Dr. Ben Potter: Climate Change and the Peopling of the Americas
By Robert Lundahl
Robert Lundahl
15,000 Years and Beyond
Let's start somewhere. So can you paint me a picture of the last 15,000 years?
Dr. Ben Potter, University of Alaska Fairbanks, Archaeologist
Well if I can I'd like to go earlier, a little bit earlier, because you know, to build a picture or narrative of the people in the Americas, it's a really complicated story and part of it is the people in Northeast Asia, and you can't disentangle them.
Robert Lundahl
So if you are standing in front of a classroom full of 10 year olds and they have an interest in learning something from you; you're visiting the school for the day and they want to know all about this, where do you start?
Dr. Ben Potter
The way I would start would be, "Why is this significant to the world" and this sort of question is really significant. It's really important because it tells us something about who we are as a species.
When we think of humans originating, evolving in Africa, we're really well adapted for mid-latitude so sort of warm areas with not so much seasonal variation, maybe some differences in rainfall that sort of thing, but lots of different kinds of animals and plants that we can eat.
As you move north it becomes more different. East and West is just fine because the way Eurasia is set out. It's East-West sort of dominated and you have the same kinds of plants and animals roughly at those different latitudes and so if you figure out how to make a living you figure out a nice life way that that sustains your population, you know, you can use your adaptation to your advantage but moving North into areas where you have in essence, less biodiversity, so there's fewer kinds of animals fewer kinds of plants and much less of the plants, that we can eat, and you get into colder regions, you get into more arid regions in some cases like Siberia and certainly Beringia, it was very dry, and that was actually more important, this lack of moisture than the coldness. And so when we look at the plant regimes–right now we've got Tundra, treeless Tundra. We've got you know some steppe conditions but mostly a boreal forest, which is full of trees like Spruce, Animals aren't really eating them there's a lot of mechanisms that those sort of plants provide that make it make it difficult, so we don't have large herds of things except for Caribou in the very far north. So animals like moose or deer, they're not very large populations.
So if you imagine humans moving this direction, it's really important for us to understand how did that happen?. When did it happen? What were those adaptations that made it possible, and why didn't it happen before, because there was the last two million years our series of glacial and inter-glacial cycles, right, so we see the peopling of Northeast Asia and the Americas in one of those going from cold to warm, so moving to warm, but there were other periods and, you know, previous past that, that could have happened.
Modern Humans
There were modern humans and they didn't do it, so this question is really important in terms of understanding humans. How did we develop those skill sets? Seasonality is another big issue. You don't have to deal with major seasonal differences in lower latitudes the way that you have to deal with them in the far north, so winter in Fairbanks Alaska is really really different than summer. We're just coming out of 90 degree weather, kind of rainy but a little bit of rain, but moving into like 40 or 50 below with just you know tons of snow and Glaciers and things like that. This is really difficult to make a living. So the story of the First Americans is the story of these these peoples, these populations, that are moving from the south to the north. We're getting better handle on it there's still areas of disagreement.
Robert Lundahl
Did you mean north to south?
Dr. Ben Potter
South. So like Central Asia or if you're a coastal proponent maybe in Japan or Sakhalin area, but in some cases I mean they're coming from the south and they're moving North, so northward into Beringia, which is that land bridge, which basically connects Asia and North America and then expanded South from Beringia, South into the Americas. So this is the broad pattern and I just want to sort of identify that there are definitely disagreements about some of the details or the mechanisms, the exact time, the routes, that were taken–maybe multiple routes–but there's broad agreement on a basic picture and I can walk you through the basic picture, and this is coming from genetics most recently, but also this is consistent with the with the archeology that we have in Asia because that's the source.
Robert Lundahl
And also can I ask you about these multiple sources of information and the meaning of the word corroborate?
Dr. Ben Potter
Yeah, so in in archeology as a science, because we deal with proxy records.. in other words, we don't we don't have a time machine, right, but we are like detectives. We're looking for clues. We make hypotheses, if this happened we should expect to see a b and c and not X Y and Z. And we actually test. We test with excavation. Do we find humans predating mammoths at a certain time? Were people in this area exchanging material culture with another area? There's all sorts of ways to test but what makes a hypothesis stronger is multiple independent lines of evidence. So if you have genetics, these would be ancient samples and even modern indigenous peoples, DNA from all across the world to understand relatedness. You can tease out things like timelines like time sense, divergence, so let's we can look at mutation rates. How many mutations have accumulated since they were one population at one point.
A Nested Tree
And evolution is beautiful because it's a nested tree; it's a beautiful hierarchy where the branches are close together when people are close together, and then you see dispersal events, even the admixture when two populations are exchanging genes. That's a great data set to look at for this kind of a problem. the second data set of course is archeology. Where do we actually have people in time, in space, in a way that we can evaluate their life way, what were they doing what were they eating, how do they deal with seasonal issues, how do they deal with resource scarcity right? You just can't just walk around and find a mammoth you can't walk around and just simply find really good quality tool stone, and so these again form nested frames of hypotheses that we can again test with with independent data and paleoecology is another sort of element. What was the environment like? What sort of constraints did people feel or did they have as this pretty amazing situation developed?
So going back to– I guess the beginning of our story, and here I'll try to identify and highlight where we have broad agreement between all of the fields and then where we might have disagreements, so broadly, the beginning I think there's very little disagreement within the archeology and the and the genetic community, and that is that Native Americans, and we'll call first Americans is a way to sort of distinguish from later Inuit, Yupik; people refer to these you know Paleo Eskimo populations–that's a much later Holocene expansion, so maybe 5,000 years ago we see that group enter in the far north and they pretty much stay in the far north.
When I say First Americans, I mean every other Native American from Canada to the tip of South America, everybody was a single population at one point. They're all related, and they're related specifically to a group that we call East Asians so they're a subset of East Asians that we begin to see the diversions around 36,000 years ago. And this would have taken place somewhere in Asia, somewhere in East Asia.
The earliest individuals we have, like Tanuon (sp) individual like the Amur River thirty three thousand, individual, is around 40 to 30,000 years ago, we actually see where they're at and they appear to be in sort of Northeast China in that basic areas where in Siberia I know and so you see the emergence of a subset a group sort of diverging from the other East Asians and these would be you know Han Chinese would be the descendants of some of the East Asians now and so this group we term the First Americans or FAM. We sometimes use you know just ways to streamline the terminology and this was this individual group and they finally split off and they stopped exchanging genes around 26,000, 25,000 years ago.
So now they're an independent group, they're First Americans, they're definitely in Asia probably in somewhere in you know Amur River Valley, we know there's individuals there. And the next item that we see is an admixture event, and they're admixing with a very unique population, we call these ancient North Eurasians or ANE. It's a population that doesn't exist now as a distinct group. Obviously we have descendants–and this was a group that seemed to have connections with Europe, certainly, connections with Asia, but all of the individuals that we know of now are around Lake Baikal. So this would be southern Siberia in modern Russia. And that also gives us an idea of where probably the First Americans were between around 24,000 and around 20,000 years ago because they're exchanging genes, and not just a little, about 20 to 30 percent of First American genomes are coming from this other group. So you see an admixture of East Asian/ANE and there's a mix, and so these are First Americans, probably in southern Siberia or northern China somewhere there we don't know exactly, but I think every there's a consensus that that's probably where it is. That's the story until about 20,000 years ago then we have something that's been, you know erroneously in my opinion, called the Beringian standstill model, or hypothesis.
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The Beringian Standstill
And you may have heard of this. This is a period where there is a genetic isolation. They're no longer exchanging genes with ANE. They're no longer exchanging genes with East Asians. They're sort of evolving in place if you will. They're together in a place we don't know where this is at. That's one of the big disagreements between 20,000 and around 16 to 15,000 we don't have–we have lots of hypotheses on where First Americans would have been at this point.
My opinion is that they were probably somewhere in south Siberia, maybe in the Trans Baikal area is probably my guess, other people have argued, Ian Buvit and others have argued that they might be in Sakhalin or Hokkaido, so this would be sort of the northern part of Japan and one of the islands that was was connected to the mainland at the Late Glacial Maximum times.
Others have argued that they might be in North Alaska along the Arctic coastal plain. There's no evidence of any people there, archaeologically there's no evidence of this last one that has been a hypothesis that's been put out there recently.
There are people we know archaeologically in Trans Baikal and also Sakhalin, Hokkaido, I mean those are both plausible solutions for where they might have been.
Robert Lundahl
What do the genetics say? What does Eske Willerslev say?
Dr. Ben Potter
So I've published with Eske, and in our models the paper we published in 2018, he would like them to be in Alaska, and that was Scenario E in our in our paper in Nature, Scenario A is what also, in that paper is where I think they were, which is in Asia Northeast Asia, but the the data don't resolve nicely.
I can give you my opinion of why I think in Trans Baikal first. In the last two years we've got a number of individuals that have been genetically analyzed in Asia. One is UKY Uskakaya, which is a little bit south of Lake Baikal, and there's a another one–I forget the name off the top of my head, put me on the spot, there are a number of close relatives of First Americans that are between 16 000 and 14 000 years and they're both in the spot bridging where I suspect the First Americans were. They're nowhere near North Alaska, were nowhere near the coast, so I suspect because the closest relatives are in those locations, that's probably where First Americans were and I can I can get you the name of the other individual, one is 16,900, the other one is like 14,000 years ago. And there's another reason.
So something happened around 20,000 years ago which was really important worldwide and that's the late Glacial Maximum. So this was the a time period where we see very cold conditions, very dry conditions, particularly in the far north. And when we look broadly at Eurasia there seems to be a depopulation in the far north so I mentioned the ancient North Eurasians, there was a small group of them that at least came as far north as the Yana site which is now near the Arctic Ocean in extreme Western Beringia, basically Northern Siberia. And that group of people were there in a warm period you know in the last interglacial. That population seems to have disappeared during the LGM or the Last Glacial Maximum, and we don't see anybody in this region until the expansion northward of probably first American ancestors and that's happening after around fifteen thousand years ago.
They're genetically distinct. They're not the same people. In Europe the same thing when you see LGM conditions hit, people hunker down south– they're moving to sort of the Southern range where there's more animals maybe more ways in which you can sort of sustain your populations. I would not predict that that would be a time period when people would be moving into maybe less hospitable terrain with with fewer animals and and fewer resources, so I think broadly, the data suggests that's not a period when you'd expect expansion, you'd expect contraction and this could explain why we see this genetic isolation because they're they're sheltering in different sorts of locations across Siberia and Northeast Asia, and the people at sense of scale Alaska is a big state we we say we could we could split ourselves in half and Texas would be the third largest state.
Sixteen Alaskas
You could fit 16 Alaska's in the Siberia to give you a sense of just how vast that area is. You could easily have the genetic predisposition and that's the only you know expectation we have is that they're not exchanging genes. That's the only requirement for the bridging standstill location is not set, right?
So anyway that's, the question is where were they then? But I think there is Broad consensus and here I'm going to have to careful with my words–at some time between sixteen thousand and fourteen thousand we see an expansion event of First Americans entering the Americas and a lot of the disagreements are among those, that's oh it's 16, then they might cite sites like Cooper's Ferry or Galt, something like that, and then there are others that well, we think it's closer toaround 14 or maybe 14 5 and they would cite you know that the Clovis record um Paige Ladson and a few of the less equivocal sites in support of that, but you see my framework they're all going to agree sometime between 16 and 14 is when this happened and for again, for you know, 10th graders, you know that's a reasonable at some point in that mix is when this happened now obviously we would love to know more detail and that's sort of what we're hammering out with with archeology and genetics today is to figure that sort of story out, but we do have a lot of pieces that make sense.
There's concerns, so first is that after the isolation period or somewhere during the isolation period you begin to see differentiation so very early structure within First Americans the first group to separate or what we term interim Beringians and they're distinct. They're equally related to all Native Americans north or south and that seems to be probably a later pulse of people that are expanding into the far north we see that at sites that I've worked on like Upper Sun River um they're probably coming in around 12,000 um maybe 13,000 years ago and we see them to persist at least till 6.000. So they're a major group in the far north but they don't seem to have went further south than Beringia. The next group is the rest of First Americans that split into what we call NNA and SNA. NNA North Native American SNA, South Native American–and that is not to say South Americans and North Americans. The way to view that would be the NNA would be peoples that remain in the far north so Na Dine peoples, Salishan, Algonquian folks like that really are in the north now. Of course Navajo, Apache that's a Na Dine group that we know in more recent periods expanded into the Southwest, coming from Canada that's sort of the origin of Na Dine and so that's it.
SNA is everybody else from, you know, the southern parts of Canada all the way to South America so that's that's a much larger group that differentiated more rapidly later. So those are the three main populations that we can glean from the from the genetics.
Shuka Kaa
Of course archaeologically, every example of ancient remains we have genetically, south of the ice sheets they call SNA, right? Until much later we we get some evidence of NNA people the earliest n a we have right now is the Shuka Kaa individual on the northwest coast around 10.000 years old or so, and there's really cool evidence of continuity of that NNA population all the way to the present so that's really exciting it it suggests to me at least that you know that if there was a Coastal Pulse or Coastal Migration, at least in that part of sort of British Columbia, Southeast Alaska it seems like that was really early and people liked what they had and this was, they were well adapted, they began to adapt to sort of salmon fishing, and all sorts of resources in the Northwest coast that make it a unique setting and then when we see other NNA groups like this ancient south Ontario population, it's around I think 4,000 years older, so it seems to be a later group.
I mean a lot of these internal you know hypotheses are still subject to debate and we need more data, but it's just that as the ice is melting you then get an expansion basically Eastward across Canada among these Northern groups the Southern Group SNA that looks like the way that genetics has referred to it is as a Star-Like Radiation a rapid star-like radiation which to an archaeologist this really does imply these are the first people coming into an area very expanding because there's no natural barriers. At that point you're south of the ice sheets and you begin to adapt to the various areas that that you find yourself in, and that seems to be we can map that on, sort of genetically, the dates are between fourteen thousand five hundred or so and about 12,900, somewhere in that which it's pretty good with archeology that sna essentially populates the rest of the Americas pretty rapidly, and then there's lots of complexities after that with multiple subgroups that are moving at different times and later admixing. There's there's an interesting story there but for our purposes in the big picture it seems like that's part of that SNA group, so a lot of relationships.
What About Boats?
Robert Lundahl
What about boats? What do we know about boats?
Dr. Ben Potter
We know very little about boats. The way archaeologists sort of come at this is we look at preservation. So what what do we find preserved, and you know 99% of the time it's durable materials like stone, stone tools, debris from Stone Tool Making, Pottery. When that shows up. Ceramics again, mineral, you know this can retain.
Organics are very difficult to preserve, so things like boats, even like bows and arrow parts, things like that, only very specialized conditions will that preserve, so I think the way we look at this in archeology is, you can't rule that stuff out you can't based on the absence of evidence, because of the technology or the preservation bias that are true, so I personally see no reason that there would not have been boats.
Certainly the thing to remember about this is we're talking about modern humans. You know everybody we're talking about from 36 000 years ago that I started the story with, these are modern humans. They're just like you and I and everybody else on the planet so, you know, the brains, the complexity, the language, all of the stuff. We shouldn't expect that there is anything different than what we see in in the recent past.
I fully expect that there were boating technologies (Series Continues).
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