How Did Humans Take Over the World?

Summary

Detailed Summary of "How Did Humans Take Over the World?"

Dan Snow's History Hit episode titled "How Did Humans Take Over the World?", released on June 12, 2025, delves into the fascinating journey of Homo sapiens from their emergence in Africa to becoming the sole surviving human species on the planet. Hosted by Dan Snow and featuring renowned paleoanthropologist Professor Chris Stringer from the Natural History Museum in London, the episode explores the complex interplay of environmental factors, evolutionary biology, and cultural advancements that facilitated human dominance.

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1. The Ice Age and Early Human Evolution [02:08 - 06:14]

Dan Snow opens the discussion by setting the stage 300,000 years ago in Africa, during a period commonly known as the Ice Age. Professor Chris Stringer explains:

“...the last 500,000 years, we had these big swings of climate where sometimes there were huge ice caps, much bigger than today...[and] our ancestors in Africa were coping with changes in rainfall patterns.”
[05:27]

Key Points:

• The Ice Age brought significant climatic fluctuations, affecting sea levels and connecting landmasses like Britain to Europe.
• Homo sapiens evolved in Africa, primarily dealing with variations in rainfall rather than extreme temperature changes experienced by human species outside Africa.

2. Diversity of the Genus Homo [06:14 - 07:32]

Stringer emphasizes the broad definition of "human," encompassing various species within the genus Homo, including Neanderthals, Denisovans, and Homo erectus.

“...genus Homo are human. And on that definition, humans go back at least 2 million years.”
[06:25]

Key Points:

• The genus Homo includes multiple species, each representing different evolutionary experiments in becoming human.
• Homo sapiens are the only surviving species among a diverse lineage that included at least five human kinds 100,000 years ago.

3. Physical Characteristics and Skull Analysis [10:25 - 12:27]

Using replica skulls, Stringer distinguishes between Homo sapiens and other human species:

“...we can certainly find them. 100,000 years ago, there were people around that had pretty well all those features.”
[11:10]

Key Points:

• Homo sapiens: High, rounded braincase, small brow ridge, small face, and the presence of a chin.
• Neanderthals: Double-arched brow ridges, larger braincases, projecting faces with large noses, robust jaws, and thick bones suited for cold climates.

4. The Extinction of Other Human Species [13:47 - 16:09]

Stringer discusses the eventual disappearance of Neanderthals, Denisovans, and Homo floresiensis (the "Hobbit"):

“By 40,000 years ago, it looks like the Neanderthals had gone.”
[15:57]

Key Points:

• Various human species persisted alongside Homo sapiens until approximately 30,000 to 50,000 years ago.
• Homo floresiensis, a dwarf species from Indonesia, likely evolved in isolation and vanished around 50,000 years ago without evidence of interbreeding with Homo sapiens.

5. Interbreeding Among Human Species [21:00 - 26:10]

The conversation shifts to genetic interactions between Homo sapiens, Neanderthals, and Denisovans:

“...there was a bit of interbreeding between us and Neanderthals, between us and Denisovans.”
[24:29]

Key Points:

• Modern humans carry approximately 2% Neanderthal DNA, and some populations, especially in Southeast Asia, also have about 4% Denisovan DNA.
• Interbreeding occurred around 40,000 to 50,000 years ago, contributing beneficial genes related to immune responses.
• Hybridization was likely asymmetrical, with evidence of Homo sapiens breeding with Neanderthals but not vice versa.

6. Reasons Behind Homo sapiens' Dominance [27:20 - 32:05]

Stringer explores whether physiological or cultural factors led to Homo sapiens' success:

“Our behavior was really more important than things like strength in winning out.”
[15:00]

Key Points:

• Cultural Advantages: Larger social groups, better networking, and more efficient knowledge transfer.
• Technological Innovations: Tools like the sewing needle allowed for superior clothing and shelter, enhancing survival rates.
• Adaptive Behavior: Rapid adaptation to changing climates through cultural and technological means provided a competitive edge over other human species.

7. Population Dynamics and Migration [32:05 - 39:47]

The episode examines the small population sizes and migratory patterns of early Homo sapiens:

“The population in Africa could have been tens or hundreds of thousands of people.”
[38:32]

Key Points:

• Early Homo sapiens populations were small, possibly numbering in the thousands during initial migrations out of Africa.
• Successful migrations led to rapid population growth and global dispersion, unlike earlier unsuccessful attempts that did not establish lasting populations.

8. Future of Human Evolution Research [40:01 - 42:50]

Looking ahead, Stringer discusses emerging fields and technologies that could revolutionize our understanding of human evolution:

“There's a new DNA paper every week. There's something new on the DNA.”
[40:56]

Key Points:

• Genetic Research: Ongoing DNA studies continue to uncover interbreeding events and genetic contributions from extinct human species.
• Fossil Proteins: Proteomics offers a new avenue for analyzing ancient remains, potentially bridging gaps where DNA is unavailable.
• Field Discoveries: Expanding fossil excavation sites, especially in underexplored regions of Asia and Africa, promises new insights and species discoveries.

9. Scientific Adaptability and Openness [42:50 - 43:40]

Stringer reflects on the evolving nature of scientific understanding:

“Once you've admitted you were wrong about something, it's easier to admit you're wrong about the next thing too.”
[42:56]

Key Points:

• Science is inherently adaptable, with theories and understandings evolving based on new evidence.
• Interdisciplinary collaboration and willingness to revise hypotheses are crucial for advancing knowledge in paleoanthropology.

10. Closing Remarks [43:26 - 44:37]

Dan Snow wraps up the episode by encouraging listeners to engage with the podcast on YouTube, emphasizing the visual aids used during the discussion, such as skull replicas.

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Notable Quotes:

• Professor Chris Stringer:
  “Our behavior was really more important than things like strength in winning out.”
  [15:00]

• Professor Chris Stringer:
  “...larger social groups with more networking across the landscape. And that's an advantage in difficult times.”
  [31:05]

• Dan Snow:
  “If you'd have asked me 20 years ago whether we interbred with the Neanderthals, I'd have said...”
  [42:25]

---

Conclusion

The episode provides an in-depth exploration of human evolution, highlighting the intricate balance between environmental pressures, biological adaptations, and cultural innovations that enabled Homo sapiens to outlast and outcompete other human species. Professor Chris Stringer's insights underscore the importance of flexibility, cooperation, and knowledge sharing in the survival and dominance of modern humans. The ongoing advancements in genetic research and fossil analysis continue to shed light on this complex chapter of our history, promising even more revelations in the years to come.

Transcript

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[Dan 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. And let's hope the story doesn't end there, but going all the way back to the guinea. How did Homo sapiens become the last human standing in a world once teeming with other species of human? Neanderthals, Denovisians, 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 mystery still be uncovered about our earliest ancestors. We got a guest who has spent years unraveling the threads of our origin. That is Professor Chris Stringer. 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 CB 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 want to 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. Enjoy.

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[Chris Stringer]

No black white unity till there is first some black unity. Never to go to war with one another again. And lift off and the shuttle has cleared the tower.

[Dan Snow]

Chris, thank you very much for coming on.

[Chris Stringer]

It's a pleasure to be with you.

[Dan Snow]

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

[Chris Stringer]

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.

[Dan Snow]

Is that partly to blame for us?

[Chris Stringer]

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, 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.

[Dan 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?

[Chris Stringer]

Obviously, yes, it depends what we mean by human. 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. 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 behavior. And so I call the Neanderthals humans as well. And so there's a group of things in the genus Homo, so there's Homo sapiensis, Homo neanderthalensis, the Neanderthals, Homo longi, dragon man, now is a relatively new one, Homo heidelbergensis, Homo erectus, all those. For me, genus Homo are human. And on that definition, humans go back at least 2 million years. And then we have this diversity of human forms. And that's one of the most incredible things, of course, the 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. And the odd thing is now we're the only ones left out of all those experiments. Even 100,000 years ago, there were at least five kinds of humans on the earth and now we're the only ones left.

[Dan 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 2, 2 million?

[Chris Stringer]

7 million probably 7 million. So we had a common ancestors which imposes around 7 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 4 million years ago, these things called Australopiths, 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 2 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 2 million years ago. So this species usually known as Homo erectus, erect humans, we think it originated in Africa probably more than 2 million years ago. And then soon after 2 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.

[Dan Snow]

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

[Chris Stringer]

Yes. 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 learned 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.

[Dan Snow]

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

[Chris Stringer]

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 dwarfed 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 have gone probably by 40,000 years. The Denisovans may have even lasted a bit longer, maybe to 30,000 years. But even they eventually disappeared, too.

[Dan Snow]

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

[Chris Stringer]

Yes.

[Dan Snow]

It's a strange thing to say. Talk me through them.

[Chris Stringer]

Yeah. So we've got replicas here of some of these other species and our own one. So this is a recent human, a replica recent human. And you can see there that we 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.

[Dan Snow]

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

[Chris Stringer]

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. And we can certainly find them. 100,000 years ago, there were people around that had pretty well all those features.

[Dan 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?

[Chris Stringer]

Yeah, pretty well 100,000 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 sapien. This is from Morocco, from a site called Jebel Ichud. 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 sapien. So this is probably what our lineage was like 300,000 years ago, before some of those later changes had evolved.

[Dan Snow]

You mentioned the lower skull dome there, Smaller brain.

[Chris Stringer]

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.

[Dan Snow]

So big old brow on that one.

[Chris Stringer]

Absolutely. So it's got that double arch brow. Ish. 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.

[Dan Snow]

Oh well thanks for noticing.

[Chris Stringer]

Yeah, 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.

[Dan Snow]

I'm an athlete.

[Chris Stringer]

Yeah, there you are.

[Dan Snow]

And so the Neanderthals, so. And big old teeth.

[Chris Stringer]

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 minimize the surface area, to maintain heat. The Neanderthals were relatively short and wide, very stocky, very big trunk, wide shoulders, wide hips.

[Dan Snow]

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

[Chris Stringer]

Well of course the Neanderthals, they've got big brains power as well. So relatively, yes, probably our brain is a little bit bigger when scaled against the 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 behavior, 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 behavior 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 for resources. 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, and the populations that could cope best with those rapidly changing conditions may be benefited. And maybe our behavior, 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. 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 them was 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 40,000 years ago, it looks like the Neanderthals had gone.

[Dan Snow]

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

[Chris Stringer]

Yes. So this lovely green replica here is a replica of a skull from China, 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 150,000 years old. So it's, you know, 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 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 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.

[Dan 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?

[Chris Stringer]

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 luzinensis. There's a strange little dwarf species in the Philippines as well. And who knows what else there is still to be discovered.

[Dan Snow]

Let's do another skull.

[Chris Stringer]

So I mentioned that obviously ideas of the common ancestor between us and Neanderthals and Denisovans keep changing. So 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. A fossil from China, from Yuntzan, which is about a million years old. And what's interesting is that I've been working with Chinese paleoanthropologists looking at this junkyard 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. 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? Ten 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 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.

[Dan Snow]

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

[Chris Stringer]

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 browage, 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. 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.

[Dan Snow]

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

[Chris Stringer]

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 we've evidenced that some of these groups, although I call them different species, some of them are doing a bit of interbreeding with each other.

[Dan Snow]

Listen, dancing knows history. Talk about human evolution. Big subject. So obviously more coming up.

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[Dan Snow]

Land a Viking longship on island shores. Scramble over the dunes of ancient Egypt and avoid the poisoner's cup in Renaissance, Renaissance Florence. Each week on Echoes of History, we uncover the epic stories that inspire Assassin's Creed. We're stepping into feudal Japan in our special series Chasing Shadows, where samurai warlords and shinobi spies teach us the tactics and skills needed not only to survive, but to conquer. Whether you're preparing for Assassin's Creed Shadows or fascinated by history and great stories, listen. Listen to Echoes of History, a Ubisoft podcast brought to you by History Hits. There are new episodes every week. I thought one of the thing that demarks a species is that they can't have children with another species.

[Chris Stringer]

Yes, that was what I learned at school in my biology lessons. You know, that species don't interbreed with each other. And that's one of the fundamental to it's the biological species concept. And that is one species concept. And actually I think some are 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, they are more different from each other than is Typical of things we call species today in 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 and 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 hybridize successfully. Many baboon species in Africa can hybridize 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. 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 mine tested, it's there.

[Dan Snow]

So we are hybrids.

[Chris Stringer]

We are sort of. Well, the hybridization was 40 or 50,000 years ago, but we are, yes, we're part Neanderthal and people over in the Far east and are island Southeast Asia, some of them have also got about 4% of Denisovan DNA. So they've got the 2% of Neanderthal DNA and then added onto 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 some of that is still active. And we know that in our immune systems, for example, 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 interbreeding with them, we got a quick fix to our immune systems and picked up some of their defenses, which was obviously good news for Coldier 50,000 years ago.

[Dan 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 much more anatomically aligned, are we, than a Denisovan to a, to a Homo sapiens?

[Chris Stringer]

Yes. 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 timescales 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 native Australian. But to get to us in a Neanderthal, I think you've got to multiply that maybe four times to get to the level of difference we find for a Neanderthal origin. So yes, we are relatively closely related today. Our DNA shows that we are one species. For Neanderthals and us. There's 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.

[Dan Snow]

Oh, so they might not be very successful.

[Chris Stringer]

So for example, one of the curious things is that there was this interbreeding in Europe, let's say 40 to 50,000 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 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, what wasn't successful for Neanderthals, or whether they just didn't like it to happen. Was it a one way process? Mainly were. One possibility is that Homo sapiens were actually taking Neanderthal females and bringing them into their groups, which would explain the hybridization. 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 Southeast Asia, and we know nothing there about what was going on.

[Dan 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?

[Chris Stringer]

Yeah, so I think, yes, weapons, 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 100,000 years ago without knowing what was going to happen, you'd have all these different kinds of humans around. And 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 40 or 50,000 years, yes, we come out of Africa and maybe within 20,000 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. Perhaps the reason why Neanderthals died out of 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 behavior 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 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 40,000 years ago for Homo sapiens could have been important there. And also I think just our bigger networks, I mentioned that already that we probably were living in larger social groups with more networking across, across the landscape. And that's an advantage in difficult times. If you're on good terms with your neighbors, 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.

[Dan Snow]

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

[Chris Stringer]

Yes, I mean, we obviously covered these vast distances in a short time. So Homo sapiens, of course, gets to somewhere like Australia maybe 65,000 years ago. The trip to America took longer. That could be the last 20,000 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 we have evidence that there was a Homo sapiens fossil in Greece over 200,000 years ago, and yet at the same site, within 30 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 that one after 60,000 which was successful, if you can put it that way, in terms of taking hold and eventually replacing those other species.

[Dan Snow]

And you've used the expression a couple of times, they had an edge. And is that what this is about? 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.

[Chris Stringer]

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 now have, 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 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.

[Dan Snow]

Classic. And that's also true then of these other species that have been discovered so recently. For example, the dwarf, the Fiorente. What's that?

[Chris Stringer]

One Floresiensis. 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 got to feel sorry for the orbit. I mean, it's there evolving quite happily for a million years and. And then it's gone.

[Dan Snow]

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

[Kristen]

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[Chris Stringer]

What else?

[Kristen]

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[Chris Stringer]

Just as predicted. So we gonna, I don't know, could.

[Kristen]

Sell, could hold the power to always.

[Chris Stringer]

Know our car's worth.

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[Dan 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, there's Perhaps a slight edge in terms of tools. Can we extrapolate? There might be an edge in terms of weapons, in terms of organized big groups, of us being mobilized for kind of organized violence. Do you think there's a. Is there a story of warfare here, of. Well, of genocide?

[Chris Stringer]

I suppose certainly later on that happens. And how far back that goes in this story of human evolution is very difficult. There are some people, 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 northeast China, and they were probably down in Ireland, Southeast 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. With us from 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 traveling 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 where I think these epidemics would not spread in the way they do much later on in urban centers.

[Dan 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 traveling all over the world for the last time? Do you want a ballpark figure for the number of Homo sapiens on the planet?

[Chris Stringer]

Well, that's a really good question because of course, 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 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, total populations of tens of thousands at the most. So at times, they certainly were low in numbers. Homo sapiens, at times were low in numbers, but obviously nothing. You know, the numbers we have today 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.

[Dan Snow]

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

[Chris Stringer]

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

[Dan Snow]

Not millions.

[Chris Stringer]

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.

[Dan Snow]

And if you'd said that within 50 to 100,000 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.

[Chris Stringer]

Yes, it would be very surprising. I mean, you know, I think 100,000 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 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 a Neanderthal onto the moon. Who knows? There could have been that alternative history.

[Dan 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?

[Chris Stringer]

Yeah, so I think it's going to be a bit of everything. So I think we've learned about these new species. As I say, we learned about Denisovans in 2010 and Homo Naledi in 2014, the Hobbit in 2004. So that's just in the last 25 years. So. 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. 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.

[Dan Snow]

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

[Chris Stringer]

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 analyzed and they last longer generally than DNA. So that can also be used to characterize different species.

[Dan Snow]

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

[Chris Stringer]

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 interbred 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 I 2010, I had to change my mind because there was the evidence, even in my own DNA that I had Neanderthal ancestors.

[Dan Snow]

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

[Chris Stringer]

They should change. That's right. And I think I've learned 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.

[Dan 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.

[Chris Stringer]

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

[Dan Snow]

Thanks very much for listening everyone. Before you go, I have to 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. 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.

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[Dan Snow]

Sam.