How Did Humans Take Over the World?

Humans are everywhere. How did we get from the savannahs of Africa across to the most northern reaches of Alaska and Greenland, to the outbacks of Australia and the islands of the Pacific millennia ago? How did we master fire, figure out how to craft tools and survive the Ice Ages? In this episode Dan is joined by Professor Chris Stringer, Research Leader in Human Evolution at London's Natural History Museum, to talk about how Homo Sapiens managed to outlive other human cousins like Neanderthals and Denisovans and cross oceans s hape landscapes and one day, build cities and space shuttles. Produced by James Hickmann, Mariana Des Forges and edited by Tim Arstall. You can now find Dan Snow's History Hit on YouTube! Watch episodes every Friday (including this one) here https://youtu.be/dzahheunCro. Sign up to History Hit for hundreds of hours of original documentaries, with a new release every week and ad-free podcasts. Sign up at https://www.historyhit.com/subscribe. We'd love to hear your feedback - you can take part in our podcast survey here: https://insights.historyhit.com/history-hit-podcast-always-on. You can also email the podcast directly at [email protected] mailto:[email protected]. Hosted on Acast. See acast.com/privacy https://acast.com/privacy for more information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Dan Snow?

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• 0:32Speaker 01

  This is a paid partnership with Apple Card. The coolest flex at brunch these days is not the Bloody Mary with the bottomless gold flake caviar topping. It's not whipping out your wallet to pay. It's not having a wallet at all. Jack's been an Apple Card user since 2019. That's the same year he tossed his wallet in the trash. Because Apple Card holders earn 2% daily cash back on purchases made using Apple Pay. It's the only credit card designed for the iPhone. I tap to pay with Apple Card at the grocery store, at the gas station, at restaurants. And yes, I use it at my second home, the farmer's market. Jack tapping to pay with his Apple Card with Apple Pay is his favourite thing to do. And the pleasant vibration and chime sound means I just got 2% daily cash back on my latest purchase. Apply in the Wallet app on your iPhone today. Subject to credit approval.

• 1:15Speaker 01

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• 1:29Dan Snow?

  Hi folks, welcome to Dan Snow's History Hit. 300,000 years ago, give or take, in the vast, open spaces of Africa, a new kind of creature emerged. It was clever, it was curious, it was built to roam. They were Homo sapiens, and they would go on to outlive their many rivals, their close cousins, as you'll hear. They would cross oceans, they would reshape the landscape, they would eventually build cities and space shuttles, and eventually, they would fly a drone on Mars.

• 2:06Dan Snow?

  And let's hope the story doesn't end there. But going all the way back to the beginning, how did Homo sapiens become the last human standing in a world once teeming with other species of human? Neanderthals, Denisovans, and even hobbit-sized hunters? What did the world look like when we took our first steps? Why did we spread across continents, adapt to fire, forge tools, survive ice ages and extinction events? This is the story of that survival, but not only that, it's the story of how we became us. In today's episode, we're going to dig into the latest science, the big theories, and the wild mysteries still to be uncovered about our earliest ancestors. We've got a guest who has spent years unraveling the threads of our origin. That is Professor Chris Stringer.

• 2:50Dan Snow?

  He's a research leader in human origins at the Natural History Museum in London. He's been just at the heart of all this, a central contributor in paleoanthropology for the last 30 years. He got a CBE in 2023 for his contributions to the understanding of human evolution. The story of human evolution is one of survival, adaptation, bit of extinction thrown in. And this story has changed in the last 30 years, so if you learn this stuff at school, buckle up. Now, we recorded this episode for our YouTube channel, and Chris brought in some of the incredible skulls to help tell this story. So if you'll watch this episode and see what the skulls look like, I'd recommend you heading over to our YouTube channel right now. To make it super easy, you can find the link in the show notes below. But for you audiophiles, I get you, here's the podcast.

• 3:35Dan Snow?

  Enjoy.

• 3:56Dan Snow?

  Chris, thank you very much for coming on.

• 3:57Speaker 02

  It's a pleasure to be with you.

• 3:58Dan Snow?

  What did the world look like sort of 300,000 odd years ago? What are we talking?

• 4:03Speaker 02

  So obviously, this is the period that's commonly known as the Ice Age. So the climate of the Earth was quite unstable, really for the last 2 million years. But particularly in the last 500,000 years, we had these big swings of climate, where sometimes there were huge ice caps, much bigger than today, and the sea level was lower. Parts of the Earth were joined up, which today are separate. So Britain was fully joined to Europe then. At times, when the sea level fell and the ice caps were large. But also, it was at times warm, as warm as today. So we live today in what's called an interglacial, a period between the Ice Ages. And people like the Neanderthals and our ancestors evolved through these cycles of climatic change, having to cope with extreme cold sometimes and relative warmth.

• 4:47Dan Snow?

  Is that partly to blame for us?

• 4:49Speaker 02

  Well, yeah, so we mainly evolved in Africa, where those climatic changes were not so much really hot and cold, but changes in rainfall patterns. So Africa, when there were Ice Ages outside of Africa, Africa was mainly affected by having more rainfall in some places or less rainfall. So deserts expanded or shrank, rainforests expanded or shrank. So our ancestors in Africa were coping with those kinds of changes. But people like the Neanderthals outside of Africa, they were much more directly affected by those changes in the climate. So at times, we find Neanderthals alongside hippos and elephants in Europe. But at other times, they're alongside reindeer and woolly mammoths. So they had to cope with much greater temperature extremes than the people in Africa.

• 5:34Dan Snow?

  Right, you mentioned the people in Africa. What's the beginning of your particular piece of science? Like, where does the human story begin, rather than the story of mammals or our ancestors further back on the Tree of Life?

• 5:46Speaker 02

  Obviously, yes, it depends what we mean by humans. So some people use the term human only for us, Homo sapiens, our own species. And then they call all the other things some other name, non-humans. And I think that's wrong. I think that people like the Neanderthals were big-brained and they shared, you know, quite a lot of our behaviour. And so I call the Neanderthals humans as well. And so there's a A group of things in the genus Homo. So there's Homo sapiensus, Homo neanderthalensis, the neanderthals, Homo longi, dragon man now is a relatively new one, Homo hydeobigensis, Homo erectus. All those for me, genus Homo are human. And on that definition, humans go back at least two million years.

• 6:27Speaker 02

  And then we have this diversity of human forms. And that's one of the most incredible things, of course, that human evolution, when we look at it over millions of years, it's got all these diverse species, in a sense, nature experimenting in how to be human. Um. And the odd thing is now we're the only ones left out of all those experiments. Even a hundred thousand years ago, there were at least five kinds of humans on the earth. And now we're the only ones left.

• 6:52Dan Snow?

  That is utterly extraordinary. So it's not like they're one after the other. Each evolution is an improvement on what went before. Us humans, we break away from chimpanzees, what, two, two million?

• 7:01Speaker 02

  Seven million, probably, yes, seven million. So we had a common ancestor with chimpanzees around seven million. Then we had some early forms which were the beginning of our line, not yet human, still small brained and rather ape-like. And then we get to around four million years ago, these things called Australopiths, uh, southern apes. And they were now walking upright and they had teeth more like ours, but they were small brained. And in other ways, they were still quite ape-like and they were probably still spending time in the trees. We get to around two million years ago, and there's this species usually known as Homo erectus, erect human. And that was, we think, originated in Africa, but then spread out from Africa around two million years ago.

• 7:43Speaker 02

  So this species, usually known as Homo erectus, erect humans, we think it originated in Africa, probably more than two million years ago. And then soon after two million, spread out of Africa into Europe, into Asia, quite widely, stayed behind in Africa as well. And that was the first, in my view, that's the first real human and the first widespread human.

• 8:04Dan Snow?

  And from that expansion, you get all of these other types of humans, like Neanderthals and all these other ones?

• 8:10Speaker 02

  Yeah. So in fact, there probably were even some more species evolving outside of Africa before we get to our common ancestor. So. Some people think that we had a common ancestor with Neanderthals maybe 600,000 years ago. I think the evidence is growing that that common ancestor was even further back, maybe closer to a million. So around a million years ago, we start to get the diversification of larger brained humans, the beginning of our lineage in Africa, the Neanderthals evolving in, outside of Africa, in Europe and Asia, and over in the Far East, these people we've only learnt about in the last 15 years that we call Denisovans. So they were a third kind of quite evolved human, large brained human that lived over in the Far East.

• 8:51Dan Snow?

  And all of those trails run until about 100,000 years ago, and then they go cold apart from us?

• 8:57Speaker 02

  Yes, well, some down to 50,000 or less. So even 50,000 years ago, the Neanderthals were still around, Denisovans were still around. We had started to come out of Africa and eventually to be the only species left. But even weirder things like on the island of Flores in Indonesia, there was a strange thing nicknamed the Hobbit, Homo floresiensis, and this was a dwarf kind of human, very small bodied, small brained, probably evolved in isolation on this island in Indonesia for maybe at least a million years. So it had its own separate evolution, and that too disappears maybe around 50,000 years ago. The Neanderthals had gone probably by 40,000 years. The Denisovans may have even lasted

• 9:41Speaker 02

  a bit longer, maybe to 30,000 years, but even they eventually disappeared too.

• 9:45Dan Snow?

  And I'm very grateful because you've brought the skulls of some of these other types of humans.

• 9:50Speaker 02

  Yes.

• 9:51Dan Snow?

  Strange thing to say. Talk me through them.

• 9:53Speaker 02

  Yeah, so we've got replicas here of some of these other species and our own ones. So this is a recent human, a replica of a recent human. And you can see there that we've got a big brain in there. The brain case is high and rounded, only a small brow ridge at the front, a nice small face tucked under the brain case, quite small teeth. If we had the lower jaw, there would be a chin on the lower jaw. And the skull is quite high, narrow at the base. So those are typical Homo sapiens features. And if we had the skeleton, we would see that we've got a lightly built skeleton, narrow shoulders, narrow hips, not very strongly built compared with some of these other humans.

• 10:30Dan Snow?

  And that's us today. That's you and me.

• 10:32Speaker 02

  That's us today. And the good thing is that, of course, the features I've talked about are preserved in fossils, so we can go back in time and look for those features. And we can certainly find them. 100,000 years ago, there were people around that had pretty well all those features.

• 10:44Dan Snow?

  Right, that's okay. That's the question you get asked all the time. How far back do you have to go when someone could still walk into that door and they would be anatomically a modern human?

• 10:52Speaker 02

  Yeah, pretty well a hundred thousand years. I mean, maybe even 200,000 years for some fossils from Ethiopia. Before that, we start to see some more primitive ones. So we've got here early Homo sapiens. This is from Morocco, from a site called Jebel Ikhud. You can see that, yeah, the face is quite flat and delicately built, as in ours, and it's tucked under the brain case. But here we can still see there's a strong brow ridge and it's rather long and low. So this is a primitive, sometimes called an archaic Homo sapiens. So this is probably what our lineage was like 300,000 years ago, before some of those later changes had evolved.

• 11:28Dan Snow?

  You mentioned the lower skull dome there. Smaller brain?

• 11:32Speaker 02

  Yeah, the brain's a little bit smaller in here. We can still find, I mean, it's within the modern range, but smaller than the average today. And of course, Neanderthals, that we'll come to in a minute, they had bigger brains too. This is a replica of a Neanderthal fossil from France, about 50,000 years old.

• 11:47Dan Snow?

  So a big old brow on that one.

• 11:49Speaker 02

  Absolutely. So it's got that double arch-brow ridge, typical of Neanderthals there. The brain case is very big, inside is a brain as big, even a little bit bigger than the modern average, but it's longer and lower. From behind, it's almost spherical, you know, almost like a football from behind. You've got a big face that juts out more, and particularly the middle of the face. So Neanderthals got this very big nose and a lot of us have got big noses.

• 12:14Dan Snow?

  Oh, well, thanks for noticing, yeah.

• 12:15Speaker 02

  High noses and projecting noses and wide noses, but the Neanderthals have got all three combined. The middle of the face is pulled forwards. So that's one of their most distinctive features, this mid-facial prognathism. Some people think it's to do with cold adaptation. I think it's really that they're being very energetic and they've got that big nose just to cope with a huge amount of air coming in and out. Their lungs were probably 20% bigger than ours.

• 12:39Dan Snow?

  I'm an athlete.

• 12:39Speaker 02

  Yeah, there you are.

• 12:40Dan Snow?

  And so have the Neanderthals. So, and big old teeth.

• 12:43Speaker 02

  Yeah, and particularly the front teeth are big, quite heavily worn on this one. Not much of a chin if we had the lower jaw and the skeleton is strongly built, muscular, thicker boned and short and wide. And that physique, we know, is good in colder conditions to minimise the surface area to maintain heat. The Neanderthals were relatively short and wide, very stocky, very big trunk, wide shoulders, wide hips.

• 13:07Dan Snow?

  And yet the slender Homo sapiens seemed to have prevailed. Is brain power more important than brute strength?

• 13:13Speaker 02

  Well, of course, the Neanderthals

• 13:14Dan Snow?

  They've got big brains.

• 13:15Speaker 02

  ...had brain power as well. So relatively, yes, probably our brain is a little bit bigger when scaled against the body size than the Neanderthals. But I think that the reason for our success might not just be physical, it might be to do with our behaviour, our culture. We had perhaps bigger group sizes, bigger networking across the landscape, so people were cooperating more widely. The store of knowledge is greater, the spread of knowledge is better between those communities. And so I think that our behaviour was really more important than things like strength in winning out. But I think rather make it seem like a kind of fight to the finish, of course, I think it might have been even indirect competition, so even competition of resources.

• 13:59Speaker 02

  So the Neanderthals were very successful, they evolved in Europe and Asia for hundreds of thousands of years. And then within their last 20,000 years, of course, Homo sapiens emerged from Africa and lived alongside them. And I think that at the time, the climates were very unstable and the populations that could cope best with those rapidly changing conditions maybe benefited and maybe our behaviour, our cultural buffering, perhaps slightly more efficient clothing, technology that's better for extracting the resources you need from the environment, just a small edge was maybe all it needed to actually outcompete economically with these other humans. And I think that was probably the key to it.

• 14:43Speaker 02

  It wasn't an intentional sort of extinction of Neanderthals or Denisovans, but by living alongside them, wanting to eat the same plants, the same, hunt the same animals, live in the best sites, I think that economic competition against a group which by then were suffering. So these climate changes had whittled away Neanderthal numbers and Neanderthal diversity. And they were possibly even a threatened species in the last 20,000 years, even before we Came to live alongside them and it may not have needed much to tip them over the edge, but it wasn't inevitable. At times the Neanderthals were probably out competing Homo sapiens. So there was this probably ebb and flow of populations where they overlapped. But eventually, yes, by forty thousand years ago, it looks like the Neanderthals had gone.

• 15:27Dan Snow?

  And you've got some other humans here, showing them to me.

• 15:29Speaker 02

  Yes, so this lovely green replica here is a replica of a skull from China.

• 15:34Dan Snow?

  That's huge.

• 15:35Speaker 02

  Which only been, you know, known in the last few years, yes. This is the one nicknamed Dragon Man. So Homo longi, a new species of human, it's absolutely enormous in size. It's at least a hundred and fifty thousand years old. So it's, you know, it's, it's, it's quite an ancient fossil. And it's got a remarkable mix of features. So great big brain in there, as big as a Neanderthal or a sapiens brain. But again, long and low, again, that very strong brow ridge over the eyes. And yet, when we look at the face, it's quite delicate. It's more like a Homo sapiens face. It's flat with quite delicate cheekbones and it's tucked under the brain case in a Homo sapiens way. And there's not much preservation of teeth. There's only one big molar preserved, but it's huge. And what's interesting is big molars like that are a feature of the Denisovans. So

• 16:20Speaker 02

  these people, first known from a cave site in Siberia, where there were some very fragmentary bones and teeth, their DNA was looked at and they were shown not to be Neanderthals or Homo sapiens, something different that became known as Denisovans. And this big tooth here is a clue that this might be a Denisovan fossil. If it is, it's the most complete Denisovan we've got. And it shows a third kind of human, not sapiens, not Neanderthal, probably a line that evolved in China for hundreds of thousands of years.

• 16:49Dan Snow?

  Is it exciting to work in a field where we're discovering new types of human beings that we did not know about when you and I were at school?

• 16:56Speaker 02

  Absolutely, yes. I mean, you know, we've also had things like Homo naledi in the last 10 years from Southern Africa, as I mentioned, Homo floresiensis from Flores, Homo luzenensis, there's a strange little dwarf species in the Philippines as well. And who knows what else there is still to be discovered.

• 17:12Dan Snow?

  Let's do another skull.

• 17:13Speaker 02

  So I mentioned that obviously ideas of the common ancestor between us and Neanderthals and Denisovans keep changing. So. The geneticists estimate we had a common ancestor with Neanderthals and Denisovans maybe 600,000 years ago. But there are some older fossils, such as, this one's a replica of a fossil from China, from Yunnan, which is about a million years old. And what's interesting is that I've been working with Chinese paleoanthropologists and looking at this Yunnan fossil. And we actually think it's close to the common ancestor of us and Denisovans, even though it's a million years old. So if that's correct, this would push the ancestry back even further for us and the Neanderthals and the Denisovans. But we're still working on that one.

• 17:56Speaker 02

  But I think the common ancestor could have been even more ancient. The ancestor may not have even lived in Africa. That's one of the uncertain questions. Where did the common ancestor of us and Neanderthals and Denisovans live? 10 years ago, I would have said almost certainly in Africa. And then the ancestors of Neanderthals and Denisovans came out of Africa. Now, with fossils like this one from China, it's possible the common ancestor lived in Asia. And then there would have to be a very early inter-Africa migration of our line of evolution. So maybe a million years ago, there was a population, let's say maybe in Western Asia. It stayed behind to become Neanderthals eventually, to become Denisovans over in Eastern Asia. And a small group went into Africa to found our lineage for the next million years of evolution.

• 18:40Dan Snow?

  Wow, my brain hurts. This is extraordinary. Shall we do that last one?

• 18:43Speaker 02

  Here I've got a model, really, of Homo erectus. So we've talked about Homo erectus a little bit, and this is, you can see, I hope, a much more primitive kind of human. So the brain is much smaller, only a half to two-thirds of the size of the brains typical of Neanderthals and Homo sapiens and Denisovans. The face is more projecting, you've got bigger teeth there, quite a robust jawbone. And you can see that it's very low at the base and really quite a poorly expanded, strong brow ridge, of course, at the front. So erectus, perhaps the longest lasting of all human species, so originating, conventional views, originating in Africa more than 2 million years ago, coming out of Africa soon afterwards.

• 19:25Speaker 02

  So we find erectus in places like the Caucasus, in Georgia. At 1.8 million years, over in China, over in Java, staying behind in Africa. There are some people who think actually that there are different species even within that erectus group, but the conventional view is that erectus lasted for nearly 2 million years and went extinct probably the last ones known in Java at about 100,000 years. So even Homo erectus could have even overlapped with that spread of Homo sapiens out of Africa.

• 19:57Dan Snow?

  There was a time when there were just loads of humans and closely rated human type species on this planet all wandering around together.

• 20:03Speaker 02

  Yeah, well, probably mainly in different locations, but at times certainly wandering around together and of course at times interbreeding and we haven't talked about that yet, but of course with evidence that some of these groups, although I call them different species, some of them are doing a bit of interbreeding with each other.

• 20:20Dan Snow?

  Listen, Dan Snow's history, talk about human evolution, big subject, so obviously more coming up.

• 20:31Dan Snow?

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• 21:13Dan Snow?

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• 22:25Speaker 01

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• 23:14Dan Snow?

  Ever wondered what it feels like to be a gladiator, facing a roaring crowd and potential death in the Colosseum? Find out on the Ancients podcast from History Hit. Twice a week, join me, Tristan Hughes, as I hear exciting new research about people living thousands of years ago, from the Babylonians to the Celts to the Romans, and visit the ancient sites which reveal who and just how amazing our distant ancestors were. That's the Ancients from History Hit.

• 23:54Dan Snow?

  I thought one of the things that demarks a species is that they can't have children with another species.

• 23:59Speaker 02

  Yes, that was what I learnt at school in my biology lessons. You know, that species don't interbreed with each other and that's one of the fundamentals. It's the biological species concept. And that is one species concept. And actually, I think someone counted, there are at least 35 different species concepts. So which one should we be applying for all these fossils? And that's a tricky one. My view is that, you know, I work in a department with paleontologists at the museum. People who study fossil fishes and trilobites and dinosaurs. So I'm someone who thinks that for fossils, we've got to look at what's preserved in the fossils, which is the bony evidence, the teeth and the bones. And if we look at us and the Neanderthals, for example, look at our skull shapes and look at our teeth,

• 24:43Speaker 02

  they are more different from each other than is typical of things we call species today. And let's say monkeys and apes, the differences between, there are two species of chimpanzee. How different are they from each other? The fact is that we in the Neanderthals, based on most studies, are more different than most primate species are from each other today, even closely related ones. So morphologically, in the skeleton, the Neanderthals qualify for me as a different species. So how can they be interbreeding? Well, the point is that we know from DNA studies now that many closely related species today do interbreed successfully. So think of jackals and wolves, for example. Think of brown bears and polar bears, they can hybridise successfully.

• 25:26Speaker 02

  Many baboon species in Africa can hybridise successfully. So it looks like it takes evolution, sometimes millions of years, for things to become separate enough that they no longer interbreed. So we in the Neanderthals, yeah, maybe we did separate a million years ago, but that was not enough to prevent interbreeding where we overlapped. And so there was a bit of interbreeding between us and Neanderthals, between us and Denisovans, between Neanderthals and Denisovans. So from Denisova Cave, incredibly, there's a little bit of fragmentary bone and its DNA shows that it's from a girl who lived maybe 100,000 years ago. And she had a mother who was a Neanderthal and a father who was a Denisovan. So she actually was a hybrid child.

• 26:09Speaker 02

  One day, we're going to find a hybrid child between a Neanderthal and a Homo sapiens. We haven't got it yet, but it's there somewhere because... Everyone outside of Africa today has around 2% Neanderthal DNA in their genomes. And I know, because I've had my intestine, it's there.

• 26:24Dan Snow?

  So we are hybrids?

• 26:26Speaker 02

  We are sort of, well, the hybridisation was 40,000 or 50,000 years ago, but we are, yes, we're part Neanderthal. And people over in the Far East and Ireland, South East Asia, some of them have also got about 4% of Denisovan DNA. So they've got the 2% of Neanderthal DNA and then added on to that about 4% of Denisovan DNA. So yes, these so-called species are doing a bit of interbreeding. And that interbreeding, obviously, initially, of course, there would be kids who are half Neanderthal, half Homo sapiens. But gradually, that Neanderthal DNA, in fact, not gradually, quite quickly, it was reduced down to a very low level, around 2% or 3%, but that, some of that is still active.

• 27:06Speaker 02

  And we know that in our immune systems, for example, where people outside of Africa have got active Neanderthal-derived DNA in their immune systems. And that kind of makes sense because we had evolved in Africa. So when we came out of Africa into Europe and Asia, we had no natural immunities to the diseases there, which the Neanderthals had evolved over hundreds of thousands of years. So we're interbreeding with them, we got a quick fix to our immune systems and picked up some of their defences, which was obviously good news, 40 or 50,000 years ago.

• 27:36Dan Snow?

  But if we're thinking about these different species of humans, they are further apart than today you'd say someone from England is from an indigenous Australian or an Inuit. I mean, we, we today in our world are, are much more anatomically aligned, are we, than a Denisovan to a, to a Homo sapiens?

• 27:58Speaker 02

  Yeah, so yes, if we look at diversity today, that's mainly developed in the last 100, at the most, probably 150,000 years. On the time scales I've been talking about, that is, that is relatively recent. And of course, people do look different around the world today, you know, think of someone, an African versus a European, an Inuit versus a, a native Australian. But to get to us in a Neanderthal, I think you've got to multiply that maybe four times

• 28:22Dan Snow?

  Okay.

• 28:22Speaker 02

  to get to the level of difference we find for a Neanderthal or a Genisven. So yes, we are relatively closely related today. Our DNA shows that we are one species. For Neanderthals and us, there are signs that there was a level of, you know, Reproductive isolation beginning to develop between us and Neanderthals, there was some incompatibility, and with Denisovans, there was some incompatibility.

• 28:46Dan Snow?

  Oh, so they might not be very successful.

• 28:48Speaker 02

  So, for example, that one of the curious things is that there was this interbreeding in Europe, let's say forty to fifty thousand years ago, between us and Neanderthals. But the evidence at the moment is that when we look at an early Homo sapiens fossil from that time, it always shows a bit of Neanderthal interbreeding is going on. But the late Neanderthals don't seem to show evidence of Homo sapiens interbreeding going in the other direction. We don't know the reason for that. It might be that the populations, you know, in one direction didn't like it happening, but it might also be a sign that there were some incompatibilities. So, for example, the pelvis shape is different in Neanderthals from Homo sapiens. So possibly a Homo sapiens mother was better able to give birth to

• 29:30Speaker 02

  a hybrid baby, but a Neanderthal mother with a different hip shape, maybe it wasn't so easy for her to give birth to a hybrid baby. So there are things we don't understand, whether it happened, wasn't successful for Neanderthals, or whether they just didn't like it to happen. Was it a one-way process mainly? One possibility is that Homo sapiens were actually taking Neanderthal females and bringing them into their groups, which would explain the hybridisation, and then they were breeding successfully in the groups. So, a lot we don't know about the process, whether it was friendly, whether it was unfriendly, we've a lot to learn. And the same for Denisovans, because the interbreeding was going on, possibly on an even greater scale over in the Far East and island South East Asia, and we know

• 30:13Speaker 02

  nothing there about what was going on.

• 30:16Dan Snow?

  Extraordinary stuff. Let's come back to the subject of why Homo sapiens triumph. Is it physiological? Is it cultural? What's the secret weapon of the Homo sapiens?

• 30:26Speaker 02

  Yeah, so I think, yes, weapon's probably the wrong term, because I think there was nothing inevitable about our success. I think that if you could have looked, you know, from, you know, down on the earth a hundred thousand years ago, without knowing what was going to happen, you'd have all these different kinds of humans around. I think it would be very difficult to point to one and say, yep, they're going to take over the earth and all the others are going to die out. I think that there was no special thing that stood out a hundred thousand years ago that was going to make us this great success. But by the time we get to forty or fifty thousand years, yes, we come out of Africa and maybe within twenty thousand years, these, these other humans are going under and completely disappearing. And we really don't know the answer, and it might be a different answer in different places.

• 31:10Speaker 02

  Perhaps the reason why Neanderthals died out in Europe could be different to why the Denisovans died out in China or Sulawesi. So there's a lot to learn, but I do think that our behaviour is the key to it, that we were perhaps just that little bit quicker to adapt with our social systems. Even something like the sewing needle seems, you know, not a, not a big deal, but if you can sew your clothing together, it makes much better insulation for your blankets, for your shelters, to keep your babies warm. So even something like a sewing needle, which we think was around forty thousand years ago for Homo sapiens, could have been important there. And also, I, I think just our bigger networks. I mentioned that already, that we probably were living in larger social groups with more

• 31:55Speaker 02

  networking across the landscape. And that's an advantage in difficult times. If you're on good terms with your neighbours, they can help you out with supplies, with resources, with knowledge too, of course, to store knowledge, those bigger groups and that bigger networking. So I think we had an advantage there in our level of networking and social group size compared with people like the Neanderthals, who were living maybe a little bit more insular lives in smaller groups.

• 32:20Dan Snow?

  And certainly seems like Homo sapiens were prepared to travel as well.

• 32:23Speaker 02

  Yes, I mean, we obviously covered these vast distances in a short time, so Homo sapiens, of course, gets to somewhere like Australia, maybe sixty five thousand years ago. The trip to America took longer, that could be the last twenty thousand years, going right up north and across the Bering Straits. But Homo sapiens actually made a few excursions out of Africa even earlier that... Well, you could say they weren't successful, they didn't take hold. So with evidence that there was a Homo sapiens fossil in Greece over 200,000 years ago, and yet at the same site, within 30,000 or 40,000 years, Neanderthals have gone back and Homo sapiens have disappeared. So there were early excursions of sapiens which did not take hold. And it only was

• 33:05Speaker 02

  that one after 60,000 which was successful, if you can put it that way, in terms of, you know, taking hold and eventually replacing those other species.

• 33:15Dan Snow?

  And you've used the expression a couple of times, they had an edge. And is that what this is about? It's over this length of time, you only need a little bit of an edge, you know, one extra child per family, per generation, whatever it might be, to actually bring about some pretty enormous demographic shifts?

• 33:29Speaker 02

  That's right, yes. So even just a 1% or 2% increase in the survival of your babies, you know, that's going to be critical. So keeping your babies warm, we know how, you know, maternity hospitals are always warm places. So keeping your babies warm is a key to survival, preventing them, you know, being injured by the environment, getting diseases, all of those things. That could have been just that edge in survival of children. Better infant mortality for Homo sapiens could have been a key to our survival. And in a sense, you know, the Neanderthals, yes, absorbing them was also perhaps part of the reason why they died out. They were small in number, and if we were taking on, you know, some of their individuals into our breeding pool, then they're being lost from

• 34:11Speaker 02

  the Neanderthal breeding pool. And in a sense, you could say they haven't even gone extinct, of course, because people have calculated that if you look at all the diversity of Neanderthal DNA around in the world today, you could probably build up 40 or 50% of the Neanderthal genome, just from the DNA surviving today. And because there are billions of us today, there's actually more Neanderthal DNA around today than there was 50,000 years ago.

• 34:35Dan Snow?

  A classic. And that's also true then of these other species that have been discovered so recently. For example, the dwarf, the Fiorinti, what's that one?

• 34:42Speaker 02

  Florisensis, the hobbit. Yeah, so we've no evidence that that did any interbreeding with Homo sapiens. It was probably too different. I think it was, you know, much more distantly related to us than the Neanderthals and Denisovans were. So we've no evidence of any interbreeding with the hobbit, but that was around on the island of Flores until at least 50,000 years ago. It may have survived a bit longer, but after that, we know Homo sapiens was there and we seem to lose sight of it. And that may have had a separate evolution in isolation on that island for a million years. And you've got to feel sorry for the poor hobbit. I mean, it's there evolving quite happily for a million years and then it's gone.

• 35:21Dan Snow?

  More humans evolving after this. Don't go away.

• 35:32Speaker 01

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• 36:15Speaker 01

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• 36:22Speaker 03

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• 37:02Dan Snow?

  Is there, I mean, military historians like to interact with you guys and talk about violence. I mean, is there something about Homo sapiens, so there's perhaps a slight edge in terms of tools? Can we extrapolate, there might be an edge in terms of weapons and some organised, big groups of us being mobilised for kind of organised violence? Do you think there's a, is there a story of warfare here, of, well, genocide, I suppose?

• 37:24Speaker 02

  Certainly later on that happens. And how far back that goes in this story of human evolution is very difficult. There was something, we think that we did actually, you know, have conflicts with the Neanderthals, but actually there's very little evidence of that. So I think it wouldn't, it didn't need to be that kind of conflict. I think economic competition was probably part of the story. Getting lucky because the Neanderthals already were maybe vulnerable because they were low in numbers and low in diversity at the time we came to live alongside them after 60,000 years ago. So maybe they were unlucky. For the Denisovans, we know much less about the process. And of course, they were much more widespread in terms of the diversity of environments. So Denisovans were living in Siberia, we think they were in North East China,

• 38:08Speaker 02

  and they were probably down in Ireland, South East Asia, in the tropics and subtropics. And yet they disappeared too. So their disappearance is perhaps an even bigger mystery than the disappearance of the Neanderthals, and we have a lot to learn about that. Some people have argued, maybe we brought diseases with us for Africa that they had no immunity to. But equally, it could have gone the other way, of course. There could have been diseases they would have infected us with. And I think that's much more like a process that goes on in more recent times with Europeans travelling and taking smallpox to urban communities. And obviously, in those cases, those epidemics are quite tightly, they're in urban environments with populations that are large and living close together. For the Paleolithic, we're talking about much more scattered populations,

• 38:52Speaker 02

  where I think these epidemics would not spread in the way they do much later on in urban centres.

• 38:58Dan Snow?

  That's a good question. How many Homo sapiens do we think we're talking about? On this explosion out of Africa, when they start travelling all over the world for the last time? Do you have a ballpark figure for the number of Homo sapiens on the planet?

• 39:08Speaker 02

  Well, that's a really good question because of course we, you know, it's difficult to get from the sites we have, difficult to make estimates, but the population in Africa was always larger because Africa's a big place and and contains a lot of genetic diversity. So we think that the population in Africa could have been tens or hundreds of thousands of people. But geneticists estimate that the group that came out of Africa and founded the people of the rest of the world could have only been, may have only been a few thousand people. And they then diversified and spread and increased their numbers quite rapidly. But we're still talking by modern standards, we're talking about very small numbers of people. The Neanderthals near the end of their time could have been living in groups, you know,

• 39:50Speaker 02

  total populations of tens of thousands at the most. So at times they certainly were low in numbers. Homo sapiens at times are low in numbers, but obviously nothing, you know, the the numbers we have today are are huge compared with these tiny populations of tens of thousands or at best hundreds of thousands of people that were around in the Paleolithic period.

• 40:09Dan Snow?

  So at times, the population of Homo sapiens on the planet was equivalent to the modern city of Hull?

• 40:17Speaker 02

  Yes, I'm not sure. Tell me how many people live in Hull. You'll have to remind me.

• 40:20Dan Snow?

  Not millions?

• 40:21Speaker 02

  No, not millions. That's right. Yeah, we're talking about those kind of, you know, populations that are minuscule. As I say, a million would be a huge number for humans, and I doubt that the time periods we've been talking about, there was ever a million humans of any of these species around on the earth.

• 40:36Dan Snow?

  And if you'd said that within fifty to a hundred thousand years, humans would dominate the planet, cause a mass extinction of other species, transform the atmosphere and put a rover on a passing comet, they'd have been pretty surprised.

• 40:51Speaker 02

  Yes, it would be very surprising. I mean, you know, I think a hundred thousand years ago, we would never have predicted any of that. And of course, a few twists and turns of the of the climates and population numbers and and cultures and things. And, you know, maybe the Neanderthals would eventually have been the successful ones, you know, perhaps we would have died out in Africa and it might have been Neanderthals who eventually got the Neanderthal on to the moon. Who knows? There could have been that alternative history.

• 41:14Dan Snow?

  Where are the big developments in your exciting field going to come from? Are they coming from the lab? Or are they going to come from the field as well? Are we going to discover objects in the field and find perhaps remote sensing, new ways of finding more stuff? Or is it going to be just delving into the invisible particles the human eye and learning about them?

• 41:31Speaker 02

  Yeah, so I think it's going to be a bit of everything. So I think we've learnt about these new species. As I say, we learnt about Denisovans in 2010 and Homo naledi in 2014, the Hobbit in 2004. So that's just in the last 25 years. So I think there will be new discoveries purely by chance, just by expanding where we're looking. Huge areas of Asia, for example, have not produced any physical fossils. Huge areas of Africa, even our African evidence comes from maybe 10% of the whole of Africa. So there's a huge amount to learn from existing places to study them in more detail, new sites to be discovered. But of course, the DNA is still leading the way in terms of, you know, there might be a big fossil discovery maybe every six months if we're lucky.

• 42:16Speaker 02

  But there's a new DNA paper every week, there's something new on the DNA. So the DNA, obviously from Neanderthals, from Denisovans, people are searching for DNA of things like the Hobbit, whether there might be some for Homo naledi. So these other species could yield DNA. And then there's also fossil proteins. So this is another way forward, that fossil proteins actually have a longer preservation life than DNA. So people are starting to look at fossil proteins. And those, I think, will be a big way forward in the future to try and relate these species, even the more ancient species like Homo erectus. There may not be DNA there, but if we can get fossil proteins, even they can be used to relate erectus to us and Neanderthals and Denisovans. So a lot more to come from that too.

• 42:58Dan Snow?

  Sorry to interrupt, Chris, what's a fossil protein?

• 43:00Speaker 02

  Yeah, so fossil proteins, I mean, they're basically the building blocks of our body. So the DNA produces things like, say, collagen or insulin or enzymes and the chemicals that make up our body, collagen in particular, found in bone and tissue like that. And this preserves much better than DNA. And so the actual constituents of collagen can be analysed and they last longer generally than DNA. So that can also be used to characterise different species.

• 43:26Dan Snow?

  When you were at university, not so very long ago, but when you were at university, was nearly everything you were taught wrong?

• 43:31Speaker 02

  Pretty well, yes. And everything, I, you know, in my early career too. I mean, I've had to change my mind about a lot of things too. So if you'd have asked me 20 years ago whether we interacted with the Neanderthals, I'd have said, well, might have happened a little bit, but it would never have been successful in the long term. We'd never find any trace of it today. And obviously, 2010, I had to change my mind because there was the evidence, even in my own DNA, that I had Neanderthal ancestors.

• 43:58Dan Snow?

  When the facts change, opinions should too. So well done you.

• 44:01Speaker 02

  They should change. That's right. And I think I've learnt to be more open minded. And once you've admitted you were wrong about something, it's easier to admit you're wrong about the next thing too. And as scientists, that's what we should do. We should be open to new evidence and we should be ready to change our mind when the evidence requires it.

• 44:15Dan Snow?

  Well, thank you very much, Chris, for coming on the podcast, giving us that useful lesson at the end as well. I am usually wrong about most things.

• 44:21Speaker 02

  Thank you very much, Dan. It's been a pleasure.

• 44:26Dan Snow?

  Thanks very much for listening, everyone. Before we go, I'll tell you that ever at the cutting edge, the bleeding edge of what's new and exciting, after 10 years of the podcast, you can finally watch it on YouTube. We are moving fast and breaking things here, folks. Our Friday episodes each week will be available to watch on YouTube and you can see me, you can see what we're talking about. I'd love it if you could subscribe to that channel over there. Just click the link in the show notes below and you can watch it on your phone, your tablet, or even a TV, or even a giant cinema movie screen, if you have one in your underground lair. See you next time, folks.

• 45:12Speaker 01

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• 45:55Speaker 01

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• 46:03Dan Snow?

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