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cc >> Welcome to University Place. I'm Norman Gilliland. About 80,000 years ago when human beings first migrated from Africa to the Middle East, they found that someone else was already there. Neandertals. For about 10,000 years Homo sapiens and Neandertals coexisted, and then for some reason the Neandertals disappeared, but why? Well, with the key to that mystery is our guest today, John Hawks. He's an evolutionary geneticist at the University of Wisconsin Madison. Welcome to University Place. >> Thanks for having me. >> Well first we should figure out what's the difference between a Neandertal and a human being. And I suppose we should even ask before that, what's the difference between a Neandertal and a Neanderthal? >> Well, Neanderthal and Neandertal. Well, this is so interesting because even people who are real familiar with anthropology, they differ on the way to say this word. And it's for obscure reasons that there came to be these different ways of pronouncing it. The original Neandertal fossils, the ones that were recognized to be something different from the rest of us, were found in Germany in a place that's a little bit outside of Dusseldorf, and it was called the Neandertal. Tal meant valley. And it was because there was this guy who lived there named Neuman and he was sort of a hermit and people started calling it Neuman's Valley and he styled himself as being a real intellectual so he rendered his name in Greek and called it Neander. So we've got Neandertal. Well, now the site is completely gone because they were digging a limestone quarry at the time, and the reason why they found the bones is that they're digging out the limestone and what was inside of a cave was just junk as far as the quarry was concerned. Well, eventually the limestone is gone. This is like a parking lot. And in the last five years really the museum that's there sort of renovated what was once really junky looking into a nice little meadow, and you can see a monument where the site was. It's very nice. But it's completely gone. Well, in the late 19th century Germans changed an archaic form of spelling, TH into a T. So although it came into English as the TH, the old version, in German it's now just a T. And a lot of anthropologists changed to go along with the Germans. Mainly those of us who thought that Neandertals had something to do with our ancestry because the TH version of course came into English and started suffering this terrible fate because everything that you don't want to be is Neanderthal. That's like, wow, if you call you a Neanderthal, this is not saying you're the valued ancestor. >> Some kind of throw back. >> Exactly. So we've got tal and thal. >> And what is the difference then so far as we know today, and we're discovering a lot I gather, what is the difference between Neandertal and Homo sapiens? >> Well if we look classically at their anatomy, what we found was fossils and in many cases subfossils, they hadn't mineralized yet, so skeletal materials, and what became obvious about them was the ways that they were different from us. And so if you look at their skulls, they tend to have a real projection above their eye orbits, it's called a brow ridge or a supraorbital torus. Their skulls tend to be quite long and their foreheads slope. Their faces are really big compared to most living people. The big faces, relatively big teeth, but those faces sort of project forwards. So it's almost like their face is lifted up in front of their brain. Whereas, most living people have faces that are sort of tucked in underneath their brain. Their jaws tend not to have a chin. And if we look then post cranially, well their bones are different from ours in some respects also. If you look at a femur bone of a Neandertal, for example. >> Let's look first just by comparison at the modern human skull. >> Here's the modern human skull. A very rounded forehead. Face tucked in underneath of the brain case. >> I assume these are comparative males then because a female skull would be a different shape. >> Exactly. You've got the robusticity. Men are sort of bulkier, more robust than women. And Neandertals differ from us in that respect, but also they have these real distinctive anatomies. And then there are little things like they tend to have a little groove on the back of their skull. We have no idea what it's for but it's there. >> Is it a muscle of some kind, a muscle attachment? >> Well it's a resorption area where you can feel the back of your skull there, there's no muscles on top of it, but their bone just tended to resorb a little bit. Why that happened, we have no idea. >> What about that great sagittal crest that men have that women tend not to have. >> Well the sagittal crest is something that earlier hominids had in the middle of the skull. But this supraorbital torus is something that's real distinctive about modern humans who tend really not to have this. It is quite rare today to see somebody with a brow ridge that goes right across the front of their face. >> You probably don't necessarily want to meet somebody on a dark night like that. >> Maybe not here in Madison. Some parts of the world it's not so uncommon. It's a trait that still varies today. As to why that's there, it's sort of a mystery. Some of these things we think are just side effects of genetic changes. >> Kind of rambled, tumbled effects. >> Exactly. Some other things are probably functional in some way. >> You mentioned the bones, some of the bones and the difference there. This we have with the upper leg bone. >> Yeah, this is the thigh bone of a Neandertal, a femur. And if we look at any of the long bones of their arms and legs, what you see about Neandertals is that they're really heavily built. Now, it's a real common misconception that Neandertals are big like professional wrestler types. They're not. The average height of a Neandertal man was something like five foot five, five foot six inches. So they're not. >> Any taller than Homo sapiens of the same time? >> They're a little shorter, a little shorter but not a lot shorter. And if you compare Neandertals to early agricultural people who had not as good food to eat, they're about the same height. So we're talking about hunter gatherers. >> How about running, how would you compare them as runners if they're that stocky? >> Now if we look at their proportions, they are generally stockier than us. So their distal segments, the shin versus the thigh or the radius and ulna versus the humerus, they tend to be short. Their limbs tend to be a little shorter. Because their bones are over built and curved, we think that they were more powerful. They were certainly capable of resisting more force than the average human. And all that attests to a real muscular strength adaptation. So if we compare them and us running, we're not talking about distance runners with these guys. I mean they are, in that sense, built like wrestlers, not professional wrestlers but college wrestlers maybe. And if you compare them to other kinds of hunter gatherers, they are definitely bigger, they have more energy output and that means that they lived a lifestyle, which in the northern frontier of human habitation at that time, a lifestyle that took a lot more energy. That's the real difference between them and us is in energetics and ultimately the effects that has on their behavior. >> When they moved out of Africa, and they got there before Homo sapiens as we indicated a few minutes ago, any kind of settlements or are these discoveries that we're making of Neandertal sites, I'll call them, are those just one night stay over places or what kind of a system of living do they have in these early sites? >> Archaeologists have a clever strategy and that is find somewhere that you think humans would have been and dig there. And so what we tend to find with Neandertals is we, of course, find a lot of them in caves but that's because the archaeologists know that these caves attract all kinds of animals in the landscape and humans are no exception. And so you go to a cave and you dig and you're likely to have a sort of large deposit of undisturbed sediments, and we learn a lot about their behavior that way. But they didn't live in these caves. They came there, they'd stay for a few nights sometimes, but they weren't cave dwellers in that sense. This cave that we've got a picture of is, to my mind, the most beautiful of all the Neandertal sites. It's in Vindija, Croatia. It's right on the Slovenian border, and you can see from inside the cave looking out it's green. Croatia is a lot like Wisconsin, especially the driftless area of Wisconsin, the part that wasn't glaciated. It's got hills, it's got a lot of trees. And looking out of this cave there are strawberries that grow around it. It's a really nice place. And the Neandertals used these places to sort of hide for a couple days. They would stage their hunting trips probably out of these places and open air sites, but they didn't tend to return and stay for weeks or months on end. They were very mobile people. They had to follow the animals. With Neandertals in particular, imagine that you're hunting, as they did, large mammals. We're talking about bison and horses. They didn't have bows and arrows. They didn't have javelins. They had big long wooden spears. Sometimes with a point glued on the top of it. >> A stone point. >> A stone point and they would have to jump on the animals to kill them. Imagine you've got a spear and you're going to jump on a bison. >> You'd have to be pretty sturdy to take that kind of abuse. >> Absolutely. There's a site called Krapina, which is also in Croatia, where they're hunting woolly rhinoceros babies. Wooly rhinoceros babies tend to come with woolly rhinoceros mamas. >> I don't think you can mention anything too much more fierce than that. >> So with Neandertals, their technology limits them, in that sense. They're living a hard lifestyle. But also when we think about the limitations that are on them, think of the strategy that works for this. You've got to know what the animals are going to do. You really got to have the jump on them. So Neandertals are like ambush hunters. They're a lot like mountain lions who are taking all ages of prey. It doesn't matter which animal comes along because what's important is that you have the position that you can surprise them. And the Neandertals are using their landscape this way. >> So they would be migrating seasonally with the game. >> We think they were. And yet they have this immense familiarity with their landscape. You really have to know where the good places are. And when we find caves that were recurrently occupied by Neandertals, they come back to this place again and again, sometimes they're hunting the same kind of animal again and again. So we get caves where 70%-80% of the animal bones are horse. And other caves where it's the same proportion bison. And it's got to be because not this is the place where the bison were but because this is the place where they had a good strategy to get the bison. And for whatever reason the landscape offered an opportunity for that or they were there at preferentially that time of year, whatever the reason, that's what they were able to do. >> They had bigger brains than Homo sapiens? >> Neandertal brains, for men, average a bit over 1600 cubic centimeters, and that's a big brain today. There are humans who are that size. The range in normal-sized brain men goes from something like 1,000 cubic centimeters to something like 2,000. So Neandertals are upper end of that range. The average today in Europe for men something like a little under 1400. So they're quite a bit brainier than us in terms of mass. Of course we don't know what difference that makes to behavior. >> So, the differences between Neandertals and Homo sapiens really have mostly to do with body structure, so far as we know. Is there anything we can tell from DNA and how similar was their DNA to ours? >> So the really cool thing, the reason why we are really excited about Neandertals now is that we've got a draft of their genome. And I'm showing you this bone, this is a little piece of a shin bone. And it came from that cave, Vindija Cave. When this was found along with the archeological excavation of the cave, they tossed it in a box with the animal bones. You can see this little piece of bone is not obviously human looking. >> Nothing too impressive about it at first glance. >> Yeah. If you look very carefully at the anatomy of its surface and considering the size and everything about it, it doesn't fit in with any of the animals that were living around there then. It looks like a human bone from that aspect. And it was Tim White who discovered Ardipithecus, he's famous for that, who went back through these boxes of fauna and found this bone there. Turns that this bone has the best preservation for DNA of any bone that we found of Neandertals yet. So it's really exciting that here's a piece of anatomy that is completely useless to us, from the standpoint of interpreting Neandertals, it's a piece of bone, it's a Neandertal. That's what you can say about it. >> Nothing in terms of the skeletal context. >> Out of this one bone comes now more knowledge about Neandertals than we've ever excavated out of the ground before. Because we've got 20,000 genes and three billion base pairs of DNA and counting coming out of this bone. To date, they've got large amounts of the genome of two other individuals from this site and a couple other Neandertals from other places, and we know quite a bit about the mitochondrial DNA, which is a very small fragment of our complete genome but it's real variable so it tells us something about population structure, we've got that from about 20 Neandertals from different sites. So we know a lot about their genetics now. >> And what are we learning? >> For me as an anthropologist, the coolest thing is that we're part Neandertal. I'm flabbergasted to be able to say that now. >> That's part of the answer to the question what became of them. >> Absolutely. When we look at the human genome and the Neandertal genome, they differ on average in such a way, we tend to, in comparing genomes, how are we going to do it? We can count the number of differences. We could say this is X proportion different. An easy way to talk about difference is time. Because if you imagine that we have ancestors, those ancestors lived at some time and they have descendants today and those descendants are cousins of each other, basically, then what's interesting about the genetics of the cousins? Well, one thing that's interesting is how long ago that common ancestor lived. That gives us an index to talk about how different they are. A human gene and a Neandertal gene, on average, had an ancestor about 800,000 years ago. Now it doesn't mean that the population that was ancestral to us and Neandertals lived that long ago. Because if we look in humans today we can ask the same question. Your DNA and my DNA, how long ago on average did we have an ancestor in common? The answer to that is over 500,000 years. >> That far back? >> That far back. And looking at humans around the world, how long ago did our genes differentiate? Well some of them very recently. Obviously we have some genes that have come from ancestors who lived in the first agriculture days. >> You mean just a mutation that occurred then? >> Just a mutation that occurred then that today is common. So lactase persistence. This effect that Europeans today can drink milk when they're adults, that's a mutation that happened 8,000 years ago. >> Because the default was to be lactose intolerant for humans. >> That's right. So everybody today who has that mutation, we can say one thing about them. They definitely have an ancestor in common that lived 8,000 years ago. So some genes are very recent. Other genes, a long, long time ago. If you're blood type A and I'm blood type B, I'm not, I don't know what you are, but as an example, somebody who is type A and type B, those two versions of that gene diverged from each other about three and a half million years ago. So what we're saying is that if we know that two people carry different alleles of that gene, we know that they didn't have an ancestor in common for that gene for the past three and a half million years. Now that's Australopithecus time. We're not saying that... >> You go back much farther than that and be in the human family. >> That's right. It's not that the type A and type B people diverged and became different populations, it's that those variations were maintained in this population. The human Neandertal ancestors were maintaining variation too. So we think that whatever divergence there was between our population, which mostly is derived from Africa before 80,000 years ago, and the Neandertal population, which mostly lived in Europe stretching across sort of the southern tier of western Asia as far as Uzbekistan, so going into central Asia, those populations look like they diverged something like 300,000 years ago. >> So we think Neandertals left Africa when? >> The first Europeans got there 1.2 million years ago. We've got a really good skeletal record of Europeans after about 600,000 years ago. We've tended to think that those people were the ancestors of Neandertals. It's now clear that the Neandertals are getting genes coming in from presumably Africa, but possibly other places too, up until at least 300,000 years ago, maybe later, and then after that time, sometime after, as you said, 80,000 years ago, humans emerging from Africa mixed again with that population. So we find this evidence of mixture in their genome. >> Do we see any evidence of a combat between Neandertals and Homo sapiens? >> A lot of people want to know what was this interaction like? And Neandertals we already know lived sort of hard lives. >> They weren't necessarily kind to each other in the first place. >> Yeah, I described this hunting method that they have, and that has its risks. This skeleton is from a site in Iraq which is called Shanidar Cave. It's in the northern part of Iraq. >> It's very famous. >> And the most famous skeleton from this cave, Shanidar 1, the most obvious thing about him is if you look at his arm bones, and I've got the two upper arm bones here, the humerus, they're asymmetrical. One of them is normal looking and the other one is wimpy and withered. It's because his arm was amputated at the elbow. And he lived with one arm. He also looks like he was blinded in one eye. You can see looking at the front of his skull there that the eyes are not symmetrical. It's because one of them was hit by something real hard and the bone fused in an abnormal position. >> What was the age of this individual when he died? >> This guy, who is one of the oldest Neandertals that we know of, died sometime in his mid-40s. >> Which sounds incredibly old, especially for somebody with part of an arm gone and probably blind in one eye. He must have had some kind of a social network to sustain him. >> He lived this way for a long time. You can see the evidence. That arm took a long time to atrophy to the point that it was. And he healed from his wounds. So there's clearly some elaborate social network that enables them to survive, and we've wondered for a long time why. Do they have some kind of ideology or knowledge that they're passing on that values these older individuals. It's very possible. >> Do we have sense of aesthetics, Neandertal aesthetics? >> What's interesting is we used to think that when modern humans show up on the scene, especially in Europe, where after 30,000 years ago there are these beautiful painted caves. >> Altamira and other places in Spain. >> The earliest one is Chauvet Cave in France. Lasco is maybe the most famous. It's a little more recent, about 23,000 years old. But these caves represent an artistic expression that was thought to be real unique to modern humans. But digging in the Neandertal sites, every so often you find something interesting. We now know that Neandertals were making beads and drilling holes in animal teeth to use as pendants. We find that they were collecting shells and carrying them inland so they were valuing these things and trading them. In one case in Portugal we've got a site, I've got a picture of one of the shells here, we've got a site where they painted shells. So this is a natural shell that on one side has got a natural coloration and on the other side of it, flip it over, the other side naturally doesn't have any color on it. The Neandertals took a form of iron oxide and painted on that to mimic the other side. In southern France we've got a site that has these pigment crayons. They're pieces of manganese dioxide, and I've got a slide of them, and they look like little nubbins, like my kids are done with the sidewalk chalk and you can't use it anymore. That's what these are like. And you can see on them there are these little striations. And looking at them microscopically, the striations that are there, it makes a real black pigment, this manganese dioxide, the striations aren't consistent with being scratched on a hard surface. They were coloring something that was soft. >> What would that have been? >> We imagine either their skin or some sort of animal hides. They're making clothing that's colored. They're the first fashionistas maybe. ( laughter ) >> We might find some DNA in common with them and, say, Calvin Klein. >> Don't let him hear you say that. ( laughter ) >> What the implication, of course, is that then there is all kinds of abstract thinking going on. >> Yeah, exactly. This has got to be the tip of the iceberg of what they're doing. And when we look at what they have to have been able to do to survive given their technology, modern human hunter gatherers, to do the same thing, they'd be talking to each other, they'd be passing down stories, they'd have social networks to help spread the risk when the animals were scarce. They'd have all those adaptations. Neandertals, they're not here anymore. So we wonder is there some element of the modern human pattern that they lacked? And whenever we find these unique sort of artifacts that show us that thing that we used to think separates us from Neandertals doesn't separate anymore. They were doing this sometimes. It helps narrow down the hypotheses that are left. >> What are we down to? >> I think, look at the mode of transition that we've got. When humans disperse out of Africa, clearly most of the genome of people who live outside of Africa now, 95% to 98% of it comes from Africa in the last hundred thousand years. So there's a big event. Neandertals, presumably when humans initially come into contact with them, they're mixing. And we've got the evidence of that mixture in our genomes today. Something like 1%, 2%, maybe 4% of our genomes outside of Africa come from these Neandertals, but most of their genes are gone. So what is it that could account for that pattern? Their anatomy is gone. The brow ridge, that kind of stuff is very rare now or absent. So you start thinking what is it about them that has persisted, and what is it that made us different from them when it looks like we do so many similar things? I started thinking of things like energetics, disease, maybe there's some pathogen that has a real different effect on these populations. We think about longevity. Today humans, it's normal to live to 60-70 years old, even in hunter gatherers who live hard lives today. Neandertals did not live to be that old. >> Did Homo sapiens? >> Homo sapiens, by the time they're dispersing out of Africa into other parts of the world, our modern hunter gatherer pattern of longevity is in place. People are living to be old. Of course today, look around the population of westernized countries, you see 80-year-olds, 100-year-olds. That's not normal for hunter gatherers. It doesn't happen very often. So there's continued change. Most of that change recently is cultural. We wonder, for Neandertals and later people, are there genetic changes that are also helping to push longevity higher? Are there genetic changes that make you better at talking or give you some sort of advantage in going beyond those large animal resources and broadening the resource base. >> For a more stable existence. >> Exactly. It's real hard for us as anthropologists to try to reconstruct what life was like before agriculture because even hunter gatherers today, people like the bushmen of South Africa, are trading with agriculturalists that live nearby. >> So you don't have a hermetically sealed culture. >> That's right. And every where that's really good hunter gatherer habitat was taken up by agriculturalists 3,000 or 4,000 years ago. So we can't look at people living in rich resource bases. The hunter gatherers we know of live in real marginal habit. The Neandertals had this weird combination. They lived in the best places but with the worst technology. >> So of that, what, 4% of our genome that's Neandertal, what is it? >> What is it. >> What do we get from it? >> We don't know. This is the exciting thing. My lab right now, we're trying to figure out what some of these places are. What do they do. We know of genes that are selected in recent human populations because we've compared humans to each other. So we know that things like skin color, they're different in different populations, there are genes that correspond to those differences. We're now looking to see do the Neandertals have any of them. It's a complication that most of the things that are real different between populations today are real different because they differ recently. Skin pigmentation is an example. We know of maybe a dozen genes in Europeans that correlate with lighter skin, and those dozen genetic changes, so far the ones that we know the age of are all real recent, 10,000 or 20,000 years. And this maybe really post-agricultural selection that's with lighter skin we're talking about vitamin D. So diet change makes a difference. >> So it wouldn't be related to the retreat of the Ice Age and the fact that Homo sapiens are moving farther north into Europe where they would need more vitamin D absorption from their skin. >> It could easily be. Now with Neandertals one of the real interesting things we no about their genome is that they had red pigmentation for hair. >> The Neandertals, they were red heads. >> They were red heads. They were red heads because they have a genetic mutation that we today, humans don't have. So this isn't something that we got from them. The human versions now are all new. So here's a change that, why are people red heads? Maybe it correlates with lighter skin. It seems to correlate a little bit. So this is may be the selection for skin color. Darwin thought that this was about sexual selection. Red heads are sexy. >> A good 19th century aesthetic that he was superimposing on science. >> So from his point of view this was all about taste and populations establish their own taste. >> Which is a very hard thing to trace through a genome. >> Right. And it's something that wouldn't work in the tropics where you need to have dark pigmentation, but in Europe you're sort of free to vary. The Neandertals had that. It's not a stretch to think they might have had other pigment variations that would still survive. We haven't found them yet. And it's that way with a lot of things. We don't know yet what the Neandertal genes did that we still have. But we're looking. And I think before the year is out we're going to have some good hypotheses about stuff that we got that came from them that does things. >> So the Neandertal was not really a different species from Homo sapiens or they wouldn't have been interfertile. >> I think that's a main message that is coming out of this. It's sort of a misconception that if you look at species in nature they could never have fertile offspring. A lot of cases of good species are good species because they look different, they live in different places, and yet if you bring them together they with reproduce. And chimps and bonobos are like this. They live in different places. They have very different behaviors, especially social behaviors. But if they're housed together in a zoo they can and do reproduce and have fertile offspring. Humans and Neandertals, they're not separated from each other as long as chimps and bonobos are. And they not only reproduce with each other in captivity, there was no captivity when they reproduced, that was their natural habitat. So we would say biological species concept, they're the same species. >> But we still don't know why Homo sapiens had this runaway success and Neandertals were, let's say, got second best just by dint of living on through Homo sapiens. >> It's completely open. We can disprove some hypotheses now, right? For example, we know from the genome of Neandertals now that there's one gene that's real unique in humans, different in humans than other kinds of mammals, it's called FOXP2, and we think that this gene has correlated with language ability in the sense that it's real strongly conserved, it contributes to the development of the language areas of the brain, and in humans that have a broken version of it, they have trouble talking. So put those things together and say this might have changed in humans because of the evolution of language. Neandertals have our version of it. Neandertals have a bone in their throat called the hyoid bone, as other mammals do, but theirs is shaped like ours. So it looks like their throat could make the kinds of sounds that ours makes. People who lived before Neandertals, if you look inside their inner ears, or their middle ears, excuse me, at the tiny bones that transmit sound, they're shaped like ours and not like chimpanzees. So it looks like they were hearing the kinds of things that we hear. So you put these things together and it looks like Neandertals probably talked. But did they talk in precisely the same way that modern humans do? That's an unanswerable question for us now. So we sort of whittle away the wrong ideas. We said, they're stupid, they couldn't talk to each other, they obviously couldn't adapt as well as humans could. We can disprove part of that. And that opens up new investigation. Can we establish what kinds of things are possible given what we know about their genetics. That will be the next 20 years of research. >> How could you ever determine what they talked about as opposed to Homo sapiens. It makes sense from an evolutionary standpoint or a natural selection standpoint that if Homo sapiens could, say, express abstract thought better that they would gain the upper hand. Certainly if you had a plan, any kind of operation, whether it's a hunting operation, a military operation, you will have the upper hand. But how can we ever determine that that was the kind of difference in the way Neandertals talked versus Homo sapiens? >> You know, some day we will know I think. We'll never have the full answers. It's not like we can put an anthropologist there and watch them. But the way that we can unravel genetic differences between people now, we're discovering health risks of all kinds that are based on very subtle genetic changes and yet have sort of effects on you at given stages of your life, we're going to discover things about Neandertals that are different from us. We can take Neandertal genes and put them into mice and see what their effects are in vivo. That doesn't mean that we can tell the difference between them and a human that way, but the first thing they're doing with this red hair version, it's inferred to be red hair because of computer predictions. Here's what the structure of the molecule is and here's how it would have received the hormone that makes them make black pigment and that would have compromised it. But the next obvious thing to do is put it in a mouse and see if they turn out red. So actually we have some really interesting ways of developing more and more knowledge about this, and we'll never get to the end. But this isn't like it was even when I started where you looked at two skulls and said I think they're different and I can count the differences and that must mean X. I mean, we can really test a lot of these hypotheses now and it's become a science of the genome age. >> How do you suppose Neandertals decided to leave Africa so much longer before Homo sapiens got around to it? What would be the difference in the two populations that would account for that? >> With hunter gatherers this is always about where is it easy to live and how many people are already living there. Hunter gatherers really don't tolerate over population in one place. And so you get to a certain point and people don't tolerate each other anymore. It's like, I'm fighting with you, I don't have to live here anymore. I can walk down to the next place, if there's nobody there already. So dispersal in human populations can happen just with lightning speed if we look at the archaeological record. We think the spread of humans from the initial people reaching the new world, which was in sort of Beringia, the northern Alaska connection are Siberia. The dispersal from there to the southern end of South America may have taken as little as a thousand years. >> That would have been spectacular. That's certainly a revision, isn't it? >> But if you think about how little it takes in terms of growth to start to spread a population in numbers, if you grow at 1% or 2% per year, you very quickly fill up the world because our population today is growing 2% per year. It doesn't take very long to ramp your population way up. Now with hunter gatherers, before there was agriculture, they're resource-limited. They're like any other species on the planet. If there's too many of them, there's not enough food or there's too much disease or they fight with each other too much. And in any event, it's resource-limited. So what happens is Africa is probably always more densely populated than anywhere else because that's where humans originated. And in the Middle Pleistocene 400,000 years ago, Africa is the densest place in the world just as it was 20,000 years ago. Well, dense for hunter gatherers is not like dense for agriculturalists. But it's uncomfortable. So if there's somewhere for you to move on that you discover is a nicer place to live, you move there. If it really is a nicer place to live, then your population grows. It doesn't take very long to fill up a new continent. >> Significance that it was the Neandertals who left town though? >> You know, I think, my guess would be that they happen to be living in the northeastern part of Africa at the right time, and they were obviously people who spread from Africa just as soon as their legs were long enough and their hunting was flexible enough to do it. That seems to have happened almost 2 million years ago. After that I imagine that there were wave upon wave of new things happening in Africa, people competing with each other, developing new methods of life. They get better at it. If they're the northeastern corner of Africa and they've got a new trick, they can spread outside of Africa. And probably those populations are constantly mixing, coming into contact. And the most recent version of this, the out of Africa movement of the last 50,000 years, in some senses it was maybe the biggest. We know that it had a huge genetic impact on the rest of the world's population. We trace our ancestry outside of Africa today, 95% back to those people who lived there 50,000-60,000 years ago. >> Now if we think back to the map that we saw a while ago of the Neandertal occupation of Europe, what would have kept them from migrating further if there was a problem? Do we have a sense that Europe was getting too crowded for Neandertals and that's what happened to them? >> It's sort of interesting that we have now one genetic hint of the people who were around who weren't Neandertals. There were other people who lived further east in China. In south Asia, a big population of ancient people. We don't have a lot of skeletal remains from India, from the south Asian population. We've got some from China, we've got some from Java. There's one bone, a little pinky bone from a cave in the Altai Mountains that has produced a mitochondrial DNA sequence really divergent from ours, it's really divergent from Neandertals. So these other populations were there. They were in contact with each other. In contact, what I mean is they were living in places that were next to each other. And the Neandertals, they were real successful where they lived but they couldn't just go anywhere. >> And they were already hemmed in 80,000 years ago. >> Exactly right. They couldn't go north because they couldn't live farther north. The glaciated habitat was not where you want to be hunting big animals with no cover. We think probably, and based on the signature of sites from the early modern humans, they look like they came not only from the east into Europe but also from the north. The last Neandertals, they're hanging on in Spain. So these are people who were being pressured when they finally did succumb to this growing modern population. They were mixing as they went, possibly. But it's that move of modern humans taking advantage of new resources maybe that the Neandertals couldn't that really made the difference in the end. >> We don't have any evidence of genocide? >> We don't have any smoking guns. There's one Neandertal from Shanidar, from this site in Iraq, that has a wound in a rib, two adjacent ribs actually, and it's from the fact that there's the notch in one rib and the notch in the other rib that we know this was a small point. Neandertals didn't use small points. We never found a small point with a Neandertal. So if you think, well who was it that was hitting this guy with a small point, which is an atlatl or maybe even a bow, it could be a modern human. So the story that goes along with this is that modern humans were killing the Neandertals. Maybe, maybe so. But I imagine this is something like anytime we see populations come into contact from different parts of the world with different technologies. Think of the new world after Columbus. Think of Australia after Captain Cook. Anywhere that you see these populations come into contact, there's a lot of dying of one of them and usually a growth of the other. And the Neandertals may have been one of the first examples of this. >> Not just a conflict but also a coming together. >> Absolutely, yeah. >> John Hawks, thanks for joining us for University Place today. >> Well thank you very much. >> I'm Norman Gilliland. I hope you can be with me for the next issue of University Place.