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powered by cable. >> jeremy's and enter policies at dartmouth college editor of is the editor of a most interesting problem what darwin's dissent of man got right and wrong about human evolution. he is part of the research team that discovered and described it to members of the human family tree he studied wild chimpanzees in western uganda in early human fossils and museums that eastern and south africa from 1998 through 2003 he worked as an educator at the boston museum of science. senior editor at scientific american but she has been writing about the evolution of humans and other organisms for the magazine since 1997 she is also co-author with donald johansson of lucy's legacy the quest for human origin. tonight they'll be discussing

jeremy's new book first steps, how upright walking made as human part in it desilva explores the history ofng bipedalism, the ability unique to humans among living mammals to walk on two legs but he makes the case that bipedalism was a crucial change allowed for the evolution of humans despite the difficulties opposed to the gene forever after bread publishers weekly praises desilva love a fossil discovery and collaborating with colleagues come through and the experiences in examining bones of firsthand but hiss ability to turn anatomical evidence into a focused tale of human evolution and his enthusiasm for research believe it readers both informed and uplifted. i'm so pleased to turn things over to our speakers. the digital podium ensures y jeremy and kate. >> thank you. i really appreciate the introduction. hi kate, thank you for being here. >> great to see you. thanks so much nell and jeremy

and to harper's bookstore. i love the opportunity to pepper jury with questions about his fabless new book which is about all of the things i get most excited to write about. it is really a pleasure to be here. i thought may be jeremy if you're up for it will kick off the conversation by having you tell us why. humans have a number of traits the other mammals some other primates. why focus on this? we have these differences of these other differences as well upright walking is one of those

they knuckle walk and climb. your typical mammal runs on all four should think about a cow, goat, sheep, dog cow squirrel was run on all fours. only humans will navigate the world on their extended hind limbs all the time. it's a strange way to move it. and when a nether mammal does it we kind of lose our minds. we take out our cameras appeared to videotape what's happening, we posted to he gets millions of hits. in researching this book i found examples of bears moving on two legs in new jersey. a bear nameded paddles. bear walking a gorilla in the philadelphia zoo, lewis started walking on two legs occasionally. out frequently just occasionally. someone got a video of it and ended up on the cbs a news. and so that's do all the time.

we even use the word pedestrian, right to describe something ordinary. the fossil record i am a paleoanthropologists so i study fossils. and what we can tell by going back in time to the common ancestor we sure the further back we go the larger brain those things happen more recently. stone tools. what is then most ancient characteristically think on our 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 all set our lineage off. and i argue in the book it was

that led to those other anatomic and behavioral changes that make us human. >> it's a very interesting lens to view the entirety of the human evolution in a sense. this might sound like a weird question but about the biomechanics standpoint upright walking way to relatively take it for granted. we don't really think about it. so whatpe is special about it fm the standpoint of biomechanics? would you describe the act of walking on two legs and what is unique about it how do you convey that? >> it is a i balancing act movig on two legs. when i talked to my students aboutk is if i gave you an assignment to design me a chair. you would probably design it with four legs.

there might be some clever students to make a barstool and make it out of three legs. but if you make a chair out of two legs is probably not going to work. they will fail the assignment. two legged locomotion is a pretty unusual way for a mammal to move around the world today. we canar get into bird locomotin at some point in the deep in the past we find evidence of a bipedalism in dinosaurs and even in an ancient crack dealing and lineage which is really fun to think about. but from a biomechanical standpoint this is about balance. things from adapted to move on two legs is because they have these specific shapes to them. this individual bones that would align the joints inif a way that would prevent them from tipping over. or would change the action of

certain muscles would act in a way to again prevent you from tipping over. one of the classics examples is a hip joint. take a step and lift your other leg you fall over. when the pnc walks on two legs out if they do they wubble from side to side. but in humans we have evolved a pelvis. we evolved a pelvis with the muscle attachments here are on the side of the body. while being on the side they will counteract that tilt every time you take a step. so he find this part of the body and it looks like this you can tell you have something moving on two legs. here is lucy's a pelvis sure enough she has got those hip joints are arranged in a very humanlike way. so even if this was the only part of her wef found we would e able to tell she was able to

balance on a single leggett. and why else do that unless you are moving around on two l legs? but from a biomechanical standpoint and really connecting it to the actual selection it is not a great way to move around your world. unstable underly two legs. we fall a lot. and that can be quite dangerous as 30,000 americans who die every year falling. in addition to that we are stunningly slow for a mammal. the fastest human is far as we know has ever lived. the fastest ever ran was 20 miles an hour infa his 100-meter -- in 2009. 28 miles an hour. it sounds impressive and it is i cannot come close to that, right? it is half the speed of a

galloping zebra half the speed of a galloping antelope. perhaps more importantly half the speed of a lion in a leopard. evolving this locomotion made a slow period and so raises some really interesting questions and what ways was this beneficial and allowed us to overcome some of those amount adaptations you could frame it as, the lack of speed. >> you anticipated my next question why ohue evolved this o be a sub car way of getting around? i know there's been a lot of scholarship over many decades with people coming up with all kinds of ideas about why we could come to have this unusual

kind of locomotion. there are really interesting ideas going back as far as lamarck and darwin. some ideas if you would not mind indulging us. >> it's one of those things if there's another mammal that moved on two legs regularly we would be able to test this more. do some science and say what is this other mammal do question but what it eat? what are its mating patterns are what ecology doesn't live in it which is form the scientists you always want to look out into the or else we see examples like this? the fact we don't have other mammals that habitually walk run on two legs mixes that really difficult scientific problem to solve. it is one of the reasons we haven't solved it.

take it right up to 2021 people are still hypothesizing why bipedal is him was selectively advantageous for our ancestors. you've got ideas of seeing over tall grass. being able to stando at sea off into the distance. if you look off into the distance and you see a predator the worst way would be bipedal e. gallup await you would be much faster. that is never made any difference to me. there are ideas darwin saw this connection between our small canine teeth bipedalism and tools. this isg about freeing the hands for tools. that becomes somewhat problematic it's an interesting idea and worthha revisiting.

problematic because of the emtiming. bipedal listen at six and 7 billion years old terrestrial. and we do notld have evidence fr stone tools 3.3 billion years old this reported evidence for stone tools. showing off your body if you can free the hands not to wait make weapons oro food, and lovejoy we

are energetically very efficient. one of the best ways to explain this talk about these ideas and they said that in order to lose a pound of weight you would have to walk about 70 miles. because we are too good at it there were two energetically efficient. don't lose weight but if you need to get enough food to survive and may beat there's not a lot on the landscape those individuals are moving in a way that is energetically efficient. veit might survive a little better. and so that is a possible idea as well. lots and lots of hypotheses.

and we still do not have a handle on it and that is okay. there's going to be plenty of things that new discoveries new fossil discoveries will allow us to revisit some of these ideas and retest some of these ideas. really the issue for me is not figure out which one is right. it's beginning to narrow that down and eliminate the ones that are clearly clearly wrong. by refuting ideas rather than proving them. >> right. so we do not know yet why. we do have a lot more information that we used to about the timeframe in which it evolved. we could talk about some of the discoveries have allowed you and your colleagues to start to piece together when this all

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 1970s. lucy is a magnificat skeleton that got her back here the cast of her the original is in ethiopia of course. not long after lucy was discovered there werea footprins found in tanzania were due some of my research as well. pushed bipedal as a back to about three and half million years ago. those were remarkably important discovery assuring human like bipedalism existed three and a half million. and yet the genetics would point towards a common ancestor we shared with chimpanzees at about sixes or 7 million. the split between the two

lineages is probably complete my 6 million years. that is a big gap of 300 million to 6 million what's going on in that timeframe? i'm in the last 20 years there have been really remarkable and important discoveries that have been made to begin to piece that story together. it is a partial skeleton like lucy from ethiopia that's one half million years old known as already. and has some of the key of the pelvis and the foot. that would indicate it was at least able to move around on two legs when it was on the ground. it also has a big grasping toe in the foot. this is an excellent tree climber, log curved figures. really good tree climber bone it came down to the ground didn't knock a lot? no it appears it didn't. it could actually move on two legs. thatnu is foreign a half a milln now with got something bipedal.

if you go further back than that the evidence becomes much more controversial. and a little more difficult to interpret. so this is a toe bone from a half and nitrogen it matches the shape especially the end of the bone of a human toe that would push off the ground when you are walking were as a chimpanzee the toe actually curves the other direction for grabbing. this has a curvature to it that's more like an ape. but hasn't angulation to its base like yours and mine. meaning it probably would have been able to push off the ground. so this is a cool fossil it's just the toe. it be nice to have more. here's a beautiful femurta from kenya that is 6 million years old. what's unique about this one

issue compared to a chimpanzee here is a chimpanzee the head or the ball part of the hip joint very similar. but look how short the neck is on the chimp and how long that neck is on this fossil. and what that would do is similar to what i talked about earlier, repositioning the hip muscles to balance on a single leg by drawing those muscles further from the hip you are making them more efficient. i would think of that anatomy is evident for bipedal locomotion this is a fossil from overrated. and then if they go back further than that than 7 million years there is this remarkable's goal that was discovered in chad. and is very controversy open to the researchers who found it in first interpreted it argued the hole at the base of the school where the spinal cord would exit the brain was in a very

humanlike position. and therefore this creature would have been able to hold itself upright. and maybe even walk on two legs. we do not walk with our heads. i like to see fossils from other parts of the body. and there is a femur now that has been published by one team and another team has a preprint out. they come to completely different conclusions on whether this is an upright walker or not. as you converge on the common ancestor you are going to get something that is not quite like any of that living apes and is a fabulous combination and may be a frustrating combination of anatomies that are difficult to interpret. it's might what you would expect in a common ancestor. >> so do you think this femur looks like that of a biped?

or no? >> well, i like to talk about fossils i've been able to see. this is not a fossil however there are even older fossils now do not have much but there is this new discovery from a site in germany and it might sound surprising to some of the folks listening because we been talking about sites in africa. apes expanded all around the mediterranean. what is today the mediterranean were living a in force in southn europe and.fossils in spain, france, turkey and hungary. this new fossil 11 half million

year old deposits in germany looks like it's very i upright. that's a very interesting find. it could imply it was still trying to figure this out 20 hottest topics in our field right now of what is the body form from which it evolved? there are a lot of t-shirts and off the cups and bumper stickers that would suggest a chip turned into a human, right? and chimpanzees are not our ancestors they are our cousins. the common ancestor is an ape that wheat branch from but so did chips and chimps have evolved to. so it's not a given that common ancestor was a knuckle walker principally fossils we are finding and those deposits might indicate the common ancestor it was more upright in the trees.

and knuckle walking could be a more derived form of locomotion where there's plenty of researchers that would disagree with that and say knuckle walking is the form from which bipedalism evolved and they made compelling cases for that we need more fossils to figure this out. >> it's really revolutionary idea. it is what to think about that. now if bipedalism is a uniquely prominent trait, and did dubious at 10 million years old is a biped was up potentially homonym? >> i do not think so. i do not think the timing is right in the genetic data show very clearly when these lineages were branching. having said that our field has

always operated under the assumption if you findys anythig that shows characteristics of upright locomotion it is automatically by definition a homonym. meeting it ancestor or a distinct relative of us and would be more closely related to us that any of the other apes. that assumption is on the table as maybe not being one 100% correct. because if you had apes experimenting with different forms of locomotion including ocupright apes in the trees, navigating in the trees they might have some anatomies that look a little more humanlike. the tibia in some ways not always but in some ways looks very much like lucy's. and i think that is telling us

about leg petition positioning. not necessarily weight-bearing on a terrestrial bipedal leg but an animal that's in the trees and moving with hand assisted bipedal is unlike orangutans, gibbons will doh this. spider monkeys will do this. but rates it would mean finding evidence for bipedal is him may not be enough anymore to claim a competent status. this is going to be fun. as we find more fossils that five, six, seven, eight, nine, ten time. i think we'll see lots of experiments going on with f locomotion. and lots of false starts lots of places where bipedal is him as they attempted but may have evolved. and then that animal died out.

it just was not a selectively advantageous form of locomotion as a habitat that changed. so we will see. it will be thawed. >> definitely. we've talked a little bit about the fossil records show the origin of bipedalism. you mentioned this brick very briefly. there are otherth kinds of data that we can look at to study the emergence of this kind of locomotion. you mentioned a place i always wanted to visit. seems like the most iconic bites even just thinking of it gives me chills. and so you are seeing behavior of an animal. what does that tell us about the

evolution of bipedalism at that point in time which is what 3.6 billion compared to what you know about it going back to dubious or aurora? >> bipedalism 2.0. it is a really good biped. those footprints i was in 2019 and 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 fossilizedov bones -- mike i love fossils sethese are wonderful we can squeeze information out of them until stories about our ancestors were like from these

bones. but footprints are alive. they're telling you about this moment in time and a life of a living is a lot like us. a lot of the recent biomechanical work that have been done it is telling the story of a very human like a biped. something moving a lot like us. it is not hunched over, crouched down, he hip bit need like a road to mark's walk or chimpanzee moving on two legs. this is something that from a distance it will look like you and i walking. now if you could put on a treadmill you pick up some subtle differences probably. that is a fun thing to think about you can never put on a treadmill. but from the footprints and from the bones it looks like they're not pushing off the big to quite as much as we do. their arches are a little flatter than ours are.

their legs are littlehe shorterb and they may be not extending at the hip quite as much as we do when we walk. but those differences are subtle. of the amazing discoveries of the last ten years is that we often will think of bipedal evolution in a linear way. i even just didn't talk about bipedalism 2.0. but what we see instead are different forms of bipedalism evolving in different species. and so at the same time lucy and her species was around her species were making this human like footprints there was a another species that had a divergent big toe that was in ethiopia not far from where lucy was found, climbing trees. and walking in a bio mechanically very different.

this was a fabulous discovery made in ethiopia in 2009. and showed there were different forms of walking and coexisting. and then behind me, the skeleton here was discovered by lee berger it's the first pieces by his 9-year-old son in south africa. also in 2009 is when they're published 2008 was the discovery. i worked on the foot and the leg of the skeleton. when i first started working on it is common to me i just finished my phd, i'd studied the foot, ankle, leg of a common noise and i'd seen these fossils. to me there is variation but not functionally meaningful variation until this thing. this thing was so different from any that i have ever seen with it to heal, it's ankle, it's the aspects of the hip and the lower

back that we have hypothesized it walked in a very different kind of way lucy and her kinds. what is neat is this it carries right up until. even on the doorstep of homo sabeans you have neanderthals in europe, you have in asia you have an right in south africa some of them bread with. probably never did. the bones of the leg bones these different flavors of walking.

jumping att a time machine in ay different time periods and see these different kinds of us. different species of our ancestors. not only look a little different and maybe be eating slightly different things but they would be walking in slightly different ways. >> it is really wild to think about that degree of experimentation occurring for the vast majority of human illusion. not just something that happened in the biasing the planet of the apes. but when they were first appearing, right up until virtually yesterday in geological terms. >> that's right, that is amazing. i was in grad school at the university of michigan story very much was right up to homo sabeans than what do with the other souls? that's we argued about pay where the different species or were they part of our heritage? so to me the study of upright

walking it was really interesting. already evolved human bipedal is him. so let's go back. now the scene is really interesting there's a lot going on there. >> if we go back to the earliest evidence we have walking more or less like we do it is interesting the oldest known tools are a few hundred thousand years younger than those footprints. so were getting a little bit closer what darwin was talking about potentially. and i am just wondering sort of how you see things aligning there. could it be bipedalism 2.0 is

what frees the hands to start doing stuff like making stone tools for quick setting that possibility us back on the table. this wasse darwin's idea of bipedal origins. he also incorporated brain size enlargement which we know now is not part of the story that does indeed happen later. but you are absolutely right. if you go back to the 1970s , 80s we have the life of print 3.6. the oldest known tools at 1.8. and it looked like darwin was wrong look like the two are chronologically not aligning for the stone tools found under 2.6. 3.6, 2.6 were getting closer. human like did get pushback thanks to a tibia discovered

about four-point to million years old. and it is very humanlike. i would love to sit the rest of that creature looks like. honestly i would say my hopes but my expectation given how remarkable my colleagues are fighting these fossils, i love being out there looking for them. they are much better at finding them. i think it was just made extreme discoveries in eastern africa in the last decade or so or less decades. knowing more about that is going to be really important. but back to the point they're controversial. but at that time, 3.3 million to me behaviorally i do not see why

they wouldn't be making stone tools. they are walking like us. there is slight brain enlargement about a 20% increase in brain size. there is that new discovery on the basis juvenile skeleton that shows they had slowed down brain growth. it slowed down brain growth is tied in mammals to learning relied very heavily on learning. this is as horrible idea for a slow biped. also something going to be heavily predated a part in the environment. you would want to speed up your growth rather than slow it down. there are plenty of carnivores on the landscape there were more than happy to eat in early hominid. the fact selection wasn't favored slowed brain growth tells the story of heavy reliance on learning and learning what?

learning how that might involve learning how to make stone tools. it's also a story of cultural buffering and social buffering. how do you survive on a landscape like that when you're small? how do you avoid being picked off by the leopard all the time is that you look out for each other. you have each other's backs. our sociology is built into bipedal locomotion. bipedal locomotion is simply not going to be an evolutionary success unless it happens in something that is either superfast or is super social. and compassionate like they are. the fact that that was really fascinating point you made in the book you start out by talking early ideas begin bipedalism to violent behavior.

now you making the argument that it could never have works. if our ancestors did not have the capacity for empathy and cooperation. >> i think so. i think that idea about uprightness freeing the hands not just for tools but for weapons both support the popular culture. we both in 2001 space odyssey. the beginning with the wielding of the weapons. intellectual roots back to raymond dart to discover the very first i was over my child here this wonderful little fossil. later in his career in the 1940s, post-world war ii he

worked at a site he discovered bones that have been smashed and he formulate a hypothesis the hominids themselves were doing a blood thirsty killer apes. that idea has had roots in a still again part of the popular culture. even though we know now is bones are smashed up because of hyenas. it was not sprayed the signs has refuted those ideas but it is hstill part of how we think abt ourselves. and instead of draw attention to fossil like this discovered in the 1970s by richard and his team in kenya. this is a leg bone and operate like bulk of it early hominid about 2 million years old. long tilton upright walking. the cool thing about this fossil the amazing thing about this fossil has a healed fracture.

bolts of bone sticking out of the inside but is a healed fracture. think about breaking your femur. don't fire no shelter. when you break your leg? but you healed? you survive? that cannot happen unless other individuals are helping you out. it's not just 2 million. back tohe lucy's bc thursday skeleton, a second skeleton. he was about three to half million years old. we think he is a large mail and he has a healed ankle fracture. he stepped in whole, fell out of a tree, something happened and he broke his ankle. now if you are a zebra you break your ankle that is not a good situation but you're still able get from point a 2.3 on your

three legs. if you are a biped and you break your ankle you are already slow at night you're hopping around your landscape. i do not see how you survive and yet this is a healed fracture. so thathe individual did surviv. and again if connected intimately these vulnerabilities that we have is bipeds but then the fact that we have injuries that make particularly feeble pit and again i think explainable only if we were and continue to be empathetic and compassionate and generous and prosocial one another. it isro fascinating don't have some questions from the audience that she was put to you. will turn it over to her perfect

hi, thank you i had not heard that about the healed ankle print that is amazing. i had no idea what that barbaric. this is -- (that was a discovery in 2010. eleven years ago now but still it is an indication of just how rapidly my colleagues are.t and putting them out there in each of these fossils has this amazing story to tell about why we are the way we are today. it would be easy for one to get overlooked. that one is a call fossil. i think he definitely did not do it the attention it deserved. >> that is amazing. until these questions but i feel like the memory i havehe of it when i heard there's not

evidence of that until -- anyway i'm sorry part off them, that's we can beat nicer than we think that's very reassuring. we have a question let's see here. if you werest able to change hun anatomy to make bipedalism easier on us what you adjust? >> left foot. the foot is a disaster. the study faints. the foot is sort of like evolution's example of a good try. back you did your best. but what happened here is you converted a grasping eight-foot and do something that to be rigid. moments of flexibility but push

off the ground any rigid way. with the same 26 bones in our foot that chimpanzees do. imagine you trying to create something from scratch and it needs to be able to contact the ground, absorbed elastic energy and kick off the ground into your next step. you make it out of 26 parts? do you feel that engineering course that just would not happen. look at this. now there you go. here is foot from an ostrich. what is happened over avian evolution, bird evolution as the bones of make up their ankle and foot have fused together into a single rigid structure that is composed of incentive 26 bones it so the foot of an ostrich. this ends up looking a lot like the blade at prostatic but a lot

of para- olympians will use in youth with great effect run very fast. i would totally change now known as the first place i would go. the knee is a disaster as well but will stick with the foot. looks kind of branching off of that we have another question. the question, is it possible for bipedalism in humans or anywhere else to evolve to improve do we represent what this is going to be? is not possible to speculate on? but that's a great question. it's a kind of things i like to talk to my students and speculate about.

i do not think so. if you see these different body existed, i don't to the human body today, homo sabeans, was having some advantage over the others. looks like the joints are smaller. i certainly do not think we have reached the pinnacle of bipedal locomotion. i would much rather have the skeleton of an ostrich if i wanted tost get from point a to point b on two legs. ort rex for that matter. if you look back in the past when the fun things i got to research this book were bipedal animal to the blog got extinct. for instance there is a

crocodile discovered in north carolina by lindsey who is a paleontologist at north carolina state. she reconstructed the date of this ancient crocodile lien as being up on two legs. i imagine a 9-foot tall crocodile would jump up on two legs and could sprint. that is horrifying. it did not have evolutionary legs. what happened to crocodiles? there on all fours. being bipedal was not successful ultimately. we see that dinosaurs stupid the earliest dinosaurs wereli biped. okay up out of, brontosaurus, stegosaurus those are quadruped.

bipedalism seems to pop up occasionally. and honestly fail. either convert or be a dead end lineage. 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 hunched over and can't move quickly or efficiently so in that circumstance i foresee this happening incredibly fast or it happens incredibly slowly if the common ancestor is something like a large given or smaller orangutan up in the trees moving on two legs and if there is environmental change and you get past the forests it has to move across the landscape but it already has the body form to doh that so it's not a new locomotion it's an old locomotion in a new setting and in that case it would be very gradual and whate we would be looking for i think our anatomies not from oil but

something that is terrestrial and we haven't even thought what that would be. as a field how would you distinguish something between walking two legs on the ground versus something moving on two legs and assisted where the trees are more compliant so the forces would be different you probably wouldn't have to have those hip mechanics because you're holding your body with your hands so you're not going to 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 the different scenarios it would be easy to fall into the trap about some of these. maybe the time you're in your position, i don't know for the laymen term that would seem it would pre- delete could be a

pretty easy trap to fall into. >> ima darwinian graduate and i think this probably happened gradually and there is probably not one explanation but it was a host of things in our efforts to search for the answer is probably pretty wrongheaded. however, so yes you've got a population and there is a variation and certain individuals that move and they end up having more food and reproductive opportunities and off you go, and we are just trying to figure out what allows those individuals to have those opportunities. there are other scholars that think this was, so richard dawkins has written about this that he thinks it emerged as

just a cool thing to do and that the chimpanzees and gorillas occasionally move on two legs and if that became the reason the fact in that population then you could have more and more individuals. because bone is plastic to an extent, you might get some of the add-on of -- anatomies not because ua inherited them but you acquired them through your life so the best example of this when you're born your femur is perfectly straight but as you start toddling around, the femur beginsr to angle and you become mock need but we are not born muthat way so when you find a femur as he did in 1973 that has an angle to it, it tells us this

individual had to have walked on two legs because there's no other way to get that angle so there is a cool combination of anatomy that you are born with and anatomies you acquire that blend together in your muscular skeletal system thator allow you to move on two legs. >> what circumstances are making it easier today? >> great question. like any science, you build on the work of previous generations and there are lots of false starts that happened and mistakes made. you learn from the mistakes of predecessors but having said that there's also a lot of technological advances happening so for instance in south africa

one of the reasons that my colleague has been able to find as many fossils sights as he had is by using satellite imagery and looking at the clusters of trees that grow. when you're on the landscape walking it's 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. i also would argue the decolonization of the science has played a huge role in this and instead of parachuting science and dropping into these places into spending a couple of weeks and going back to the united states and western europe a lot of it is being done by individuals from those

countries. i'm curious what you would think about that and why we are getting this. >> also i wonder if there is a bit of a snowball effect like the cradle of humankind which was already supposedly really well explored and found these amazing things so maybe we all need to start going back to places that we thought didn't have any more fossils for it. >> that assumption that many of the great discoveries had already been made.

colleagues are finding things i don't think any of us could have predicted. i certainly wouldn't have predicted any of them so it's been this really wonderful awakening in our field and just the humility that there's a lot out there for us to discover, and a lot of ideas are going to end up being wrong and that's okay as long as we are following the evidence, it's okay to have an idea.

>> i think we can leave it there. thank you for the fantastic, and thanks to you for joining us. please learn more about thisf incredible book and i posted the link in the chat, harvard.com/macbooks. there's also a link to donate. thank you so much for tuning in. stay safe and have a lovely night. thanks again to both of you.