The Ancients - Ice Age America

Episode Date: November 21, 2024

A group of hunter-gatherers encounter diverse habitats full of creatures they’ve never seen before. A land of opportunity, but also danger.Join host Tristan Hughes and expert Dr David Meltzer as they delve into the Ice Age in North America, over 10,000 years ago, a land of saber toothed tigers, direwolves, woolly mammoths, mastodons. They discuss how ancient DNA is revolutionising our understanding of human displacement and extinction events and how these explorers adapted to their new world.Presented by Tristan Hughes. The producer is Joseph Knight, audio editor is Aidan Lonergan. The senior producer is Anne-Marie Luff.The Ancients is a History Hit podcast.Sign up to History Hit for hundreds of hours of original documentaries, with a new release every week and ad-free podcasts. Sign up at https://www.historyhit.com/subscribe. You can take part in our listener survey at https://www.surveymonkey.co.uk/r/6FFT7MK.All music courtesy of Epidemic Sound.

Hi, I'm Tristan Hughes, and if you would like the Ancient ad-free, get early access and bonus episodes, sign up to History Hit. With a History Hit subscription, you can also watch hundreds of hours of original documentaries, including my recent documentary all about Petra and the Nabataeans, and enjoy a new release every week. Sign up now by visiting historyhit.com slash subscribe. But the rewards of their left. They've been walking south for some time now, but the rewards of their journey will be worth it. They're adventurers, some of the first humans to have ever walked that path. Out in front of them, the land will soon open up. Unknown plants and trees await them, diverse habitats full of creatures they've never seen before. A land of opportunity, but also of danger. These first Americans were populating a brand new world.

It's the Ancients on History Hit. I'm Tristan Hughes, your host. And today, while we're heading to North America in the Ice Age more than 10,000 years ago, it was a land home to some of the world's most famous prehistoric mammals, including saber-toothed tigers, direwolves, woolly mammoths, mastodon, giant sloths, although, alas, probably not saber-toothed squirrels. Sorry, Scrat.

But the Ice Age was also when the first humans reached this continent and quickly spread all across the Americas. So what do we know about their arrival, the animals they coexisted with? Did early humans play a role in the extinction of woolly mammoths? And what can DNA tell us, not just about these first Americans, but also about these awesome now extinct beasts that they lived alongside? Well, to answer all of this, our guest today is the wonderful Dr. David Meltzer, professor of prehistory at Southern Methodist University.

David, he's an expert on the ever-evolving story of these first Americans and the perfect guest to give you a taster of Ice Age America. David, welcome back. It's been too long. It is great to have you back on the podcast. Hey, thanks so much. I enjoyed it the last time and I'm sure I'll enjoy it this time. I mean, Ice Age America, this is an amazing time period in North American history. There are so many stories varying from the arrival of humans to saber-toothed cats and mammoths. It's so much to choose from. There's a lot of characters on the landscape, and the landscape itself is nothing we moderns have ever imagined. It was a very, very different place, a very, very different time, and yet a wonderful opportunity to explore what modern humans did the first time they ever

encountered a completely new world, a hemisphere that was teeming with animals, was far different than anything they'd encountered before, in a landscape on which they entered and at some point must have realized there's no smoke on the horizon. There's no freshly killed animals. We're the only ones here. What the hell? Can you imagine the sensation that must have been when they realised nobody else is home? And we'll delve into all of that, that kind of mindset of

those early humans reaching North America, David, and how they did it. But am I right in thinking that DNA plays a big part in this story? In the last, oh, let's make it a decade, it has completely changed our understanding. It's been a remarkable sea change. Look, I'm an archaeologist. I've got rocks. Occasionally, I got bones, but that's pretty much it. If I want to do population history, I want to know who these people are, where they came from, who they're related to, who these people are, where they came from, who they're related to, how often they got together. Did they survive? Did descendants of theirs survive to the present or did they disappear? I can't do that. I can't do that with rocks. I can't do that with bones. But with ancient DNA, I can. And since 2014, I've been fortunate to be involved in quite a number of the papers

that have explored human population history. That's really what we're talking about here. Ancestry, relatedness, admixture among different population groups. With ancient genomic evidence, we can do that. And so this is answering questions that I, as an archaeologist, have had for many years about, again, who they were, where they came from, who they're related to, what are the ancestral populations that contributed to the group that would ultimately make their way into the Americas. It's been a game changer. And also because this episode, we're going to focus on those early humans, but also

these well-known Ice Age animals that they coexisted with. And dare I say, we might be talking about a very popular and fun movie franchise from when I was growing up too, as we go along with our chat. But this DNA research, it's not just with humans, is it? It's also regarding these animals too. Well, absolutely right. Not only can you, of course, extract DNA from animal bones, you can extract DNA from sediment. A gram of sediment, and this is just mind-blowing stuff, a gram of sediment contains literally billions, that's billions with a B, DNA fragments in just a gram of sediment. And in those fragments, you've got the ecosystem.

So you can trace what plants are growing on the landscape at that instant, what animals are passing over and shedding skin or doing their business, right? Every time a mammoth would drop one of those, well, gigantic mammoth poops, that DNA gets worked into the sediment. And so there've been some really phenomenal studies, and this is even more recent than a lot of the human DNA, in which, well, in one particular study, for example, we were able to track the last 50,000 years of Arctic vegetation and animal communities. And among the things that came out of that work, and this is work that was done in concert with and under the direction of my collaborator at the University of Copenhagen, Eski Willerslev, we were able to show, for example, that mammoth, woolly mammoth, right, survived up until around 10 or 11,000 years ago across most of the Arctic region, right?

We had samples that were literally, you know, sort of circled the Northern Hemisphere. We had samples from North America. We had samples the northern hemisphere. We had samples from North America. We had samples from northern Europe. We had samples from northern Asia. And one of the just astonishing finds that came out of that work was that mammoth, as the Pleistocene is coming to an end, of course, are going extinct across virtually the entire Arctic, except in far northern Siberia. They survived up until around 4,000 years ago, which is just, you know, we never... That's like, it's a little mammoth enclave, as you're saying there,

far after the end of the Ice Age. Yes, exactly. That's the exact correct term, because what happened is, and we know this from the vegetation record that we have in that sediment DNA, is that for all intents and purposes, in terms of the vegetation, the Pleistocene didn't end until 4,000 years ago. Now, let me just add something because I suspect there'll be savvy listeners out there who will say, well, we've always known that mammoths survived on these islands in the Arctic seas. And that's true, right? But these were mammoths that survived on the mainland, right? The mainland of what's now the Timur Peninsula up until around 4,000 years ago when the vegetation finally changed from that sort of mammoth step these animals favored

to the vegetation that we have in that region today. So again, DNA in all its forms, ancient forms, whether from sediment or from bone, has been just a sea change. Well, I'll tell you what, that's such a great way to kickstart the episode off because it also hammers home straight away how exciting this research is at the moment and how much more there is to uncover. And the stories that it's revealing, we could do a whole another podcast episode on the last mammoths in its own right, based on that research there, David. Absolutely fascinating. But let's then go to North America. And quite a generic question to kick it all off, David. When we say Ice Age America, I mean, how much time are we talking

about with the popular Ice Age in North America? Well, so the Ice Age proper, for all those geologists out there listening, it goes back 2 million years. Wow. But it was never sort of frozen the entire time. It was never that we had ice sheets. The Ice Age goes in cycles where you have glaciers advancing, glaciers retreating. In terms of our story, the story of the Americas and people coming in and animals going extinct, we're really talking about the last, say, 30,000 years. Because starting around 30,000 years ago, we start to see glaciers building up over what's now Canada and expanding. And they will expand basically in all directions and ultimately will reach what's

known as the last glacial maximum. That's the period of which ice was at its greatest extent on the landscape. And that last glacial maximum, the dates vary depending on who you ask, but we're talking about say, oh, 24,000 years ago up until around 18,000, 19,000 years ago. We don't need to be terribly precise about it. But that was the window of time when the ice was at its maximum. It was coldest globally, as well as in North America. This was also the time when sea levels were at their lowest worldwide. And we know why that is. If you're building a glacier over North America, and at the same time building one over Northern Europe, the so-called Fenoscandian ice sheet, basically what you're doing is you're interrupting the

hydrological cycle. The hydrological cycle, just to put it in very simplistic terms, you've got evaporation from the ocean, clouds move over the land, they rain, the water drains into rivers, it goes back into the ocean. Okay? Real simple. Well, simplistic actually, but for our purposes, that'll work, right? If you stop that water by freezing it on land, it doesn't get back into the ocean. What happens? Ocean levels go down. And the amount that they've gone down is going to vary geographically because of a bunch of things that are related to gravitational forces, the pull of an ice sheet, continental shelves, mass. But on average, it's going to be about 130 meters lower than it is today. Okay. What that does, of course, is it exposes

shallow continental shelf, continental margins, and those become land, areas that are now underwater are land. That includes, of course, the continental shelf that lies underneath the Bering Sea. So that's northwest? Indeed, indeed. That's Alaska area. It's only, if you go out to the Bering Sea today, it's only about 52 meters. That sea level is about 52 meters above what's the continental shelf below it. So all you have to do is drop sea level 52 meters and you can walk from Asia to America. You can walk from Siberia to Alaska. Okay. All right. So we assume, and there's no reason to doubt that the way in which humans got here, and in fact, the way in which animals over time may have come to the Americas

is that during these episodes where you have a lot of ice on land, there were these bridges, these land bridges. And so people came across, but at the same time, let me just give you a quick geography of the ice sheets themselves. There's two major ice sheets in North America. There's the Laurentide ice sheet, which extends from what's present day Northern North America down to Central Ohio. I don't know if that's going to work for all of your audience, but basically past the Canadian-US border. And it goes from Newfoundland and Labrador all the way across Canada and laps up against the eastern flank of the Rocky Mountains. That's one big ice sheet, and it's literally kilometers thick. On the other side of the Rocky Mountains spine,

you've got the Cordilleran ice sheet. And these are a series of mountain glaciers that come down from high elevation and coalesce to form an ice sheet. That extends from the western edge of the Rocky Mountains down to the Pacific coast. You've walked across from Asia, Siberia, into Alaska, but then you're going to have to stop because you've got those two big ice sheets between you and the rest of North America. David, can I stop you there? Picturing that is quite difficult at first so we've got that it's that huge belt of ice as you say covering lots of what is today canada and then below that you've got these diverse habitats where no humans are at that moment in time and we're going to explore that in a bit but am i right then and also thinking that these glacial belts that you've highlighted there, they don't cover the entirety of all the land in North America, north of that point in North

America today. In that Alaska area then, where humans are arriving, you say people are crossing the Bering land bridge. Is there a bit of land there that isn't covered by glaciers then? Yes, exactly. Good. Thank you. I should have clarified that. Yeah. Alaska is a cul-de-sac, as it were, right? It's a dead end. You can get into Alaska because Alaska was glaciated along the Aleutian Islands. And in Southern Alaska, it was glaciated on top of the Brooks Range in sort of Northern Alaska, but otherwise, it was ice-free, okay? So you walk across the land bridge, you get into Alaska, and you're thinking, you know,

you're checking your watch and you're thinking, I could be in Miami, Florida if I just keep moving. But no, you can't because the glacial conditions that produce that land bridge by reducing the sea level at the same time are an obstruction. Now, what that means is that it sort of sets some general parameters for when people could have come in, because it basically means that if we're assuming that they walked across, and at this time period, that's the most likely scenario, they could either come in after the glaciers have started to expand and sea level has dropped at least 52 meters, and before it has, the ice sheets that is, have completely obstructed the route south,

or they have to wait until after the ice sheets begin to melt. Because when the ice sheets begin to melt as the world is warming at the end of the ice age, you've got a couple of routes that will open up, that will take you from that cul-de-sac where you've been parked for however many centuries or millennia down into what we refer to here in the States as the lower 48, right? The lower 48 States. One of those routes is along the Pacific coast, and it appears to be ice free starting around 17,000 years ago, but probably for sure by around 16,000 years ago. And then there's the so-called ice-free corridor, which opens when the Laurentide and the Cordilleran ice sheets begin to melt. And there opens between them an unglaciated route down to the south, an unglaciated corridor down to the south.

This is like a corridor, isn't it? A narrow route almost. Yeah. The width of the route obviously grows over time and it opens in kind of a funny way. You know those winter coats that we wear that have a zipper that zips up from the bottom and zips down from the top? Well, this was the ice-free corridor, right? So it opens, it's pretty wide at the top, it's pretty wide at the bottom. And then in the middle, it still hasn't quite opened up yet, right? So people basically have to wait for the whole

thing to be open. But, and this is an important point, and this is something that we found with ancient environmental DNA, just because the corridor is open doesn't mean it's a passage. Because when the ice retreats, you've got nothing there, at least immediately after the ice retreats, except mud water flats, lakes, nothing's growing there. And so at the end of the Pleistocene, when the corridor opens up, you can't pack a lunch in Fairbanks and say, you know, if I'm really careful and I don't eat too much on the first day and the second day, I can make that thousand kilometer trek with my sack lunch. No, you've got to wait for animals and well, with my sack lunch. No, you've got to wait for animals and well, you've got to wait for plants and then animals to basically make that corridor biologically viable. You've got to have something

to eat in there, right? And so one of the things that we found, and this is again work with Willerslev's group, in particular Mikkel Pedersen, who's one of the specialists in that group on ancient environmental DNA, we had cores from that center of the zipper, as it were. It was one of the last places within that corridor to open up. And what we found was that, again, with ancient environmental DNA, you know when the plants show up. You know when the animals showed up. The scientific core into the sediments, is it? Exactly right. Sorry about that. Yeah. We go to a lake, we drill, we get a core of sediment,

this tube of sediment, and you slice it up like a salami. And then you look at what the DNA is in the different slices that are of different ages. And what we found was that that corridor was not biologically viable until around 13,000 to 12,500 years ago. And of course, we've had people in the Americas already for a few thousand years. So what that tells us is that the ice-free corridor was not the initial route into the Americas because it didn't become a route and available until well after people had already been here, which tells us they must have come down the coast. Before we get to humans reaching the southern part of that belt, David, I want

to ask one more thing about the cul-de-sac in Alaska. You were talking about how animals slowly moving into the corridor as well. For that time when humans are stuck in that cul-de-sac before they're able to make their way further south, when I think of Alaska today, I must admit, I think of tundra. I think it's quite a hardy, maybe difficult place to live. But was it different back then if they were living in that area of the world? I mean, I've seen that, I believe one archaeologist, this is from your book, describes it as like the great mammoth step. So was it actually quite a nice place for them to be waiting for a bit of time before they're able to make that next step of going southwards into what is today the United States of America? Yeah, exactly right. This was a very, very

different landscape at the end of the Pleistocene and the land bridge itself. I mean, look, for all intents and purposes, if you walked from Northeast Asia and Siberia into Alaska, you wouldn't have noticed the difference in terms of the environment. It was cold, it was dry, it was a grassland. The tundra, as we think of it today, is a much more geologically recent phenomena, and it has to do with warming and increased precipitation and that kind of thing. So during the Pleistocene in Alaska and across the entire land bridge, you had horses, you had mammoth, you had giant bison, and these are animals that needed to be dry underfoot, right?

These are not animals that do very well on tundra. Caribou do great on tundra, but they're really not around during this time in the numbers that mammoth and horse and bison are. Well, let's move on to humans then reaching what is today America, having gone past that great ice belt. Now, David, when they reach this area of North America, describe the landscapes that they would have seen. I mean, is this, because it's such a huge landmass, was it a great diverse range of habitats at that time? Well, exactly right. These were diverse landscapes. You've got everything from vast

grasslands to deep forest and forests that vary tremendously in terms of the nature of the vegetation. You've got boreal forests, you've got deciduous forests, you've got, as you go further south, of course, you're getting into tropical stuff. And so, one of the key things that's really important that we still haven't quite got our finger on is the whole issue of landscape learning. How do you figure out what to do if nobody's been there before, if the landscape is unfamiliar to you? How do you identify resources that will help you, that will cure you, that might hurt you, or that might even try and kill you, right? You've got to learn about the geography. You've

got to do wayfinding. How do you move out across that landscape and make your way back? You've got to learn about the geography. You've got to do wayfinding. How do you move out across that landscape and make your way back? You've got to figure out the climate and the weather. And there's a distinction between the two, of course, right? Weather is what you see outside. It's what's going to come tomorrow, what may be here next week. Climate are those larger trends. And so if you are somewhere in the Northern Plains and it's fall of the year, and you don't know that winters can be pretty darn harsh in that environment, this could not work out well for you, right? So there's going to be a strong incentive to learn as much as possible, as quickly as

possible about as large an area as possible as you can. On the other hand, there has to be a compromise because if you're just running willy-nilly around this entirely new landscape, you're not going to learn enough about what's going on in places with particular resources, right? So you need to figure out, well, how do the animals in this locale, how do the animals on this landscape in this kind of environmental setting, how do they behave? How do they behave at different seasons? How do they behave when there's young? How do they behave when there's other predators around? Because you've got to figure out enough to be a successful hunter-gatherer.

So there's this sort of tension between wanting to go as far as you can, as fast as you can, to learn as much as you can, and pulling in the opposite direction, the need to stay and observe, stay and experiment, right? You've got plants in front of you. They have really lovely little red berries. Do you eat them? Well, no, actually, you give them to your younger brother and make him eat them. And then if he gets violently ill, you know, this is not a good thing. The whole process of adapting to a new landscape, finding your way around, finding your way back, learning about it is really fascinating. And that's one of the really interesting things that has great potential in terms of the DNA. Because one of the things that we would suspect is that when groups come into a new environment, they're going to disperse. Because more eyes in more different places,

then you come back from time to time, you get together, you share information. Okay, you don't need to go in that direction. We've been there, it doesn't work. Or we've been there, and this is where you need to refurbish your stone tools. There's a wonderful geological outcrop there. This is how you deal with the animals that you're going to find there. that have perhaps been separated by decades or centuries as their ancestors dispersed across the landscape? Can we see them coming back together? We do know that dispersal process was in fact very, very rapid. The genomic signatures that we have in 10,000 to 12,000 years ago time period in North America are very, very similar to the ones of ancient individuals in places like Southeast Brazil 10,000 years ago. Is it surprising then how quickly you see them spreading out, just given the huge amount of land that they'll have to traverse and the fact that

you said the word hunter-gatherer there and Ice Age applies to scene. You think there are small groups that are making that journey down from the Bering Strait. I wouldn't have thought it was possible, I must admit, first of all. I didn't know that there was the quantity of people there. I would actually use the word stunning rather than surprising because we'd always suspected archaeologically because of the near-contemporaneity of radiocarbon dates north and south in the hemisphere. But now we have genomic evidence that seems to, in fact, affirm that, where it looks like, you know, the difference in sort of the genealogies, as it were, the genetic genealogies of these populations is that we're just talking

about a limited number of generations before descendants of these groups that are in North America are already in South America. We actually call it a quick wave where small groups are just scattering. And then one of the other things that we found, and I can't remember if we talked about this or not, but it's such a cool finding. I have to repeat it. If we didn't, they took their dogs with them. One of the studies that we did, and this is work with my friend and colleague, Gregor Larson at Oxford. Gregor's a specialist on ancient dog DNA. And he had a student and colleague, Angela Perry, also a specialist in dogs. Oh, yes. We've interviewed Angela

about the first dog in Siberia, the origins. Yeah. Fantastic episode. Oh, fantastic. Yeah, yeah, yeah. So I was talking with Gregor and Angela one day about their dates on dog dispersal based on dog DNA. And as I was listening to them, I was thinking, hmm, those sound a lot like the human dates that we have. And then it dawned on me, I can be really slow about this sort of thing. It dawned on me, dogs are not going to colonize or move into the Americas by themselves, right? They must have come with people.

So as people are moving through the hemisphere and splitting off and radiating out, of course, their dogs are going to have a similar kind of pattern because the dogs are going with people. People can go without dogs, but dogs don't go without people. And so we published this paper and it was just a lot of fun to work up, to be sure, because we had these two very independent sets of evidence, which very nicely tracked one another for obvious reasons. Also, I said dogs is an ever popular topic, dogs always sell, and it's a fascinating part. It makes them all relatable, doesn't it? We were mentioning at the start, and you always get this sense of these

people emerging into america getting past that ice belt and you say brave new world new types of plants new types of animals but they have their trusted dogs by their side as well which is very kind of relatable thing that we can think with the love that many of us have for dogs today but that does lead us nicely on to dav, another part that I'd love to talk about in this chat about Ice Age America. It is the animals, the Ice Age animals that were living there when people arrive. And this is when I would also bring in the movie franchise Ice Age, because I feel it's a great staple to talk about some of these. I mean, first off, David, I know there were diverse habitats, but what were some of the most

recognizable, the most interesting carnivores, the predators that were there when humans arrived? Well, formidable ones would be the answer. You have everything from Brachyprotoma obtusata, which is the short-faced skunk. There will be a quiz afterwards on the genus and species names for all of your listeners. There was the spectacled bear, there was the giant short-faced bear, there was a saber-toothed cat, there was a scimitar cat, there was an American cheetah. These are all distinct genera. And then there were species such as the dire wolf and the American lion, Panthera leo. And I have to give one more scientific name for the saber-toothed cat just because it's so cool. The saber-toothed cat's name was Smilodon fatalis, which is kind of a mashup of Greek and Latin,

which basically means roughly deadly knife-toothed. I mean, you had these sabres that were some six inches, these two fangs, basically, canines. Six inches? Six to eight inches long. They were probably about a quarter of an inch wide. They were serrated front to back. This was an animal that would rip your throat with one chop. Do we know much at all about their interactions with humans? Are there archaeological remains that shows that yet? None.

None. They probably didn't mess with us. I mean, we wouldn't have been much of a meal. Not when they can go after a bison or a mammoth, for goodness sakes. There's just a whole lot more meat on the bone for that other prey. And they tended to hunt around what's known today, I think it's the Los Angeles County Museum, the La Brea Tar Pits, very classic environment in which animals would come and these folks would be ambush hunters, jump out, grab them by the throat, and then hang on

as the animal tried to twist its way out. If there were people that were eaten by saber-tooths, we have no evidence of it. I could only imagine it would have been over very fast. Absolutely. Well, let's move on from that. But I want to keep on saber-tooth because one of my favorite characters from Ice Age is, of course, Scrat and his acorn. But were there actually any saber-toothed squirrels in Ice Age America? Or whatever he is? Yeah. Well, I'm at a disadvantage here because I actually haven't seen that film.

Okay. But I'll answer your question as best I can, which is to say, yes, there were all sorts of small mammals in North America. And let's take it one step further. If you're coming into an environment that you're unfamiliar with and you're a hunter gatherer, you're not going to be terribly picky about what your next meal is. And so, if there were small mammals that humans encountered and that they were able to kill, we don't want to put the vision of people killing cartoon squirrels and eating them

in your listeners' heads. But yeah, these folks were probably fairly generalized foragers, which is to say that they were eating up and down the body size chain. So, small mammals, the body size chain. So small mammals, turtles, large mammals, yeah, they were probably hunters of great strategy and tactics, but also opportunistic. If the resource was there, they're going to take advantage of it. And that's something we hear again and again, isn't it, at this time in the Paleolithic and then in the Mesolithic before farming, that these communities to survive in these new environments, they foraged all these different things, but it wasn't just about the hunting. It was then making the most out of the prey that you caught, whether it was a big mammoth or mastodon that you've mentioned or something

else, but nothing went to waste in these ice age societies. Well, I mean, I think that just makes a lot of sense. You don't have a ready food supply. You're not necessarily building up a surplus, right? You haven't got corn that you harvested last fall that's still available in your corn bins. So you will take advantage. prehistory where we've got a large bison kills where bison, because they were sort of susceptible as a herd animal to being driven into arroyos or fall into big pits, natural pits, solution cavities and the like, you're not able to control how many animals get killed. And so you're not necessarily able, given the numbers of hunters that you have, to be able to fully exploit the amount of meat, right? So some stuff gets left behind, but certainly you're going to take what you can, as much as you can. And because these are highly mobile groups, they're also thinking a bit in

terms of how much can you carry? Yeah, you can kill an elephant, but are you going to be able to make use of all six tons of it? You know, you move the whole camp there and you spend, oh, probably several weeks, you know, roasting it on the barbecue. But, you know, at a certain point, it's just you move on. That's depending on how often they made these kills. And one of the things that's really becoming clear, I mean, think about it. You're a hunter-gatherer. And let's just simplify it.

You've got a stick with a sharp rock at the end of it. And you're staring down the very long nozzle of a Pleistocene elephant, a mammoth, which weighs six tons. One of the things that we've done recently is a fair amount of experimental work with their weaponry, their projectile points. with their weaponry, their projectile points. And what we discovered, and obviously we weren't using these on mammoths because, well, they've been extinct for 10,000 years, but using experimental conditions that as best we could replicated the conditions of hunting a mammoth in terms of thickness, the material that you're going to throw your spears into and that sort of thing. These projectile points that they were using, these so-called Clovis points, absolutely could bring down an animal.

There's no question about it, right? These were weapons. On the other hand, what we discovered was that they probably weren't all, they were described, they have been described as these quote unquote magnificent killing things, these magnificent killing tools. Turns out they weren't all that magnificent. When you think about, and we have data on this, when you think about the skin thickness of a woolly mammoth, it has to, a spear shot into it has to get through all the hair. It's got to get through the hide. It's got to get through layers of subcutaneous fat. And what we discovered with the experimental stuff is that, well, penetrating distance isn't very good. These things can go in about maybe 18 centimeters.

So not very far. Well, all the vital organs of a mammoth are basically hidden behind a picket fence of large ribs, right? And scapula, other large bones. And so these weapons were effective. There's no question about it. We know that they went after some of these mammals and they were successful, but they just weren't successful all that often. And moreover, what we realized when you look at the wear patterns on these tools, when you look at the breakage patterns on these tools, they're probably more like Swiss army knives rather than weapons made specifically for killing elephants, right? highly specialized weapons, it actually doesn't make a lot of sense. If you're a highly mobile hunter-gatherer and you've got a limited amount of stuff that you can carry, wouldn't it be better to carry a tool that can be used for all manner of different tasks rather than a tool that's solely for the purpose of bringing down six-ton animals? Because one of the things that we know from modern-day hunter-gatherers is that going

after a really big game like that is actually a low probability of success activity. So more often, you're shooting a deer, you're prying open a turtle. And so if you've got that Swiss army knife, you've got the tool that you need for all occasions. And if on occasion you run into an elephant, you can use it on that. But don't count on it being all that lethal counter the argument, I think we did talk about this last time, but I think it's fair enough to highlight this again, as this leads nicely to it,

that there was the age-old argument that the arrival of humans south of that glacial belt then you got the end of the ice age you know a few thousand years later you then have these woolly mammoths these great ice age animals dying out and that humans are responsible for the extinction of these great mammals are over hunting and so on but from what you're saying there, David, it sounds like actually, when you look at it closer and the low chance of success with the weapons they had, that doesn't seem likely, that argument. Well, I think that argument is just flat wrong in terms of human impacts. Look, there's lots of reasons to doubt that humans had an impact on these animals,

right? And the entire ecosystems, I'm guessing as well. Yeah. Well, okay. Thank you. Because in fact, we're talking about 38 different genera in North America alone. And the estimates of how many animals were out there range upwards of 100 million animals. Okay. And you got a small band of hunter gatherers coming in with sticks and sharp rocks. Okay. I'm exaggerating to make the point here.

They're coming into a landscape that they still don't fully understand, that they still don't fully know well. And as a wonderful archaeologist by the name of George Frizen, who actually did subsistence hunting as a child in the 1920s, has said, to successfully match wits with wild animals with the intent to kill them requires a thorough knowledge of the hunting territory and the behavioral patterns of that animal. And you're not going to get that as you're running pell-mell through the hemisphere, right? And further, that as a hunter-gatherer, when you're coming into a new landscape, this is not like, let me use a sort of a Civil War analogy where William Tecumseh Sherman, a Union general, basically burned his way through Georgia on his march to the sea. 62,000 men marching 300 miles, just basically devastated everything in a swath about 50 miles wide. The hunter-gatherers coming into the Americas were not an army, right? They were not able to

sort of devastate the ecosystem like that. But really, this all comes down to the empirical test. If overkill, if the notion that people were responsible for Pleistocene extinctions is correct, we should see ample evidence of kill sites, right? We've got 38 different genera, possibly tens if not hundreds of millions of them. we ought to see dead bodies all over the place with Clovis points stuck in them. And if in fact humans were responsible, then the extinction of those 38 genera should all have occurred within the window in which human hunters arrived and spread throughout the hemisphere. Okay, so we've got two... Sorry, you mentioned Clovis points there in passing. Sorry, what do we mean by Clovis points?

Oh, those are the weapons that are used by the folks who are blamed for the extinction, right? This is the first group of serious hunter-gatherers that we see. They come into the Americas sometime around, they are in the Americas, let me correct myself, around 13,000 years ago. They're around for 500 to 1,000 years, depending on where you are in the continent. The Clovis point is the so-called smoking gun of the whole extinction scenario. All right. Okay. So we've got our two empirical tests. We should see lots of kill sites and the animals should all go extinct basically simultaneously, coincident with these Clovis groups. Okay. All right. So the first test, we have looked at all of the claimed sites for which it is said humans are responsible for the

death of one of these giant animals. And there's about almost a hundred of them. Of those claimed sites, only 16 of them actually give clear, compelling, and secure evidence that people were responsible for the death or the scavenging of the animal that was found there. There's another element of that, which is that of those 16 kill sites, there is only mammoth, mastodon, gompothere, which is a form of mastodon, camel, and horse. Camel, wow. Yeah, Pleistocene camels, pretty cool, huh? So, there's only five of the 38 genera have been found in these sites. What about the other 33? We have absolutely no evidence of any kind of interaction of humans with these animals.

Then the second issue, the timing issue. What we see is that most of these animals are actually not well dated. We know that only a limited number of them have radiocarbon dates. And of that limited number, less than half of all those animals survive of those 38 genera survive up until the time humans arrive, which means that some of them may have been gone long before people actually showed up on the landscape. So how could they be responsible for the disappearance of an animal that happened 6,000 years before they even got there?

There's a couple more pieces to that, okay? So the timing issue doesn't work, the kill site issue, not enough, right? We also know what extinctions might look like in terms of the kill site record. And let me explain. Humans have been hunting bison for 12,000, 13,000 years. And they've been hunting them in sometimes large numbers. There are sites in Colorado that are 10,000 years old, for which we have 190 bison that got stampeded into an arroyo and died a horrible death. I mean, you've got skeletons that are on their backs and they were clearly riding around, but they were then piled on by three or four other layers of

bison. It must've been a terrible way to go. There's a site in Southeastern Wyoming, it's a sinkhole where an estimated 10,000 or more bison were stampeded into the sinkhole repeatedly over several centuries. And yet, after all that intensive hunting, bison are still around. So here we have a record of heavy-duty, almost, I hesitate to use the term industrial scale, but heavy-duty hunting of a species for 12,000 years, but it didn't go extinct. And yet people claim that these 38 genera of animals, for which we have only 16 sites giving us evidence that they were hunting, went extinct and they call that or they blame that on humans? That seems kind of unlikely.

That seems really unlikely. Let's not hedge it. I mean, it absolutely does. And David, that's a great way for us to kind of start wrapping up this episode. And I guess the last question that I then ask, it's a nice one to end this episode on, is, so what do we think then happens to these great animals of the Ice Age that are no longer with us? What is the end of the Ice Age in America? What should we be thinking? So this is really the tough question. Lots of stuff is happening at the end of the Pleistocene. really the tough question. Lots of stuff is happening at the end of the Pleistocene. We've got an increase in the amount of incoming solar radiation, a rapid rise in atmospheric CO2.

We've got warmer climates. Patterns of seasonality are changing. So we're getting in some areas, which had been sort of relatively mild winters, relatively mild summers, we're now getting really, really cold winters, really hot summers. We're changing moisture regimes. Ecosystems that had been in place for literally thousands of years are fragmenting because in response to these changes in the climate, species are going off in different directions depending on their ecological tolerances and their thresholds, right? You've got feedback effects because when megafaunal populations die off, they're no longer clearing out certain types of vegetation from an environment. So you've got changing habitats, you've got changing competitive relationships. So lots of different things are happening in the environment. The real tough question is how do you link that to the processes that would have led

to the extinction of these animals? And the first thing that you need to do is recognize there's not going to be a one-size-fits-all solution to this problem. Because each animal, each of those several dozen genera of large mammals, which includes actually a number of small animals, which includes for that matter, trees going extinct at the end of the Pleistocene, turtles going extinct, snakes going extinct. You've got to figure out on a species by species basis, how are they being impacted by this whole constellation of changes that are taking place at the end of the Pleistocene. So what you have to do is figure out how are all these individual species responding to this constellation of changes

that are occurring at the end of the Pleistocene. It has to be done on a species by species basis. What are their thresholds? What are their tolerances? What happened in the environment that caused them to spiral into extinction? Here's where ancient DNA comes in. We've not been able to figure this out. You can't learn this from the fossil record when you've got a bone here and a bone there, but you can use ancient DNA to look at changes in genetic diversity. You can use ancient DNA to measure demographic or population size changes. You can basically, if you get a DNA record through time, and this is something that we're actively working on at the Center for Geogenetics, you can measure, you can actually start to

see when species begin to spiral down toward extinction. When they begin to basically lose population, you start to see inbreeding, you start to see changes and reduction in genetic diversity. You can see that the vegetation, and this goes back to something we talked about earlier in the podcast, you can see when the vegetation that had been supporting them for tens of thousands of years is no longer around. So with ancient DNA, we are finally going to get past the impasse that we've long had. Blaming extinctions on humans is just a kind of a simple-minded answer, and it doesn't work. It's actually hard work to figure out the link between the climate changes and the extinction of these animals. And that's work that's all in front of

us, but work that's being actively done. There's so much exciting work with DNA, that you and your many, many colleagues are doing that is revealing more and more about this. You know, there's still lots more to learn about Ice Age America. So lastly, but certainly not least, David, you have written a book which gives people a lovely overview of Ice Age America, it is called? First Peoples in a New World, Populating Ice Age America. And it's published by Cambridge University Press. It's actually in a second edition. Came out in 2021.

As for all of the late-breakingna work well stay tuned oh maybe if we have this conversation again in a couple three years we'll be able to update uh your listeners david i'd love that and i've also got the last mammoths on my on my notebook now too it just goes to me to say thank you so much for taking the time to come back on the podcast it's been my pleasure. a big favour. You can also follow me on social media. I'm on both Instagram and TikTok at Ancients Tristan, where I do all things ancient history, even more on there too. Don't forget, you can also listen to The Ancients and all of History Hits podcasts ad-free, and watch hundreds of TV documentaries when you subscribe at historyhit.com slash subscribe. That's enough from me, and I will see you in the next episode.