done by individuals that are from those countries. ethiopia, tanzania, kenya and many others. kate, why do you think we get

this? >> i also wonder if there is a little bit of a snowball effect. so the cradle of humankind and we found these amazing things so maybe we need to see a something we haven't looked at yet. with a fresh outlook. >> i agree. that is true. there are many great discoveries had already been made. so the last ten years i have been astounded by the number of fossils. it's not like were getting more but we already knew about. that is happening to some

degree. but my colleagues are finding things that any of us could not have predicted i cannot have predicted any of them. it has been a wonderful awakening in our field and it goes to humility there is a lot of us out there to discover and a lot of 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 that you have. look at this new fossil that shows that i was wrong. so well. >> i think we can leave it there. we are out of time. thank you so much jeremy and

kate this is fantastic thank you for joining us read more about this incredible book is also a link to donate and thank you for tuning in. stay safe have a lovely night and thank you to both of you

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