Human Origins: Did We Begin in Africa?

Evolution of human origins

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0:30The story of modern human origins is often imagined as a simple journey out of Africa. Homo sapiens emerging somewhere on that continent before spreading across the world and replacing other forms of human life. But how is that story still evolving? Is the full truth of our beginnings actually much more complex? Over recent decades, evidence in the form of fossils, improved dating and ancient DNA have transformed the traditional picture, revealing a deeper, much messier tale of shifting African populations,

1:07multiple migrations, and sister species like Neanderthals. I'm Tristan Hughes. This is The Ancients. And today I'm joined once again by leading paleoanthropologist Professor Chris Stringer to explore what the out-of-Africa theory really means today, why it still matters, and what exciting new discoveries could still be revealed about where we come from.

Africa as the mothership

1:44Chris, it is such a pleasure to see you again. Welcome to our new studio. Yeah, it's great to be here. It looks great, yeah. And, well, we couldn't think of anyone better to come on the show to talk about human evolution and our story and the fact that Africa was, and still is, I guess, the mothership for our species. Yes, it still is the main place. But obviously, the more we learn about some of these other places, particularly places like China, we realise that they're an important part of the story too. And I guess it's, as we'll delve into, there's going to be quite a science-y chat

2:17and how the out-of-Africa theory, it has developed a lot over the decades, hasn't it? Yes. I mean, since even the 1970s and early 1980s, when I and a few others were proposing this, very much a minority view then, it was a very simple version that we had based on really slender evidence. And it's developed so much now, particularly, obviously, with the DNA evidence, but also new fossil discoveries and new methods of dating things. And so, for how long then has this idea, this proposal that, you know,

2:50Homo sapiens originated from Africa, how long has that been around? Well, I and a few others started to tentatively propose it in the early 1980s. 1980s, okay. And it was based then just on the fossil evidence. But, you know, there was so much we didn't know, there was so much uncertainty that it was put forward very cautiously. And then in 1987, of course, we had the story of mitochondrial Eve appearing, which argued purely from recent DNA evidence, mitochondria,

3:24mitochondrial DNA inherited only through women, it argued that everyone in the world today could trace back their ancestry to a woman who lived in Africa maybe 200,000 years ago. And this was based purely on data from present-day humans, but it matched, obviously, very well with what some of us were saying. It gave an even clearer and apparently more confident picture that we had a recent African origin. I just wanted to ask that because I was wondering if anyone had, like, potentially put forward that theory before the 1970s and the 1980s,

3:55but it does sound like that was actually where it really is. Yeah, that was the beginning. I mean, people like Bill Howes, the anthropologist, he had argued for quite some time before that that Homo sapiens was so different to the other things, the Neanderthals and so on, that we probably had a different origin and a single origin somewhere. But when he was proposing that, even in the 60s and 70s, he couldn't say where that place was. And it turned out later, of course, that it was Africa. And when talking about a recent African origin,

4:26what time period should we be thinking of, roughly? Yes, well, the main exit that leads to the diversity of people today outside of Africa happened, geneticists estimate, around 60,000 years ago. So Homo sapiens having evolved for a long time in Africa, a small group got out of Africa and then founded the populations of the rest of the world. So that's the kind of recent out of Africa bit of the story. And we now know that it's more complicated than that,

4:57that there were some earlier exits of Homo sapiens out of Africa that didn't end up giving rise to the populations today. And also we know that it wasn't a pure out of Africa. You know, some of us argued that it's virtually 100% recent African origin. But now we know that other humans contributed to our ancestry. People like Neanderthals, Denisovans, which we'll come on hopefully to talk about. They contributed a bit to our ancestry as well.

5:27So now I use the term, which I think was first used by Svante Parble, mostly out of Africa. I think that's the best way of describing it for Homo sapiens origins. And I guess also, is it, this is also something I find fascinating, the fact that actually our story, our Homo sapiens story, the majority of it is before 60,000 years ago. So there is a lot of archaeology still to be found in Africa itself, do we think, to kind of trace that earlier story of Homo sapiens? That's right. Yes, the main part of the story earlier on is certainly an African story.

5:59And probably a lot of our behavior originated in Africa, as well as our anatomy. And certainly most of our DNA comes from that African ancestral population.

Anatomically modern and archaic humans

6:10One other big question, first of all, we say things like anatomically modern humans and archaic humans. What do we mean by that? Yes, those terms, I've used them a lot in the past. I'm not sure they're very good terms, but they're certainly widely used. And so we better sort of go into what they mean for most people. So yes, our own species, Homo sapiens, if we look at people around the world today, yeah, we come in many different sizes and shapes and colors. But if we strip away the superficial features of the skin and hair and so on,

6:42get down to the bones and the teeth, the things that preserve in fossils, there are certain shared characteristics that we can call anatomically modern human characteristics. And so I've got an example of a replica here. Fantastic. Of a fossil from Romania that's over 40,000 years old. But here it is with a lower jaw actually from a separate individual. But they show the features of anatomically modern humans. So in the brain case, it's high and rounded, small brow ridge at the front,

7:16or maybe no brow ridge at all, quite a small face tucked under the brain case. It's quite narrow at the base and expanded higher up. So the whole brain shape is different. And when we look at the lower jaw, we can see there's a nice chin on the front. And if we had the whole skeleton, we would see that that too is distinct, that there is a narrow pelvis in Homo sapiens, a narrow shoulder girdle. We're much less heavily muscled.

7:47So anatomically, you know, we've got more gracile skeleton, if you like. We're slenderer than those earlier species, which mainly seem to be built for strength and power in their skeletons. So those are the shared features that we can look for. And there are many more of them. If we take CT scans, even inside the ear bones, we can see that the ear bones of Homo sapiens are distinct from those of Neanderthals. So even these tiny little bones that we can't even physically get to, except with CT scans, they're even distinct in Homo sapiens

8:18than from people like the Neanderthals. So that's the anatomically modern. And archaic is used as the flip side of that. So the things that don't show those features are called archaic humans. And that would cover the Neanderthals and Homo hyderbergensis and Homo mantisessa, Homo erectus. They're all called archaic humans. I don't think it's a good term because, of course, it's a big lumping term covering a huge amount of diversity. And actually, the Neanderthals are not, in some ways, they're not really archaic.

8:48They're very evolved, as we are. So if we look at Neanderthal evolution, we can see that they evolved bigger brains, as we did. Their teeth got smaller, as ours did. So they underwent changes too. And they're actually derived in their own direction, as we are derived in our direction. So I prefer to talk about derived Neanderthals and derived Homo sapiens. Interesting. But, you know, the terms archaic and anti-modern are still around. And, yes, as a shorthand, I talk about modern humans,

9:20by which I mean things that in the skeleton show these sorts of features. Yes, because I've either termed, like, derived humans and basal humans as well. Yes. And so in terms of archaic, I've tended to try and use the term basal. So these are things which are, you know, if you like, if we had an evolutionary tree, they'd be closer to the base of that evolutionary tree. They show more primitive features. So we've got an example here of a skull from Jebel Ihud in Morocco. Yes. Again, a replica. But this one is about 300,000 years old.

9:53And I call it a basal Homo sapiens. So it doesn't show all the features of anatomically modern humans. It shows some of them. So, for example, here, the brain case is still quite long and low, and there's still a strong brow ridge. But the face, and if we had the teeth and the lower jaw, you can see there there are some Homo sapiens features, but they're not fully developed. So this, for me, would be a basal Homo sapiens. And this is the key point, isn't it? A human skull from, and we'll explore Jebel Ihud a bit more in time, a Homo sapiens skull from 300,000 years ago

10:24could look very much different to one from 100,000 years ago, and the same in Neancetals, early Neancetals compared with late and so on. That's right. Yes, if we had an Atapuerca fossil here from 400,000 years ago, from Europe, from Spain, that would show, it's what I call a basal Neanderthal. It shows some Neanderthal features, but it lacks some of the features of the late Neanderthals. For example, the brain's smaller, the teeth are a bit larger. And also, there's even DNA from the Atapuerca fossils at 400,000, showing that they are early members of the Neanderthal line.

10:57Sadly, for Jebel Ihud, we don't have DNA. DNA, of course, in an African environment doesn't survive so well. So whereas we've got quite good early Neanderthal DNA, we don't have really any DNA of early Homo sapiens in Africa, unfortunately. And all this evidence that is coming to light now, I'm guessing the more, I mean, the previous view, the theory that we descended from Neanderthals, or Neanderthals came before Homo sapiens,

11:28that's now been very much pushed aside. Yes, so the idea that we evolved directly from Neanderthals, that was something I was testing in my PhD back in 19, I finished it in 1974. And one of the views I was testing was this view, which was a very common view then, maybe the dominant view was that, yes, we evolved directly from the Neanderthals and people like them around the world. And so if we had a complete fossil record in Europe, we would see Neanderthals gradually changing into Europeans of today. So the brow ridges would get smaller,

12:00the teeth would get smaller, the skeleton would get more lightly built. They'd gradually develop a chin on the lower jaw. So we'd have this sequence from Neanderthal to Homo sapiens. I was testing that in my PhD and I could see no evidence for it. The Neanderthals seemed to be going in their own evolutionary direction as we were. So in that PhD, I could conclude that we didn't evolve from European Neanderthals, but at that stage, I couldn't say where we did evolve from. That came later. That came later and that's where we get out of Africa

12:30and we're going to that now. We will delve more into, we'll delve into the nerdy details of the particular theories around out of Africa. But can you give us a bit of an overview right now as to what kind of the key developments in this theory, this hypothesis, what these key developments have been

Key developments in out-of-africa

12:51over the past few decades? Yeah. So if we go back to the 1980s, when the ideas really started to take off of recent African origin, there already were a few fossils from Africa that seemed to look quite modern at an early date. So there's one in particular from Omo Kibish in Ethiopia and I worked on that with Michael Day and we did a reconstruction of the skull and it showed for us modern human features. It had a small brow ridge,

13:21it was high and rounded, there was a chin on the lower jaw. There was also a skeleton, part of a skeleton to go with it that also seemed to show recent Homo sapiens features. Now back in the 1980s, it was argued by some people that it was at least 100,000 years old and Michael and I accepted that dating and therefore this was evidence of a Homo sapiens existing, you know, at the same time as the Neantiles were alive and it was in Africa. So this pointed to an African origin but at that time,

13:52we didn't have an ancestor for it, we didn't know where that, it was kind of isolated in a sense in Ethiopia. It certainly pointed to a recent African origin but there were people saying, well, it's wrongly dated or you're over-interpreting the anatomy. There are fossils in China and elsewhere that look like Homo sapiens too and are just as old. So there was just no clear framework to really say that was the story. There was conflicting data and it took a while for more fossils from Africa to emerge,

14:24better dating to emerge and for some of those other what seemed to be anomalies in other parts of the world got clearer with their dating. So some of those supposed ancient Homo sapiens in China were not actually Homo sapiens fossils or they were wrongly dated and were much more recent. So we got clarification of some of the more confusing bits of the story but it really started to come together, yes, at the end of the 1980s with the arrival of the first bits of DNA DNA from recent humans that started to point to it.

14:56And then as the evidence accumulated in the 1990s and the early 2000s, we got this picture building up that we were pretty certainly, at least in my view, we looked like we were virtually 100% recent African origin. So I was interpreting the fossil data, the behavioural data, the genetic data as all pointing to a recent African origin with Homo sapiens and one where if there had been any interbreeding with those other forms of humans, it was minimal. So I was aware

15:27that closely related species can interbreed and I regarded the Neanderthals as a different species. That was a view that kind of I started to pick up on with a few other people in the 1980s that we went back to using the name Homo neanderthalensis for the Neanderthals which they'd been given way back in 1864. Then for a long time,

15:49you know, certainly when I was doing my PhD, it was common to call the Neanderthals Homo sapiens. They were regarded as a form of Homo sapiens. So I started with a few other people to argue in the 1980s that actually we should go back to having a separate species name for Neanderthals and a separate species name for what became Homo heidabergensis, reviving that name. But I was aware that in modern mammals, for example, you can get interbreeding between closely related species. So for example, jackals and wolves,

16:20brown bears and polar bears, a number of species of monkeys in Africa can hybridize even though we regard them as different species. So I thought it could have happened between us and Neanderthals. We could have interbred, but I thought that it wouldn't have been a normal event. It would be a rare event. And then it happened 40,000 years ago. We're never going to find evidence of it today. Of course, I was wrong about that because in 2010, we got the first reconstruction of a good quality Neanderthal genome.

16:52That was published in the journal Science and it showed that indeed people outside of Africa have around 2% Neanderthal DNA in their genomes. And that's because there was an interbreeding event maybe 50,000 years ago. So Homo sapiens came out of Africa in this exit maybe 60,000 years ago. Soon after that, they met some Neanderthals. They did some interbreeding with them. And then as they spread around the rest of the world, they took that bit of Neanderthal with them. So not only is there around 2% Neanderthal

17:22in people in Europe, but it's there in China. It's there in Australia. It's there in Native Americans. So everyone outside of Africa has this Neanderthal component. So we have this kind of paradoxical situation that we did not evolve from Neanderthals, which is what I was testing in my PhD, but they're partly our ancestors because we've got Neanderthal DNA. So it's kind of, you know, they're a distinct lineage evolving for a very long period of time, hundreds of thousands of years, but not evolving

17:54to such an extent they couldn't still be a bit of interbreeding. And not evolving in Africa alongside ourselves until we go out. So it's also further evidence for the African origin. So it sounds like it's this combination of improved dating over time, the discovery of some really remarkable new fossils, and of course, the introduction of DNA and the building up of this incredible DNA database. All of that combined, as we'll explore, helps make it, you know, why in academic circles, especially,

18:24this recent African origin is so persuasive today. Yes. I mean, for me, it's persuasive. Of course, there are still people who argue that it's still an over-interpretation of the data, that actually the picture is much more complicated, that we should acknowledge these contributions from populations in the rest of the world as being more significant. So we have models like the braided stream model, which says that the evolution of our species is more like a river,

18:54which has many different tributaries that separate off, but then they come together and merge, and this pattern's been going on for the whole of the evolution of Homo sapiens, probably been going on for one and a half million years, and that really, there's no point in having these separate species names, because there was a bit of interbreeding going on between many of these different branches that we should call everything Homo sapiens. So it kind of goes back to that view that was around in the 70s and 80s, that actually, let's call everything Homo sapiens, that's essentially

19:25Genus Homo. So even to Homo erectus back that far, to one and a half, even close to two million years, people argue that we really shouldn't call that a separate species, even that should be called Homo sapiens. Now for me, you know, I come out of a paleontological background, I'm in a department with people who work on fossil fishes and fossil reptiles and so on, and the methods they use to establish species in the fossil record are similar to the ones I use to establish fossils in the fossil human record

19:56and the level of difference between us and Neanderthals, certainly in my view and the view of many of them, is at the level which in any other animal would be called distinct species. So I still regard them as distinct species even though we know there was a bit of interbreeding. But, you know, I'm not sort of wedded absolutely to the idea, but it seems to me that if you call all of those things Homo sapiens, you really lose any meaning to the term because, you know, how do we describe what is a Homo sapiens?

20:27Well, has it got a big brain? Well, not really because the erectus ones are very small brain. Small teeth? Well, not really because the early ones have got big teeth and Denisophanes have got big teeth.

20:39Lack of brow ridges? Well, no, there's brow ridges in most of them. So even to say what is the brain size? What is the brain size of Homo sapiens? Well, it's everything from down virtually the size of a gorilla up to the huge size of a Neanderthalus. So the term Homo sapiens become meaningless morphologically, I think, if you have this very wide definition. Gosh, we're getting deep into those theories already, aren't we, Chris? And we won't go into the weeds of what is a species today because I know that is also,

21:10that's another episode in its own right. If you may allow me to ask a superlative question because we have all this different evidence today, but have there been any landmark discoveries that we can say is the strongest evidence that we have today for evidence of an African origin for our species? Well, I think it has to be the genetic data, which is not a single thing. Of course, it's a mass of data that keeps building up, you know, tens and tens of thousands of genomes

21:41and all of them show that, first of all, if we partition variation in Homo sapiens today, by far the greatest part of it is in Africa and there are deep lineages there and if we look at the variation of people outside of Africa, it's a tiny subset of that whole variation that we find. So, just the pure fact of this, you know, huge diversity in Africa and all of the rest of us being a tiny subsample

22:12out of that diversity really does point to a recent African origin and that's true for the white chromosome, male inherited, for the mitochondria, female inherited and for the whole genome. So, overall, I think genetic data are the strongest but we now have a number of other fossils, not just Homo kibir, but there's other fossils in Ethiopia such as from Herto. We've got evidence from Southern Africa from sites like Classes Rivermouth and we've got the stuff as we mentioned from Jebel Ijud in Morocco and later Moroccan fossils

22:42that all point to the existence of Homo sapiens features at a much earlier date in Africa than we find them

Jebel Irhoud fossil discoveries

22:49anywhere else. So, Chris, let's explore some of these fossil discoveries and let's touch on the one for which you have a replica and you brought it up just a bit earlier which is Jebel Ijud. So, can you set the scene of where this is what we should be thinking with Jebel Ijud? Yes. So, yeah, this is a replica of the first fossil that was found. So, yeah, this was found before I'd done my PhD. It was called an African Neanderthal when it was discovered

23:20around 1960. So, it's from a quarry, a working quarry in North East Africa in Morocco. In North West Africa. In North West Africa. So, there's a quarry there and in that quarry were sort of cave deposits within the quarry and a number of fossils were found there and this is one of the most complete ones that's been found. Was it an accidental discovery whilst they were working there? It was an accidental discovery. So, this was a commercial quarry and these bones were being found. We don't know if any were found

23:50before that that were lost but there were. So, a Moroccan scientist did conduct some excavations there when bones were showing up and this turned up and as I say it was regarded by many people as being an African Neanderthal and originally dated only about 40,000 years old. So, when I did my PhD I was lucky enough to be able to measure this when it was in Paris before it went back to Morocco and I could see straight away that it wasn't a Neanderthal because by then I'd seen a number of Neanderthal fossils in my trip

24:20around Europe in 1971 and the face on its own was unlike any Neanderthal face. It was like a slightly bigger version of our own face. So, for me this certainly didn't look like a Neanderthal but at 40,000 years old you know it was also too primitive to be an ancestor for Homo sapiens so at that time it didn't seem to be particularly relevant for our origins. It maybe was a relic persisting from an earlier stage over in a remote area peripheral area like Morocco

24:50but a team went back to the site in you know from about 2015 onwards and did new excavations and they recovered more material more fossils more stone tools more animal bones and they did much improved dating work and that showed that these Jeboli Hood fossils and by then there were a number of different skulls and teeth and jaw bones these were actually about 300,000 years old and the stone tools

25:21were very nice examples of early middle stone age tools so at 300,000 years suddenly this was back in the scene as an important fossil because it did show although primitive it did show some sapiens features and so what do you mean by early middle stone age tool yeah so yes we've got these stages of the stone age which archaeologists have set up and in Africa we've got the early stone age the middle stone age and the later stone age so the middle stone age in Africa is equivalent to also the middle

25:52paleolithic that's another term lower paleolithic middle paleolithic upper paleolithic paleolithic being old stone age so we've got these stages of the stone age and in Africa the middle stone age is the stage that's associated with the beginnings of homo sapiens things like Jebel Ikhud and the equivalent stage in Europe and Asia is associated with the Neanderthals and then it's called the middle paleolithic so yeah sorry

26:22about those technical terms but yes the fact that Ikhud is associated with middle stone age tools also showed complex behaviour these are very nicely made tools so it suggested that you know again this was not a backward population in a peripheral area of Africa it showed that Morocco was important in the story of our origins and more work is being done there down to the present day I mean all of a sudden you know in recent years you know redating that is now one of if not

26:52the oldest evidence of homo sapiens we have from Africa and more to come hopefully yes I mean it's I don't think this can be the oldest evidence of homo sapiens because work I've been doing with Chinese scientists on fossils from China suggests that the roots of the Chinese population that we know as didisovans also known as homo longi dragon man that lineage seems to go back at least a million years as a separate lineage and if that's correct

27:23that also implies that our lineage and the Neanderthal lineage had split off and that means our lineage and the Neanderthal lineage must also go back at least a million years to a common ancestor so if that's true then Ehud in fact is actually a relatively young homo sapiens compared with ones that would be at the beginning of that evolution so this is still very controversial the genetic data suggests that we had a common ancestor with Neanderthals and Denisovans

27:53maybe 700,000 years ago we would suggest on some of the fossil data it could be at least a million so this is ongoing work but it certainly pushes back the ancestry further even on genetic data and that means that Jebelie Hood is by no means the oldest homo sapiens there must be some older ones either we've already got them and we can't recognise them or they haven't yet been found well that's the thing that's the exciting thing could there be almost a million years of story still to learn about

28:24from Africa in the story of homo sapiens well absolutely I mean there must be a deep history then for sapiens to be uncovered in Africa and equally exciting really there must be a deep history for Neanderthals to be recovered outside of Africa probably and a deep history for the Denisovans and the homo longi lineage that's beginning to be uncovered in China and then potentially

29:01I guess the next question would be more evidence of early adventures out of Africa by earlier by as you used the term earlier more basal homo sapiens that we don't know much about as of yet

Earlier exits from Africa

29:14yes that's right so of course the implication will be that is it really only one very late exit for homo sapiens or could there be earlier ones and yes we do seem to have evidence of earlier exits so I was involved in studying a fossil from a cave site in Greece called Apidema Cave and a few years back we published evidence that from that site there's the back of a skull which had been considered to be Neanderthal but on our analyses it actually looked

29:44like the back of a homo sapien skull and the dating evidence suggests that it's at least 210,000 years old and what's intriguing is that after that fossil is in the site we also have a proper Neanderthal fossil at the site maybe 30 or 40,000 years younger the Neanderthals were there and whatever evidence there was of early homo sapiens had disappeared so the Neanderthals came back and that early homo sapiens population if it was there has disappeared now not everyone accepts that this is an

30:14early homo sapiens and we have to be cautious it is only the back of a skull what was the rest of it like but on that evidence it certainly looks like there could have been an early homo sapiens dispersal and that actually ties up with some genetic data because there's quite an intriguing pattern when we look at Neanderthal and homo sapiens DNA I mentioned that we have a separation time maybe of 700,000 years for us and the Neanderthals based on the whole genome but when you look at the mitochondrial

30:44DNA of us and Neanderthals that's inherited through females when we look at the Y chromosomes of us and Neanderthals inherited through males they have a younger ancestry a younger common ancestry maybe only half the age of what the whole genome would say maybe 350,000 now that's very strange and so geneticists have proposed that there must have been an early exit of homo sapiens out of Africa maybe 300,000 400,000 years ago there was some interbreeding with the Neanderthals

31:15and yes that put a little bit of homo sapiens DNA into their genome but also it replaced their own mitochondria and Y chromosome with a more homo sapiens like from a more basal homo sapiens yes these will be basal homo sapiens getting out of Africa meeting Neanderthals doing a bit of interbreeding and changing basically they're replacing their mitochondria and Y chromosome with a more homo sapiens like pattern which is why they have a younger divergence on mitochondria and Y from us

31:46than they do on the whole genome so it's a complicated story but the epidema fossil might match that by showing us that there were indeed homo sapiens in somewhere like Greece more than 200,000 years ago and there's also evidence of earlier exits which we can pick up in China and even Australia because there are fossils in China that look sapiens like and in Southeast Asia that look sapiens like that are well over 60,000 years old

32:16so I've mentioned you know the geneticists estimate the main exit was 60,000 years onwards that gave rise to populations outside of Africa today but the fact that you've got fossils in China in Sumatra for example in Laos that are probably 70,000 80,000 years old means they predate that 60,000 exits so there must have been earlier exits and there's controversial evidence from Australia too so a site called Magia Bebi 2

32:46in northern Australia it's got a very deep sequence and you know beautifully stratified layers and at about 65,000 years ago on the dating from the sand deposits there's a layer that has complex technology a lot of use of pigments and dated at 65,000 again before the 60,000 exits supposedly and we assume that's Homo sapiens because of the complexity of the behaviour of course some people say well how do we know we don't have fossils

33:18but that would suggest there was even an early sapiens arrival in Australia at least 65,000 years ago so these earlier exits seem to have happened but they didn't take hold in the same way either those populations died out as seems to have happened in Europe after epidemia or maybe they were swamped by the main dispersal that came out at 60,000 that ended up being in larger numbers and it's actually over printed any signal of those earlier populations that

33:48were there I love it though that these days are still being pushed back Australia is a good example as well of that now we've kind of explained all of that and looked at some discoveries and the importance of DNA I hope you don't mind if we now kind of delve into the theories themselves in regards to out of Africa because it's all well and good saying oh they spread out from here and went there and there and there but what we actually mean by that there's a lot of debate and lots of different theories

Theories and models of origin

34:14aren't there yes I mean you know as you know I've already shown my own views of out of Africa have changed really since those very early simple models things are more complicated the evidence of interbreeding makes things more complicated so yes we could say that you've got the strict recent African origin model and that's the model which the mitochondrial DNA seem to suggest that really we can talk about almost a pure out of Africa so homo sapiens evolved in

34:45Africa pretty much entirely came out of Africa and replaced completely all those other populations and that is just the traditional the plain old simple recent African origin that's the model if you like the one extreme version of a recent African origin and I was always I was never really wedded to that idea although the mitochondria suggested it I was always aware that there could have been a bit of interbreeding but again I thought that would be trivial in

35:15the big picture so we were effectively 100% recent African origin even though there might have been some interbreeding okay then people like Gunter Breuer proposed a model called recent African origin and hybridization so he that's right he proposed that from the end of the 70s into the 80s and we worked together on publications and papers with that model as well and so he argued that yes it was mostly a recent African origin but there was some interbreeding on maybe a

35:47bigger scale than I was arguing but we could therefore expect to find some fossils that might show evidence of Neanderthal features but again in the big picture this would not be very important and I think Gunter's model is probably closest to what we've ended up with with the interbreeding evidence it's recent African origin and hybridization and hybridization because we're talking about interbreeding between you know what I regard as different species so you know there will be these species coming together even though their evolutionary

36:18separate and I mentioned really that this is something that we know happens quite commonly in mammals and birds someone estimated that 16% of bird species today have hybridization with neighboring species so it's not as though this is a rare event genetic data shows it's actually a very common event and so that seems to have happened in our ancestry then there was a model called the assimilation model and this was proposed by people like Fred Smith and Eric Trinkhouse again in the in the in the late

36:4970s and early 80s and they were proposing that yes there was an African origin for homo sapiens but it was a much more gradual and diffuse process so basically Africa dominated the picture because of a larger population so Africa in a sense was pumping out these genes of more derived homo sapiens features and these were then being assimilated in by the populations outside of Africa so Neanderthals were picking up those bits of DNA and becoming more sapiens

37:20like and over in the far east populations were picking up those sapiens like genes that were coming out of Africa and were being picked up by populations there so those populations outside of Africa would gradually transform with this mixing of DNA into homo sapiens so it's a kind of blend of an African origin and regional continuity so you've got kind of both side by side so it means Africa is important but not as important as the recent African origin hybridization model or

37:51the real single origin model would propose that's that's three third model three and then we've got the classic multi-regional model which argues that basically you've got ancestral populations for homo sapiens all over the place where everywhere that genus homo lived and evolved they evolved towards homo sapiens so the Neanderthals were evolving to homo sapiens in Europe we have populations in China evolving to homo sapiens there populations in Java in

38:24Indonesia are evolving from what we would traditionally call homo erectus into recent populations in Australasia and in Africa of course there's also a transition from early homo populations towards homo sapiens so homo sapiens evolves all over the world where ancient people lived but there's not speciation they're not going their separate ways because gene flow is keeping them together so gene flow acts like a kind of glue holding them together populations in

38:54Africa are interbreeding mid-ones in Western Asia who are then interbreeding mid-populations in Europe and over in the Far East and so there's never enough genetic separation for speciation and it's essentially the evolution of one species homo sapiens over one and a half million years yeah those are the four traditional yes those are the four traditional models and there's also the braided stream model yes I've got this as well so these are these are newer models that are emerging it's yes it's a newer name I think essentially it's the

39:24multi-regional model really under another name so for me it's very difficult to separate it from well probably the assimilation model and the and the classic multi-regional model braided stream is really like both of those so it's suggesting that you've got continuity over most of the inhabited world it doesn't get in so much to those tricky issues of species but it argues that essentially there is no single place where homo sapiens evolved and what I've said is well if it is a braided

39:55stream then it's a braided stream out of Africa so the braided stream the main by far the main flow is coming from Africa and yes there are these subsidiary channels which pick up some DNA from these other populations but Africa is still the dominant part of the story and lastly the African population structure model yes so I've been involved with people like Elena Sherry in developing that model and she's really developed this

40:25into what you can call a pan-African model so the idea is that homo sapiens did not evolve in one place so back in the 70s and 80s with fossils like Omo Kibish we were arguing some of us that East Africa was going to be very important in homo sapiens origins maybe the most important maybe the single center where it happened the birthplace the birthplace of homo sapiens would be in East Africa other people argue that it could be South Africa so there are these different ideas about where homo

40:57sapiens originated and the problem is that of course these models were built on where you had the best fossil evidence which of course may not be where it was all happening and people have compared this with you know the drunk guy who's looking for his car keys and you know it's night time and he's lost his car keys and he goes and looks under the streetlight because that's where the light is but in fact his car keys are somewhere else in the dark so it could be that that's our situation that of course we look at the areas where

41:27there's the best evidence of homo sapiens origins and that could include Morocco now but what Ellie argued and some of the rest of us joined in on that was that actually there were probably a number of parts of Africa that contributed to our origins so homo sapiens early homo sapiens populations were widespread in Africa they were in Morocco certainly they were in Ethiopia they were in Central Africa they were down in South Africa and these populations when they were separated by climate change

41:57so for example the spread of deserts at times may have pinned them back and separated them and they went their own way in evolution but at other times when climates improved and there was more rainfall these populations spread into newly greened areas met each other exchanged genes exchanged ideas so we get a much more complex network a braided stream if you like but just in Africa where homo sapiens is evolving as a composite of these different populations that finally come together maybe a hundred

42:28thousand years ago to become the homo sapiens that then spreads across the whole world so the combining of these populations I said that seems to happen very late in the story of homo sapiens then in their development and from what you were saying earlier that's right yes so this is a complex picture that goes on for hundreds of thousands of years and we only get a kind of coalescence to a homo sapiens pattern both in anatomy and behavior that comes together maybe a hundred thousand years ago or so and then emerges from

42:58Africa and stays behind in Africa as well and there are some even more complex models which are kind of you know there as an undercurrent that a number of geneticists are saying well even these models are too simple and actually there is evidence that there's a very deep split in the evolution of homo sapiens that might go back one and a half million years in Africa and this is an astonishing model it argues that there could have been basically there was one ancestral population maybe one and a half

43:29million years ago in Africa it then split into two distinct lineages which then evolved alongside each other one of them then gave rise to Neanderthals and Denisovans and later on to the homo sapiens that we find later on in in Africa and then going out of Africa but that second lineage is evolving alongside them for a million years and maybe 300,000 years ago it interbreeds with the homo sapiens that are in Africa and

44:00then produces the final push to make homo sapiens as we know it today anatomically modern anatomically modern homo sapiens and that population then disappears conveniently so it's an incredible story but there are several geneticists now arguing for these kinds of complex models so if that's correct it's even difficult to decide where where homo sapiens starts is it is it one and a half million years ago is it when you get that interbreeding event maybe 300,000 years ago so this these are newly emerging

44:31models and it's going to take a while for them to be integrated and also for the fossil evidence to be put together with them but you know if they're correct then it might bring something like our old friend homo heidelbergensis back into the picture so I mean first of all Chris before we go into that it sounds as if then like that theory then us today was it not basal what's the word derived or anatomically modern homo sapien we're you know from that converging we're almost like a blend of different basal

45:05homo sapien groups coming together which I'm getting my head around now yeah I mean we're all having to get a head around it and of course these are models they're they're based some of them on modern genetic data purely some of them do incorporate ancient DNA but they're revolutionary models of course in the the depth that they argue for our origins and something

Homo heidelbergensis and lineages

45:26like homo heidelbergensis so this is a replica of the skull from cab wave broken hill in Zambia Zambia okay and we can now date it at about 300,000 years old and it's you know certainly a not an anatomically modern human we've got a massive brow ridge a long low skull angle angled at the back rather like homo erectus quite a large brain though that's a modern-sized brain in there but a big face so this is part of what I've called homo heidelbergensis it's a species that was widespread it was

45:57in Europe it was in Africa probably in almost certainly in Asia as well and I used to argue that it was probably the common ancestor for us and Neanderthals at that time many people dated this skull at 500,000 years right and that seemed a reasonable date from which we could go to homo sapiens and Neanderthals from something like this that's what I used to think but of course as we found other fossils as we've got younger dating for this fossil of 300,000 I mean

46:28that means it's about the same age as and it's much less sapiens like than so I then said well actually I got that wrong the heidelbergensis is not our common ancestor it's a side branch that died out but these basal deep split models that I'm talking about from the genetic data they argue that there could have been a lineage alongside homo sapiens in Africa for maybe a million years that then interbred with homo sapiens about 300,000 years ago and then disappeared well heidelbergensis

46:58might come into the picture back into the picture as being that other lineage that coexisted with this evolving sapiens lineage in which case even this could be part of our ancestry too I was about to ask could this actually be a basal homo sapien well it doesn't I mean it doesn't look like homo sapiens I would have trouble calling it a homo sapiens for me it's a distinct species but it would suggest that there was an interbreeding event which put in maybe 20% DNA into the evolving homo sapiens lineage so a much higher level than has been talked

47:30about for for the Neanderthals and Denisovans so it would be a significant part of our ancestry but again in my view we wouldn't have evolved from heidelbergensis but it would be part of our ancestry an important part of our ancestry if those models are correct but I stress that they're newly emerging models and we're all looking at how they can work and that they need better testing of course Chris I have to get you on every couple

48:10of years because it always seems that more complex things are coming out and more complex models it's yeah I mean of course it's an exciting time with all these all these different ideas coming through but it's very difficult to give an overview a simple overview certainly that you know the experts are confused now as much as everyone else is and also the fact that like I was getting my head around it first of all that they're not being this idea of one birthplace but then the same time is saying that there are several different birthplaces of homo sapiens also a

48:41bit misleading at the same time yes I mean Africa is still the dominant place in our in our story but of course which parts of Africa I mean if if this story is correct of these two deep separate separate lineages for a million years we've got to ask ourselves how could these lineages remain separate for a million years in somewhere like Africa what was keeping them apart did they live in completely different areas or were they in some way different behaviorally that they didn't actually

49:11interbreed much until this last interbreeding phase at around 300,000

Migration climate and conditions

49:16we've covered a lot about the homo sapiens story and how complicated it is now for before the main exodus migration out of Africa itself but if we focus on that 60,000 years ago how easy would it have been for homo sapiens to leave Africa yeah I mean that's a good question because we we don't know the precise date of exit we think it was a small group of people or maybe a successive small groups of people but close in time

49:47and we don't know what the climatic conditions were at that time because we don't have it precisely dated so at times we know that that region northeast Africa and and the Levant at times it was relatively arid at times it was well watered with with more rainfall so we guess that it was probably a time when the climate improved and that allowed homo sapiens to move into the region and of course they would have been following their food so if there was an expansion

50:17of grasslands and even sort of woodlands and an expansion of the animals that are feeding on that new you know expansion then the humans are going to follow because that's where their food is so it may be that these people were just following their food in coming out of Africa and you know of course for them well Africa you know they didn't know they were leaving Africa they were going into a new area and that then was the beginning of that out of Africa expansion there are some people

50:48who think that it might have been more a forced exit that perhaps there was a deterioration of climate in northeast Africa and these populations were pushed out and that would explain the larger numbers yeah in in trying to find a new area so yes so we're not sure if it was push or pull were they pushed out into western Asia or were they pulled out into western Asia by improved conditions and in regards to the routes that they would have taken back then should we just be thinking of Arabia and the Levant you

51:19know Syria Palestine Israel today that that area or could they potentially those in Morocco at the Straits of Gibraltar have made that short crossing to southern Spain well Gibraltar and southern Spain today as well yeah so in terms of the the western route via you know the Straits of Gibraltar some people do believe that there were crossings early crossings so there are stone tools on an island off the coast of Morocco that look Neanderthal like but of course we don't have the fossils to show Neanderthals were

51:51there so most of the evidence and this includes evidence of the of the large mammals as well suggest that there were not any early crossings across there of populations in either direction but from North Africa to Europe or Europe to North Africa and that those crossings came much later you know the waters there are actually quite dangerous you've got very strong currents through there and so and of course even if a small population got across you know it may not have survived so the majority opinion

52:22is that we didn't have early crossings on the western side and that yes it's over in northeast Africa some people think that there could have been crossings at the southern end of the Red Sea where it's very narrow and it would have been a crossing direct into Arabia and a more verdant yes and and Arabia at times has been much greener yeah so perhaps there were crossings down there but again majority opinion is that it would have been further north through the Sinai and into you know the main parts of Western Asia okay well let's go to China and

Peking man and regional continuity

52:53let's go Peking man which is I guess this is we can we can use this skull a little bit for yes how does Peking man and explain what Peking man is as well if you don't mind I've got a skull in front of me yes how this story potentially fits into the kind of the recent African origin or people used to think it did yeah so this is an example of course of Homo erectus one of the classic Homo erectus populations from China so these finds began to be made at Jigudian near

53:26Beijing in the late 1920s and in the 1930s there were controlled excavations there that recovered a wonderful suite of fossils that were similar to the ones known from Java and what we now call Homo erectus so these populations were in the Beijing area about 500,000 years ago and for people who believed in regional continuity the multi-regional model these were going to be the ancestors of modern

53:58East Asian populations for example the modern Chinese and people argue that you can see features in these fossils that come through to modern populations in East Asia today for example having a particular shape of the incisor teeth a relative lack of wisdom teeth third molars these were features that were thought to be there in Pekin man as these fossils became known and that can be found in modern Chinese populations at a higher frequency so that was the continuity idea of course the recent African

54:29origin would suggest that there is no continuity with erectus there is continuity with Denisovans who are a lineage that we think evolved alongside erectus so in China we had the continuation of Homo erectus down to maybe three or four hundred thousand years ago so there for over a million years but also alongside them we've got the evolution of Homo longi dragon man we've got this replica over there green colored replica is the harvin

55:00cranium which we think is so it's the type specimen of Homo longi dragon man but also pretty certainly a Denisovans so that lineage was in China as well evolving and the erectus lineage died out the Denisovans continued for much longer interbred with Homo sapiens and then they died out too so is this idea that you know once thought that this meant that kind of contrasted with the recent African origin theory but more recently with the discovery of the Denisovans and

55:32so on actually this has been largely debunked now do you think well there are some people in China who are still wedded to the idea that peaking man fossils are important in the ancestry of modern Chinese people so you know there are some political factors in there as well which are influencing those views and because it's it's possible there is a little bit of DNA even because there is evidence that there was archaic introgression from a very early population into the Denisovans so

56:02possibly erectus well in fact almost certainly there's evidence that erectus interbred with Denisovans and then Denisovans interbred with Homo sapiens so there could be some transmission via the Denisovans of erectus DNA into Homo sapiens today in the Far East so they could even be a little bit fair enough never say never recent Asian origin recent Africa it's it's it's it's so interesting I guess but it's going to be a very small amount of DNA but it could

Mostly out of Africa today

56:30be there at a very small level and Chris like what do you think is the best one sentence answer to Homo sapiens origins today I would say that we are mostly out of Africa mostly out of Africa that summarizes it for me I think that's quite nice isn't it as well you brilliantly detailed although that the complicated how it's getting more and more complicated the thinking about our story before we leave Africa multiple birthplaces converging

57:01populations to form anatomically modern Homo sapiens and new discoveries coming out it seems like there's still so much we don't know and why it's still so exciting but bound to get even more complicated in the years ahead absolutely I mean just think that you know since I did my PhD just how much has happened it's incredible how much our knowledge is growing and yes in some ways it gets more complicated in other ways it gets simpler because along the way we can dispense with the incorrect ideas you know as we have new dating we can dispense with the confusion that was

57:33created by bad dating where we get fossils that have been wrongly interpreted we can get rid of that confusion so yes in some ways it's a more complicated story I would say it's a richer story it's a more honest story of our origins and I think what it shows us is that actually Homo sapiens origins in my view is not something special if we had this degree of information about the evolution of let's say lions or pandas or hyenas they would be similarly rich if

58:05we ever have the evidence of gorilla and chimpanzee evolution which we mostly lack they would have their own rich stories to tell as well so I think this is showing us the way forward that you know when you get more data yes it's a complex story it's a richer story and it isn't just our story all of these other species had their own wonderful origin stories to tell and we shouldn't forget them and of course that's true for the Neanderthals for the Denisovans for Hyderbergensis all of them have their own rich evolutionary history that we're only beginning to tell

58:37Chris you are one of if not the leading expert on human evolution and early Homo sapiens and the developing story in the Neanderthals we'll have to get you back on as well in the future it just goes to me to say thank you so much for taking the time to come back on the show it's been a pleasure again thanks so much for joining us on the ancients today I hope you enjoyed the episode and if you are loving the ancients then why not become a history hit subscriber as a subscriber you will have access to hundreds of hours of

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