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.
Chapter 1: What is Ice Age America about?
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A group of hunter-gatherers walk along the coast, with the boundless ocean to their right and towering mountains in the distance to their left. They have been walking south for some time now, but the rewards of their journey will be worth it. They are 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.
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Chapter 2: Who were the first humans in North America?
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.
And 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, and 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 realized 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? Right.
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, if I want to know who these people are, where they came from, who they're related to, how often they got together, Did they survive?
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Chapter 3: What role did DNA play in understanding early humans?
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 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 rights 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 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?
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Chapter 4: How did humans migrate across the Bering land bridge?
And that extends from the western edge of the Rocky Mountains down to the Pacific coast. So 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.
Can I stop you there? Because picturing that is quite difficult at first. So we've got 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 in 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, right? 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.
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Chapter 5: What was the environment like for early humans in North America?
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, right? 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 mean, I want to ask one more thing about the cul-de-sac in Alaska, because 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 the great mammoth step.
So it was 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. 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?
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Chapter 6: How did Ice Age animals coexist with early humans?
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? 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 there.
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.
With ancient DNA, we can potentially identify those sort of rendezvous moments where different populations 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.
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Chapter 7: What challenges did early humans face in a new environment?
Does that then 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've got the end of the Ice Age 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 overhunting 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, I mean, 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. And you've got a small band of hunter-gatherers coming in with sticks and sharp rocks. 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?
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Chapter 8: What are the implications of ancient DNA research?
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 in 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, 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 breaking DNA work, well, stay tuned. Maybe if we have this conversation again in a couple, three years, we'll be able to update your listeners.
David, I'd love that. And I've also got the last mammoths 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. Well, there you go. There was our episode on Ice Age America with Professor David Meltzer. Thank you for listening to this episode. I hope you enjoyed it.
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