What Was the American Ice Age?

Summary

Podcast Summary: American History Hit – "What Was the American Ice Age?"

Host: Don Wildman
Guest: Professor David J. Meltzer, Southern Methodist University
Date: December 1, 2025

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Episode Overview

This episode explores the profound impact of the last Ice Age on the peopling, landscape, and ecological history of North America. Host Don Wildman and archaeological expert Professor David J. Meltzer dive into the science and story behind glacial cycles, early human migrations, extinct megafauna, and how these icy origins still echo through American history today.

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Key Discussion Points and Insights

The Ice Age and Its Deterministic Role

• Determinism and Possibleism in History
  • Don Wildman introduces the concept of determinism—history driven by environmental forces—and asks if this explains the Ice Age’s impact on American prehistory.
  • Prof. Meltzer reframes the debate: “At some level that's correct... But in a sense, it's more about possibleism. Possibleism with a historical contingent element factored in as well.” (04:55)

Geological Setting of the North American Ice Age

• Formation of Glaciers and Sea Level Changes

  • Around 30,000 years ago, two vast ice sheets—Laurentide and Cordilleran—spanned North America, with ice up to 2.5 miles thick. (05:41)
  • The lockdown of water in these glaciers dropped sea levels by as much as 134 meters (~390 ft), exposing land bridges.
    • “It’s not rocket science to figure out that's going to have an effect on everything.” – Don Wildman (07:39)

• Pleistocene Epoch and the Last Glacial Maximum

  • The Pleistocene featured cycles of glacial advance and retreat. Its last intense phase, the Last Glacial Maximum (LGM), was 23,000-18,000 years ago.
  • A sudden warming phase (from ~14,500 years ago) rapidly changed the environment; then a brief cooling event, the Younger Dryas (~12,900–11,700 years ago), delayed modern conditions. (08:54)

• Legacy on Today’s Landscape

  • Ongoing effects include isostatic rebound—land rising after the glaciers melted:
    • “Portions of far northern North America are still rising...due to the lifting of the weight of all that ice.” – Prof. Meltzer (10:23)
    • Glacial lakes and altered river systems are remnants of this epoch.

Human Migration into the Americas

• The Bering Land Bridge: Not Just a 'Bridge'

  • With lower sea levels, a vast plain called Beringia linked Siberia and Alaska. This was a grassland, not covered in ice.
    • “Don't think of this as a land bridge, as some sort of...rope bridge. If you’re walking across that landmass, you probably have no idea you’re going from one continent...to another.” – Prof. Meltzer (15:31)

• Migration Routes Controversy

  • The classic view holds that early humans followed an ‘ice-free corridor’ between retreating glaciers.
    • However, "We now know...that was not the route taken by the first people into the Americas." – Prof. Meltzer (16:36)
  • The Pacific coast route likely opened earlier (~16,000 years ago), allowing southward movement. (17:22)

• The Archaeological & Genetic Evidence

  • Few Siberian archaeological sites exist to trace the migration.
    • “We quite literally have only two sites...that’s pretty much it.” – Prof. Meltzer (19:31)
  • Genetic evidence shows Native American ancestors split from Northeast Asians around 24,000–25,000 years ago, with humans in the Americas by at least 16,000 years ago. (20:23–21:38)

Why Did People Move? Motivations for Migration

• Push & Pull Factors
  • Climate and resource changes were likely drivers, but human “mobility is insurance”—a way to survive uncertainty. (18:37)
  • A quirky aside: The “wanderlust gene” (DRD4) theory suggests those who migrated possibly had a genetic trait fostering wanderlust—plus, humorously, “marital infidelity!” (30:22–31:01)

Speed and Scope of Human Expansion

• Rapid Colonization
  • People moved astonishingly quickly through new landscapes, from Montana to Brazil in very few generations.
    • “It’s stunning how similar ancient individuals from southeastern Brazil are to ancient individuals in Montana...There’s not a hell of a lot of generations between going from the Northern Plains to southeastern Brazil.” – Prof. Meltzer (26:48)
  • The landscape changed rapidly, with new forests, lakes, and grasslands shaping migration and adaptation. (35:30)

Technological and Cultural Development

• The Clovis Point Phenomenon

  • The iconic Clovis spear point (~13,500 years ago) spread rapidly across North America, reflecting mobility and perhaps shared identity.
    • “Clovis point may well have been...your Swiss army knife...when you bump into somebody, you...look at them and, hey, they’re using the same kind of tools as you are. Right. Maybe they’re related. Maybe they’re friends.” – Prof. Meltzer (32:53)

• Regional Adaptations Post-Clovis

  • As environments diversified, so did human cultures and toolkits. Continuous populations in areas for 10,000+ years, others saw repeated arrivals and departures. (37:27)

The Fate of American Megafauna

• Extinction Debate: Overkill or Climate?
  • “Humans had nothing to do with it in the larger sense...We now actually have about 16 archaeological sites where we have evidence that humans did in fact interact at some level with these now extinct large animals...But 38 different genera went extinct at the end of the Pleistocene. They did not all go extinct at the same time.” (38:22)
  • Environmental stresses and shifting food webs were the main causes. New DNA techniques are helping understand extinctions at a granular level. (41:03)

Lasting Legacy of the Ice Age

• Impact on American History and Disease
  • The extinction of domesticable animals led to North American populations without immunity to Old World diseases.
    • “In the Americas, there really was no significant domestication of animals...So we don’t see any sort of zoonotic diseases developing...the downside...is that you have, you’ve developed as a population, no immunity [to diseases like smallpox].” (45:31)
  • This had tragic consequences after European contact, shaping the fate of indigenous peoples.

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Notable Quotes & Memorable Moments

• On Environmental Determinism:

  • “At some level that's correct...But in a sense, it's more about possibleism.” – Prof. Meltzer (04:55)

• Visualizing Beringia:

  • “If you’re walking across that landmass, you probably have no idea you're going from one continent, one hemisphere to another, because basically it would have looked just the same as everything you'd left in Siberia.” – Prof. Meltzer (15:31)

• On Human Mobility:

  • “Mobility is insurance. Things start to go badly where you are, it’s really good to know where to go next.” – Prof. Meltzer (18:37)

• Light-Hearted Genetic Theory:

  • “The DDR4 dopamine receptor is also associated with marital infidelity. The reason the Americas was populated was that it was cheating husbands and wives fleeing their spouses...” – Prof. Meltzer (30:22)

• Rapid Dispersal:

  • “It’s stunning how similar ancient individuals from southeastern Brazil are to ancient individuals in Montana...” – Prof. Meltzer (26:48)

• On Megafaunal Extinction:

  • “Humans had nothing to do with it in the larger sense of were they responsible for the extinction...It’s what happened thousands of years earlier that started them on a sort of death spiral...” – Prof. Meltzer (38:22)

• Echo of the Ice Age in Modern America:

  • “After people get here, they basically spend the next 15,000 years in glorious isolation...with the loss of all of those very large mammals...it’s a very different landscape.” – Prof. Meltzer (43:44)

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Key Timestamps

• Introduction and Ice Age overview: 01:33–04:55
• Ice sheets, geology, and sea level: 05:41–10:23
• Migration theories and genetic evidence: 14:21–21:38
• Why humans moved & Beringia details: 18:08–23:09
• Clovis culture and technology: 32:27–34:45
• Changing landscapes & cultural complexity: 35:30–38:10
• Megafaunal extinctions: 38:10–42:18
• Ice Age resonance, disease, and historical consequence: 43:27–47:22

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Conclusion

Professor Meltzer wraps up with the observation that the Ice Age set in motion a cascade of events—climate change, migration, ice sheet retreat, ecological transformation—that made America what it is today. Its echoes are seen not just in the land but in the biological and cultural legacy of the continent.

Further Reading:
First Peoples in the New World: Populating the Ice Age by David J. Meltzer

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A fascinating, multi-layered look at how ancient ice, stone, and gene shaped the American story—and still shapes us today.

Transcript

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[D]

Imagine standing on a stretch of land that today no longer exists. We're around 12,000 years ago, at the very end of the last ice age. To the west, a glacier rises higher than any mountain you've ever seen. A wall of ice stretching from horizon to horizon. To the east, a vast plain spreads before you. No ice. This is land dotted with grasses, scattered spruce trees, and herds of animals unlike anything alive today. On this plain off in the far distance, a small group of human beings, people, are moving across this barren landscape, following a route their ancestors charted generations earlier. These are skilled, resilient people, deeply connected to the land, land that around them is changing faster than any living person can remember. The ice is melting. Rivers are shifting, coastlines are flooding. Entire ecosystems are rearranging themselves. And the animals, these giant animals they've relied on for millennia are growing scarcer and new plants and forests are taking their place. These people don't realize it, of course, but they're living through one of the great turning points in human and environmental history. A moment that will reshape the land, the wildlife, and the future of the American continents. Good day. You're listening to American history hit 19. Nice to be with you. I'm Don Wildman. In scholarly circles, there's a broad school of thinking called determinism. It's in all disciplines goes way back. The general theory that any event in history is the inevitable consequence of factors in motion preceding it. Pretty sensible, straightforward. Nothing happens in a vacuum. But many consider this simplistic and convenient thinking, where especially in the history of human development, matters are more complex. Our subject today can be viewed through this determinist lens. The Ice Age, that vast geological period that lasted more than 2.5 million years, ending some just 12,000 years ago, had everything to do with determining the arrival and settlement of the earliest humans to the continent, North America. Depending on your outlook, it had much to do with how humans here developed, laying the foundations for indigenous cultures that thrived and spread once the planet warmed. It was the great frozen time of giant glaciers, land bridges, woolly mammoths, saber toothed tigers, the story of the land itself, which played such a vast role in how humans lived together and moved around. Cool stuff. In more ways than one. And we'll discuss it all in the expert company of Professor David J. Meltzer of SMU Southern Methodist University. Pony up. Where he serves as the Henderson Morrison professor of Prehistory. He authored the book First Peoples in the New World Populating the Ice Age, just one of a prolific list of 10 books and nearly 200 scientific articles. Dr. Meltzer studies how human arrival interacted with changing environments, which is so much of what we will discuss today. Welcome, Professor David, to American History. Nice to have you.

[C]

Thanks very much, Don. And thanks for that welcome. And thanks for that setup. Determinism. This is a great lead in because I would argue that at some level that's correct. Right. The conditions had to be right. But in a sense, it's more about possibleism. Possibleism with a historical contingent element factored in as well.

[D]

Oh, you just gave me tingles. You just gave me academic tingles. That's good.

[C]

Well, this is what we do. You kick us in the middle of the night and we start talking before.

[D]

We dive into the whole movement and migration of human beings. A controversial subject, by the way. There are many different theories on this subject. Let's Brief listeners on the basics of this rather amazing epoch.

[C]

Sure, absolutely, absolutely. So what happens is, is that starting, oh, 30,000 years ago, plus or minus, in North America, you end up with two massive ice sheets. And when we say massive, we ain't kidding. They stretch from basically the Arctic Circle down to central Ohio. They span Canada from Newfoundland and Labrador to the Pacific Coast. But they actually form in two separate entities. One goes from Labrador, Newfoundland and laps up against the eastern flank of the Rocky Mountains. The other is an ice sheet that forms between the western flank of the Rockies and the Pacific Ocean, the Pacific shore there in Canada. And it's actually a series of mountain glaciers that coalesce as they grow and form what's known as the Cordilleran ice sheet. The larger one that's east of the Rockies is known as the Laurentide. It's a huge amount of ice. It's two and a half miles thick.

[D]

Okay, yes.

[C]

When you lock up that much water on land, you essentially stop the hydrological cycle, which is to say you've got water that's no longer. When it forms as rain or snow over land, it gets into the rivers, it goes and drains back out into the oceans. Well, if you stop that because you've frozen all that water and snow on land, it's not getting returned to the oceans. What happens to the oceans? They go down. They go down in sea level. We know that at its maximum sea level during this period, when you have these massive ice sheets on the land is about 134 meters. So, you know, what is that in feet? Triple the distance. Right. About 390ft lower than it is today. Now, when you lower that sea level, anything that's part of the continental shelf that's relatively shallow, it's going to turn into dry land.

[D]

Well, this is so much the story of this time. And in fact, it's worth noting. I mean, it's kind of what we're talking about in reverse right now with the ice, you know, the ice caps melting and huge amount of water going into the sea. We've got rising sea levels. So it's not rocket science to figure out that's going to have an effect on everything. When we talk about ice age, of course, we're talking about different periods. I mean, we're talking about 2.5 million years. Of course, there's many different phases throughout this period. What does the Pleistocene period mean? What does that refer to exactly?

[C]

It's a geological epoch. You had ice on land. It was never constant ice. You had different episodes different cycles of ice advance and ice retreat. The environment was fundamentally very different. You had, at least in North America, a zoo of animals that are now extinct. You mentioned some of them at the outset. So North America was a very, very different place that back then, environmentally, climatically and in terms of the kinds of resources out there on the landscape. Sure.

[D]

And that last period goes about 150,000 years ago to what is a blink of time geologically. 11,000 years ago.

[C]

Yeah, yeah. What happens is that the last really cold period, we refer to this as the Last glacial maximum. The LGM dates between around 23,000 and say, 19, 18,000 years ago. That's the. The height, or perhaps more correctly, the depths of the Ice Age in terms of temperature. Starting around 18,000, it begins to warm, and then it begins to warm much, much faster. So that around 14 and a half thousand years ago, you've got a rapid rise in sea level, you've got a rapid rise in temperature, and that continues for a couple thousand years. And just when you think things are going to basically turn into the present, nature pulls a fast one. And it's called the Younger Dryas. And this is about an episode that lasts about a thousand years where you have a sudden return to cool, not necessarily cold, but cooler conditions. And then around 11,700, the younger Dryas comes to an end. And that's when we see the real onset of sort of the contemporary landscape or the emergence and the conditions that will lead to the emergence of the contemporary landscape.

[D]

This creates the, as I say, early ecosystems through which certain mammals flourish. We talked about them mammoths, the saber tooths, the colossal bison, which is a fascinating difference than the tiny ones we have today. Where do we see the most lasting impact of Ice Age on the geography of North America today?

[C]

Well, let's not think about this in terms of past tense. Portions of far northern North America are still rising, but due to the lifting of the weight of all that ice.

[D]

Oh, that's interesting. But even talk about that, you got this two and a half mile thick ice pushing down on the land, which really does have this effect, of course. And then when it goes away, the land uplifts.

[C]

Absolutely. It's called isostatic rebound.

[D]

I was going to say that. Yeah.

[C]

It was right on the tip of your tongue. Yeah. Don't think of this as a trampoline, but it's the same process in principle with rock.

[D]

Exactly. Not to mention the obstacles and barriers that are created, geologically speaking. Mountains aren't created by the Ice Age, but that certainly has an effect on them and around the land around them. So all this geological stuff, this is not a science episode just to warn people we're going to get on with the human development of this, but it's really important to understand what was happening for so long that suddenly made it possible for mankind to arrive. And when we come back after the short break, we'll talk about just that when the humans come in the picture. The longer you stay alive, the longer you can enjoy Boost Mobile's unlimited plan with a price that never goes up. So here are some tips. Do not parallel park on a cliff if you want to enjoy an unlimited plan with a price that never goes up. Do not mistake a wasp nest for a pinata if you want to enjoy an unlimited plan with a price that never goes up. Do not microwave a hard boiled egg.

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[D]

Okay, welcome back. We're talking about prehistoric times when humans first came to North America. And we're about to discuss where they made this journey. It's up for discussion. Many times I did a TV special about this very thing. My goodness, there are people with some crazy theories. But let's talk about it. Most commonly discussed as hunter gatherers moving from Asia to North America. By what route? David?

[C]

Well, so as we talked about, the sea levels are dropping over the course of the Ice Age. During these periods when we have massive ice sheets on land, if you drop the sea levels 134 meters, you expose the continental shelf that exists between Northeast Asia and Alaska because the sea level there is only about 52 meters above the shelf. So you drop it 134 meters, you've suddenly got yourself a land bridge. That's the better part of, you know, 1200 miles north, south, you can walk to America. Now don't think of this as a land bridge, as some sort of, you know, rope bridge strung over a river in the Amazon where it's swaying back and forth.

[D]

Yeah.

[C]

If you're walking across that landmass, you probably have no idea that you're going from one continent, one hemisphere to another, because basically it would have looked just the same as everything you'd left in Siberia. But then you get to Alaska and you basically run into a cul de sac. Because the same geological processes that create the conditions that lower the sea level also mean you've got an awful lot of ice that's blocking your way from Alaska down to the lower 48. And so you've got to figure out a way, and this depends on when you get to Alaska. You've got to figure out a way. How do I get south? Can I go down the coast? Well, that depends on how much, what time you're there and whether ice is still coating the coast or can I go down an interior corridor? That is to say, when those two ice sheets, which are right along the spine of the Rockies there, as they start to melt back, a route opens up between them. When that happened is actually now getting resolved to the point where we know that was not the route taken by the first people into the Americas.

[D]

That's where the possibilityism comes in. Maybe they did this, maybe they didn't.

[C]

Yeah, yeah, yeah, exactly right. Because we know that the ice physically parted. Think of Moses parting the Red Sea. Right. Okay. So we're parting these ice sheets. Those ice masses pull back, but there's nothing growing there. It's just mud and meltwater lakes. So you've got to wait. We now know probably a thousand, two thousand years before there's anything living in there. Well, by the time that happens, people are already in the Americas. How did they get there? Well, the coast opened up earlier. By around 16,000 years ago, maybe slightly earlier, it was possible to go from Alaska down to the lower 48, make a left turn in the state of Washington, and boom, you're in the continent.

[D]

Amazing. Let's just back up a little bit, because we're talking about an area that, when you first learned this in grade school, and I do remember them teaching us, I remembered thinking, oh, there's a little tiny spit of land that would have been there between Alaska and Russia. No, this is a massive region you're talking about, and it's called Beringia. The Bering Strait is there. I guess it's derived from the same word. Beringia is a sheet of ice over what is now the Bering Sea that becomes then the land. That's where I'm confused. They call it a sheet of ice, but there's actually land there that you can walk on, right?

[C]

Oh, yeah, yeah, yeah. No, it's not iced on. It's a grassland. You lower the sea levels. That part of Siberia and Alaska was not that part of Siberia, and Beringia was not glaciated.

[D]

There you go. The land bridge, just like you said. Got it.

[C]

Yeah.

[D]

And I love the distinction that you make that they wouldn't have even had a clue that they were moving to a different continent at that point.

[C]

Well, exactly right. And there's the contingent element. Right. Why were they heading east? They may have gone south. Some of them probably did go south. Right. You've got groups that are living in northeast Asia. And. And for reasons unknown to us, we really don't know the motives for migrations.

[D]

Well, they've been around for a long time, these people. They've gotten good at hunting. You know, they may be just looking for more prey.

[C]

Well, possibly, possibly. But the other thing is, and this is something that sort of humbles European histories of the globe where they always talk about the great explorers. There isn't a place on this planet that Europeans got there that humans weren't already present. We've been very good at moving around the planet. And so obviously some groups, you know, there's one of the things that is sort of very true of humans. Mobility is insurance. Things start to go badly where you are, it's really good to know where to go next. And it may well be that these folks were just, you know, looking around, seeing, you know, what's over the next hill and over the next hill, and pretty soon you find yourself in America without realizing it.

[D]

I imagine they have tracked this movement in Siberia and so forth through archeology and paleontology and all sorts of things. Right. As far as knowing how they can kind of mark when people arrived at the northern regions. Yes.

[C]

Well, I, you know, I wish that was true, Don, but the reality is, is that, you know, Siberia is a vast place and the amount of archeology that's been done is relatively limited. And we're talking about small groups of people spread out on that vast landscape. And they're highly mobile, so they're not leaving a lot of sites behind. So we quite literally have only two sites. The ANA RHS site, which is around 30,000 plus years old in the far north of Siberia, and duktai Cave around 16,800. And that's pretty much it.

[D]

Wow.

[C]

So we really don't have a sense of, you know, being able to see people moving their way across the landscape archeologically. Now the genetic evidence is starting to give us hints about who was there and when. And that's proving very helpful.

[D]

In what way DNA proves a link between populations?

[C]

Well, exactly right. We now have genomic evidence that identifies who the ancestral Native Americans were, their ancestors, and in turn, how they relate to present day Native Americans. And so we can use the genetic evidence as a molecular clock. Right. By looking at the genetic distance, you're actually looking at time, that is to say, the genetic distance between populations tells you something about how long they've been separated in time. And we now know, for example, that Native Americans and Northeast Asians went their separate ways around 24, 25,000 years ago. So at some point after that, they must have been in Siberia, and a portion of that group must have started to make their way at least away from their other groups that were out there and ultimately into the Americas. So genetics actually gives us a maximum age for when that process must have started. And we know from archeology where we've got sites in the Americas of around 15 and a half, maybe 16,000 years, that gives us a minimum age. In other words, people must have been in America by 15 and a half, 16,000 years ago, but they probably got there before. We just haven't found the earliest site.

[D]

Interesting.

[C]

So somewhere in that window between about 24 and about 16,000, that's when it's happening.

[D]

You mentioned two paths. I just want to circle back to that for a second. When they arrive, as you say, there's two choices they can make. They can either go down the coast, where it was probably a lot easier to do this, versus cutting off and going more centrally. And it's really the split between the two plates of ice, isn't it?

[C]

Yeah, yeah. What happens is, is that ice melt begins, you know, it starts around 18,000, but out in that part of western North America, it's probably not until, oh, make it about 15 or 16 that we really start to see the ice beginning to retreat. And so both of those potential routes are opening. But the coastal route down the Pacific coast from Alaska, British Columbia, into the state of Washington, that opens sooner. That's the key.

[D]

Okay. I just want to paint this picture visually for folks, the Laurentide Ice Sheet. Imagine all the way across what's Hudson Bay, everything in northern Canada, just a massive vastness. That's what causes all those lakes that are up there, even the lakes in Minnesota. All that's glacially created by what's called the Laurentide Ice sheet. Okay. And it's exponentially larger than what we're talking about on the coast, which is that Cordelia. So people understand that this is all what's happening in that late glacial period. This major shift in the climate is causing this. What, what does cause this change is just a hot temperatures that are change. I mean, warming temperatures.

[C]

So look, the ultimate cause of glacial episodes has to do with the Newtonian cotillion of the planets as they're orbiting the sun and as they're being. Their orbits are being jostled by other planets. There's a. Basically, you know, we tend to think of the Earth's orbit as a very fixed thing, but it's not. It varies in terms of the tilt. It varies in terms of the shape of the orbit from circular to more oval. It varies in terms of the wobbling of the Earth. And what that does is that changes the amount of solar radiation received on the surface of the Earth. And when you sort of turn on the heat or turn off the heat, that's going to impact whether ice will grow. And let me just give you a really quick sort of way of understanding this. If you have snow in the far north, say 60 degrees, 65 degrees north, and it's a little cold through that spring and summer and the snow doesn't melt, then next year snow piles up on top of that and the next year it does it again. And it does it again. And well, you do that over about 10,000 years and pretty soon you're going to get ice building up. Okay. And so we can look at the history of glaciation. Really what we're looking at is a history of these global factors, orbital factors that are influencing the amount of solar radiation hitting the far north. But there's also greenhouse gases that are involved. And in fact, when we're looking at the retreat of the ice after, you know, starting around 18,000 and accelerating around 15, what we see is that we've got not only a rise in global solar radiation hitting the Earth and melting, but we've also got a sharp rise in CO2, greenhouse gas. And so the combination of those things is what's leading to the substantial and at some point rapid melting of these ice sheets.

[D]

One of the great concerns of our present situation that many people warn about is that carbon dioxide only increases as you lose those. As that ice melts, you get more and more carbon dioxide.

[C]

So that's, well, carbon dioxide as well as methane.

[D]

Yeah.

[C]

Because you've got a lot of these organic swamp like deposits and they're just. And methane's a much deadlier greenhouse gas. It stays in the atmosphere for a shorter period of time, but it has a more pronounced impact in terms of warming.

[D]

The term I became aware of in looking. First of all, all this is incredibly thrilling for me to talk about. I don't know why, but the holistic quality of your realm of study is so interesting because it requires understanding the science, but also how it intersects with the human culture. It's really interesting. Milankovitch cycles is the word you're talking about, or the orbital cycle changes that you're talking about. Are we going through an Omelankovic cycle right now? I guess we are, one way or the other.

[C]

Yeah. That never stops in Fact, I remember when I was in grad school, you know, we were talking about, well, you know, the next glaciation is going to start in, you know, we, we've been 10,000 years. We're due for the next one. Well, that got shot to hell with global warming, right? I mean, it's just not going to happen now because you're still not going to be cold enough that far north to allow that snow from last winter to stay on the ground.

[D]

But you're going to find some good mammoth bones as a result.

[C]

Well, you know, there's a whole subfield of archeology that's now emerging as things are emerging out from under the ice is called icefield archaeology.

[D]

Wow, interesting. So as the Ice age ended, how did people's migration patterns change? And I'm talking about how the new landscapes opening up allowed them to do so. Take me through those first migration periods.

[C]

The first thing to make note of is that once people get into the lower 48, once they get into North America, they move really, really fast. We know this archeologically, we know this from the genetic record. It's stunning how similar individuals, ancient individuals from southeastern Brazil are to ancient individuals in Montana in terms of their genomes. And so what that's telling you is there's not a hell of a lot of generations between going from the Northern Plains to southeastern Brazil. And that, that just strikes me as amazing because think about it, they are moving through a landscape that's completely unfamiliar. They're having to figure it out, you know, what can I eat? What will cure me, what's going to try and kill me? You know, how do they, how do they deal with a, a landscape in which there's nobody else home, there's nobody to give them any suggestions, any tips, any, you know, you, you can eat this, but don't eat that. If you follow this river for X number of days, you're going to come onto this. They're moving incredibly fast, and yet they're learning this landscape rapidly in such a way that they were probably extraordinarily successful in spreading out. Now, over time, they will start to settle in. But that first pulse is a rapid radiation.

[D]

Oh, I see. Interesting. We just had one of those just like a couple days ago, a pulse from the sun. So that is going on even as there are people in, you know, buffalo skins going around in this world. It's amazing, David, there are many obvious theories. I've heard so many myself. Why do people move? What is their migration motivation at that point?

[C]

Well, you know, don it's just really hard to say. There are things that could be pushing people out of an environment. And we see this today, sadly. Warfare, strife that pushes people to move. Changing climates, that pushes people to move. I don't think warfare or strife was an issue in Siberia 16,000 years ago. Probably not. Climate, yeah, that could have been an issue. Climate 16,000 years ago. Maybe it was starting to ameliorate, it was getting better. That might have made people inclined to move. Then there's also pull factors, a sense of adventure, wanting to see what's over the next hill, thinking that maybe you're going to find something, you're going to find another population, you're going to find a different area to live. You don't have to be right about wanting to go someplace hoping to get something in particular. You just have to have the motivation to go look. And so I don't think there's not an easy answer. It wasn't as though they were simply following, oh, look, the mammoth are all heading that way. Let's go that way with them.

[D]

I think it was because they wanted to get away from their mothers. Right.

[C]

Well, okay, I have a. After we finish this, I'll tell you a wacky theory. But let me finish the serious bit. When you get to Alaska, one of the things that you do notice, you are looking south and all you see is ice. But in the summer, suddenly large flocks of migratory water birds are showing up. And then come winter, they all fly south. That's a clue that there's something down there below the ice. And so that might have actually been kind of a pull factor that would have pulled people south. Okay, here's the other story. There's a couple of crazy guys who have been looking at a particular dopamine receptor. It's DDR4 and it is said to be the quote unquote wanderlust gene.

[D]

Oh, interesting.

[C]

And they've made the argument that this wanderlust gene occurs in increasingly higher incidences in Native American populations as you get further and further south. And the idea is, is that this DDR4, this dopamine receptor, is getting concentrate in these populations, which makes them want to move quickly. Well, the problem with that theory is that the DDR4 dopamine receptor is also associated with marital infidelity. So what that does is that tells us that the reason the Americas was populated was that it was cheating husbands and wives fleeing their spouses and they had to go further and further south in order to escape.

[D]

Oh, that explains so much. Thank you. When we come back, there is a really interesting development in archaeology, or at least a theory that has been around for a while that backs up exactly what you're talking about. And we'll talk about that when we come back.

[B]

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[D]

David I did a program some time ago that was about the arrival of something and we, we talked about the Clovis point, the arrowhead that dictates. And, and I remember we were talking about it down in Georgia. I mean this refers to what you said before the break where humans moved so fast. And the importance of the Clovis is that it indicates a certain technological leap forward as to how they were hunting. Right. It's so fascinating to try to track this out.

[C]

Well, it's a couple things actually. So it's an iconic spear point mounted on the shaft of the spear. It wasn't just a point, it was also a knife. It was also, think about it. If you are moving quickly across an unknown landscape and you're a pedestrian forager, you haven't got beasts of burden. You may have had dogs actually with you, but they can only carry so much. Are you going to take a highly specialized tool or are you going to take your Swiss army knife? You're going to take your Swiss army knife Right. And the Clovis point may well have been that. Now, the interesting thing is, is that we see Clovis points throughout North America. It's the last time in prehistory where we have a common form across the entire continent. And what I think is going on there, and this is speculation on my part, never to be confused what might actually be correct. But what we see is this. This variation. But people are still maintaining that template. They're still maintaining that form. And I think it has to do with the fact that they're pretty much, you know, they're. They're radiating out across the continent. They're scattered. They're not necessarily seeing any other humans for weeks, maybe months at a time. So when you bump into somebody, you don't want to shoot first and ask questions later. You want to ask questions. And one of the ways that people might have. That might have sort of eased that process was you look at them and, hey, they're using the same kind of tools as you are. Right. Maybe they're related. Maybe they're friends. Maybe we should start talking to them. Maybe they can give us information. Maybe we can marry off our kids to their kids. Right. So I think that tool, that very distinctive tool, became in some way a currency for groups to identify and recognize themselves as kin, even if it was distant kin.

[D]

Exactly. Well, part of the thing is that you've got such small numbers, is that it's not such a threat to each other. And so they begin gathering for purposes of festival, not festivals necessarily, but in hunting grounds and places that they begin to know. And these. These overlaps become the way that these. These messages are. This communication happens between them. One of the factors in this conversation is how quickly land changes in this time. I mean, it's different than, you know, building up snow over 10,000 years. You have the appearance of forests and plains, and fresh water systems begin because of the runoff. I suppose that's a big difference in everything. But also, you've got more water in the ocean. So at some point, that Bering Strait becomes. Well, at some point, the land bridge closes. Right, doesn't it?

[C]

Well, absolutely. And in fact, it's by around 12,000 years ago that it drowns. That sea level has gotten. Crept back up above 52 meters below the present. And as a result, there will not be any other humans coming into the. Into the Americas for about 6,000 more years. Because it's only after about 6,000 more years that you've got groups that develop the sort of maritime technology for getting across that Very harsh, very cold, Bering Sea. But I should also note too, that the environment is changing, but it's changing in very different ways in very different areas. Right. So northern species that had once, you know, you used to have caribou in Kentucky, for goodness sakes, you had musk ox in Tennessee. They're beating a retreat back to the north. Southern forests are expanding. The Great Plains is becoming a very distinctive grassland with actually less water than it had during the Ice Age. But you're absolutely correct that you've got all of these new lakes that are developing in the upper Midwest. So the environment becomes very, very different, at least on a geological timescale, very rapidly. And so what you see at the end of the Clovis period is that groups are starting to settle down. They're developing new technologies that are tied to sort of resources within particular regions. So it's no longer the case that kind of everybody's doing the same thing all over the continent, Right, Exactly.

[D]

It's that adaptation to the land, and we're back to determinism, you know, that creates certain cultural aspects of what, how people start to behave and therefore the traditions behind them. And I'm thinking about the Northwest, you know, native cultures and these amazingly unique totems that are created. And that's down the road. I know, but I'm saying that's the beginning of how these cultures change according to the land that they live on.

[C]

Yeah, well, and it's important to note, too, that in some instances, we have populations that are changing as well, in the sense that in some places in North America, we have evidence that populations were basically continuous in a region for the better part of 10,000 years. And other places, you know, populations came and went for a variety of reasons. And so it's. It's a really complex history. And then, of course, later on, you've got a lot of movement still, and so you've got a lot of admixture. Right. So the complexity, not just the sort of cultural complexity, but the population level complexity is really something over time.

[D]

Let's talk about those animals more. I mean, it is. They're so fabled, the mammoth, the sabertooth. What does destroy them? I mean, they go extinct, or did mankind have that impact on them?

[C]

This one is an easy answer for me, but I will tell you that there are people that will disagree, but I'm the one that has the microphone today. So here's the correct answer. Humans had nothing to do with it in the larger sense of were they responsible for the extinction? Humans May have killed off. Well, we now actually have about 16 archaeological sites where we have evidence that humans did in fact interact at some level with these now extinct large animals. That's 16 sites of five different genera. Mammoth, Mastodon, Horse, Camel, and Gompothere, which is an elephant. But 38 different genera went extinct at the end of the Pleistocene. They did not all go extinct at the same time. We don't have any evidence that humans interacted with any of those other 33. Right, yeah. Some of these animals may have been extinct before people even showed up. And while people showed up just at the very end when the last of these animals were disappearing, if we're going to talk about the cause of the species going extinct, it's not the last mammoth standing. It's what happened thousands of years earlier that started them on a sort of death spiral toward extinctions. The example that I give in my classes is Bethlehem Steel goes out of business on Saturday and declares bankruptcy. Was it because of the price of steel on Friday, the day before? No, there's a whole series of processes that started 100 years earlier in terms of global competition. The raw materials that they were using to produce the steel in Pennsylvania, et cetera, et cetera, et cetera. We haven't really got a sense of what those processes are.

[D]

Yeah.

[C]

More to the point, we have evidence of intensive hunting by people of species that didn't go extinct. Right. You mentioned bison at the outset. People have been hunting bison for 11,000 years, 12,000 years, and sometimes in huge numbers. There's a site in southeastern Wyoming called the Vore site, where it's estimated that 10,000 bison met their demise in a sinkhole. They were stampeded in there repeatedly by humans around 1300 or so AD and yet bison are still around. Right. So we have this intensive evidence of hunting, but the animals survive. And then we have virtually no evidence of hunting and the animals go extinct, and yet people are blamed. Makes no sense.

[D]

Well, a more direct answer would, of course, be the food chain.

[C]

Right.

[D]

That's what you're referring to. And the pressures of the environment change on that. At whatever point you're talking about, at some point, there's not enough food to support that population.

[C]

Well, and this is the challenge that we face if we're trying to understand these sort of climatic and environmental changes that are happening. I mean, the Ice Age is coming to an end. It has to have an impact. Right. The challenge is, is we've got 38 different animals, 38 different genera, to put it in the scientific terms. And what are the factors that are going to lead to the extinction of all 38 of them? Well, they're not going to be the same. Right. So it's not like you sort of turn on the heat switch and then they all go extinct. Yeah. So what we're trying to do is figure out on sort of an individual genus, step by step, process what was causing them to go extinct. And here's where ancient DNA is really going to come to the fore because we're now able to retrieve DNA from sediment so we can track changes in a high resolution manner, changes in the environment. Over time we can see species starting to decline, we can see reductions in genetic diversity. So in 10 years, 15 years, I'm being optimistic here, we'll actually have a pretty good sense of the kinds of ecological and climatic changes that were taking place that led to the extinction of all these animals. Because it wasn't humans.

[D]

Wow, how interesting. The other thing that always fascinates me is that we're talking about the northern parts of the, well, the northern hemisphere, but way up. And then you have the equatorial area, which is never affected by this, by the Ice Age, certainly by ocean levels and so forth like that. But it's a whole different way that, that cultures evolve as a result, isn't it?

[C]

Oh, absolutely, absolutely. And in fact, let's, let's, let's make the problem even more complicated. We have. So In North America, 38 different genera go extinct. In South America it's over 50. So what the heck's happening down there? Because we don't have kill sites down there either to account for humans having killed, you know, done the deed. So yeah, once people settle in, that's when you really start to see this, this flourish of, of cultural emergence. Emergences. I don't want to say emergencies. Right. They weren't. But what you see is that all these very distinctive cultures that, that will develop across the Americas and that will be tied into the types of environments and the opportunities and challenges that each of those environments presented.

[D]

And then mankind develops technologies and it all changes. And that's the, that's no longer.

[C]

And then there was the Internet boom. Yes.

[D]

So, David, with the Ice Age in the distant rear view mirror, you know, we're long past this now. Humans have settled elsewhere. Are there still effects of it to be felt? I mean, does it resonate through human civilization?

[C]

Well, it does in a sort of indirect but yet very potent way. So after people get here, they basically spend the next 15,000 years in glorious isolation from the rest of the World, okay? And with the loss of all of those very large mammals at the end of the Pleistocene, which is basically 80% of the large mammal fauna that was here when people arrived, it's a very different landscape. And, and one of the things that is happening on the other side of the world is that you've got the domestication of animals. So horses, cattle, camels, a whole, literally a zoo of animals is getting domesticated in the Old World, the so called Old World. And one of the things that happens when people start to domesticate animals and this is a process that begins, oh, 10,000 years ago, is that when you're living, when you're domesticating animals and you're living cheek by jowl with them, you're breathing the same air, you're drinking the same water, you're using their waste to fertilize your fields, you start swapping pathogens and what happens? And these are called zoonotic diseases, right? Diseases that you get from animals. So, you know the obvious example, cowpox.

[D]

Right.

[C]

It leads to smallpox. Okay. So Europeans by, or, I'm sorry, Old world populations by 3,000, 4,000 years ago or so are starting to really show evidence of these zoonotic diseases. These, these epidemic diseases.

[D]

Right.

[C]

Diseases that require large crowds and over time they adapt. So what initially begins as a disease that affects adults and children becomes ultimately a childhood disease.

[D]

Yeah.

[C]

Okay, now let's go back to the Americas. In the Americas, there really was no significant domestication of animals. There was a whole lot of plants that were domesticated. But if you're living in North America and you've got, say, 30, 40 or 50 million bison living out on the open plains, why bother to corral them? Yes, right.

[D]

They're just coming by again.

[C]

Yeah, yeah. I mean, domestication is a solution to a problem, and there really wasn't the problem there. And so we don't see any sort of zoonotic diseases developing in North America. Now the downside of that, of course, is that you have, you've developed as a population, no immunity.

[D]

Exactly.

[C]

So when Europeans arrive and they bring over smallpox, and we know exactly when that happened, it was basically the fall of 1519, when Cortez and one of the ships that was sent over to Mexico to bring Cortez back, somebody had smallpox. And it transferred immediately over to the Aztec population, and it caused just horrible decimation and death and destruction of the population. And smallpox would have just a horrific impact on, on Native American populations, indigenous American populations, because they hadn't had that history of living with the disease. If you play the tape of history differently, if some of those animals hadn't gone extinct, if they had been domesticated, if, if Native Americans had their own diseases that they could trade back to Europeans. Right. It might have been a, a less unfair fight at the, at the disease level.

[D]

Exactly.

[C]

But the sort of echoes of what had happened and, and this is also very historically contingent. Right. You know, if this happens at this time and this happens at that time, then, you know, the balls are going to go down a certain, you know, pathway and that's what's going to happen. But if they had gone a slightly different pathway, American history might have been very different.

[D]

Let us end with that note, but I hope we have triggered a few new careers or at least new avenues of study for young minds, because I think this is so fascinating to go into it. Professor David J. Meltzer is of SMU Southern Methodist University, where he is the Henderson Morrison professor of Prehistory. The book we referred to is called First Peoples in the New World Populating the Ice Age. This is a really great read and you should definitely get it. Thank you so much, Dr. Meltzer. It's been great to meet you.

[C]

Thank you.

[D]

Hey, thanks for listening to American History hit. You know, every week we release new episodes, two new episodes dropping Mondays and Thursday, Thursdays. All kinds of content from mysterious missing colonies to powerful political movements to some of the biggest battles across the centuries. Don't miss an episode by hitting like and follow. You help us out, which is great, but you'll also be reminded when our shows are on. And while you're at it, share it with a friend. American History hit with me, Don Wildman.

[C]

So grateful for your support.

[B]

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