The Ancients - The First Americans

Episode Date: June 26, 2022

Modern humans thrived in the Americas for thousands of years before the first European colonists arrived, but how and when did they get there?What's more, did their arrival spell disaster for indigenous megafauna such as giant ground sloths and wooly mammoths, or was there another culprit behind the mass extinctions across North, Central & South America?In this episode, Tristan is joined by Professor David Meltzer, an archeologist from Southern Methodist University, to explore the nature of human migration into the Americas and how scientific developments now allow us to discover more about those very first Americans.Tickets to Tristan's talk 'London in the Roman World' with Professor Dominic Perring on July 4 are available here: https://shop.historyhit.com/product/london-in-the-roman-world/

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. It's the Ancients on History Hit. I'm Tristan Hughes, your host, and in today's podcast, where we're going away from the ancient Mediterranean, we're going to the Americas, to North America, to the story of how the first modern humans, the first Homo sapiens reached the Americas. How did they do it?

When did they do it? And what do we know about their spreading out into the Americas, their interactions with the fauna of the Americas and even now extinct mega fauna, such as woolly mammoths, saber-toothed tigers, and so much more. Let's talk through all of this. I was delighted to get on the podcast Professor David Meltzer.

David, he's an archaeologist from Southern Methodist University and he is one of the leading experts in this field and it was a pleasure to chat to David because he explains how this field, how this study of when the first modern humans came to the Americas well it's evolving it's growing every year with new scientific developments in genomics in genetics being able to find out so much more about this nature of human migration into the Americas. David this this was an amazing chat. We cover all things from the Great Land Bridge between Siberia and modern-day Alaska tens of thousands of years ago. We cover the descent down into the Americas, into the modern-day USA, and we also look at why this

field is looking so exciting in the years ahead. So without further ado, to talk all about the arrival of the first modern humans in the Americas, what the science, what the archaeology is telling us, here's David. David, it is great to have you on the podcast today. Thanks for inviting me. You are very welcome indeed. I've been waiting to do a topic on America for so long, and I'm so glad that we're now doing this one, because when looking at when the first modern humans reached the Americas, David, it feels like this is an extraordinary field where even recently, in only the last few years,

the wealth of knowledge available is just growing and growing. It's a really exciting area of archaeology to really look into, and anthropology. Well, absolutely. You know, there's been a sea change just in the last decade or so, which is a combination of both advances in archaeology. We're finding more and more ancient sites, but at the same time, revolutionary developments in genetics, which have enabled us to literally get into and answer a question that I've been wondering about for, well, a very long time. I'm not going

to tell you how old I am. And that is the population history of the first peoples who came to the Americas with DNA and specifically with ancient DNA and ancient genomics. We can reconstruct who these folks were, where they came from, or at least who they're related to among other populations in Ice Age Asia and Northeast Asia. We can approximate when they got here, but of course, it's the archaeology that actually gives us reliable and secure dates. So this combination, this wonderful combination of new advances in genetics and archaeology have really enabled us to, in a really substantial way, kind of narrow the window within which

this whole process took place. And what are these sorts of developments in genomics are we talking about in recent years, David? So with genetics, we've long understood that there are certain corners of the genome where we can trace back specific single locus markers, like for example, mitochondrial DNA and the Y chromosome. These are inherited matrilineally or patrilineally, respectively. And we've known for a long time that humans, modern humans, came out of Africa. And I suspect you've talked in the past about things like mitochondrial Eve, which enables us to sort of trace back the sort of female lineage to an individual who lived in Africa some two to three hundred thousand years ago, plus or minus, right? And to a male, but that's only

two individuals. The human population history is this incredibly complex skein of people and groups who mixed, admixed, got isolated from one another, the later gene flow. It's a complex story. With the development of genomics, the ability to see the whole genome, and more specifically, the development of ancient genomics, the ability to extract from human skeletal remains genomic signatures, we can now start to piece together who these people were, who they're related to, the sort of budding and lineage splitting, admixture coming together later on of these populations as they moved out of Africa, across Eurasia, interacted with Neanderthals and Denisovans, and ultimately found themselves on the edge of the Bering land bridge and then pushed into the Americas. It is quite something. And I love that idea, David, for what you said there. It's a lovely example, isn't it? Where it's combining these new advancements in science with archaeology to get more of a picture of this particular field. It's so exciting indeed. I mean, if we therefore do

talk on the archaeology and then go on to the genomics and how it works hand in hand, as you've hinted at there, when looking at the archaeology for this field, what's the earliest secure archaeological evidence that we have for early modern humans in the Americas? And I say secure with a key emphasis on that word. Yeah, I was just going to say, yes, and you underlined it and italicized it, and that was important because there is, and in fact there has been for the better part of a century and a half, considerable controversy over when the first people came into the Americas. The controversy had its first resolution in the 1920s when it was demonstrated for a fact that people had in fact arrived by the end of the Pleistocene. That subsequently triggered another question and debate, which was, okay, well, so they got here by the end of the Pleistocene. Did they get here earlier? And that issue took another, oh, half a century to resolve, maybe a little bit more, with the discovery of the Monteverde site. This is work that was done by Tom Dillehay in southern Chile, which demonstrated pretty clearly that

people had been in southern Chile as long ago as, say, 14,500 years ago, which obviously raises the question, well, if they're in southern Chile 14,500 years ago, my goodness, what time would they have come across the Bering Land Bridge and made their way down through North America? So obviously, the implication is that there ought to be older stuff. In the last decade or so, there have been quite a number of candidates put forward that suggest evidence of humans, more or less reliable evidence of humans in North America, by 15, 15 and a half, plus or minus, we're archaeologists, we like to deal with plus or minus, right? And it seems more or less reliable. It actually matches up more or less well with the

genomic evidence, recognizing again that genomic evidence is not very good on age in any sort of precise way. It gives you sort of ballpark figures. And so the secure evidence seems to be pointing to an arrival south of the massive continental ice sheets that covered much of Canada during the Ice Age, sometime after around, say, 15,500 years ago. There are, however, much earlier claims, which at the moment are sort of being held in check. It's not entirely clear that they're secure, to use your very good term, and we're waiting. Archaeologists have a long memory. It's sort of an occupational hazard, we think about things of the past, and we've seen so many sites come and go that we've become fairly skeptical about claims of truly great antiquity, claims that say push human presence in the

Americas back 10,000 years or more. We're not entirely, well, some people are cynical. I'm just skeptical, right? So if you've got a claim that pushes back what we understood to be the case by, say, 10,000 years, I'm not unwilling to consider it, but I really want to see the evidence. And I want to be convinced by the evidence, and I want to have compelling evidence if we're going to take that sort of chronological leap, as it were. It sounds from what you're saying, David, that the archaeology, and you've mentioned this in your papers that you've written, can provide the minimum age. So we got a site, it proves that people, humans, early modern humans are there at that time, but they were probably there before then. Well, that's the issue, right? Is that you're never going to find the very first footprints of people in the Americas, right? The odds of finding that very first site are infinitesimally small. So you know that they were there when you have a site, that they were there by that time.

Obviously, they came earlier, and especially if your site is in Southern Chile. So if they're in Southern Chile by 14,500, they had to have come across much earlier. And that's the nice pairing and synergy of the genetic evidence with the archaeological evidence, which is that genetics gives you a maximum age to complement that minimum age that archaeology provides. Because what genetics does is it says, okay, this is the point that we estimate this population who would then go on to cross the Bering land bridge and make their way into the Americas, separated from their Northeastern Asian relatives and split off. Now, the moment that they sort of split off genetically does not necessarily correspond to the moment that they physically packed up and said, okay, it's time to head to New York, right? Rather, it's the moment

where the two populations became isolated from one another. And at some point thereafter, the ones that were headed to New York left. So that gives us a maximum age, just as archaeology gives us that very minimum age. And somewhere in that window, and that window at the moment is around 8,000 years. It's between about 23,000, plus or minus, that's our genetic maximum estimate, and about 15,000, 15,500, that's our archaeological maximum estimate, and about 15, 15 and a half thousand, that's our archaeological minimum estimate. So somewhere in that 8,000 year window, which happens to coincide precisely with the last glacial maximum, just to complicate matters, this is a period of time where you don't expect people to be moving across the vast frozen north,

but apparently it was. So in that window is when that process took place. You mentioned so much there. I want to definitely get into that geographic context very, very soon. But I've got to ask a couple of questions first, because you also mentioned these earlier in your answer there. The first one, actually, I've got to talk about is in regards to genetics. And I guess ethical questions surrounding it now, because how important has it been when now looking at genomes and genetics in this area for collaboration with the indigenous American community? It's absolutely vital. You know, archaeologists, biological anthropologists, we haven't always done right by the indigenous

peoples of the Americas. And that's changing. You know, I've been involved for the last, oh, I guess, dozen or so years with a number of studies of ancient genomes. And we've made an effort. And I say we, really, this is to the credit of my collaborator, Esky Willerslev at the Center for Geogenetics at the University of Copenhagen, ESCIE's really made a tremendous effort to reach out to the Native American communities. We understand that so far as our interests are, they may not overlap with the interests of the indigenous peoples whose histories we wish to understand. On the other hand, we also feel that we have things that we can offer

in terms of understanding their past and contributing and helping them to understand that past. And the best example would be the so-called Kennewick Man, the ancient one, which was in legal limbo for a decade or more and was the subject of a legal tussle between scientists who wished to study the remains. I was not part of that group. I mean, I wanted to study the remains, but I understood that these were also remains that had been claimed by five Northwest Coast tribes who wanted Kennewick to be returned to them and reburied under the conditions of the Native American Graves Protection Repatriation Act, NAGPRA. It was all sort of stuck. And it was stuck because the courts and scientific decisions should never have to end up in court and have a judge who knows nothing about the science decide how things should go.

But the courts had decided that Kennewick was not Native American. We had the opportunity to look at Kennewick's genome, and it was unequivocally Native American. And so we were able to contribute through the genetic study, the genomics of Kennewick, that we were able to show that he was Native American and that among his descendants were the five claimant tribes in the Pacific Northwest. So in that case, doing the genetics and the genomics had a real practical, substantive payoff and value to the tribes, just as it helped us get a better understanding of an individual who had lived over 8,000 years ago in this region

and see how he fit into that larger pattern. So those kinds of efforts, which were collaborative, we received permission. And in fact, one of the claimant tribes actually provided DNA samples for us to compare to Kenwick. Those kinds of collaborations can really have positive benefits. It's wonderful to hear you say that positive, how that in itself is helping drive so many advancements in this field, and hopefully will continue to do so in the months and the years ahead. Just going on from that, something else I'd love to ask about before really delving into when these first modern humans reached the Americas, is what you also mentioned during your previous answer, which was regarding footprints. Because recently last year,

we had a chat with Professor Sally Reynolds about the new discovery of footprints in New Mexico. I'd love to ask about your thoughts around this, about this new discovery, what it is, and the significance of it for this field. As it happens, I do field work literally across a fence from that footprint site. That footprint site is at the White Sands National Park, and I've been doing field work on the White Sands Missile Range. And a couple of years ago, I knew about the site. I'd heard about the site, and so we just hopped the fence and wandered over to look. It's an interesting locality, but maybe for your listeners, I should sort of give a little bit of the background here. This is a really interesting site because a series of human footprints, human trackways, along with the tracks of other animals, including giant ground sloths and mammoths, have been found in this area. And the tracks were dated. And

actually what they were dating was, obviously you can't date a footprint, but what you can date is little bits of vegetation that got sort of tromped down by the people. And those dates came back surprisingly old. Specifically, they sort of range in age from around 21,000 years ago to about 23,000 years ago. It's one of those cases where suddenly we had all sort of assumed and believed and had evidence to suggest that people were here as early as 15, but now we've got to push it back 8,000 years. And does that work or not? Well, here's the thing. Nature has a mischievous streak and we've been fooled before. So the operating principle, when we hear about a site that is

going to push human antiquity back substantially, our operating principle is trust, but verify, right? I trust the folks who are doing the work. I know they know what they're about because in fact, some of my colleagues are on the team that work there. But you've still got to verify that nature has not pulled any fast ones. And the fast ones here are really down to the dating. They're dating a plant. It's an aquatic plant that absorbs dissolved inorganic carbon, which has the potential, and I'm underlining the word potential here, it has the potential to give you dates that are older than they

ought to be. So you really want to understand and be very, very secure in your understanding of the dating. Is it reliable? Is it accurate? And does it date the event in question? After you address that issue, and if in fact it can be demonstrated that it is as old as advertised, there's still a couple of other issues that are really puzzling to me. As I hopped over the fence and I wandered over to the site,

I'm looking around, you're literally on the floor of an ancient lake bed. There's nothing there. on the floor of an ancient lake bed. There's nothing there. And look, I'm an archaeologist. If I have a site where people have been coming back repeatedly to over a thousand to two thousand years, I want to know, what is it about this place? Are there resources here? What brought people back to the spot repeatedly over more than a millennia? And then the next question is, okay, why didn't they leave a single artifact behind? If you come to a place repeatedly over 1,000, 1,500, 2,000 years, how is it you manage not to drop a darn thing on the ground? There's no artifacts there. There's nothing there, right?

on the ground. There's no artifacts there. There's nothing there, right? And I got to say, I've also dug through those same sediments and I am literally a hundred meters away, okay? We had a trench in the same deposits, a hundred meters away, same deep deposits, and we were taking samples. And we were sort of perplexed because we're pounding our sampling tubes into the side walls of our trench. And literally it took rock hammers and sledgehammers to sort of chip out the dirt. And I was thinking to myself as I'm wailing away at the wall of this trench, how did they find footprints in this stuff? How do you excavate down through what's essentially the equivalent of dirt concrete and find something as fragile, vulnerable as a footprint? I don't know. I read the articles about it.

And when I went out to the site, I could see these big blocks of the same sediment that we were in, in our trench. And they'd been excavated with what they refer to as a dirt-rated chainsaw. I've never excavated with a chainsaw, I have to say. So that was a new one on me. But how do you find footprints when you're excavating with a chainsaw? I mean, the whole thing, I don't doubt that these are absolutely honest players

and they're pros, every one of them. But I sure want to know more about this site before I'm going to say, okay, the dates are good. The footprints are real. They were wandering around the landscape with mammoths and grassloss. I get all site before I'm going to say, okay, the dates are good, the footprints are real, they were wandering around the landscape with mammoths and grassloths, I get all that, I'm in. And as we now delve into how these first people, early modern humans, made it across the Americas, just preceding that, this idea of when and how there are still these questions that,

as you say, you have the minimum age with the archaeology, but even with these new discoveries, there are still hints of doubt to exactly when these first early modern humans really did venture. It seems like we have an approximate thousands of years dating range for that, but that is just it at the moment. It's still an approximate. Well, that's it. Look, if this site, if all the T's are crossed and the I's are dotted and it proves to be as old as it is, then it just means that we've been wrong, and we need to readjust our thinking. And I'm perfectly okay with that. But when you're going to, you know, the old phrase, right? Extraordinary claims require extraordinary proof. This is an extraordinary claim. Let's give it the extraordinary proof, and then we'll just rethink what we thought, because clearly we hadn't been correct before. That doesn't bother me at all. I mean, that's the whole point of advancing the science, right? Absolutely, absolutely. Well, let's therefore move on, because you did mention it earlier. I'd love to really talk now about the geographic context of

this time period that we're talking about. First off, you mentioned the name earlier. Right. What is the last glacial maximum? So the Ice Age, the Pleistocene, begins approximately two and a half million years ago. And there's a whole series of repeated episodes of glacial periods when global temperatures drop, you have massive ice sheets move out of the far north down latitude, and then you have interglacial periods. We are in an interglacial period. But at the time that this whole scenario and story of the peopling of the Americas was taking place, the world was moving into the grip of the last major glacial episode of the Ice Age, of the Pleistocene.

So people are in far northeastern Asia, as best we can tell archaeologically, by around 30,000, 35,000 years ago. So it took a long, long time for modern humans to make their way out of Africa. Bear in mind, we are tropical creatures, right? long time for us to move out of Africa, get into the far north, be able to sort of weather glacial conditions at 55 degrees latitude, 60 degrees latitude, 65 degrees latitude. And that doesn't happen until much later in prehistory. Like I said, around 30,000, 35,000 years ago, we have people in the far north at actually latitudes of about 70 degrees. They are literally right on the Bering Sea. So at that point, and right after that point, the world starts to sort of slide into this really cold period that we refer to as the last glacial maximum. It is essentially the coldest episode

of the last portion of the Pleistocene. Global temperatures will drop substantially. You have a massive ice sheet, actually two massive ice sheets, that will grow one over much of Canada from Newfoundland and Labrador all the way west to basically the border between British Columbia and Alberta. And that ice sheet, known as the Laurentide Ice Sheet, will ultimately join up with and abut a massive ice sheet that grows as a series of mountain glaciers that coalesce over British Columbia. That's known as the Cordilleran Ice Sheet. With those two join up and ab one another you've basically got 3 000 miles wide of ice which reaches from the pacific coast to the atlantic coast it reaches from the arctic circle

down to central ohio and portions of the northern now united states in places it is several kilometers thick so it is a massive block of ice. It's insane to think that nowadays, and with the same time as these massive ice sheets, so much of what is now North America. The Americas at that time weren't their own separate continent. Were they connected to Asia in where modern-day Alaska is? Right. That's the thing. If you lock up that much water on land, all these ice sheets are a function of precipitation, snow and rain falling over the northern latitudes. If it then locks up as ice, if it freezes as ice, it doesn't get returned to the oceans, right? So the

hydrological cycle is interrupted. You interrupt the hydrological cycle and ultimately build an ice sheet that's, again, 3,000 miles wide and several kilometers thick. That's an awful lot of the ocean water that doesn't get returned to the ocean. When that happens, shallow areas of continental shelf become exposed because sea levels are dropping. And sea levels dropped worldwide on average, though it varied tremendously depending on where you were on a continent, on average, you know, 130 or so meters. You drop sea level that much, you're going to expose large areas around each continent of shallow continental shelf. But more importantly, from the story, in terms of the story of the peopling in the Americas, you're going to expose the shallow shelf beneath the Bering Sea. If you drop sea levels just 52 meters, the Bering Sea becomes dry land. You drop it 130 meters, then you've got yourself a huge land bridge that connects up Northeast Asia and

Alaska. And don't think of this land bridge as some sort of rope bridge that you're crossing the Amazon and you're kind of hanging on and you're walking, you know, one foot in front of the other very carefully. If you were moving from Northeast Asia into Northwest North America across the Bering land bridge, you probably had no idea that you were crossing from one continent into another because the Bering Land Bridge itself was a thousand kilometers wide. So if you're just walking down the center of it, you have no idea that you've left one landscape behind and you're moving into a completely new one. Now, of course, here's the complication.

During times of maximum ice on land, you have lowest sea level. That enables you to walk into Alaska. But once you're in Alaska and you're looking south, all you're seeing in front of you is the massive ice sheets, right? So you've got to wait. It's kind of a two-step process, depending on the timing. If you come across the land bridge in the depths of the last glacial maximum, the coldest portion of the ice age, what ice volume is at its maximum extent, you're stuck there until the ice begins to melt back and retreat. When that happens, there are two potential routes that will open up that will allow you to get from Alaska down to mid-latitude North America. The first route that opens up comes down the Pacific coast. That route is opened by around 16,500 years ago. The other route that will open actually opens at the junction of where those two ice sheets had bumped into one another. basically runs down the spine of the Rocky Mountains between British Columbia and Alberta. And we refer to it as the Ice Freak Corridor.

As the ice sheets begin to retreat, this corridor opens between them. Now, we know that in glacial geological terms, that corridor probably opened physically around 14,500 years ago, plus or minus. But biologically, what's the first thing that's going to grow in a recently deglaciated landscape? It's going to be mud and it's going to be water. That landscape's not going to become revegetated, let alone have animals in it for a substantial period of time. So it looks like that corridor, while it was physically open as early as 14 and a half thousand or so years ago, it was not a biologically viable route until probably as early as around 13,000 years ago. So do the numbers. If you've got people in Southern Chile at 14 and a half,

they did not come down through the ice-free corridor because it wasn't available to them at the time they must have come across the land bridge. So that, in turn, has shifted a lot of our archaeological attention to the Pacific coast as the route that the First Peoples took into the Americas. If you've always wanted to know more about some of the key events that shaped the medieval period and the modern world, then Gone Medieval from History Hit is the podcast for you. From this...

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and we're waiting for you to join us. Well, if we stick on the land bridge, first of all, before talking about this Pacific Coast route. So is it therefore viable before 16,000 years ago when those ice sheets were impenetrable for people crossing over or coming over the land bridge that these early Homo sapiens could have gone across the land bridge thousands of years before and just had to stay in that region for quite a long period of time because they literally couldn't go any further? Or do you think it was more a brief stop in Alaska and then they continued down when the Pacific coastal route opened? Right. Well, that's the question we're all asking, right? There is some genetic evidence of what's been referred to as the Beringian standstill,

where basically folks get up into this region and then they just cool their heels for several thousand years. And estimates range from as little as 2,400 years to as much as 9,000 years. But we just don't know, right? We've not found any archaeological evidence that would directly test that hypothesis that people had been hanging around in either on the edges of the Bering Land Bridge or on the Bering land bridge itself. Obviously, the Bering land bridge is now drowned. So any evidence is going to be under 52 meters of water. So the likelihood of finding that is quite limited. But we still haven't found any archaeological evidence of people close to the land bridge at that time. Okay. So if people were hanging out in that part of the world, the earliest dates that we have in Siberia are around 16,000 at a place called Duktai Cave.

But that's still a thousand or more kilometers away from the land bridge itself. The earliest evidence that we have in Alaska is around 14,200. So, yeah, it's really hard to say where people were and whether they, in fact, came across the land bridge and had to cool their heels in Alaska for thousands of years or if it was as you also suggested a sort of one-shot deal they came across the land bridge just as the pacific coast route was opening up and so they didn't have to pause they didn't have to stand still they could just keep coming all the way down into the lower 48 or I mean I mean, let's take our footprints in White Sands. If they were here 23,000 years ago, well, they could have actually crossed the

land bridge at that point, and there would not necessarily have been any barriers to their southward movement. I mean, there would have been ice on the landscape, but it would not necessarily have restricted their ability to come down into the lower 48. So, you know, the answer is we don't know the answer. But we sort of know that at the moment we know the parameters based on our current knowledge. But, you know, when you work in the sciences, current knowledge is only as good as today. Tomorrow it might give you a different story. Well, indeed.

tomorrow it might give you a different story. Well, indeed. I mean, what is fascinating to therefore think, if you put yourselves in the footsteps, in the footprints, literally footprints, of these early Homo sapiens coming to the Americas, you know, if they are going down that Pacific coastal route and they get away from the ice sheets, David, do you think it would have felt like a whole new world?

I mean, what sorts of geographic landscapes are we talking about? What sorts of animals and the like would have greeted these early Homo sapiens? Well, as soon as they got past that ice barrier. Yeah. So actually coming down the coast, it would not have been too terribly challenging or as challenging as it might be. Let me actually give you an analogy and then we'll talk about Pleistocene. And the analogy is going to be British settlers landing in Virginia in the 16th century, 17th century. They had no clue. They didn't know what to do. You had colonies that got lost. The famous Roanoke colony disappears. Why? Because suddenly they're transported from an economic system where they understood how

everything worked. They had markets, they had villages, they had towns, they knew crops to grow. And they're basically transported. I don't know. What does a transatlantic ship crossing take in those days? Months? Ooh, I wouldn't ask me. That's too modern for me, I'm afraid.

But let's say it would take a long time. It would take quite a few weeks. Takes a long time. And suddenly you're deposited on the outer banks of Virginia or North Carolina. And they say, okay, see you later. We'll send a ship back in a year. And the ship comes back in a year or two or whatever it was. And they're all gone.

What happened to them? Well, I suspect what happened to them was they suddenly got dropped into a completely alien environment. And they had no idea what to do. I don't know that that's the cause of the disappearance of the Roanoke colony, but it's certainly a good possibility. Now, let's go to the Pleistocene. You've got people that have been in Northeast Asia for some time. They've been working their way across the Bering land bridge.

They understand the environment. It's got mammoths. It's got horse. It's got giant bison. They can go out to the coast and they can see the coastal resources. As they're moving south down the Pacific coast, they're seeing the same kinds of things. Now, obviously, as the coastal route just opens, there's not going to be a whole lot of mammoths wandering around on the beach of the Pacific Ocean. of the Pacific Ocean. But as groups have adapted to that coastal environment, say on the edges of Beringia, on the edges of the land bridges, they're working their way south. It's not going

to change that much. So it's actually fairly easy to move through environments, to move across distances, so long as the structure and the resources of the environment have not changed dramatically. These folks were not picked up by a helicopter in Asia and dropped off in Texas. So they're working their way into the continent. Now, what happens is once they get south of that ice sheet and they turn inland, now that's more of a challenge. Imagine what it's like to come into an environment where you've never been before. It's completely unfamiliar.

You are seeing plants and animals that you don't know whether they could feed you, help you, cure you, maybe even try and kill you, right? The first time somebody saw a rattlesnake, what did they do? Oh, what a wonderful noise that snake is making. Let's go take a really close look, right? You only do that once. You may not be given another chance. So, you know, they're coming into a completely new land and as they go further and further south, it becomes increasingly less familiar. So the process of landscape learning, figuring out how to survive and indeed thrive in this new landscape, must have been a process that was at once challenging and at the same time well within their capabilities. Mind you, these are people whose ancestors had crossed Asia. These were by no means cultural dopes. They knew how to hunt. They knew how to gather. They knew how to experiment. They knew how to observe. You want to find out if something poisonous or not,

you give it to your younger brother. Let's see if Mikey gets sick. Are the animals eating those red berries? If they are and they're not keeling over, maybe they're okay for us. red berries if they are and they're not keeling over maybe they're okay for us so you're learning as you're going you know how to make stone tools you know how to find good stone sources right you drop down into a river valley and if you see some really high quality stone that you want to use to make your tools well if you see it in gravel in the river valley, go up valley and maybe you'll find the outcrop where the good stuff is, right? The mountain of, you know, wonderful chert that you can use to make stone tools. So these folks were extraordinarily adept at adapting and extraordinarily adept at adapting

to new landscapes. So this was not like getting on a boat in Liverpool and ending up in Virginia and having no clue about anything, right? These were folks who were working their way slowly into a landscape and learning as they went and ultimately thriving. Ultimately thriving, as you say. It's quite interesting you say that learning curve, probably that very deadly learning curve which occurred.

I mean, what sorts of animals would they have been becoming? I guess if we're talking about a hunter-gatherer society at that time, what sorts of animals would they be coming up against in this new landscape? Yeah, so there are large predators on this landscape. At the end of the Pleistocene, or toward the end of the Pleistocene, we know that some 38 genera of large mammals go extinct. And among those 38 genera are seven genera of large carnivores. So you've got saber-toothed cats, you've got cheetah, you've got giant short-faced bear. Now, the question that people have always sort of wondered about is, were these animals in any sense dangerous to people, an impediment to people, that people ever interact with them.

We don't have any archaeological evidence. In some cases, it may well be that some of these large, nasty predators had gone extinct by the time humans arrived. But that's not to say that herbivores aren't just as dangerous. You've got mammoth wandering around the landscape. And if mammoths behaved anything like their modern elephant relatives, they were not a species to be trifled with. As folks who today live in areas that are occupied by elephants, folks in Africa will tell you elephants don't behave like animals, they behave like enemies. And if mammoths were like that, that would have been extraordinarily dangerous as prey and potentially dangerous if you tried to sort of mess with them. I mean, think about it. You're

coming into a continent and you've got to stick with a sharp rock on the end of it. You're well-equipped for the Pleistocene, but are you well-equipped to take after and bring down five, six, seven ton animals. So if the archaeology is therefore not there at the moment, I know this is something you've done some work around and kind of linking into that. This whole idea of these hunter-gatherers leading to over-hunting these big creatures, sometimes herbivores such as the mammoths, and leading to their extinction. But how likely do you therefore think that argument is that these first Homo sapiens in the Americas would ultimately lead to the extinction of these megafauna? I don't think there's really evidence or reason to think that people were responsible for the extinction of all of these animals. It's been estimated that when Clovis people arrived,

there were anywhere from 100 to 200 million of these large mammals on the landscape. Yet when you systematically look at all the sites for which it's been claimed that humans were preying upon these animals, we quite literally have only 16 or 17 now. We just got another site added to the list. 17 now, we've just got another site added to the list, 17 occurrences in which humans were clearly responsible in some form or fashion for killing, scavenging, or dismembering the critter. So first point is that there's no archaeological evidence for it. Second, only five genera of these animals are found in those sites. So you've got mammoth, mastodon, gompothere, camel and horse. But what about the other 33 genera? There's absolutely no evidence that humans had anything to do with them, let alone were the cause of their extinction. And in fact,

it appears as though most of these animals, or at least the majority of these animals, most of these animals, or at least the majority of these animals, may well have disappeared before humans even got to the Americas. Now, the complication there is that we don't actually know when all of these animals did, in fact, vanish from the landscape. We've got radiocarbon dates on about half of them that suggest that they did, in fact, survive up until, or at least approximately, the end of the Pleistocene. But for the majority of them, they may well have disappeared, or we just don't know when they disappeared. So we can't really say that people were contemporary with these animals or not. It's also the case that the one species for which we do have substantial evidence that humans were hunting these animals, that species is bison, the American buffalo. We have abundant evidence of people hunting these animals, and yet bison are still around.

And in fact, bison were not only hunted starting in the Pleistocene by some of the first people into the Americas, they were hunted over the next 12,000, 14,000 years by Native American groups out of the Great Plains. And ultimately, they were hunted almost to death by commercial hide hunters in the 19th century. And yet, after all that intensive predation, bison still didn't go extinct. So we have 38 genera for which there's virtually no evidence whatsoever that humans were preying upon these animals, and they go extinct. And yet for the one species for which we have abundant evidence of human predation, they don't go extinct. So the notion that people were somehow responsible for the extinction of all of these animals

really doesn't make any sense from an archaeological perspective. Does it therefore seem to make more sense that climate change is the real killer of these megafauna? Climate change, in fact, is involved in all of this, right? So climate change is the ultimate driver of all of these processes. It's the process that, or the trigger, that leads to humans moving into the Americas, right? Because you've got onset of last glacial maximum climates, you've got sea levels dropping, people can come across the land bridge and so on and so forth. So yes, it's responsible for that portion of it, but it's also at the end responsible for a huge number of changes that will take place in the climate and in the ecology of the Americas,

particularly North America. Because of course, as the ice sheets are retreating, there's all manner of changes that are sort of coming along with that ecological changes. So ecological communities and biotic communities that have been in place for thousands of years that had adapted to ice age climates will start to fragment and come apart. Different species will be responding to the increasing warming and other changes, such as changes in seasonality, changes in the composition of grasslands. A colleague of mine refers to it as a biogeographic free-for-all. Basically, the end of the Pleistocene is coming. There are substantial changes in the climate and

these will ripple through the whole ecosystem in and basically it's every species for itself they're all going off they're dispersing they're finding their new niche in these warmer climates and so when everything gets pulled apart that's going to endanger that's going to endanger, that's going to destabilize ecosystems in a way that will impact the ability of animals to respond to these changes. And let me just give you an example from a recent paper that the Willerslev Group just published in Nature last year, which was a detailed study of environmental DNA recovered from throughout the Arctic. study of environmental DNA recovered from throughout the Arctic. And one of the things that we were able to show in this paper was that in far northern Siberia, the plant communities, the vegetation communities, and the climate, basically there was a sort of a lag. Everywhere else at the end of the Pleistocene, there's substantial changes going on, but for all

intents and purposes, and I'm putting sort of air quotes around this, the Pleistocene, there's substantial changes going on, but for all intents and purposes, and I'm putting sort of air quotes around this, the Pleistocene hung on in far northern Siberia for thousands of years after it ended everywhere else. And what do we see? Late survival of mammoths and woolly rhino, because the environment didn't change, right? The plant community stayed stable. So where we do have stability, yeah, everything hung on. In North America, where the end of the Pleistocene brought a wide range of ecological changes and climatic changes, I mean, think about just the weather effect. Ice sheets are just giant weathermakers. If you have an ice sheet parked over in Canada, it's going to have a profound impact on the climate south of there. Remove that ice sheet, all sorts of things are going to happen. So with all of those sort of destabilizing

processes taking place, animals are scrambling. And clearly, some of them, it got past their threshold to adapt, their tolerances, their adaptive challenges. And so it's important to add to this as well. So extinctions is one end of that response. It's sort of the extreme consequence. same time, it wasn't just animals that were going extinct. We had massive range changes. We used to have caribou living in the southeastern United States. Today, they live in northern Canada. They're having to respond. Ecological communities are changing. Smaller animals are going extinct too. It's not just sort of the big succulent animals that everybody envisions people going after giant game like ground sloths and mammoths. Smaller animals are changing their ranges, some of them are going extinct, some of them are going locally extinct but surviving elsewhere. So there's this incredibly complex set of changes that are taking place. So it's no surprise that at one end of those complex of changes, animals are disappearing. Thank you for that explanation, David, because I was keeping thinking of animals

and the like because my mind is for some reason is just keep going back and back and back and back again to of all these megaphone and how they change at that time but there seems to be one animal from what you've been working on from your papers and the like which seems to have been there from the start since the first humans arrived in north america and you know survives and adapts during these changing climate times and it is man's best friend, dogs. So we do see, we see dogs since the start of Homo sapiens coming to the Americas. Yeah. So the dog story is a wonderful story. And this was, if you don't mind me sort of tooting our horn a little bit here.

You go for it. You go for it, Dave. I've got the microphone. Yeah. So a few years ago, I was giving some talks at Oxford and visiting my colleague and friend, Gregor Larson there, who does dogs. And Gregor was telling me about their reconstructing the history, the phylogenetic history of dogs based on their genes. And he was giving me their estimated ages of when the dog populations kind of split from one another, what the oldest dogs were in the Americas, the oldest dogs in Siberia. And he's giving me this timeline. And I'm looking at his timeline and I'm thinking to myself, oh goodness, that looks like the human timeline. And then it finally dawned on me, I can be really slow at times, it finally dawned on me that, well, people can come to the Americas without dogs, but dogs aren't going to wander over to the Americas without people. They're domesticated animals. And so we started to sort of play on the whiteboard in his office there. This is with Angela Perry, a PhD student of Gregor's

who had just finished a few years earlier, who was an expert on the archaeological side of the dogs. And we realized that we've got a really nice sort of co-evolutionary story here, where people will domesticate dogs somewhere in Northeast Asia. We don't know exactly when. I'm going to leave that one to the dog people. But when people come into the Americas, it appears as though they brought their dogs with them, because we see in the genetic record and the genomic record of humans, these splits that are taking place as populations are moving further and further south into the continent.

And we see corresponding splits in the dog populations. So clearly, you know, as groups would come in and some of them would say, you know what, we're tired of hanging around here in California. We're going to go continue on down because we're due in Monteverde in Chile at 14,700. So we need to get moving. So they take some of their dogs with them. And we see the isolation of these human populations, the isolation of these dog populations, and it's showing up in the genetic record of both. So it makes perfect sense that they would come in to the Americas, that they came into the Americas with their dogs, their dogs were,

I suspect, part of the cultural repertoire. If you're coming in, this gets back to the issue of coming into an unknown landscape, facing potential predators that you've never dealt with before. If you've got a dog, hey, that's a bit of defense right there. That's a warning sign and signal and system that you've got that you can use, right? So I suspect it was evolutionarily advantageous to the first people into the new world to show up with their dogs, not just because everybody likes dogs, except for the people that like cats, but because dogs actually served a very useful purpose.

dogs actually served a very useful purpose. And I'm guessing, does the evidence, as these groups of people diversify over the years following their descent down the Pacific coast, as they start spreading inland across the Americas, and I guess then reaching down to ultimately places like Chile through Mesoamerica and South America, as they diversify through all these parts of the Americas, inland and further south, I'm guessing the dogs stay with them. And that's one question. And the other question, I guess, because I've mentioned diversifying, do you start seeing these groups of Homo sapiens really emerging into distinct groups?

So dogs and then distinct groups, I'm asking about. So dogs are diversifying as well as they're moving into the Americas and their patterns of diversification in chronological terms are sort of matching up nicely with the diversification of human groups. And indeed, human groups are diversifying, but think of these not so much as, you know, we're not evolving new species. What we're getting are new populations emerging, which if they stay isolated for long enough, will become distinctive genetically. And let me sort of clarify what we talk about when we're talking about distinctive genetically.

When we're looking at these genomes, we are looking at neutral traits. It's been uncharitably referred to as junk DNA, but that's a kind of a misnomer. This is DNA that does not have or is not seen by natural selection. All of us carry in our genomes, which are 3.2 billion base pairs, there's about 20,000 to 25,000 genes. Genes are segments of that genome that have specific functions and purposes and that are sort of seen by natural selection. That doesn't, at least at the moment, appear to do anything at all. Those are the neutral traits. And that's the thing that we're looking at. So when we're looking at two different populations and we're saying they're distinct, it's not necessarily, or even, distinct in the sense of this group runs faster, this group jumps higher, anything like that. They're distinct in terms of those long strings of letters that have no effect on a person's fitness, their health, their abilities, whatever, that are just part of

that neutral portion of our genomes. So yeah, we see differences because these people are no longer part of the same gene pool. They're separating out from one another. And mutations are constantly occurring in the neutral portions of the genome. So if you had a T or a G at a particular site, now it's an A or a C. These are mutations that don't really have any consequences, except from the point of view of history and understanding who's related to who, if you see groups that have long shared strings of these letters in this neutral portion of the genome, you say, okay, well, they're pretty closely related. When they don't share those long segments and they share only shorter segments over here on this chromosome and shorter segments over here, you say, okay, well, they must have separated from their most recent common ancestor a long time ago. Does that make sense? I think so, yes. No, yes, it does. It's so interesting. I guess it's a great example, David, isn't it, about this recent, if we're going back full circle to how we started the interview,

how recent advancements in genetics, in genomes, can start revealing so much about this aspect, this period of ancient history, in what you've just said there, in trying to understand more about how these groups, first of all, how they get to the Americas, and then how they spread out in the years following. Absolutely, absolutely. Because what we can say when we look at genomes from two apparently widely separated individuals, oh, these folks share long stretches of their genomic sequences. Therefore, even though I'm going to give you a specific example in a moment, but let me give you sort of the general idea. Even though they're separated by 2, 3, 4,000

kilometers, 10,000 kilometers, we can tell by virtue of these long shared sequences and the relatively few differences in their sequences that they in fact are fairly closely related. Here's the specific example. So we have genomes from an ancient individual in Montana, dates to around 12,700-ish years ago, very closely related to an individual that was living in Nevada 10,700 years ago, so a couple thousand years later. And the both of them are fairly closely related to an individual who was living in Southeast Brazil around the same time. So we can actually, with archaeology, we could never do this, right? You find an artifact in Montana and an artifact in Nevada and an artifact in Southeast Brazil, you'd have no clue that these were made by populations that had a fairly recent common ancestor and that not too long ago earlier,

maybe just a few thousand years, they'd been part of the same population. So that's the one thing, right? Genetics enables us to make these long distance links. The other thing this is telling us is that the first people that came into the new world were probably moving pretty fast, right? into the new world, we're probably moving pretty fast, right? Because how else would you have a close relative from Nevada living in southeastern Brazil? There hadn't been that much change in the intervening period, right? They're fairly closely related genetically. That gets back to the question of landscape learning. You're moving into, I mean, imagine going from

Nevada to Southeast Brazil. Think of the environments you're passing through. You're going through the tropics, right? So you're going from essentially what's near desert, though it wasn't that rough in the Pleistocene. It wasn't a great environment, but it wasn't quite what it looks like today. You're going through the tropics, you're ending up in Southeastern Brazil, and you're doing it sort of in the wake of a genomic eye. It's happening very, very quickly. So this gets back to the point that I was making earlier. These folks knew what they were about. And apparently there was some sort of incentive for rapid movement across the landscape, which raises the other question, what's the motivation? If you get south of the ice sheet and you land in Montana, I'd look around and say, you know,

Montana's not such a bad place. Maybe I'll stay here. But these folks didn't stick around. Now, some populations did, right? It wasn't as though, you know, you had the single group that went all the way down to Tierra del Fuego in one shot. No, you had populations that were settling in different areas, but some of them kept moving and some of them kept moving south. What was the motivation? I don't have the answer, by the way. But if you think about it, one of the things that if you're a hunter-gatherer, and all these folks were hunter-gatherers, they're not farmers, they're not traveling with crops that they're planting or anything like that. If you're a hunter-gatherer, your best insurance is mobility. If you're a hunter-gatherer, what's important is not what's around you right now. It's what's going to be your destination when things go badly where you are right now. destination when things go badly where you are right now? Where do you go when things go south? Well, maybe in this case, you literally go south. There are so many questions that are still unanswered in regards to that,

but it's wonderful to try and piece together that movement, as you say, and how quickly that movement could be from Montana to Brazil, then ultimately to Chile, over a pretty short amount of time when you look at it in prehistory i mean david it just all sounds you can see the passion in what you said just there it feels like with these recent developments this whole field of the first people coming to the americas the first homo sapiens that in the immediate years ahead not the far future but the immediate years ahead we're going to find out so much more. We're going to uncover even more information that's going to reveal even more about this

really significant, important area in our prehistory. Absolutely. Sort of a golden era in the sense that every new genome that gets sequenced is telling us things that we just didn't know before. And so I lecture on this topic. And every year when I get to, okay, here's what we know, we take last year's lecture notes and we burn them and we start afresh because it literally is almost a sort of a case of day by day, we've learned something new. And it really is quite remarkable, the reach of the techniques and the technologies, the analytical techniques and technologies that we have today, which is not to say that good old-fashioned archaeology isn't helping as well, because we're finding sites. People are making interesting arguments and claims about antiquity, like White Sands footprints, right?

man's footprints, right? If those in fact can withstand critical scrutiny, then yeah, we're going to have to sort of rethink a lot of what we've thought. So these are interesting times, no question. Indeed. And I wonder how many of your notes will be there as you say this time next year for your next series of lectures in the years ahead. Finally, you've written a book, a new edition on this topic, this ever-changing topic, Shifting Sands. It is called David. Yes. In fact, it's funny. When the first edition of that book came out, I could see both genomic studies on the horizon and I could see ancient DNA on the horizon. The book was published in 2009. By 2010, that chapter in the book was obsolete. It was like, oh, I should have waited a year.

But it's okay. Because when it comes to the genetics, it's never going to be up to date unless you're publishing your book online and virtually. And then you're just constantly every night putting in, oh, okay, well, there's been a new sequence. And here's now what we think is wrong. And here's what we still think is right. So yes, the new book, First Peoples in a New World, came out last year through Cambridge University Press.

And in it, I try and indeed sort of update everything that we've learned in the decade or more since the first edition was published. And honestly, it was a wonderful experience doing the second edition, but it was exhausting because there was so much literature in both the genetics and in the archaeology, in glacial geology, in sea level studies that had come out in the intervening decade, dozen years, that it was a real learning experience and an exhausting experience because I hadn't realized I knew it was going to change a lot. I hadn't realized it was going to change that much. Well, David, as mentioned, it sounds super exciting indeed. And I can't wait to see where things go in the future. As you said, this golden age in this area of prehistory and the first Homo sapiens coming to the Americas. This has been a great chat and it just goes for me to say thank you so much for taking the time to come on the

podcast today. Tristan, I've enjoyed it greatly. you well there you go there was professor david melzer explaining all about what the science what the archaeology is now telling us about when we believe the first homo sapiens arrived in north america arrived in the americas i really do hope you enjoyed that conversation it was great to get david on i've been waiting a long time to cover ancient America, and this is just going to be the first episode of it. Because if you enjoyed this episode and would like to know more about America's ancient history, well, you've come to the right place because I'm keen to cover topics varying from the Great Serpent Mound to Poverty Point to so many others in the weeks and months ahead. So stay tuned for those episodes.

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