Where Did Humans Evolve? Gazing at the Changing Nature of the Garden of Eden ~ Denise Su

This is the On Human's podcast, a show which makes new research about humanity more accessible to everyone and more meaningful to the big questions about who we are. I'm your host, Ilari Mackeller, and today's episode joins a small select group of past episodes on the show where we take one angle and try to understand the whole big arc of human origins of the early human story from that point of view. And this time it's going to be nature, it's going to be ecologies going to be the weather's. I think that the question about the nature, it's so important for two reasons. One is just that it's such a vivid part of how we imagine the story if we are going to draw or paint or narrate the scientific version of the garden of Eden. What are we going to paint? Are we going to paint forest? Are we going to paint a vast dry savannah? But this is not just a question for the aesthetic imagination. This is also very much a question about understanding the forces that made us who we are. In the long term listeners will know that a big part of the story that I have been telling on the show is a story of climate change. It's a story of how the African climate was changing during the course of human evolution, how the forest cover was disappearing, shrinking the habitat of the apes, clinging to those forests and opening up a possibility for an curious ape that would leave behind a life on the trees and explore the dangers and the opportunities of the opening plains, slowly evolving to be not a very good climber, but an impeccable walker, even able to do the weirdest of things that we do today, such as running a marathon. So that's a famous story, often called the savannah hypothesis. I've been telling versions of that story on the show and very many senior guests have told versions of this story on the show. And if you listen to the last episode on the show, with Richard Lee, who has done field work with modern day hunter, gatherers living in the very, very dry African, not even savannah, but actually the desert in the Calary Desert. But one of the reasons why people might think that studying their life start might tell us about the past is not just that they are hunter, gatherers, like we all used to be, but that they live exactly in this kind of very dry African landscape. Well, the other hand, if you go to Google and Google savannah hypothesis, you're going to very easily find articles saying that it's a myth that it's dead and that it should be buried. So what exactly is going on? My guest today is Professor Dennis Sue. She is a paleoecologist at Arizona State University's Institute of Human Origins and she is someone whose work comes very much up in those savannah hypothesis is dead style articles. So I thought that it would be great to have her on the show explain what exactly is going on here. And I was actually very happy to have this conversation because this was exactly the kind of one where I learned a lot, but I was also happy to see that if you read behind the headlines, there is a story. There is something that quite a lot of the scholars do actually agree on. So what exactly is that? Well, I'll let Professor Sue explain more. Now one thing is that we in this episode, we do discuss a fair amount of dates, millions of years. If you're not used to this, don't worry. We make our best to make them tangible. We are actually going to use a metaphorical clock, which I thought might be good to introduce here to give the context. So the last common ancestor with humans and chimpanzees lived around seven or six million years ago. If we imagine that it's just 24 hours as we're going to do in this conversation, that's the strike of the midnight hour. Let's zoom out first a little bit. Life on planet Earth started almost four billion years ago. What does that mean? That means almost two years ago. The first vertebrates, animals built of blood and bone who crawled from the seas to the open land, becoming all the birds and mammals and dinosaurs that lived. Now they were, you know, maybe two months ago. The dinosaurs, they died 66 million years ago, meaning around 10 days ago. So life has existed for almost two years. Land creatures on all fours have existed for around two months and dinosaur disappeared just over a week ago. And now the hominin story leading to humans begins. A lot of the conversation we are going to have is going to focus on the time period between four and two million years ago. So that is roughly between breakfast and afternoon tea, something between eight a.m. and four p.m. And just for context, our form of human homo sapiens only appears very much after sunset around 10, 11 p.m. So that's kind of mental model you can have in mind when listening and if you want to dig deeper into those dates, there's a time when in the show notes. But there we go. I think very, very much. Oh, you already, Danny, see you's voice. So let's get started. Thank you so much to all the wonderful people who have supported the work. I do a Patreon.com/OnHumans. This episode is always is dedicated to you. But whoever you are, whether you're a supporter or not, whether you have just discovered the show or are a long-term listener, welcome to this flyover over millions of years of human evolution. Now let's go. Professor Denny Sue, welcome to On Humans. Well, thank you so much for having me. So where did humans evolve? That's going to be the topic of our conversation. Before we get into all the exciting details about it, people who don't know much about the topic would probably begin by saying, well, probably somewhere in Africa. Is that right? Yes, that is correct. So our lineage and our lineage is pretty long. The origin of our lineage goes back to about six to seven million years ago. And now modern humans probably didn't appear until about two hundred to three hundred thousand years ago. So people who look like us, who are us. Homosapiens. Homosapiens, exactly. That's a much more recent origin. But our whole lineage goes way back into six or seven million years old. That's when we split from the chimpanzees. And that was in Africa. And we evolved in Africa. That is really, that is our birthplace. Who we are today is very much tied to where we originated. If we think about modern humans as the last possible, the most recent possible question in the where did humans evolve? And the earliest possible question is this question about the human lineage, the last common ancestor with humans and chimpanzees six or seven million years ago. In the middle of that, there is a period which is going to be the focus of our conversation, which is the origin of what perhaps we might be able to already call humans, archaic humans, who married the fancy Latin name starting with homo, something homo, habilis, homoerogaster, et cetera, et cetera. Let's maybe get a bit of a timeline. So if we imagine the six, seven million years as a kind of 24 hour clock, where the beginning from the last common ancestor with humans and chimpanzees, that would be the strike of the midnight hour. What kind of creatures would we find around the dawn, let's say seven a.m. eight a.m. So that would be like four million years ago. Okay. What kind of did we have a genius home yet? Did we have proper humans yet four million years ago? No, not yet. Our genius, homo, has not yet appeared. We won't appear for a little bit yet. And at that time, there were a few different early homin species kind of running around the landscape that we know of. There was something called artypithecus. And there was also species that belongs to the genus astral pithecus. And that is one that really proliferated during that time period. But they're, they are still very ape-like in terms of their brain size. And even the in astropithecus, that's the genus that the famous Lucy is in. So astropithecus afferences. That is a bipedal species. That's walking on two legs. And this is a species. It's not just that they're walking on two legs because actually just about every primary, modern primate can walk on two legs if they want to when they're like picking stuff up. If you notice in nonhuman primates, when they're picking stuff up, unlike your dog or your cat, they don't pick them up with their their mouth, they pick them up with their hands. Oh, very true. Yes. So if you're holding me through their hands, you have no choice but to get up on two legs and walk, right? There was just a very very naughty monkey that tried to steal my lunch at the Shoshan Park in Ingossian, in Taiwan. Very much just sending them to legs reaching for my backpack. Right. Exactly. And so that's that's a primary ability. And so what was different about us and our ancestors that were bipedal that walked on two legs is that we have no choice but to walk on two legs. Our morphology, our anatomy has changed in the last six to seven million years that really prohibits us from being quadrupeds or walk on four limbs, right? On the ground, those early hominins were not habitual bipeds. They were not required to walk on two legs. They could. And there was clearly changes happening. And so it wasn't really until Australopithecus afference is Lucy species between like three and three point seven three point eight million years that we really see the anatomy in place that forces us to walk on two legs while on the ground. And this other creature on the landscape, um, Australopithecus was not a habitual biped. It had changes in its anatomy in the pelvis that indicated that it it walked bipedally. It walked down two legs when it was on the ground, but it had a lot of morphology that indicated it was really using the trees a lot and that it was only when it was on the ground did it walk on this two legs. And you know, it had these really big hands with long curved fingers. It's big toe was opposable. It was basically had a grassy big toe. So that's very an interesting point, by the way, because I remember once seeing a photo about chimpanzee food that I've talked about as on the show before, it really looks like a hand. Exactly. And so already in this dawn of human evolution around a second, you said that already still had that kind of chimpanzee like toes. It's very much a climber. Yep. But so what about the Australopithecus like like Lucy? You said they start to be they start to lose that already. Is that right? Yes, they're their big toe was no longer opposable, but it's still more curved than ours. Our our feet are really quite specialized. All other primates other than us modern ones have feet that kind of look like hands. Their big toes, you know, can grab things. Our feet are like platforms. It's really it's really meant to be a stable platform for the way that we walk. And that came later in our evolution actually. So in this early time period, even in the habitual bipeds, you know, they're they had no longer had opposable big toe, but their feet still didn't look quite like ours. The toes are still kind of a little bit longer and more curved. They would not be running a marathon. No, they would they would probably not be running a marathon. But there was another species Australopithecus d'Aramada that was around the same time that Australopithecus afrens was. But this one had an opposable big toe. Okay. And just make sure. So these are two forms of Australopithecus in the same way. As for example, Neon the toes and homo sapiens are two forms of humans. Exactly. So part of the big family of Australopithecus seeds. That's right. Then you say that actually some of the Australopithecus seeds have this chimpanzee already like opposable some in the fruit. What does that tell us? Well, it tells us that it was using resources in the trees a lot. Otherwise, why retain that big toe? Because it's not very efficient for on the ground walking if you're going to be. So that's what that tells us really that it was still relying on the trees. And they also did chemical analysis on the teeth. And they found that it was eating a lot more C3 resources. And C3 food items are those that come from trees and bush. So think flowers and fruits and berries and leaves, those sort of things that their diaries really focused on that. Whereas Australopithecus afferences was the first species in our lineage to expand its its dietary repertoire to include C4 resources. And so those are things coming from grasses. Not necessarily meaning they're eating grass blades, but like the parts of grasses. Yeah. I mean, it's it's incredible. We can know all that stuff. I mean, these are creatures living three, so something million years ago. We can know what the eight. Yeah. And this C3, C4, just for these centers, we're not used to this topic. We're not going to be throwing a lot of this kind of science, the acronyms in this conversation, but this is super important. It's such an important way to try to understand what's going on in the past. Yeah. And I'm actually curious. Now that we are on it very briefly. How do you actually do that? Of course, this is your work. Like this kind of like what you take it into the lab and you put it in a test tube, you're wearing a white coat or like how do you go about studying this stuff? Oh, the isotope. So that is I actually don't do those that type of analysis. But it requires taking a little tiny bit of a mammal. So whatever you eat gets incorporated into actually your bones and your teeth. And so as your enamel is being formed, when your teeth are growing, so as you're a, you know, a baby and a child, a little, little child, as your teeth are formed and the enamel is being put down. It carries with the foods, the chemical signatures of the foods that you eat. And so so there are like my colleagues who do this, they take teeny tiny little samples of the enamel and then it's ground into powder and then they have to wash it in order to get rid of all the things that you wouldn't want to analyze. And then they they do run it through a process where then they can actually look at what the chemical composition is. It is quite an amazing technology and a lot, I have many colleagues who's really focused on working out what it is that these hominins are eating both from the chemical perspective, but then also some are looking at it from a wear perspective. What are the little micro scratches and pits that's being left on the surface of the teeth? And and so combined, we can get a pretty good picture of what it is that these early hominins were were eating. And by the way, you've been saying that these are the pithecus who do have a chimpanzee like food, they're clearly more in the trees, although they can walk upright, but they're clearly spending a lot of time in the trees. And in the osteopathythesens, we now have two branch is at least. I mean, they have many branches, but there you mentioned this clear contrast between on the one which is still more chimpanzee like with the tree climbing ability and is eating more tree stuff fruits leaves whatever. And then we have this one kind of form of osteopathythesensus spending more time on the ground eating more grassy ground stuff. Some people might even say Savannah stuff we'll get to that soon. Does it suggest that are the pithecus? Are they came first and maybe gave rise to osteopathythesens that then one of them stays like their ancestor and the other one goes away or are these are the are they actually just a kind of cousin that's probably not really on the direct ancestry line to modern humans. And yeah, he's already our ancestor. Ah, depends on who you ask. What do you think? What do I think? I am not a taxonomist and so I don't know that my opinions matter so much, but but I think that you know in the 70s, what we knew about human number of evolution was the earliest hominem we had was actually osteopathythes. Osteropathythes afrensus. Lucy? So these are more land-leabing already more human like? Yes, that's right. So in the 1970s, that was the earliest that was the earliest hominem. And and then we knew of some early homo species that I know we'll talk talk about a little later. And then we knew about homo erectus, which looked a lot more like us and had a modern body plan and then we had neanderthals and we had homo sapiens. In the 1970s, that was kind of the picture. Now let's fast forward to today. The fossil record has more than doubled. We now know the origins from the fossil fossil record perspective extends all the way back to 67 million years. And we have all of these common species that we do not know existed all around the same time as osteopathythes afrensus. The story is a lot more complicated. And so where did we actually come from? I think that it's hard to say, but because I'm not taxonomist, I look at things from a quite ecological perspective. For me, honestly, it doesn't matter so much. What's really important is to me, what are the factors that sort of drove our evolutionary changes? And that's what I really focus on. You mentioned ecology. That's what you study. You study what was the nature like? What were the weather like? Wherever in Africa they were. And how do you do that? How do we even know something like we've already mentioned the C3, C4? That tells us something about what they ate and that's going to be super important. But what else can we even know about? Where did artily or especially importantly, where did the astrolopytocinaphyrinsis that seems very clearly to be on this peak push towards our kind of creature? How do you know anything about what was the nature like? How does it work? You have to use a lot of different strands of evidence. A lot of what I do is very much based on the animals that were discovered with these commonins. And they tell us a lot from just what is there and what they were doing. So you would not expect to see a lot of grazing animals in a rainforest community. You can also study the soil itself. We have specialists who take soil samples. You can do the similar chemical analyses with soil samples that tells you whether or not there were C3 or C4 plants there. And also the ancient soils also often preserve plant material. So plants obviously like you know, degrade very quickly, decompose very quickly. But plants have a silica structure. It's essentially like bones and animals. It's it's called bones and plants. Okay. It's clearly not bones, right? But you can think of it that way. It's kind of the hard bits of plants and and their their microscopic, like you can't see them with your naked eye, but you can see them on a microscope and those are preserved. But it's kind of pulling together all of these different strands of evidence to try to put together picture of what the past was like. And I always like in it to putting together a puzzle. You have all of these pieces. The difference is that my pieces don't come from in a box and there's not a reference picture. Imagine the pieces are are that you only have a quarter of them and they're spread out all over your house. You have to go find those pieces first. Yes. Yes. And you have no idea what it's supposed to look like. Yes. Yes. Yes. And then you have to kind of put it together and probably a lot of the pieces won't join each other because you're missing about 75% of them. So that's what putting together the past is like essentially. This is usually that what I like to sort of say when I talk to people about what it's like to be a to be a paleontologist. That's essentially what it is. And I guess it's it's exactly like you said we don't have the puzzle image of this is what it should look like. But then of course some people might think well okay then why is this even interesting but what we have instead is we can have theories stories that we test. The after these puzzles fit into a story and one of the greatest story about that ties together all of these things that we've been discussing is that when we start from the midnight you know seven million years ago or something and we turn the clock what's going on in Africa is a climate change. Yes. It's it's much slower much much slower than what we are causing now could the planet but it's more dramatic in absolute terms. I mean we're not talking about two degree changes. I can't remember exactly but I've seen the other and they are dramatic. How much the game's this year goes down you get and forests are shrinking. And so this this this story is that we have a climate change we have less and less forest. Well we have a choice either you stay climbing those trees with that very nimble toe that prevents you from walking very well upright on the ground and you stay in the shrinking forests. Or you do what our ancestors did which is you start venturing more into the open into the great vast African savanna that's now opening up because of this climate change and as you become better and better adapted to that life on the savanna on the open grasslands humanity is bored. Yes. Yes. It's a great story. Now you're telling me I'm going that's I don't mean no wonder people clung to it for so long. I'm I'm I'm bearing much off invested in the store. Yes. Despite all the the the the the tricky things about it and and you are some of the people who have been very sober minded at trying to look at the these these pieces of the puzzle. Does it fit that story or not that I think that's really why I wanted to have you about people here on the show is to discuss how much of this story still fits within the puzzle that we have and what exactly has come down because anyone who wants to google the savanna hypothesis is dead you will find plenty of things about all the new pieces of puzzles which supposedly show that this great story is wasn't the just that a great story. So where should we where should we start? Where should we start? Well, maybe that start with what a savanna is. How's that? That's exactly by the way what the past yes I have this conversation with Jessica Thompson from Yale that was that was that was kind of what she also said is that look people often imagine this kind of Sarah and get the plane really vast almost zero trees. Well, but the savanna can actually be much more well why don't you yeah what what's the what should we think when we think of a savanna because I don't want to put her words into your mouth. Are you savanna is a huge it's a why I'm really quite diverse set of abatats. savanna at its core just means that the ground cover is grass that's it. So there's there's so there's grass that see four things but other than that it can ring from what we all imagine right when you watch those nature documentaries of these wide grasses with this lone tree in the background there yes yes yes and the elephant and the giraffe by the tree at the sunset that's right and so or so a little scatter of bushes here and there so that's on one end of the continuum to all the way to really quite vegetated types of landscapes or you could it could be very bushy could be lots and lots of bush and when we talk about bush in Africa we tend to think of bush as these little tiny things but bush in Africa can be like seven or eight feet tall so you could have something that's quite really heavily wooded so a lot of shrubs and bush and even even trees but there's still a ground cover of grass and that would also be a savanna we what really then what that means is that you know it's nothing savanna hypothesis is wrong in the sense that we evolved in savanna's because we we did our origin was not so at the very beginning of the human lineage it seems like those early homins were all in places that were really like densely wooded but let's jump ahead a little bit more so sort of to modern humans we are everywhere in the world right we occupy every single earth the world basically you can uh there's not a place on earth where there's not some human impact and so how is that possible and people have hypothesized and talked about through our ability to really adapt just how adaptable we are and that this is really why it is we're so successful as a species and as somebody who studies at the very kind of beginnings of our lineage uh I would argue that that ability to be very adaptable is probably pretty far back in our past when you look at you know something like Australopithecus aferences that is able to live in a variety of environments they're all savanna's but there were very different types of savanna's and and the fact that you find you know between like three and three point seven three point eight million years the species of hominin that's really quite widespread bound in lots of different environments I think tells us something about where our ability to adapt comes from that it is something very deep in our history and the something very core to being a human and so when I say that you know we did evolve in savanna's I mean but it's not the savanna hypothesis that that that has been out there for so long because the savanna's that always hominin species lived in range that whole continuum and we were not finding them in these kind of wide open grass lands and I'm not even sure that those really existed on the landscape at that time like there were grasses and there were probably quite large patches of grasses but they weren't like this kind of serringet-esque type of landscape do I hear you right that the problem with the big story that I told was not this big idea that there was a climate change for us the big dams rainforests jungles they were indeed shrinking in size human ancestors really did become more and more adapted to something that we can call savanna because it was grassy area but what was wrong was that they used to be this idea that humanity became adapted to one particular kind of environment and that is a very dry serringet-like playing where you have that long-metry and the beautiful sunset with that you're off do I hear you right that why that really matters is that we shouldn't think of it as just our ancestors they evolved to fit to one particular kind of place but rather they actually became quite flexible in going through between very different kinds of environments. Yes exactly and I think that you know think of the landscape as this patchwork right you know global climate change was happening things were getting cooler and drier across the globe on average but how local communities including plants right the plant community and then the animal communities follow them how they would have responded to that would be quite different depending on local circumstances and eastern Africa was really interesting at that time because it wasn't just that there was this kind of global climate change going on there was a lot of local tectonics I was happening so at the sites in Ethiopia in the Afra region where a lot of the evidence for you know early human evolution is coming from like that was a very the landscape was very active as then it was changing very quickly basically just the whole rift system was being formed at time it was starting to pull apart and you can still see that today I mean top any today still right so that's a very active landscape so you can imagine when the landscape changes the river with the water system would change and then when water systems change that impacts how the hominins would have lived on these pay the landscapes if you know there's not a lot of rain falling but there are these large river and lake systems and what that means for the vegetation that's growing there and and then the kinds of resources the hominins would have been using water seems to be key for not only because all you know all animals needs some water and but we do that particular amount modern humans because we have we've lost our fur is one of the other most striking things about us yes we have so little body body hair and and I think one of the main reasons for that seems to be I don't know if this is settled but at least the main leading explanation is that we sweat a lot and that's a way for us to cool the body and this relates to this kind of the big story is that one of the reasons we lost the fur is that when you move away from the rain for us from the jungle into that more open savannah and you start walking more you're more exposed to sunlight you have to find ways to cool the body and one of the ways is to lose the fur and unfortunately I guess fur is not so easy to read from the fossil record as standing upright that's much standing upright yes you know the bones are there the fur is not doing no at what point did we start being this weird naked apes and we start losing the thick fur was it with our the anerleostroepithesines was it laid osteopoeytocines early homo do we know I think most people would probably agree that it probably didn't happen until later in our evolution when you start seeing the modern body plan so that would be in homo erectus homo erectus so this is like what was it two million years ago so we are now like five p.m. or something yeah and and so before then the body plan was not like us at all basically we humans like in our as one of the trends in our evolution is that our legs got longer and longer and longer okay okay I mean if you look at chimpanzees right you notice they have very long arms relative to their legs and in these really early hominins they still had really long arms and if you look at like reconstruction of our the arms were incredibly long the the proportion the body was definitely much more like a chimpanzee and even even the habitual the early the early habitual bipeds like osteopathy is afrens is still had quite long arms you look at the the um reconstruction of Lucy for example I still had quite long arms and you saw that and you still even saw the relative long arms in what people would would call early homo who is the early homo homo a homo habilis or yes homo hamperless homo root offenses but what you do see in a trend in sort of evolution as a lineage into you know homo sapiens is that our legs just got longer and longer and longer it's not that our arms got shorter is that our legs got longer and you don't and we don't see the modern body plan of having these really long legs until about homo erectus and and you know that is linked to really efficient walking right on two legs for very long distances and so so that is so I think that a lot of people would would tie the loss of the body hair to the modern body plan because the body plan then suggests that homo erectus was able to travel very long distances and then that becomes much more important in terms of you know being able to thermoregulate I certainly when I do feel work and you know all the animals during the hottest time of the day are resting in the shade nothing is moving except for us yes like sometimes sometimes I look around going what is wrong with us yeah yeah but you probably sweat a fair amount right so you do because that's that's how we cool down right that's um it works by when you sweat your your skin is wet and then so when the wind blows right it dries this sweat and it kind of it cools it just imagine those fans with the water right if you think about the like those misting fans in really hot days there's some water and then the fan comes and how much cooler you feel so you're currently in Taiwan oh but this is it is not very humid right now but if you were to go to Taiwan in in the summertime what you would discover is a sweating does not cool you down oh interesting and this is because there's so much moisture in the air already that it doesn't cool down because the mechanism doesn't work oh interesting interesting you mentioned that one of the things about these these uh savvanas is that they are much more diverse than we used to think and you mentioned something about how that is actually quite telling given that the one form of human left is able to live everywhere you know in the desert on the high mountains in the Arctic and that in some sense maybe that story has deep roots is what you said in that already in this let's not just be stuck to the rainforest let's start going more into these very diverse vina habitats but i'm sure the rainforest is not all identically looking everywhere so there was probably some diversity also in the rainforest if they just go from one place to another place and they're both a bit diverse or or it was there really a kind of expansion in this story into being able to actually live in more different more but scientists would say heterogeneous in more diverse environments is there is kind of niche expansion going on and how early do we see evidence of that if there is certainly to me it certainly seems like there was niche expansion because before all sort of there's references when you look at we return to the diets and we look at the chemical signatures in the teeth of these earlier hominins of of already it looks like an Australopithecus antimensis which is a presumed ancestor to Australopithecus afrenses they had very C3 focused diets like they were there is not any in their chemical signatures there was nothing in there that indicates they were eating any C4 foods so like they were not you know eating anything that's coming from grasses and and then and then afrenses was the first hominins species that when we look at their chemical signature in their teeth was eating C4 resources and it was and it's just kind of and it's across the board when you look at those chemical signatures is all over the place there are individuals that's that's eating actually quite just just C3 resources oh that's interesting yeah yeah there are individuals who are eating a mix and then there are individuals that's eating mostly C4 and so we get this picture of of Australopithecus afrenses just kind of occupying that whole kind of continuum of food items right and so you know to me one of the it's like they're they're kind of eating what's available that's what it feels like yeah they become more of a generalist that's super interesting yeah more flexible in some ways so already around three million years ago around the lunchtime of this 24 hour clock of food evolution we we start seeing this expansion into more kinds of foods not just that that species has a more varied diet but the different individuals look different and that sounds like this makes perfect sense if we think of what the next step in the line from this point on towards us is which is the early homo which and I know that some people say that already of Australopithecus were using tools it seems to be increasing in the case that they were using even stone tools but I mean tool use which is which is such a big part of humanity and our dependence on technology that to me sounds like it's a logical next step and it kind of goes pretty much like a glove to the hand do you think that that's that's kind of part of what what what takes us on this cycle towards more and more dependence on technology it's certainly your tools obviously rise to put out tools tools as a huge part of what makes us human today right and and it's unclear at that time period what was going on we know chimpanzees use tools so it'd be really surprising if these early hominins did not use tools right and now was it we tend to think of tools as stone tools because that's what for me yes right so I think that these hominins for me they seem like okay they're eating all these different things they're venturing into different habitats like it seems to me that it would not be unreasonable to think that they were really kind of using whatever they can find right to help them get the foods that they want and at this stage it was probably all about the food and and you know and and also people have have positive that when they come across carcasses on the landscape that had not yet been ravaged and eaten by the hyenas certainly can use your your teeth to tear me away but if you do have something sharp it's a lot easier yeah and I mean one of the really dramatic things that happens in this next kind of you know moving towards the homo erectus you start having smaller and smaller teeth smaller and smaller gut so small less apparatus for digesting food while studying bigger and bigger brain so this very energy seriously organ and I think this is just one of the things that keeps kind of blowing my mind when I reflect on the human story is that somehow we we really became a dependent on technology very early on because we cannot eat with these teeth and this got yeah we we can't live without technology and by the way we don't we're not born with knowing how to use technology very well and so I think that that shows that from very early on we couldn't live without someone teaching us how to do things totally and I talked to my students about our overall trajectory of human evolution and it's exactly what you pointed out our brains get bigger our teeth get smaller everything right our kind of our our our facial skeleton gets smaller and more grass-ile and and a lot of it may be driven by the brain and we have colleagues who would be able to talk about how much better than I would but but this kind of this trajectory of brain getting bigger teeth getting smaller like when you look at the evolution of our lineage like that certainly is the trajectory and it's a really interesting one right because that suggests that we do become much more reliant on the brain and it probably it did happen relatively I mean it wasn't at the very beginnings and it's kind of all coupled together I feel like with with this modern body plan and what it is that we were doing because with the big brain and the small teeth is also when we see the the modern body plan and the ability to to travel really far distances because homo erectus is also the first to leave the continent Africa how about the origins of homo erectus so when we don't look at this four to three million years ago already and earlier so bit of things when we look at the more you know around two million a bit more years ago approaching tea time and maybe early dinner time in the 24 hour clock there these is the environment that we should envision and imagine is the environment pretty much just what you already said earlier or is there a change is there a change where when we move from Australopetus in a for instance like Lucy to the early homo do they become even more see for even more grassland even more the classic seven imagery like or is it pretty much the happening in the same kind of nature because I have seen graphs where it looks like homo erectus becomes increasingly see for dependent oh yes and yes and that to me it does suggest that you know the that the thread from our these time towards our more recent ancestors it does look like they are not leaping from the jungle onto the serengetis does a banner but nevertheless there is a clear direction where they are increasingly moving away from the jungle yes and and I think you can think of it like like a river right it meanders it may even fold back on itself but it is like there is a trajectory for it and as as we get closer and closer to us yes the environments were shifting things definitely are getting more open and drier there's just like you know pockets where maybe it's not and but generally speaking right that is the trend and and so you can imagine how a hominin think about austropithecus early homo that is that really had adaptations to help it do quite well in these open patches of a mosaic heterogeneous landscape would then do really well a in an environment where most of the landscape is actually quite open and to do really well in that environment you had to become better a long distance walker to search for the foods wherever it was to lose the fur perhaps to cool down better what else should we have to to the way that that surviving in that kind of habit that crafted our ancestors and then you know brain increasing three part of it. Omar just had a substantially larger brain than what came before much closer to actually within the lower end of modern human range and so that was clearly an important development as well and and and so you know all of that is probably linked together there's you know feedback loop and and that that we seem to be a species that was particularly well adapted and evolved in these more open types of of environments and even though at the very very early part the very first stages of our lineage was not but that sort of built the foundations I know if global climate was not becoming cooler right and drier then the lineage has better adapted for these kind of for resources in more open places would not have been better. Yes. Yes. It would have been something like de remada right that would have been better situated and so I think that that's another thing to be very mindful of when we think about human evolution. I think we tend to think of human evolution as this like this march towards us like this we are the only option. This is the culmination of million years of evolution which is true but the nuance here is that if the external factors weren't exactly what they were with this culmination of seven million years be what we are today and the answer could very well be no. Okay, two questions before we finish and the first one is about us homo sapiens the modern forum of human we emerged like you said earlier around 30 that's 300 sorry around 300,000 years ago so that's very late on this 24 hour clock that will be like after dinner time maybe like 10 11 pm that's also in Africa. Yes. Do we know any do we know more less about the environment, about the ecology, about the nature around that event or is that I know that we for example don't know where exactly in Africa it happened and there are even debates about was it in one place or in several places. Is there something we should add to this conversation about how how the nature around us shaped the human story if we try to focus not in this very early period in the morning and lunchtime but rather in the late late story that brings rise to us. Yeah so you know this is non-air that I know a lot about because obviously I work on the the breakfast and lunch times of of human evolution but you know why that time the 300,000 Africa probably is not that different from Africa today if you were to take away humans which is hard to do because everything that even even reserves where we think is untouched by humans has been touched by humans for hundreds of thousands of years let me think of it that way. So I think that you know it would it probably would have been still sort of fairly similar to what we are what we know and experience today if you can do the imagination of taking away away humans. By that time the sort of the the opening that was very dramatic early on in our in our evolutionary history all the sort of rapid changes all of that would have settled down by then so if you were to teleport back to that time it probably wouldn't look so so different. Whereas if we teleport back seven million years ago it would have been much more genre almost all jungle. Yes it would have been much more wooded that you know so it would look different like everything would have it would have looked very very weird and you would know that you know it's not not quite what you you know today. Well my final question to August is how has all your research shaped your outlook on humanity? One of the things that's most impactful for me personally is this idea that we are all connected. We all come from the same ancestors in our in our deep past. We carry in us right the DNAs of our ancestors of each other because everyone carries the DNA of their ancestors and you can even extend this more. We are all connected to every single living thing on earth. I include a little like single cell organisms and to me that is a that's a really powerful thing to think about our place and I hope that it would inform how we interact with each other as well because if we all carry in ourselves pieces of others right that should matter in in our interactions and I always talk to people about how science is a process. It's a way of understanding the world around us. There are lots of different ways for us to understand the world around us. Science is one of them and it is one that's based on data and evidence. It can change based on new data and new evidence because that's the process itself. And so so when I put those two things again I think about you know like our world it feels like that seems very important that that our connection isn't just what we feel right but that connection is something rooted in something real that had happened in the past and that we are on many levels like we are our past right because everything we are today is is very much what happened in the past so this is how I try to interact with the world it is my perspective on that that's the world view right that my work has given me is that we are all fundamentally connected with each other and it seems like a very I don't know for me personally seems like a very important way to look at the world and hopefully that can help mediate how we all interact with each other with the planet as well right because we all live in it but I think that's one thing we forget too is that we're part of this ecosystem we're not just plunked on here what we do that impacts the plants and animals and the land will come back and affect us as well. Dennis you thank you so much for your research and your generous time today. Oh thank you so much for inviting me. Okay so that was it for today thank you so much for sticking with us until the very end. If you enjoyed this and you're new to On Humans please subscribe to get more episodes such as this where we cover not just the very very origins of the human story but also more recent history and sometimes questions about the brain and about consciousness and about human nature and if you are a returning listener and you appreciate the work do consider joining the wonderful group of people who support me at pay3on.com/OnHumans but that's it for today and I hope that you tune in next time. Until then take care.