David Reich - How One Small Tribe Conquered the World 70,000 Years Ago AI transcript and summary - episode of podcast Dwarkesh Podcast
Go to PodExtra AI's episode page (David Reich - How One Small Tribe Conquered the World 70,000 Years Ago) to play and view complete AI-processed content: summary, mindmap, topics, takeaways, transcript, keywords and highlights.
Go to PodExtra AI's podcast page (Dwarkesh Podcast) to view the AI-processed content of all episodes of this podcast.
View full AI transcripts and summaries of all podcast episodes on the blog: Dwarkesh Podcast
Episode: David Reich - How One Small Tribe Conquered the World 70,000 Years Ago
Author: Dwarkesh Patel
Duration: 01:56:06
Episode Shownotes
I had no idea how wild human history was before chatting with the geneticist of ancient DNA David Reich.Human history has been again and again a story of one group figuring ‘something’ out, and then basically wiping everyone else out.From the tribe of 1k-10k modern humans who killed off all
the other human species 70,000 years ago; to the Yamnaya horse nomads 5,000 years ago who killed off 90+% of (then) Europeans and also destroyed the Indus Valley.So much of what we thought we knew about human history is turning out to be wrong, from the ‘Out of Africa’ theory to the evolution of language, and this is all thanks to the research from David Reich’s lab.Buy David Reich’s fascinating book, Who We Are How We Got Here.Watch on YouTube. Listen on Apple Podcasts, Spotify, or any other podcast platform. Read the full transcript here.Follow me on Twitter for updates on future episodes.SponsorThis episode is brought to you by Stripe, financial infrastructure for the internet. Millions of companies from Anthropic to Amazon use Stripe to accept payments, automate financial processes and grow their revenue.If you’re interested in advertising on the podcast, check out this page.Timestamps(00:00:00) – Archaic and modern humans gene flow(00:20:24) – How early modern humans dominated the world(00:39:59) – How bubonic plague rewrote history(00:50:03) – Was agriculture terrible for humans?(00:59:28) – Yamnaya expansion and how populations collide(01:15:39) – “Lost civilizations” and our Neanderthal ancestry(01:31:32) – The DNA Challenge(01:41:38) – David’s career: the genetic vocation Get full access to Dwarkesh Podcast at www.dwarkeshpatel.com/subscribe
Full Transcript
00:00:00 Speaker_00
Today I have the pleasure of speaking with David Reich, who is a geneticist of ancient DNA at Harvard.
00:00:07 Speaker_00
And David's work and his lab's work and his field's work has transformed, like really transformed, our understanding of human history and human evolution. It's very fascinating stuff for many perspectives. In its own light, it's very interesting.
00:00:22 Speaker_00
From the perspective of AI, which I plan on asking you about, it's interesting to understand human evolution and what that implies about what the future of AI might look like. Anyways, I'll stop doing the introduction.
00:00:34 Speaker_00
David, we were just chatting before we started recording about what new information you've been studying since the book came out about archaic humans and the relationship between modern humans and Neanderthals.
00:00:46 Speaker_00
Can you explain again what you're studying these days?
00:00:48 Speaker_01
MG Well, I think what's very interesting is that what we have data from now are modern humans, the sequences of people living today.
00:00:56 Speaker_01
We also have data from Neanderthals, who are archaic humans who lived in Western Eurasia for the last couple of hundred thousand years, and we have now sequences from many Neanderthals. We also have DNA from Denisovans.
00:01:08 Speaker_01
Denisovans are archaic humans who were discovered from the DNA. from a finger bone that was found in a cave in Siberia, not anticipated to be a new group of humans, but were sequenced.
00:01:21 Speaker_01
So we have DNA from these different sources plus bits of DNA from these sources mixed into modern populations. And based on this in the last 10 years or 14 years, we collectively have been piecing together an understanding of how
00:01:36 Speaker_01
modern humans are related to our closest relatives, who are now no longer with us in unmixed form. The Neanderthals, Denisovans, and maybe others who are no longer, not yet sampled. And the model that we have is really a model based on accretion.
00:01:50 Speaker_01
So we start with the modern humans, and then we add the Neanderthals once we obtain that sequence, and we add the Denisovans. And then the model doesn't quite fit, and we add other mixture events to make the model fit.
00:02:03 Speaker_01
At this point, there's a number of these mixture events that seem increasingly implausible.
00:02:07 Speaker_01
They feel to me a little bit like, I don't know if you know the history of models of how the Earth and the Sun relate to each other in ancient Greek times, but there's these epicycles that were attached by
00:02:21 Speaker_01
the Greek Hellenistic astronomer Ptolemy, to make it still possible to describe the movements of the planets and the stars, given that a model where the Sun revolved around the Earth. And we've added all of these epicycles to make things fit.
00:02:38 Speaker_01
And one wonders whether there's some pretty fundamental differences that might explain the patterns that are observed.
00:02:44 Speaker_01
So just to give you an example of this, the standard model is basically this, that modern humans separated from a group that is ancestral to Denisovans and Neanderthals, these two groups for which we have sequences, somewhere between maybe 500 to 750,000 years ago.
00:03:02 Speaker_01
That's what the genetic papers beginning in about 2012 and 2014 said, and that's still used as the explanation for the vast majority of the genealogies, the DNA lineages connecting them.
00:03:15 Speaker_01
So maybe except for 5% of the DNA, that's what we think is going on. Modern humans are one group, and then there's a sister of modern humans, the Denisovan Neanderthal group, and they separated 500 to 750,000 years ago.
00:03:28 Speaker_01
But what's become very, very clear in a really important series of papers since that time is that, in fact, there are exceptions to this.
00:03:37 Speaker_01
And one exception to this is the mitochondrial sequence, what you get from your mother and she gets from her mother and so on going back in time.
00:03:44 Speaker_01
And there the shared ancestor between Neanderthals and modern humans is only maybe three or 400,000 years ago, which is after the split that's very well estimated from the whole genome.
00:03:54 Speaker_01
And what we've also learned is that's also true for the Y chromosome. So that's inherited from your father and his father and so on. And that true, it too is only maybe three or 400,000 years separated between Neanderthals and modern humans.
00:04:07 Speaker_01
And like the mitochondrial DNA, the Denisovans are much more distant maybe. 800,000 years, 700,000 years, a million years.
00:04:16 Speaker_01
So the story told by these two parts of the genome is one that's really, really different from the rest of the genome and incompatible with the main story, two recent sharing.
00:04:24 Speaker_01
And we know in these papers that maybe a few percent, 5%, 3%, 8% of the DNA of Neanderthals comes from a gene flow event, a migration event into the ancestors of Neanderthals from the modern human lineage a few hundred thousand years ago.
00:04:40 Speaker_01
And it's tempting to think that both the Neanderthal mitochondrial DNA and Y chromosome come from that event, but the probability of that happening by chance is only 5% squared, which is a very, very small number.
00:04:52 Speaker_01
And people have evoked epicycles, for example, natural selection for the mitochondrial DNA coming from modern humans.
00:04:59 Speaker_01
natural selection coming from the Y chromosome, coming from modern humans, somehow being more advantageous and pushed up in frequency.
00:05:06 Speaker_01
But that would have to really happen on both these parts of the genome to produce this pattern, and it just seems surprising. So what's been put together is a complicated model and epicycles, ideas like natural selection, to kind of make it work.
00:05:20 Speaker_01
It's not impossible. It may be the case. But one wonders whether profoundly different models might actually explain the data. And so that's something that we and others have been thinking about. Can there be other models?
00:05:33 Speaker_01
An example of another model that might be able to explain the data that we've been playing with is one where there's much more DNA in Neanderthals from modern humans than the three or 5% that's been estimated.
00:05:44 Speaker_01
And we can get such models to fit, but here it's 30% or 50% or 70%. So in that view, Neanderthals and Denisovans are not sisters. In fact, modern humans and Neanderthals are just as qualified to be sisters as Neanderthals and Denisovans.
00:06:00 Speaker_01
And in that case, maybe it's not clear what's modern and what's archaic. Are modern humans archaic? Are modern humans modern? Are Neanderthals archaic? Neanderthals are modern.
00:06:10 Speaker_01
What's also become clear in the last few years in a separate thread of research, not based on ancient DNA, but based on using more and more powerful and sophisticated ways of pattern finding in modern data, is that modern humans are also highly substructured.
00:06:24 Speaker_01
We can see that even without having ancient DNA yet. Of course, once one has ancient DNA, it's so much clearer.
00:06:29 Speaker_01
But it's very clear that you can't explain, for example, modern African DNA without invoking very extreme substructure as deep as the mixtures that contributed and mixed between Neanderthals and modern humans.
00:06:41 Speaker_01
And so that mixture, which of those groups were archaic? Which of them were modern? Were they both archaic? Was one of them modern? Was one of those more closely related to Neanderthals and the possibly higher proportion of ancestry?
00:06:53 Speaker_01
It's not obviously wrong that the model's very, very different from the standard one that we currently have.
00:06:59 Speaker_00
Interesting. So, I mean, from your book, I remember that there are lineages of modern humans that are over 200,000 years separated from other groups, like the San hunter-gatherers from everybody in Eurasia today, or everybody descended from Eurasia.
00:07:18 Speaker_00
So then you're saying that 100,000 years before that is when we have a sister lineage with Neanderthals. Actually, I'm not sure what
00:07:28 Speaker_00
The new findings we're finding about how closely related Neanderthals are to us and how much mitochondrial and Y-chromosome DNA they share. What model do you think is the most plausible to explain why there's so much shared ancestry?
00:07:40 Speaker_01
I'm very agnostic. I really, really don't know.
00:07:43 Speaker_00
But the models you were just talking about, it sounded like you thought they were low probability. Is there one you think is more plausible?
00:07:49 Speaker_01
I think the models that are considered to be standard dogma are now low probability. So there's a standard dogma that's developed over an accretion of papers where the history gets patched.
00:08:02 Speaker_01
someone sequences a genome, someone performs an analysis, someone proves something that wasn't known before, and so we claim a mixture event we didn't know about it before, an event that we didn't know before.
00:08:12 Speaker_01
And that gets patched onto the current model, which is now a series of patches. And nobody has really rethought the whole thing very hard. And the whole thing is not obviously very, very different.
00:08:25 Speaker_01
So you can actually reassemble the whole model in a new way without doing it from the ground up or from the simple model up, but in fact, thinking about it again and seeing if it can be all related in new ways.
00:08:36 Speaker_01
And in fact, it might be actually quite different in the way that I just described.
00:08:41 Speaker_00
Where did the gene flow between, the most recent gene flow between Neanderthals and humans?
00:08:45 Speaker_00
I guess not the most recent, because the most recent was 60,000 or whatever years ago, but like the one you're referring to here, where physically did that happen?
00:08:53 Speaker_01
Even that's not clear, but probably such a thing would have occurred somewhere in the Near East or in Western Eurasia somehow. And it's not even clear where the modern human lineage at that time was residing.
00:09:07 Speaker_01
So probably the modern human lineage was leading to the great majority of the ancestors of people today was in Sub-Saharan Africa for the last 500,000 years at least, and maybe might be much more.
00:09:19 Speaker_01
Certainly our main lineage was in Africa probably 3 million, 5 million, 7 million years ago. But in a period between about 2 million to 500,000 years ago, I think it's not at all clear where the main ancestors leading to modern humans were.
00:09:34 Speaker_01
There were humans throughout many parts of Eurasia and throughout many parts of Africa with a
00:09:40 Speaker_01
a parallel increase in brain size and not obviously closer ancestrality to modern humans in one place than in the other, it's not clear where the main lineages were.
00:09:51 Speaker_01
Maybe they were in both places and mixed to form the lineages that gave rise to people today. So I think there's been an assumption where Africa's been at the center of everything.
00:10:00 Speaker_01
for many, many millions of years, and certainly it's been absolutely central at many periods in human history.
00:10:05 Speaker_01
But in this key period when modern humans develop from Homo habilis and Homo erectus all the way to Homo heidelbergensis and the shared ancestor of Neanderthals, modern humans, and Denisovans, that time period, which is when a lot of important change happens, it's not clear, as I understand it, based on the archaeology and also certainly based on the genetics where that occurred.
00:10:29 Speaker_00
So can I just say for the audience, what is so interesting here that we, I don't know, we're humans and like you would think one of the things history would have figured out is how did humans come to be, right?
00:10:39 Speaker_00
Like that's probably one of the biggest questions you could imagine asking of history, of archaeology, of anthropology, of genetics. And the fact that
00:10:48 Speaker_00
I don't know, this is the thing, at least a conventional model is the thing you're taught like third grade. This is one of the first things you're taught about the world, right?
00:10:55 Speaker_00
And the fact that many parts of it could be wrong, or we're learning in greater detail what those parts look like at the very least. And we're doing that right now because of new technology that's being used by labs like yours.
00:11:06 Speaker_00
I think that's really wild. I'm just thinking like the audience tonight might not be aware of how much of a change this is in our understanding of the human past. And I just sort of really want to emphasize that.
00:11:18 Speaker_00
So if the gene flow event you're talking about a few hundred thousand years ago happened between quote unquote modern humans and Neanderthals happened outside of Africa, then did that lineage go back to Africa and then come back out again?
00:11:33 Speaker_00
How do we think about that?
00:11:34 Speaker_01
Well the simplest version of this is that the main lineage leading to modern humans is in Africa at this point.
00:11:39 Speaker_01
And Africa, as I understand it from talking with the archaeologists and the climatologists, is that Africa and the Near East are continuous ecological spaces at certain periods of time.
00:11:49 Speaker_01
And so there's no difference between what's now the Near East and Africa. fauna and the flora are pumped from Africa into the Near East, or pumped from the Near East into Africa.
00:11:59 Speaker_01
And so the African range goes into that region, and so it's a place of overlap between Eurasian fauna and flora and African flora and fauna. And so that's a very natural place for interactions to occur, especially in periods of climate change.
00:12:16 Speaker_01
Animals, for example, from one region get pumped into the Near East, and then in another period of climate change they get pumped into Eurasia or the rivers.
00:12:24 Speaker_00
Because there's a land bridge during different climactic events?
00:12:26 Speaker_01
I think there's always a land bridge. But the ecology with deserts and so on makes certain areas permeable or impermeable. And so in some periods of time, the Near East gets reclaimed by Eurasia somehow ecologically.
00:12:39 Speaker_01
And in other periods of time, it gets reclaimed by Africa. So it's kind of a place of movement of flora and fauna out and in again and again and again and again.
00:12:49 Speaker_01
So I think the simplest model – I'm not an expert on this – but the simplest model would be one in which an extension of the modern human substructure leading to us, the ones that some of those lineages coalesce to form people living today, the great majority of the ancestors,
00:13:04 Speaker_01
gets into the Near East several hundred thousand years ago, and then mixes there with the ancestors of what we have now sequenced as Neanderthals, and the skeletons that we have now are Neanderthals.
00:13:15 Speaker_01
That gene flow event occurs there, and it's modern humans from Africa, or the part of the African population that extends into the Near East, pushing into Neanderthals at that time.
00:13:25 Speaker_01
We have evidence of modern human incursions since that time into Neanderthal parts of Western Eurasia, also in intermediate periods from the skeletal record, and maybe even claims recently in the DNA data.
00:13:38 Speaker_01
But certainly the genetic data attest to a very strong event a few hundred thousand years ago.
00:13:44 Speaker_00
So, how many humans are around at this time?
00:13:47 Speaker_00
Because to the extent that all modern humans are descendants of this group, there's like, there's, were there just, like, how many different groups of humans are there such that, by groups I don't mean genetically distinct necessarily, but just like separate locations or so forth, such that there was enough gene flow between all of them that there's a shared common descent.
00:14:08 Speaker_01
I don't know. One of the things that is really interesting, we just published a couple of years ago a paper on relatively recent hunter-gatherer populations from mostly eastern and central Africa.
00:14:20 Speaker_01
This included individuals going back up to about 15,000 years ago, which is the oldest DNA from sub-Saharan Africa, which is not very old at some level in order to be able to discern these deep
00:14:33 Speaker_01
population exchanges that really we would like to know in order to understand human evolution, which really we would like to be able to probe two million years ago. We can't.
00:14:41 Speaker_01
But with 15,000-year-old individuals, what you see is many, many groups at many, many places, all with very reduced diversity.
00:14:49 Speaker_01
So in other words, they look like they're living in tiny populations of hundreds of people and not exchanging DNA with each other very often at all over time. And this is again and again, we see this again and again.
00:15:01 Speaker_01
And so if you take such a population, put it into a model and say it's this small, what will happen over time? It will lose its diversity over time and it will become very non-diverse. So over time, Africa will have very little diversity.
00:15:14 Speaker_01
But of course, Africa today has great human diversity in it.
00:15:17 Speaker_01
And so what seems to be happening is that the whole continent of sub-Saharan Africa, and probably Eurasia at this time, is full of hundreds, thousands, tens of thousands of little groups that are communicating hardly at all with each other, are in very small sizes, are losing diversity.
00:15:33 Speaker_01
And when we sample them, this is a group that leaves hardly any descendants at all, maybe none, amongst modern people. And what's actually happening is occasionally these groups merge together and recharge their diversity.
00:15:43 Speaker_01
So the diversity is maintained in the ensemble of rarely mixing groups.
00:15:48 Speaker_01
And you can't really appreciate the diversity by studying any one group, but rather you actually have to think about the whole ensemble of hundreds or thousands, of tens of thousands of them as preserving the diversity.
00:15:59 Speaker_01
So there's some question about the migration rate amongst these groups, which are an archipelago of little groups losing diversity, going extinct at some level.
00:16:08 Speaker_01
But together, there is enough recontact to recharge the diversity and create the incredibly diverse populations you see today, for example, in Southern Africa or Western Africa or Central Africa.
00:16:19 Speaker_00
I want to go back to what you were saying that for hundreds of thousands of years, not just with modern humans, but with even the so-called archaic humans with Neanderthals and other species, that there's been selective pressure for larger brains.
00:16:34 Speaker_00
And this is despite the fact that they're in different parts of the world.
00:16:40 Speaker_00
if you're in Eurasia or if you're in Sub-Saharan Africa, either way, somehow these like, finally we got to a state where the niche we're in rewards marginal increases in intelligence and is willing to bear the cost of that and keep chugging on that variable.
00:17:00 Speaker_00
Do we know why that was the case? What was happening in the world or what was happening with maybe primate brains such that the selective pressure of us turning towards greater intelligence?
00:17:10 Speaker_01
So that's a super interesting question, and I think there's a lot of insight and ideas about this topic. I think it's an area to which genetics right now has contributed almost nothing. I have this book that I wrote
00:17:27 Speaker_01
who we are and how we got here, Ancient DNA and the New Science of the Human Past. It's a bit of a misleading title or a bait-and-switch title.
00:17:35 Speaker_01
The way in which it's a bait-and-switch title is you might read it thinking you're going to learn something about how we became whatever we think is distinctive about us relative to other animals.
00:17:45 Speaker_01
I try very early in the book to say that unfortunately, with the genetic data available up to this point, we don't really have very meaningful insights about what makes us distinct, how we became to be distinct from other animals.
00:18:00 Speaker_01
But what I'm going to tell you about is how we came to be how we are from another perspective through mixture and migration. So it's very surprising how we came to be, how we are through migrations and mixtures.
00:18:13 Speaker_01
A lot of people used to think that we were not mixed, but in fact it's been mixture again and again in the past in many populations we didn't anticipate. But with regard to your question, which is how it is
00:18:24 Speaker_01
that humans evolved into a distinctive niche which includes having a strong reliance on a large brain, putting a large amount of metabolic energy into the brain, brain relative to body size much bigger than it is in the past.
00:18:39 Speaker_01
I have two things that are striking to me about that. One of them is that I think genomics actually has promised to learn about those things and I think we are potentially on the verge of learning a lot about those things.
00:18:52 Speaker_01
I just think we don't have important new qualitative insights about that topic right now. The other is that the large brain was already in place prior to the separation of Neanderthals and modern humans and maybe Denisovans as well.
00:19:05 Speaker_01
So, already the common ancestors of Neanderthals and modern humans probably had a brain as large as ours. It's not obvious that there's parallel evolution in multiple parts of the world.
00:19:14 Speaker_01
It may be that it's a sufficiently interconnected group that it's not a parallel evolution event, but a single process.
00:19:26 Speaker_00
When you say that there's a single interconnected population, are you referring to basically all of not only Eurasia, but also Africa? Possibly.
00:19:35 Speaker_00
So basically the whole world, even hundreds of thousands of years ago, can be thought of as having a gene flow and being one global population.
00:19:43 Speaker_01
I think that's almost certainly true. We don't yet know the frequency of exchange between Africa and Eurasia, but this is two million years. It's a lot of time. Paul Salopek is like walking around the planet in like seven, years or something like this.
00:19:56 Speaker_01
People move incredibly quickly, and Africa and Eurasia are not really separated by barriers that mean anything very important to a species like ours over periods of even dozens or hundreds or thousands of years.
00:20:10 Speaker_01
So the idea that being in Eurasia or Africa is such a profound barrier that you would not expect people to move from one region to the other in periods of tens of thousands of years or hundreds of thousands of years, that's a strange idea.
00:20:23 Speaker_00
That's fascinating. So people, quote unquote, by the way, it's so interesting that like, it's hard to think of the correct terminology of like, when we say people, which kind of people are we talking about?
00:20:35 Speaker_00
But anyways, so the ancestors of modern humans are at least in a position to have gene flow with other archaic humans in the Near East, but they, at least it doesn't seem like they expanded out hundreds of thousands of years ago.
00:20:51 Speaker_00
And if you're right that they had the brain size, or at least, you know, like a lot of the brain size had already been accumulated before this with Neanderthals, then they should have been pretty smart hundreds of thousands of years ago, but they're not expanding out.
00:21:03 Speaker_00
And then something happened 60,000 years ago. And then, uh, This group that's descended from the people in Sub-Saharan Africa just explodes all across the world. So something seems like it changed. What do you reckon it was?
00:21:18 Speaker_01
So this is outside my area of expertise of being very much like a scientist right here, but I'm very sympathetic to the idea that it's hardly genetic. So I think that this is cultural innovation.
00:21:29 Speaker_01
It's very natural to think that this is cultural innovation. And humans sometimes develop a new technique of storing information, sharing information, and so on.
00:21:42 Speaker_01
For example, writing, which allows you to record collective knowledge in a library, or computational knowledge, or large storage devices, and so on and so forth. Language, conceptual language, which allow you to create a cultural body of knowledge.
00:21:58 Speaker_00
You talk in the book about how the FOXP2 gene, which modulates language ability, not only in humans but other animals, obviously all living humans have it. So it's at least 200,000 years old when the human lineage starts to split off.
00:22:14 Speaker_00
Everybody has language, so what do we think it was?
00:22:17 Speaker_01
MG Well, I don't know what the language was. I mean, it's almost certainly the case that Neanderthals were using sounds and communicating in ways that are probably pretty complicated, complex, and amount to some kind of language.
00:22:33 Speaker_01
But some people think that language in its modern form is not that old and might coincide with the later Stone Age, Upper Paleolithic Revolution, 50 to 100,000 years ago, and might be specific to our lineage, and that there might be a qualitative shift in the type of language that's being used.
00:22:47 Speaker_01
There's been one incredibly interesting and weird line of genetic evidence that was so weird that a lot of people I know dropped off the paper.
00:22:58 Speaker_01
They just didn't want to be associated with it because it was so weird, and they just thought it might be wrong. But it's stood up as far as I can tell. It's just so weird. So this is one of the things that surprises that genetics keeps delivering.
00:23:10 Speaker_01
I think that that's probably going to come across in this conversation, which is I am pretty humbled by the type of data that I'm involved in collecting. It's very surprising, this type of data. Again and again, it's not what we expect.
00:23:25 Speaker_01
And so it just makes me think that things are going to be surprising the next time we look at something that's really not looked at before. So the line of evidence I'm talking about is one based on epigenetic modification of genomes.
00:23:40 Speaker_01
So just to explain what that means, the genome is not just a sequence of letters, DNA letters, adenines, thymines, guanines, and cytosine, ACTG.
00:23:50 Speaker_01
It also is decorated in anybody's cells by modifications that tell the genes when to be on and off in what condition. So an example of such a modification is methylation in cytosine-guanine pairs.
00:24:04 Speaker_01
So this turns down a gene and makes it not functional in certain tissues. And this methylation is bestowed by cellular environments and differs in different cells and also in different species to identify which genes are more active or more passive.
00:24:20 Speaker_01
And it's not directly encoded by the ACTGs locally. It's encoded by something else and sometimes even passed on by your parent directly. So it's really very interesting. So this can be read off ancient genomes.
00:24:33 Speaker_01
the methylation pattern survives in Denisovan and Neanderthal genomes, and we can actually learn which genes were turned down and turned up.
00:24:40 Speaker_01
So work by David Gochman and Liron Carmel and colleagues created these maps of where in the Neanderthal genome, where in the Denisovan genome, and where in modern human genomes, genes are turned on and off.
00:24:52 Speaker_01
And there's a lot of technical complexity to this problem, but they identified differentially methylated regions, several thousand sections of the genome that were consistently and very differently turned down or turned up in Neanderthals and modern humans.
00:25:07 Speaker_01
And when they looked at the set of differentially methylated region, roughly a thousand of them, that were systematically different on the modern human lineage and asked what characterized them, was there particular biological activities that was very unusual on the modern human-specific lineage, there was a huge statistical signal that was very, very surprising and very, very unexpected, and it was the vocal tract.
00:25:33 Speaker_01
So it was the laryngeal and pharyngeal tract. And because you can actually learn from little kids with congenital malformations, when you knock out a gene, when a gene gets knocked out by an inborn error of genetic transformation, of genetic
00:25:49 Speaker_01
inheritance. Kids will have, for example, a face that looks different, or a vocal tract that looks different, and so on. You know what the effect of knocking out these genes is.
00:25:59 Speaker_01
We can actually imply directionality to how the modern human-specific changes are.
00:26:05 Speaker_01
And the directionality is to change the shape of the vocal tract, which is soft tissue not preserved in the skeletal record, to be like the way ours is distinctive from chimpanzees.
00:26:15 Speaker_01
So in the shape that we know is very helpful for the articulation of the range of sounds we use that chimpanzees don't have in their laryngeal and pharyngeal tract.
00:26:25 Speaker_01
So even though we don't have surviving hard tissue like skeletons from this part of the body, we now have this methylation signature which suggests that these changes have occurred specifically on our lineage and are absent in both the Neanderthal and Denisovan lineages.
00:26:39 Speaker_01
So if you think this change in the vocal tract is important in language, which seems possibly reasonable, then maybe that's telling you that there's very important changes that have happened in the last half million or few hundred thousand years
00:26:53 Speaker_01
specifically on our lineage that were absent in Neanderthals and Denisovans.
00:26:59 Speaker_00
What's significant is that to the extent that humans have had it for hundreds of thousands of years, it's not clear then why humans weren't able to expand out of Africa.
00:27:11 Speaker_01
We don't know that. We just know that today we have it. So it could have been only a couple of hundred thousand years ago, or a hundred thousand years ago, that these changes happened.
00:27:19 Speaker_00
But then we know all modern humans have them, and different groups of modern humans have split off.
00:27:24 Speaker_01
Separate 200,000 years ago.
00:27:25 Speaker_00
Right. So we know it's at least that old, right?
00:27:27 Speaker_01
Right. Although there is gene flow between all groups of modern humans, at least at low levels, going to 100,000 years. It's just most of the separation between Khoisan and other groups happens 200,000 years ago.
00:27:39 Speaker_00
Let me just motivate for the audience why this is so fascinating. First of all, it's obviously so interesting. What happens is that 70,000 years ago, there are half a dozen different human species all around the world that are pretty different.
00:27:52 Speaker_00
Fast forward to now, there's one. The fact that that happened is kind of wild. It's interesting just from that. Another reason that makes it interesting for me is because I talk to these people who talk about AI.
00:28:06 Speaker_00
what some of them have a very strong perspective that you just make the model bigger and the thing just wants to learn and so you just make it bigger you give it more space and it'll just become intelligent and one of the pieces of evidence they use for this is that something something happened with human brains dot dot dot bigger dot dot dot um dominating the entire earth and so that's the perspective that like you make these ai models bigger dot dot dot you know like something very powerful is going to come on the other end
00:28:32 Speaker_00
To the extent that that story is accurate or inaccurate might actually have interesting implications for AI, which is sort of wild, right?
00:28:40 Speaker_00
Like our anthropology or genetics about the ancient worlds has some Bayesian update on how well we think these AI models will do in the future.
00:28:50 Speaker_01
So one thing that what you're saying makes me think about is that it doesn't map on in a simple way, as an analogy.
00:28:57 Speaker_01
So one of them is that the human brain is maybe only three times larger than that of a chimpanzee, and that's not the kind of increase that computability has had since 40 years ago or something like that, which is many, many orders of magnitude increase.
00:29:15 Speaker_01
Not a factor of three, but many, many orders of magnitude increase. In fact, I'm aware of studies that have, for example, compared raw computability of chimpanzee babies to human babies. In fact, it's similar.
00:29:27 Speaker_01
For example, the ability to solve logic puzzles is pretty similar between chimpanzees and humans. Some people argue that humans are not even more intelligent than chimpanzees.
00:29:35 Speaker_01
at some fundamental ability to compute, and that what makes human distinctive is social learning abilities, and that that's where a lot of our ability has gone.
00:29:43 Speaker_01
Our ability to see other people, to empathize with other people, to copy other people, to incorporate bodies of information that are learned by other people.
00:29:51 Speaker_01
And so, I am not an expert in this topic, but it's a very appealing group of ideas that the adaptations that humans have are ones that allow us to access a rich amount of shared knowledge and not just to rely on figuring out each thing.
00:30:09 Speaker_01
So that's not obviously the same as just add more computability, but maybe it has some similarities.
00:30:17 Speaker_00
Yeah, so I guess I still don't understand is the answer to we just don't know what happened 60,000 years ago, such that before humans and other modern humans and other types of humans were interacting, but no one was in a dominant position, at least in Eurasia.
00:30:32 Speaker_00
And now humans, not only do we dominate, but like, in fact, we drive them to extinction. None of them are around at all. Do we have any idea what would change between that time?
00:30:43 Speaker_01
The model that – this is really outside my expertise – but ideas that have been floated, and I will summarize them possibly badly, are that in every group of human beings of hundreds of people, which is the size of a band or sometimes a thousand of people, they accumulate shared cultural knowledge, shared
00:31:04 Speaker_01
knowledge about tools, knowledge about life strategies, and they build up a shared knowledge more and more and more and more.
00:31:11 Speaker_01
But if you have a limited size group of people that's not interacting with a sufficiently large group of people, either occasionally this group has an information loss, you know, there's a natural disaster, key elders in the group.
00:31:24 Speaker_01
die and knowledge gets lost, and there's not a critical mass of shared knowledge.
00:31:28 Speaker_01
But once it goes above some kind of critical mass, the group can get larger, the amount of shared knowledge becomes greater, and then you have a runaway process where an increasing body of shared knowledge of how to make particular tools, how to innovate, patterns of innovation
00:31:47 Speaker_01
and so on, language, conceptual ideas, run amok. An example that I've heard talked about in this context is what happened with, for example, Indigenous Tasmanians. You probably know this story.
00:32:02 Speaker_01
About 10,000 years ago, the ancestors of people in Tasmania, which is this large island south of Australia, were continuous with the Aboriginal populations of Australia. They had fire, they lost it.
00:32:14 Speaker_01
And they lost fire because it got forgotten somehow, and it's a cold place. And they just forgot it. The cultural knowledge lost it. So what you actually have in the world 50,000 years ago is tens or hundreds
00:32:28 Speaker_01
or thousands or tens of thousands of different human groups, each of them possessing local knowledge, rarely exchanging with each other.
00:32:34 Speaker_01
When we get lucky in ancient DNA and sample them, they're quite isolated from each other, and they have reduced diversity in the last tens of generations. The great majority of them go extinct.
00:32:43 Speaker_01
The great majority of them are wiped out by encounters with natural disasters or other groups of humans or other animals. And so what you have is a vast experiment with an archipelago of these groups.
00:32:55 Speaker_01
what might be happening is that you just have a process of accumulation of cultural knowledge and loss of cultural knowledge.
00:33:02 Speaker_01
But since there's many of these experiments going on, maybe something takes off somewhere and maybe that's what happens 50 to 100,000 years ago in people who all have the capacity to do these things.
00:33:12 Speaker_00
One thing I didn't realize until I read your book is how small the population that expanded out into Eurasia was, and how small even generally human population was 50,000, 100,000 years ago.
00:33:25 Speaker_00
And I remember one of the papers you cited said that there might have been a population bottleneck around this time period. People talk about the Toba eruption. I don't know if that's a cause, but there's many potential causes.
00:33:35 Speaker_00
But anyways, I think I remember somewhere that the ancestors of everybody in Eurasia was initially like 1,000 to 10,000 people. Tell me, how small was the human population that was like the seed of this modern period?
00:33:51 Speaker_01
So the bottleneck occurred, by bottleneck we mean founder event, a relatively small number of people giving rise to a large number of descendants today.
00:34:00 Speaker_01
It occurred well before the mixture with Neanderthals, which is probably somewhere like 50,000 years ago, plus or minus 5,000 years or something like this. So, we don't know where it occurred. Maybe it occurred somewhere in Arabia.
00:34:14 Speaker_01
Maybe it occurred somewhere in the Nile Valley. Maybe it occurred somewhere else. But maybe thousands or even tens of thousands of years before the encounter with Neanderthal that pushed in some Neanderthal DNA into modern humans.
00:34:27 Speaker_01
So one way to see this is, in fact, this was not an unusual thing, that this was not an unusual thing to have a group with low diversity.
00:34:34 Speaker_01
In fact, the great majority of African groups would have had very low diversity, and it's just the one that started expanding into Eurasia also had low diversity, but it was so successful it didn't mix with very many other groups and recharge its diversity by remixing with other groups.
00:34:49 Speaker_01
And maybe it also expanded inside of Africa, so there's lots of reasons to think that the expansion of the early modern human group outside of Africa would have been accompanied by a within-Africa expansion of the same group, and that it would not have been unidirectional.
00:35:06 Speaker_01
So, one way to look at the expansion of modern humans into different parts of Eurasia where we have data, is almost as a kind of forest fire of some kind, where it throws sparks into different parts of Eurasia. and interacts with the local people.
00:35:20 Speaker_01
So for example, if you look at the first modern humans of African and Near Eastern origin who get to, for example, Europe, where we have the best data. We have a number in Western Siberia, where we have the best data so far.
00:35:33 Speaker_01
We have a number of these very early ones from about 45,000 to 40,000 years ago, which are called initial Upper Paleolithic. And a good fraction of them have had Neanderthal ancestors in their last two to four to eight generations.
00:35:45 Speaker_01
So that's a kind of crazy result. So we have only a couple of dozen or a dozen or so of these very early humans, and a very large fraction of them recently mixed with Neanderthals in their ancestry.
00:35:57 Speaker_01
So, a model that might explain the data is that you have sparks coming out of a kind of forest fire in the Middle East or the Near East of humans expanding.
00:36:05 Speaker_01
They come in and they start going to places like Western Siberia or parts of South Asia or parts of Europe.
00:36:11 Speaker_01
They mix with the Neanderthals and they produce these mixed populations, like these initial Upper Paleolithic groups we sample in the record, and they all go extinct. like including the modern human ones.
00:36:20 Speaker_01
There's just extinction after extinction after extinction of the Neanderthal groups, of the Denisovan groups, and of the modern human groups. But the last one standing is one of the modern human groups, and that's what we happen to see.
00:36:31 Speaker_01
So the interbreeding event that we see, the great majority of the ancestors of modern humans, for example, in Eurasia, are not from the initial upper Paleolithic ones, but from a later wave from the core in the Near East after 39,000 years ago that re-people a place that's been
00:36:48 Speaker_01
sort of affected by these sparks coming out of the same region, and those groups too disappear.
00:36:54 Speaker_00
Oh, that's so fascinating. So not only is a group that starts 60,000 years ago and eventually makes its way around, not only does that one not survive, but then the group that starts 39,000 years ago, that one is replaced.
00:37:05 Speaker_00
And then obviously we'll later talk about the Yamnaya and like, you can just keep going. Then the hunter gatherers were replaced 8,500 years ago by the farmers coming from the Near East. And then after that, by the Yamnaya from the steppe.
00:37:19 Speaker_00
Okay, so it is interesting that it just like, group comes there, is replaced by the next group, that group stays there, is replaced by the next group.
00:37:25 Speaker_01
I don't know if that model... I think that that's probably right at some important level. I think it's not a triumphal march of superiority and inferiority with the group that now comes in having a advantages somehow establishing itself permanently.
00:37:41 Speaker_01
I think that what you have is a very complicated situation of many people coming together and natural disasters or encounter with animals or encounter with other human groups resulting in an almost random process of who
00:37:55 Speaker_01
spreads, or who ends up on top, and other groups coming in afterward. And so, it may be that from a big-picture perspective, you end up having African lineages spreading into these different parts of Eurasia. That's certainly what happened.
00:38:09 Speaker_01
But at a local level, I think it would be very difficult to understand what's going on.
00:38:14 Speaker_00
So, yeah, the big picture is interesting in two ways. First, that you're not thinking crudely in terms of the major species or the major subgroups of humanity, like Neanderthals, Denisovans, and modern humans.
00:38:28 Speaker_00
It's like, no, in fact, even among these, there were so many subcategories of, you know, different groups in this archipelago.
00:38:35 Speaker_00
And then, like, if you do a fine-grained analysis, that's even more fascinating than that, and how much contingency and randomness there is in that process.
00:38:43 Speaker_01
I think that's right. There's lots of analogies that you have later. There's European farmers encountering steppe migrations. There's Native Americans encountering Africans and Europeans as they come from the old world.
00:38:55 Speaker_01
There's various other groups encountering other groups. You have people who have cognitively or
00:39:02 Speaker_01
Culturally, all the capacity to thrive in other contexts, but just because of the nature of the interaction that happens, one group declines demographically and one group doesn't. And it's just complicated.
00:39:14 Speaker_01
So I don't think you should conclude necessarily. It's very tempting to think.
00:39:18 Speaker_01
that, at some level, it's innate biological — I'm not trying to be politically correct — that it's innate some better biological hardware that makes it possible for these African lineages to spread into Eurasia.
00:39:31 Speaker_01
I have no good insight into that topic. I don't think there's very good genetic evidence or any other kind of evidence to say that that contributed in a very strong way.
00:39:41 Speaker_01
I think that it's just complicated, and we certainly have many modern examples where people with better or more competitive cultural complexes encountering each other, and the ones that are more organized in a certain way sort of thrive somehow demographically more.
00:39:59 Speaker_00
Yeah, okay, so let's jump forward to then, since you mentioned this, the way in which after agriculture was developed in the Middle East, I don't know, 10,000, 12,000 years ago, and then after that, the
00:40:14 Speaker_00
The way the Native Americans, the population of Native Americans declined was because of disease.
00:40:22 Speaker_00
And one of the hypotheses that you talk about in the book is potentially this happened with respect to people in Europe from the Amnaya with literally the bacteria that causes the bubonic plague, Yersinia pestis.
00:40:39 Speaker_00
The question I'm trying to ask is, going back a bit, so James Scott, who I think just died a couple of weeks ago, in his book, Against the Grain, the whole book is like, you know, agriculture sucked, but we were forced to adopt it because it allowed some humans to organize nation states that are very abusive, but did allow them to get the barbarians and co-opt them because they needed the labor to do this monotonous activity.
00:41:06 Speaker_00
And one of the things he talks about is, well, One thing I didn't realize until I read that book is just how new all the diseases or most of the diseases that afflict humans today are.
00:41:16 Speaker_00
Everything from Colorado typhus to tuberculosis, if you just go down the list, and because of agriculture, because of domestication of animals, and because of the density that created.
00:41:27 Speaker_00
And so the theory he talks about in the book is that potentially the reason the hunter-gatherers, the quote unquote barbarians, couldn't fight back against these early nation states was because they were getting killed off by the diseases.
00:41:40 Speaker_00
And I don't know how much evidence there is for this. Basically, the question I'm trying to ask is the way in which Europeans encountered Native Americans in the New World. Did that just happen again and again throughout history?
00:41:51 Speaker_00
Basically the way, if you go back to Europe 9,000 years ago or 5,000 years ago, is that just what human history has been like? That wasn't a one-off event?
00:42:01 Speaker_01
There's an amazing book by Kyle Harper called, I think it's called The Fate of Rome, and it's an argument about the history as a historian, a Roman historian.
00:42:10 Speaker_01
It's a history of three major plagues in the Roman period, two of which are really not even very well known, and argues that the decline of the Roman Empire is due to just weakening as the result of plagues and other climatic, biological, climatological worsening events.
00:42:28 Speaker_01
There is a lot of reason to think that some of these events have been recurrent throughout history, and that it's not just difference between farmers and hunter-gatherers, but actually a lot of different types of interactions that are occurring.
00:42:44 Speaker_01
So the example that you mentioned is something that's been a big shock from the ancient DNA revolution. So this is now maybe eight years, nine years old.
00:42:53 Speaker_01
So when the first large number of DNA sequences from people who lived five and six and four thousand years ago in the steppe north of the Black and Caspian seas and in Europe were being published about in 2015, this group in Denmark led by S.K.
00:43:09 Speaker_01
Willerslev and Christian Christiansen and colleagues, looked at their DNA and they discovered in their sequence from the 100 or so humans they sequenced, that there was also pathogen DNA.
00:43:18 Speaker_01
And in 5-10% of the random people they sequenced around 4-5,000 years ago, there was Yersinia pestis, which is the agent of the Black Death. But actually, without the
00:43:30 Speaker_01
without the plasmid that contributes to bubonic plague that's required for flea rat transmission. So it must have been, for example, pneumonic plague with aerosolized transmission or something.
00:43:40 Speaker_01
But 5-10% of random deaths means that actually the percent of people who were dying must have been even higher, because they weren't detecting everything that was there.
00:43:50 Speaker_01
A study by another group, Johannes Krauss and colleagues, of people in plague pits in London from the 1300s epidemic, found that when you apply this method to people we know died of Black Death, you only find a quarter of the people, so the rate was even higher.
00:44:06 Speaker_01
If people are bacteremic when they die, if they have bacteria in their teeth, they probably or almost certainly died of that agent.
00:44:13 Speaker_01
So paper just came out a few weeks ago in Scandinavia looking at these tombs from about 5,000 years ago of farmers who were just on the verge of encountering people from the steppe, and a huge fraction of them have black death when they die.
00:44:28 Speaker_01
They're buried in tombs, even higher than 5 or 10 percent. So this whole pedigree with many, many generations, so it's not all at the same time.
00:44:36 Speaker_01
just like the parents, generation to generations, a very large fraction, like well more than 10%, have black death and have Yersinia infection. It looks like this particular agent has been killing
00:44:52 Speaker_01
people for 5,000 years, four or 5,000 years in Western Eurasia, and in fact is killing a scarily large fraction of the population. As a quantitative person, which I am, reading this literature, I think people are embarrassed by the implication.
00:45:07 Speaker_01
The implication is that a third, a quarter, a half of deaths in this entire period are from this.
00:45:13 Speaker_01
It's so unbelievable, so ridiculous, that such a high proportion of people over such a long period of time are dying from this one agent that people don't even say it.
00:45:23 Speaker_01
They just publish one paper after the other, publishing more sequences, and they just don't think about the implications of such a high rate of death.
00:45:32 Speaker_01
It's really hard to imagine that people have bacteria in their blood and they're not dying of these things. It doesn't seem that people are ignoring ... People are selectively picking tombs. These are tombs that are buried properly.
00:45:43 Speaker_01
They're not grave pits. The implication seems to be this one agent that we happen to be able to detect is killing a very large fraction of people in Western Eurasia over this period. What's the implication of that?
00:45:54 Speaker_01
One thing is that it seems to be coming from steppe rodents, probably. Maybe the people on the steppe are somewhat more protected of it than it spreads into farming Europe maybe 5,000 years ago, which is when we start to see it.
00:46:12 Speaker_01
Maybe this results in disorganisation of the population, giving such a high rate of death. Maybe it creates a type of situation that the Europeans encountered when they got to the Americas, where societies were disrupted.
00:46:24 Speaker_01
So in the last few years, we had COVID-19 that killed a half percent of the world population or something like that, and it was so disruptive. So this thing is killing a third of people or half of people randomly.
00:46:36 Speaker_01
randomly killing people with cultural knowledge, randomly ripping into structures.
00:46:44 Speaker_01
I don't know, was it Montezuma died or one of his parents resulting in civil wars in the Inca when the Europeans encountered them, just disrupting the cultures that were there? Maybe this would have created a situation where
00:46:58 Speaker_01
there was disruption in the old ways of life, and maybe combined with other things, or even just by itself, could have created an opportunity for people to move in from elsewhere, even though they were not as densely spread.
00:47:08 Speaker_01
Because the big observation we haven't talked about, and it's something that we as an ancient DNA community have been looking into again and again now
00:47:16 Speaker_01
and keep making progress on, is that about 5,000 to 4,500 years ago in Europe, there's a radical transformation in the ancestry of Europeans. An example of this is what happens in Britain.
00:47:26 Speaker_01
So about 4,500 years ago, the farmers who are there, they arrive there 6,000 years ago, they build Stonehenge. The last big stones of Stonehenge go up 4,500 years ago, and then within 100 years, 90% of them are gone.
00:47:41 Speaker_01
and they're replaced by migrants from the continent bearing majority ancestry from the steppe north of the Black and Caspian Seas. This is one place where we know what happened very well, but we see it all over Europe.
00:47:51 Speaker_01
We see it in Spain, we see it in Portugal, we see it in the Netherlands, we see it in Germany, we see it in Czechia, we see it in Italy, we see it in Switzerland, we see it everywhere.
00:47:59 Speaker_01
This wave of people from the East arrives and it displaces these successful
00:48:06 Speaker_01
impressive, densely packed farmers with new people who have this ancestry from the East who are not as focused on farming, although some of them are, as the people who came before.
00:48:17 Speaker_00
This is so crazy. So just for the audience, if you're keeping tally, this one bacteria, Yersinia pestis, is responsible.
00:48:28 Speaker_00
I mean, we learned in grade school that it's responsible for killing a third of Europeans, more recently causing the Black Death, right?
00:48:34 Speaker_00
And there's even theories that this helped with the Industrial Revolution because it drove wages up in Britain, and because of higher wages, they had to make machines, and dot, dot, dot. Robert Allen, the economist, has a theory about this.
00:48:46 Speaker_00
So potentially caused the Industrial Revolution. That one's more tendent.
00:48:50 Speaker_01
So it ends, I mean, in the medieval one creates a lot of inflation, and the serfs, as I understand it, were sort of on fixed wages. And so they had to be paid more. It basically inflated out their sort of signorial responsibilities.
00:49:03 Speaker_00
Yeah. So that's one of my things. The other is during the Bronze Age, it allows the steppe people basically to replace the existing hunter-gatherer or farmer population in Europe.
00:49:12 Speaker_00
Like literally all of Europe allows a population from the eastern steppes to like, replace the existing people who build the Stonehenge, doing other things in Europe.
00:49:24 Speaker_00
And the Kyle Harper's book talks about this, where the Plague of Justinian, I think the final one that killed off the Empire, was also Yersinia Festus. Definitely.
00:49:33 Speaker_01
That's documented with Kinect.
00:49:35 Speaker_00
So, the fall of the Roman Empire, the entire, like, twice the sort of, or at least once, the replacement of the population in Europe, and it's the second time you know, basically like modernity happen afterwards.
00:49:45 Speaker_00
It's crazy one disease, and potentially the new world as well in terms of, I don't know how many people, what percentage of the deaths in the new world.
00:49:51 Speaker_01
It's estimated to be not the primary pathogen. Okay. But who knows? And in any case, I mean, there's others too, right? So some of the other plagues in the Roman Empire are definitely not Yersinia.
00:50:03 Speaker_00
So that's crazy that not only disease, but this one in particular has had this bigger role in human history. I'm curious if you can talk to
00:50:11 Speaker_00
There's anthropologists and historians who have different theories about what the early history of humanity really looked like. basically like, what kind of gods did they worship? How big were the communities?
00:50:23 Speaker_00
And this informs their political philosophy today, James Scott obviously being the main example here, right?
00:50:31 Speaker_00
Can you, does genetics shed any light on whether, for example, the, in fact, agriculture was terrible for humans and the first nation states were abusive and so forth, or is this stuff that is not available through ancient DNA?
00:50:44 Speaker_01
We have indirect information about some of these things. So one thing that you might hope to learn about is whether our genomes reacted to the innovation of agriculture in a disrupted way.
00:50:58 Speaker_01
So you might think that our genomes would have been in some kind of steady state, sort of natural selection had adapted us to the previous environments we were in. And you might expect that in reaction to a change so economically
00:51:14 Speaker_01
dietarily, cognitively transformative as agriculture, the genome might shift in terms of how it adapts, and so you might actually see that in terms of adaptation on the genome. You might expect to see a quickening of natural selection or a change.
00:51:28 Speaker_01
I don't think we know the answer yet to whether that's occurred, although there are beginning to be hints, and we could learn that from the DNA data.
00:51:35 Speaker_00
Hint in which direction?
00:51:36 Speaker_01
So one question is, there's an increasing view amongst geneticists that natural selection is a process where there's relatively little directional selection to adapt to new environments.
00:51:53 Speaker_01
One piece of evidence connected to this is the finding that there's very few genetic changes that are 100% different in frequency between, say, Europeans and East Asians, or West Africans and Europeans, or West Africans and East Asians.
00:52:05 Speaker_01
If there had been genetic variants that had had modest selective advantages, 1%, half a percent, 2%, that's actually a lot, but year by year that had arisen, and then that's
00:52:17 Speaker_01
in a few hundred generations, they would have risen from very rare to very common, and in fact gone to 100%. There's thousands of generations separating Europeans and East Asians, and West Africans and Europeans, and so on.
00:52:29 Speaker_01
So if that was a common process in evolution, we would expect many genetic changes to be 100% different in frequency between Europeans and East Asians, or West Africans and Europeans. We see almost none.
00:52:40 Speaker_01
So what that suggests, at some level, is that there's not strong adaptation over the last 50,000 years, because if there was, we would have seen genetic variants driving to 100% frequency difference across different groups around the world, which have hardly been connected with each other genetically over the timeframe that we're talking about.
00:52:57 Speaker_01
We don't see those variants, so maybe selection hasn't been important.
00:53:01 Speaker_01
But maybe over a shorter period of time, selection has quickened and variants have started rising in frequency in the last maybe a few hundred generations or something like that, and we might be able to appreciate that.
00:53:12 Speaker_01
So maybe we could see whether there's been a quickening of natural selection over that time period.
00:53:16 Speaker_01
There's a question about, I think the view amongst common trait geneticists is that we've been at a kind of steady state where almost where the natural selection that does occur is just there pushing down slightly bad variants, not
00:53:31 Speaker_01
not adapting to new situations. We're at a kind of stable point. So it's not clear how that works, because over a scale of two million years, we're clearly genetically quite different from our ancestors.
00:53:42 Speaker_01
Our brains are bigger, we do some things differently, our proportions are different. And yet over the last 200,000 years, we are not profoundly different. There's not genetic changes that differ dramatically across populations.
00:53:56 Speaker_01
So it's like a kind of disconnect. It's tempting to think evolution has stopped from one perspective because there's so little fixed differences. But on the other hand,
00:54:08 Speaker_01
Somehow, if you look in the last 10,000 years in West Eurasian DNA, which we're doing now, it looks like a lot of change is happening. So it's a very confusing situation.
00:54:18 Speaker_01
It feels like we don't really understand what's going on, but there's a lot to learn.
00:54:22 Speaker_00
Do you have a sense of what the changes might look like, or is it too early to tell?
00:54:30 Speaker_01
We're working right now on a study which is documenting changes over the last 10,000 years in Europe and Western Eurasia, based on tracing changes in about 8,500 high-quality DNA sequences from people from this period that have been collectively accumulated by us and others.
00:54:49 Speaker_01
We've been working very hard at this, led by Ali Akbari in my group. We think we have many, many hundreds of places where the there's been very strong change in frequency over time, where we're confident of.
00:55:05 Speaker_01
And we think there are many thousands that we can see traces of. That is, the whole genome is seething with these changes in this period.
00:55:13 Speaker_00
And can you give us a sneak peek on, do we know what phenotype any particular ones correspond to?
00:55:19 Speaker_01
So it's very clear. that there is extreme over-representation of change on variants that affect metabolism and immune traits. And so if you look at traits that we know today affect immune disease or metabolic disease, these traits
00:55:47 Speaker_01
are highly overrepresented by a factor of maybe four in the collection of variants that are changing rapidly over time.
00:55:55 Speaker_01
Whereas if you look at traits that are affecting cognition that we know in modern people modulate behavior, they're hardly affected at all.
00:56:03 Speaker_01
That is selection in this last 10,000 years doesn't seem to be focusing on average on cognitive and behavioral traits. It seems to be focusing on immune and cardiometabolic traits. on average, with exceptions.
00:56:17 Speaker_01
But on average, there's an extreme over-representation of cardiometabolic traits.
00:56:21 Speaker_00
The immune thing makes sense, obviously, more diseases. In what direction is the metabolic thing pointing?
00:56:27 Speaker_01
So one example of this is that there's very clear downward selection against body fat. and against predisposition to high body mass index, predisposition to what today manifests itself as type 2 diabetes.
00:56:45 Speaker_01
So that genetic combination in West Eurasia has been pushed down again and again over the last 10,000 years under the pressure of natural selection, without a doubt, in its action on many, many independent genetic variants, all pushing in the same direction and overwhelmingly
00:57:02 Speaker_01
statistically significant way. So one possible interpretation of this, and this is speculative, is that you're shifting from a mode of survival that's more feast and famine to one where food is more regular and it's not as advantageous to store fat.
00:57:18 Speaker_01
And so there's selection against sort of fat storage.
00:57:22 Speaker_00
That really seems to point against the narrative that agriculture was terrible and, you know, if there had to be selection against storing fat, that seems to suggest that in fact, yeah, things must have been pretty good.
00:57:35 Speaker_01
well, on a time scale. I mean, I don't know how you think selection acts, but at some level, it could be terrible on the individual level and good on the population level.
00:57:46 Speaker_01
I'm not doubting the evidence that you're, I think, maybe referring to, which is that there's a lot more sort of skeletally unwell people. associated with the beginning of agriculture than there are in the hunter-gatherer period.
00:58:02 Speaker_01
I think on an individual level, life could have been experienced more harshly. In terms of survival, different animals have strategies of investing less in their young, but having many more young, or investing more in their young and having
00:58:18 Speaker_01
You know, fewer young, and maybe the hunter-gatherer strategy might be the latter, and the farmer strategy might be having more young, and some of them survive longer or something, more of them survive.
00:58:28 Speaker_01
And on average, over a lifetime, there might be a stable enough food that if you don't rely on such adaptations, it might be better.
00:58:37 Speaker_00
Hey everybody, here's a quick message from today's sponsor, Stripe. Stripe is how millions of businesses accept payments, bill customers, and move money.
00:58:45 Speaker_00
That includes some of the world's largest companies, Amazon, BNW, Marriott, and it includes some of the world's smallest, like of course, my podcast. And it is indeed true that I use the same payments method as Amazon.
00:58:58 Speaker_00
The reason so many companies decide to use Stripe is because moving money is surprisingly complex. Every country has its own regulations, its own payment methods, and how people wanna pay in Japan is really different from how they do it in Sweden.
00:59:11 Speaker_00
Stripe solves all of that. They can let customers pay however they want to pay. A credit card in the US, PIX in Brazil, even crypto. That obviously means higher conversion rates, and as a result, more revenue for you.
00:59:23 Speaker_00
Anyways, you can go to stripe.com to learn more. And now, back to David Reich. So one thing I'm very curious about is whether we have any sense of what it looked like when different populations came into contact with each other.
00:59:37 Speaker_00
Because in many of these cases, you're talking about 90, 95% of the population being replaced to the extent that sometimes you refer to them as ghost populations because only in the aftermath with this modern genetic technology can we even tell that there was some other population here.
00:59:53 Speaker_00
We can see the trace of that. And
00:59:56 Speaker_00
You know, for example, if like the Yamnaya, like when they're coming into Europe, I know there's obviously many different cases and many different cases look different in terms of how violent was or what the clashes look like.
01:00:06 Speaker_00
But the fact that, for example, the Yamnaya, if you focus on that one example, replaces, like becomes a dominant group in so many different parts of Europe.
01:00:17 Speaker_00
It's not like Genghis Khan where it's like one empire and there's the great Khan who's like everybody's Everybody's pledging fealty to is this they're not organized in that way, but like they're still organized enough that they can go from
01:00:35 Speaker_00
go from place to place and we are the Amnaya and we're taking over? What did that concretely look like?
01:00:40 Speaker_01
Yeah. So that's super interesting. And I'm going to back up a little bit because in my book I have a section where I describe when we had these findings for the first time and the conversations we had with archaeologists about these findings.
01:00:54 Speaker_01
So ancient DNA has been very disruptive to conventional understanding of the past.
01:00:59 Speaker_01
And what happened when we had these findings of massive disruption of the local population in Germany about 45 to 4,700 years ago, based on arrival of people from the steppes north of the Black and Caspian Sea, was some of our archaeologists, co-authors, really just were very distressed by the implication.
01:01:20 Speaker_01
Because after the Second World War, there had been a reaction where people said this initial idea that people had based on archaeology, where in the beginning of the 20th century, when people would see new types of pots in a certain layer of the excavation, they would argue that this is the arrival of a new people coming through
01:01:41 Speaker_01
invasion or through movement into a region. And it's a very disruptive event, the arrival of the Corded Ware Complex or the arrival of the Bell Beaker Complex or something like this. This is a very disruptive event mediated by invasion or so on.
01:01:55 Speaker_01
And that was used by, for example, the Nazis to argue that these were spreads of Aryans moving across the landscape and being very disruptive and violent, for example. The reaction after the Second World War was to say, we don't know this.
01:02:10 Speaker_01
In fact, when you see the arrival of new types of material culture, pots for example, or tools or ways of organizing life, what you might be seeing is more the spread of culture.
01:02:22 Speaker_01
You might be seeing, for example, something like people copying use of a cell phone or something like this, which can be used by people of very different backgrounds, or a new religion spreading. It's not actually movement of people.
01:02:33 Speaker_01
In fact, how could there be a big movement of people? You're looking at densely settled Europe with well-developed agriculture. How could it be that new people are coming in from outside?
01:02:42 Speaker_01
will unseat these people, disrupt these people, especially after a period of stasis. Especially once when you have farmers who are densely settled, and how could these be pastoralists coming from somewhere else? They're not as dense on the ground.
01:02:58 Speaker_01
In India today, the British were sort of in control, the Mughals were in control for hundreds of years, but made hardly any demographic impact. How could people from outside with less density make much of a demographic impact?
01:03:12 Speaker_01
But then you look at the genetic data and there's a 50%, 70%, 90% population disruption. You take the DNA from people after these events, and almost all their ancestors are from Far Eastern Europe, right across most of Europe.
01:03:25 Speaker_01
And so the DNA proved that that idea was wrong. It was very disruptive. So the question that you had is, what does it look like on the ground?
01:03:33 Speaker_01
And so the DNA results were extremely disruptive to people in archaeology who had made these arguments that change wasn't possible, that large-scale migration, large-scale disruption probably didn't occur in the past. And so it was a real challenge.
01:03:49 Speaker_01
It was a real challenge to our understanding of prehistory. It was sort of a case example, a prime example that's been important for me in showing that we really don't know what the past was like until we actually
01:03:59 Speaker_01
look at it and have hard data telling us what it's like. Our guesses, our models, including many of mine, are likely to be wrong because we can see that. When we have hard data, we're surprised. I'm sorry for that long preamble.
01:04:14 Speaker_01
What's happened in the last few years is there's been something of a reconciliation after the book. Archaeology is trying to reconcile itself with the DNA data, and it's arguing about the subtlety of these interaction events.
01:04:26 Speaker_01
People talk about what's happened in Britain, for example. Well, maybe the arrival of the Beaker phenomenon, which happens about 4,500 years ago, maybe it's not an invasion. Maybe it's a kind of peaceful event. Maybe the previous people
01:04:39 Speaker_01
The reason we're seeing such a disruption is the previous people we know cremated their dead, and the Beaker people buried their dead, so it looks like a much more abrupt change than it did.
01:04:49 Speaker_01
Maybe what happens in Iberia, when there's a 40% arrival of these foreigners from the East, and 60% local people, but the Y chromosomes are completely replaced, so the local men don't contribute their DNA to local later populations, it looks somehow like that must be extremely disruptive to the local male population.
01:05:09 Speaker_01
But people are saying, well, maybe this is female mate choice. Maybe this is a somehow kind of not what you think it is.
01:05:15 Speaker_01
Maybe it's not what happened 4,000 years later amongst the descendants of the Iberians in the Americas, where today in Colombia, 95% of the Y chromosomes are European. 95% of the mitochondrial DNAs are Native American. We know what happened there.
01:05:28 Speaker_01
It wasn't friendly. It wasn't peaceful. It wasn't nice. But maybe what happened in Iberia 4,000 years ago amongst these ancestors of people was much more peaceful, was much more calm.
01:05:39 Speaker_01
If you look at detail in Iberia, what you see is the period of this change is actually over 500 years. But if you look at a micro-scale, now that we have better data, it's immediate each place. So in southern Spain, it's very fast.
01:05:51 Speaker_01
And then in central Spain, it's a little later, but very fast. And so actually, there's these rapid changes occurring in one place or the other. People thought in Britain, maybe this was actually a slow process.
01:06:01 Speaker_01
But we now have data not yet published from the Netherlands, which is clearly the same population of beaker people that's spreading in Britain. And there it's very disruptive, and you actually have the whole series of people before and after.
01:06:12 Speaker_01
You see that earlier Corded Ware people are local, which is actually very unusual for Corded Ware. They're actually local people adopting the religion of the Corded Ware, but mostly local ancestry. And then the Beaker arrival is incredible disruption.
01:06:24 Speaker_01
There's almost no continuity, very little continuity. So probably what's happening with the Beaker individuals is one way or the other, you have some kind of people who expand demographically,
01:06:38 Speaker_01
and displace people somehow, rapidly displace people over a period of well less than a century.
01:06:44 Speaker_00
And do we know whether they were organized? Because more modern versions of this, when Cortes goes over to the New World, he's like serving fealty to the emperor of Spain and so forth, or like, I don't know, the Mongols and Genghis Khan or something.
01:06:58 Speaker_00
In this case, I assume there wasn't enough hierarchical organization that something like that was available, but there was enough organized, I don't know if organized is the right word, but there was enough sort of like,
01:07:08 Speaker_00
persistent invasion that we're going to keep going town to town, settlement to settlement, until we've reached the ends of Europe.
01:07:18 Speaker_00
And so was it just like the Yamnaya were just lots of different independent groups that were doing this at the same time? How organized was this, basically, is what I mean to ask.
01:07:28 Speaker_01
So we don't know, and I think there's debates even about that. I think one example I've heard archaeologists I work with think about is is the Comanche in the U.S. Southwest, where it's another horse-based expanding group.
01:07:44 Speaker_01
They expand super dramatically in parallel to the Spanish expansion and alongside the U.S. expansion before encountering the U.S. sort of militarized United States at some point. And
01:07:57 Speaker_01
It's local, there's local bands of people expanding, they go on campaigns, they expand to certain areas. The Beaker people and the Cordedware people, they're contemporary to ancient Sumer and to a lot of the
01:08:16 Speaker_01
Egyptians that we actually have written history from. It's not so ancient. They weren't writing, but they were contemporaries of these people not so much far to their south. So we really don't know what was going on.
01:08:27 Speaker_01
But if you were part of a community where there is a culture where, say, the
01:08:32 Speaker_01
males, as we think from reconstructions from Indo-European myth, which is probably the class of cultural shared knowledge these people were operating from, because we think these people were the spreaders of Indo-European languages in this part of the world.
01:08:46 Speaker_01
If you think about this as a world where a certain age, males would band together and go on raiding parties and so on, and that would then maybe settle down later in life.
01:08:56 Speaker_01
You can imagine a process where, built into the culture, you have a process of expansion, exploitation.
01:09:01 Speaker_01
One thing that's really interesting that has actually emerged in the last years and was not really strong at the time that I wrote my book was an understanding of the relationship between the Yamnaya and groups like the Corded Ware and the Beakers.
01:09:17 Speaker_01
So the Yamnaya are these groups that thrived between about 5,300 and 4,600 years ago in the steppes north of the Black and Caspian Seas.
01:09:26 Speaker_01
They're probably the first people to domesticate the horse, or that's arguable, and they use the horse and the cart, which was newly invented, and the wheel to exploit the open steppe lands and be able to economically expand much more rapidly.
01:09:41 Speaker_01
They're the world's first extreme mobile pastoralists, but they can't get further than the steppe. So they expand into Europe, they expand into the little island of the steppe that's in the Great Hungarian Plain in the Carpathian Basin, and they stop.
01:09:53 Speaker_01
They can't expand their way of life to
01:09:57 Speaker_01
to the forested parts of Europe, which is most of Europe, and somehow the ancestry of the Yamnaya gets absorbed by the Corded Ware group, and then later the Beaker group, and that takes it further through Europe.
01:10:09 Speaker_01
But the Corded Ware group is quite different from the Yamnaya culturally, and in fact a lot of archaeologists think that they're so different they can't be the same. They have some shared features, but the Corded Ware have many different traditions.
01:10:21 Speaker_01
One possibility is that the Yamnaya expand and they encounter early Kordidwer.
01:10:26 Speaker_01
The Kordidwer learn some of the adaptations of the Yamnaya and then they actually take Yamnaya women, absorb them into Kordidwer, mostly male communities, and create a new community and that group expands.
01:10:39 Speaker_01
So one of the mysteries of the Yamne expansion was everybody had this cognitive bias to think this is very male-driven. People have these Indo-European notions of sort of male-centered mythologies and so on.
01:10:49 Speaker_01
So this must be an extremely male-centered migration, a very male-centered migration. You look at the genetic data and you look at the Y chromosomes, which track male migration,
01:10:59 Speaker_01
the mitochondrial sequences, which are more sensitive to female migration. It looks like the step expansion from the east to west is very both sexes, both males and females expand.
01:11:09 Speaker_01
People have found this confusing and there's been a lot of incredulity about this. People expect to see that it's an even movement of males and females, but it's quite clear that the bias is not so strong.
01:11:21 Speaker_01
And we think the most likely explanation for what's happening now is that it actually is a male-biased process, but it's one that's interrupted. So the Yamnaya expansion is very male-biased. It expands to the edge of the range.
01:11:34 Speaker_01
They encounter the Corded Ware complex people. And then what happens is the Corded Ware complex people interact with the Yamnaya people, And in fact, the Yamnaya people actually lose out in that interaction.
01:11:51 Speaker_01
And in fact, the Corded Ware males absorb and take Yamnaya females. And they actually also take farmer females, because you actually see these sites in early Corded Ware sites in Czechia, where both things are happening.
01:12:04 Speaker_01
Females from farmers and females from Yamnaya are being absorbed into the Corded Ware community, and then they expand further.
01:12:10 Speaker_01
So what you actually have is a two-step process, where you have a male Yamnaya expansion, and then that ancestry from the step is carried further through females being absorbed into the Corded Ware, and then another male-driven expansion under the Corded Ware.
01:12:25 Speaker_01
and so on. That brings both female and male Yamnaya lineages west, but not always with the Yamnaya ancestry being associated with the kind of intuition that you would think it's domination.
01:12:39 Speaker_01
The same sort of parallel thing in another part of the world is what you see in remote Oceania, in the Southwest Pacific.
01:12:46 Speaker_01
So if you look at Vanuatu, which is some of the first islands that people got about 3,000 years ago in the southwest Pacific – so moving to the southern part of the world – if you look at New Guinea and Australia, people are there almost a little bit after 50,000 years ago.
01:13:03 Speaker_01
People are in the Solomon Islands and the Bismarck Archipelago to the east of New Guinea maybe 35,000 to 40,000 years ago, and they stop. And the Pacific has all these fertile places that are good places for people to live.
01:13:16 Speaker_01
It's completely empty of people until 3,000 years ago.
01:13:19 Speaker_01
Suddenly, these people from Taiwan go through the Philippines, they skirt the edge of New Guinea and the Bismarck Archipelago, and they get to Vanuatu and Fiji and Tonga and New Caledonia and Samoa.
01:13:30 Speaker_01
about 3,000 years ago, super rapidly in the guise of something called the Lapita cultural complex. And if you look at the DNA of the people from this, they're almost entirely East Asian in ancestry. They look like early Taiwanese people.
01:13:42 Speaker_01
And today, people in Vanuatu in Fiji and Tonga in New Caledonia have only 10% of this DNA. So something else happened afterward. The first people are almost entirely East Asian via Taiwan and the Philippines.
01:13:54 Speaker_01
And then you look at later DNA from the same part, and 2,500 years ago, 500 years after the initial arrival, there's mass movement in a male-driven way from New Guinea and the Bismarck Archipelago into Vanuatu of Papuans.
01:14:09 Speaker_01
with overwhelmingly Papuan ancestry from New Guinea coming into Vanuatu. And that's the origin of the ancestry that's overwhelmingly there in Vanuatu, New Caledonia today. So there's a two-step process.
01:14:21 Speaker_01
The initial step, which is East Asian ancestry and these people who invented outrigger canoe technology and long-distance sailing. And then the technology becomes adopted by Papuans, who are using this culture for the next few hundred years.
01:14:35 Speaker_01
We can see them trading back and forth between the Bismarck Archipelago and Vanuatu. By the end, this culture is carried out by Papuan ancestry, and males from this group then spread into Caledonia and take local females.
01:14:50 Speaker_01
the ancestry is flipped from the way that people have this cognitive bias that it should be. People think, oh, it should be the East Asian males somehow dominating the local females or something. You see the reverse, and this is what's going on.
01:15:04 Speaker_01
It's very complicated and subtle. When you actually see evidence of males and females behaving differently, it proves that there's socially asymmetric behavior of two groups as they interact with. What it means is confusing.
01:15:20 Speaker_01
It could be female mate choice, it could be violence, it could be genocide, it could be different patterns of male and female dispersal with groups who travel being of one sex or the other.
01:15:33 Speaker_01
And we can look for clues in the genetic data, and certainly in concert with the archaeology, we can maybe figure out more.
01:15:40 Speaker_00
That's really interesting. I guess speaking of this, we're going to a totally different era, but something I'm curious about.
01:15:47 Speaker_00
So going back to archaic humans, and we talked a lot about Neanderthals, but obviously there were two different species of Denisovans, or I don't know if species is the right word, but two different kinds of Denisovans.
01:15:58 Speaker_00
And also I think the hobbits in Asia, right? And then I don't know if there's more, but like we were talking about half a dozen different like distinct groups and only one survives.
01:16:10 Speaker_00
I understand if like a new cultural technology is developed by this Near East early tribe that like then they expand out through Eurasia and I get like that might enable them to be so dominant. What I don't understand is
01:16:28 Speaker_00
How is it that none of the other ones survived? Like not even one tribe of Denisovans or like one group of Neanderthals and one group of Hobbits? Like there was no niche in which they could just like fend off.
01:16:42 Speaker_00
Everywhere, this one tribe of humans, one tribe of African humans just dominated. I don't know if I asked the question enough. Yeah. Like how did none of them survive?
01:16:51 Speaker_01
Yeah. I don't know. I think it may be a numerical issue.
01:16:55 Speaker_01
If you look at the part of the world where we have the best data in the Holocene, the last 10,000 years, there are places of long-term survival of hunter-gatherers for a few thousand more years than elsewhere.
01:17:06 Speaker_01
In the Netherlands, for example, hunter-gatherers survive for several thousand more years than in the surrounding areas, probably because they're exploiting the wetlands. But they're gone soon enough once something happens. Mammoths go extinct mostly
01:17:19 Speaker_01
14,000 years ago, but they survive on Wrangel Island, north of Siberia, until 4,000 years ago. At some point, each of these places is encountered by the spread of modern humans at high densities.
01:17:32 Speaker_01
The other thing is, it's not even clear to me what expansion means. If you want to make strong arguments, you might argue that non-Africans today are Neanderthals, who just have waves and waves of modern humans from Africa mixing with them.
01:17:44 Speaker_01
Who are the ancestors?
01:17:45 Speaker_01
So that might sound like a silly kind of philosophical statement, but genealogically – I don't know if this happened before or after my books, you probably don't know about this – but there was a super interesting series of papers that came out which made it clear – many things became clear – but one of them was that actually the proportion of non-Africans' ancestors who are Neanderthals is not two percent, which is the proportion of their DNA in our genomes today if you're a non-African person.
01:18:14 Speaker_01
It's more like 10 or 20% of your ancestors are Neanderthals. And what actually happened was when Neanderthals and modern humans met and mixed, the Neanderthal DNA was not as biologically fit.
01:18:26 Speaker_01
And the reason was that Neanderthals had lived in small populations for about half a million years, since separating from modern humans, which had lived in larger populations.
01:18:35 Speaker_01
And it accumulated a large number, thousands of slightly bad mutations, such that in the mixed populations there was selection to remove the Neanderthal ancestry. And that would have happened very, very rapidly after the mixture process.
01:18:47 Speaker_01
And there's now overwhelming evidence that that must have happened. And so if you actually look at the ancestors, if you count of your ancestors, if you're of non-African descent,
01:18:57 Speaker_01
how many of them were Neanderthals, say, 70,000 years ago, it's not going to be 2%. It's going to be 10 or 20%, which is a lot.
01:19:06 Speaker_01
Maybe the right way to think about this is that you have a population in the Near East, for example, that is just encountering waves and waves of modern humans mixing.
01:19:14 Speaker_01
There's so many of them that over time it stays Neanderthal, stays local, but it just becomes over time more and more modern human. Eventually it gets taken over from the inside by modern human ancestry.
01:19:26 Speaker_01
This is what happens to Northern European hunter-gatherers. They become farmer over time, but they're intact on the male line. Culturally, they stay on the male line intact. I'm not trying to be politically correct.
01:19:41 Speaker_01
I'm just saying that you can actually have scenarios where this happens. For example, in elephants, if you look in forest elephants, which are the smaller of the two species of elephants in Africa, They're very matrilocal.
01:19:52 Speaker_01
They have these female lines that are very intact over a long period of time.
01:19:57 Speaker_01
If you look at these savannah elephants, which are the bigger elephants in Eastern and Southern Africa, they have savannah elephant DNA overall, but their mitochondrial sequences are forest elephant, which are the smaller West African elephants.
01:20:10 Speaker_01
And the interpretation of this is that you just have waves and waves of dominant male bulls from the savannah coming into populations and eventually just replacing all of the genome in waves and waves of waves of an intact forest population.
01:20:21 Speaker_01
And so all that's left is the mitochondrial sequence, which is passed on the maternal line. This is not even obvious that non-Africans today are modern humans.
01:20:30 Speaker_01
They're just, maybe they're Neanderthals who became modernized by waves and waves of admixture.
01:20:36 Speaker_00
One question you could have, because we were talking earlier about how small the initial population that populated all of Eurasia was, that was like, well, a couple thousand people.
01:20:46 Speaker_00
And one question you can have is like, if, and we were also talking about how random and contingent this whole history of humanity has been.
01:20:55 Speaker_00
And one question you could have is like, was there some chance if a couple of variables were different that modern, like quote unquote civilization,
01:21:04 Speaker_00
basically, greater population density, greater development technology, so forth, would not have happened except for some really, really lucky chances?
01:21:14 Speaker_00
Or was it the case that even if that one tribe didn't do it, some other tribe of humans would have done it?
01:21:18 Speaker_00
And even if some other tribe of humans from Africa hadn't done it, then Neanderthals had enough cognitive sophistication that they would have done it. I know this is a very speculative question, but just how random does primate to civilization field?
01:21:33 Speaker_00
Does it feel like we had to go down the exact right path, or was it like, this is kind of the trend across many different branches of the family that leads to humans?
01:21:42 Speaker_01
I don't know. It's very speculative, but I'm very tempted to think that there's so many of these groups that some of them would eventually have gone down this route. One example of this that's
01:21:55 Speaker_01
that's interesting to think about is the parallel development of agriculture and the Holocene in different parts of the world.
01:21:59 Speaker_01
So you have in the Americas what's almost certainly a completely independent development of agriculture 9,000, 8,000 years ago. From that in Eurasia, you can argue whether the East Asian and
01:22:10 Speaker_01
Near Eastern developments are different, they probably are, but maybe you could argue they knew about each other somehow.
01:22:15 Speaker_01
Or the Papuan one, maybe you could argue they somehow knew about what was going on in other parts of the world, but probably didn't.
01:22:21 Speaker_01
But certainly the Americas one was isolated, and suddenly for the first time you have these independent evolutions of full-blown agriculture at the same time in many places in the world after the Ice Age.
01:22:31 Speaker_01
This makes you think that it's somehow deterministic. That somehow, some kind of setup of characteristics at this time causes this to happen. Why doesn't it happen at the previous period of stable climate, before the last ice age?
01:22:47 Speaker_01
Some people say, well maybe it was actually not as good as the last 10,000 years. But I I find that confusing as a statement.
01:22:56 Speaker_01
It seems that somehow some set of characteristics, it's tempting to think that some sort of cultural or biological, but more likely cultural characteristics are in place and seeded already at the time of the last ice age, such as when the re-emergence happens, this happens in multiple places simultaneously.
01:23:15 Speaker_00
Because it happens so fast, right? It's not like you have to wait for tens of thousands of years after the ice age, and it's like literally 2000 years after the ice age.
01:23:20 Speaker_01
That culture is very old in the Americas.
01:23:22 Speaker_00
Okay, so then the Ice Age, is it 100,000? Or how old is it? Because before that, humans split off 200,000, or at least some branches of the human tree split off 200,000 years ago.
01:23:33 Speaker_00
And Neanderthals split off even before that, but that's before the last Ice Age started, right? So to the extent that your earlier... about, like, a lot of cognitive sophistication was already evident 200,000 years ago, or 300,000 years ago.
01:23:49 Speaker_00
Doesn't that imply that before the Ice Age we should have seen agriculture?
01:23:52 Speaker_01
Yeah, it's tempting to think that. So I'm very confused about this personally. People say that the last 10,000 years are very unique on a scale of millions of years. If that's true, maybe we're in a very special time.
01:24:04 Speaker_01
That is somehow a period of warmth and stability of climate that's unprecedented for two million years. Maybe that's true. But the other way people often say it is that we're in these cyclical periods of a few tens of thousands of years.
01:24:16 Speaker_01
And the Holocene, the last 12,000 years or so, is a period of warm warming. And then there's a period of a couple of tens of thousands of years, which is the last ice age.
01:24:25 Speaker_01
And then there's before that, there's a few tens of thousands of years of warming. And that's when we sample the late Neanderthals from. And then before that, there's another stage of cooling. And then before that, another stage of warming.
01:24:38 Speaker_01
So this is marine isotope stage 1, 3, 5, 7, 9 are the warm periods. We're in 1 now. And marine stage 2, 4, 6, 8, and so on are the ice ages. So the last glacial maximum was marine isotope stage 2.
01:24:54 Speaker_00
If there were quote unquote lost civilizations, maybe not, obviously not as sophisticated as anywhere close to the last thousands of years, but maybe early Sumer or something like that, or like Comanche slash Yamnaya level or something.
01:25:11 Speaker_00
but that happened before the ice age or maybe in a part of the world during the ice age where climactic conditions were better, would we be able to tell based on modern techniques?
01:25:20 Speaker_01
I think we would. Okay.
01:25:21 Speaker_00
And there's just not any evidence of them?
01:25:23 Speaker_01
I think nobody has found, I mean, there's very sophisticated human burials in Europe and Africa and East Asia and different parts of South Asia and Eurasia and so on.
01:25:32 Speaker_01
Australia in the last, you know, in the marine isotope stage three in the last period of warming. Uh, and, uh, you know, burials full of beads, burials full of symbolic behavior.
01:25:45 Speaker_01
Maybe you interpret this as civilization, but extensive settled societies you don't see.
01:25:53 Speaker_00
I think we touched on this when we talked about population size, but one thing I'm sort of confused about when we talk about the lineage is like,
01:26:03 Speaker_00
In one sense, the lineage is very distributed because obviously many different archaic humans contributed to the human gene line. In another sense, it's also like maybe the main one is a couple thousand people.
01:26:15 Speaker_00
I don't know if there's a question there, but I'm not even sure how to think about... Can they just hang out in the size of Montana?
01:26:24 Speaker_01
The entire human lineage is... I think that the lesson from ancient DNA and the genome revolution has been that anyone in the world is the result of recurrent mixture, again and again in the past.
01:26:37 Speaker_01
So you might think that the last 500 years are unusual periods of history with the people of African and European and Native American ancestry coming together in the Americas, and that this is unusual because of transatlantic travel.
01:26:50 Speaker_01
But almost every group in the world is the result of many mixture events as profound as these on many timescales. So South Asians are the result of mixture between groups very different from each other, as different as Europeans and East Asians.
01:27:03 Speaker_01
4,000 to 3,000 to 2,000 years ago coming together and then crystallizing into a relative lack of mixture. Since that time, Europeans are the result of mixture of Yamnaya and farmers and hunter-gatherers.
01:27:14 Speaker_01
People in different Near Eastern groups are the mixture of kind of early Iranians and early Levantine people and Anatolians who are super different from each other.
01:27:21 Speaker_01
There's huge differences amongst East Asians, huge differences amongst Papuans and East Asians, profound differences amongst different Native American groups that come together to form groups that we have data from later, and example after example we look for.
01:27:34 Speaker_01
So if you think about any one lineage today, any one group of people, and you want to trace people's ancestors back in time and think, where do our ancestors scatter in geography at different time points?
01:27:45 Speaker_01
Almost everybody's ancestors are scattered into different geographic distributions that are not all in the same place.
01:27:52 Speaker_01
So the evidence that our lineage was mostly in Africa is based on an idea, I think, an assumption, a kind of inertial idea that our lineage must have always been in Africa because Africa is the center of human history.
01:28:08 Speaker_01
But if you look at the archaeological evidence, it's not incredibly clear. And if you look at the genetic evidence, we have many early branches from Eurasia and only one from Africa.
01:28:18 Speaker_01
and complexity and branching in Eurasia that's sampled in the DNA record.
01:28:22 Speaker_01
DNA from Denisovans, DNA from unknown archaic lineages that contributed to Denisovans, Neanderthals, and all of those are represented in the Eurasian record, not in the African record. Part of that is the fact that ancient DNA is preserved in Eurasia.
01:28:36 Speaker_01
But maybe, actually, there's a period when our lineage resides in Eurasia. It's not obviously wrong. So I think that hypothesis is out there as a possibility.
01:28:46 Speaker_00
One thing I would love to see, I don't know if, I assume this will change over time as more data comes up, but some sort of like chart that is superimposed upon a world map and it evolves over time.
01:28:58 Speaker_00
And then maybe you can like, you can just have sort of blobs representing different population groups. You can start off with the archaic humans and go back like 200,000 years ago, go back even before that.
01:29:08 Speaker_00
Because if this is, this is a global event, it's not just an African event. So you have, for hundreds of thousands of years, you can just see different populations splitting off, merging back together.
01:29:18 Speaker_00
And if somebody could make that sort of animation, I think that would be very useful.
01:29:22 Speaker_01
I think you can. People have tried to make animations like this in some way. But one way to think about it, I think there's a huge danger in being too interested in yourself. This comes across in my book, I think.
01:29:32 Speaker_01
But it's very, very tempting to be interested in your own history and think it's important. It's obviously not important compared to other people's history. However, if you think about one person's history,
01:29:42 Speaker_01
and you think about where their ancestors lived two generations, four generations, eight generations back in the past, those are your great-grandparents. And great-great-grandparents, you may even know where they lived.
01:29:51 Speaker_01
But then you can actually just plot on a map a different number of generations back in the past where your ancestors lived.
01:29:58 Speaker_01
And it's interesting to do within your family, because maybe you're from, you know, I'm from my ancestors going back a few generations or in Europe somewhere, in different parts of Europe, for example.
01:30:08 Speaker_01
So people do this, and when you get a test back from one of these personal ancestry testing companies like 23andMe, they'll say, oh, you are... 20% Irish and 30% Chinese or whatever it is, and so on and so forth.
01:30:21 Speaker_01
And what they're referring to is roll back 20 or 30 generations, where are your ancestors scattered in proportions? But then if you roll back 3,000 generations, there's some in East Africa and some Neanderthals, right?
01:30:33 Speaker_01
So what you can actually do is for any one group of people or any one person, there's different time slices that matter. 30 generations ago, you get the 23 in the output.
01:30:43 Speaker_01
3,000 generations ago, you get the proportion of your ancestors who are Neanderthals or not Neanderthals or Denisovans or something like that, if you're from one of the many populations around the world that live in Denisovans.
01:30:53 Speaker_01
If you are any population, going back further in time, presumably there's something similar happening, where mostly in Africa, but possibly outside of Africa 300,000 years ago, people's ancestors will be coming from different places.
01:31:06 Speaker_01
plausible that people's ancestors are not all in Ethiopia at 200,000 years ago, that in fact some of them are in North Africa, some of them are maybe in West Africa, some of them are in South Africa, some of them are in Eurasia, and that actually appreciable fractions are in each place, and that that braid and that trellis is coming together again and again over time.
01:31:25 Speaker_01
As you move further back, they'll collapse, some will go extinct, some will reappear, some will reemerge. And at any one point, there's never a singularity.
01:31:32 Speaker_00
I don't know if you're familiar with Nat Friedman's Vesuvius Challenge. I don't know if you saw that when it was going around. So the scrolls in the library at Herculaneum, there's a volcano. I forgot.
01:31:45 Speaker_00
It was like, was it basically during the Roman Empire?
01:31:48 Speaker_01
79 AD.
01:31:49 Speaker_00
Okay. And it buried the scrolls in that library. They all became literal ash or at least very burnt. And so Nat Friedman found this professor who had done CT scans of these squirrels, but there was really no way to decipher them.
01:32:08 Speaker_00
We just had the CT scans. But it felt like this is the kind of thing where somebody out there might be able to figure out a technique for how to do it. We know what the end result should look like.
01:32:17 Speaker_00
We just don't know what the intermediate steps look like, but it feels plausible with modern technology.
01:32:22 Speaker_00
And so you offered a million dollar prize and a 22 year old or 21 year old with, you know, a GPU and some coded up, you know, I think a CNN model to decipher these squirrels.
01:32:35 Speaker_00
And anyways, is there something in your field which has this sort of feeling where There's something we need to figure out.
01:32:45 Speaker_00
We don't know the exact right technique, but if you could put it out and just offer a million dollar bounty for it, maybe somebody will come up with a cool new technique to figure it out.
01:32:51 Speaker_01
Yeah, I don't even ... There's like many things in this area, but I'll give you the simple one and then I'll give you ... I probably should give you a single answer. But I think that the basic answer is what we need is DNA from Africa.
01:33:08 Speaker_01
So we need DNA, old DNA from 50,000 years ago, 100,000 years ago, 200,000 years ago from all over Africa, because it's super clear that our lineage is complicated within Africa.
01:33:19 Speaker_01
There's archaic forms in the archeological record and modern human data is extremely substructured with evidence of having come together from many different lineages, which must have been different archaic forms in Africa.
01:33:31 Speaker_01
and contributing to people living today. So having that would crack our understanding of how modern human lineages braided together and relate to the other archaic lineages we have data from. So that's obviously extremely valuable.
01:33:43 Speaker_00
And what does it need to do to get those samples?
01:33:46 Speaker_01
I think we need to A, identify those skeletal remains or the sediments in old caves that are well-preserved, or rock shelters that contain enough DNA to extract. And I think we need extraction techniques that will allow us to get at that material.
01:34:02 Speaker_01
Maybe we even already have them and we just need to wait until that begins to happen.
01:34:06 Speaker_01
But it would be revolutionary because the experience in Eurasia has been when we get DNA from old sites or new sites for which there's been nothing, we find people like we completely didn't expect to see before that break our understanding of the past.
01:34:21 Speaker_01
I think the other area where I am super excited and I think it would be
01:34:27 Speaker_01
a thing to reward and to incentivize would be to try to crack this body of information to try to understand how biological adaptation happened in the last hundreds of thousands of years.
01:34:43 Speaker_01
We simply don't know the answer to your question from a genetic point of view about how modern human
01:34:51 Speaker_01
cognitive and other types of propensities, how they develop, the biological underpinning of the differences that modern humans have from our closest living relatives. We just don't know how they evolved. It's not even clear how biological they were.
01:35:06 Speaker_01
But being able to interpret the genome in terms of how these changes occurred is, we just don't know how. I was at a talk a few years ago that was really shocking to me.
01:35:17 Speaker_01
There was a researcher at Caltech, and she was talking about being able to directly read the brains of macaque monkeys. A monkey would be shown 2,000 photographs
01:35:30 Speaker_01
And her student would be recording from different neurons in its visual cortex and learning the neurons' response to different images.
01:35:39 Speaker_01
And so what they would do is they would decompose the images of faces, human faces, into eigenvectors with the principal component analysis. And then the neurons, specific neurons, were responding to particular eigenvectors.
01:35:51 Speaker_01
And they learned the language of how the photographs and the decomposition of them computationally, mapped on to the neurons, and they actually learned a language for how that's the case.
01:36:03 Speaker_01
And then what they did is they showed a 2001st photograph to the monkey, they recorded from its neurons, and then tried to use the neurons to reassemble a photograph. And it was a perfect reassembly of the photograph.
01:36:14 Speaker_01
They had actually completely learned how the brain, this cat's brain, represents the photograph. going through the brain representation.
01:36:23 Speaker_01
So in that case, they were able to completely figure out the language of appreciation of a photograph through the biological representation of it.
01:36:31 Speaker_01
And if you look at the parallel problem of the genome, how does the genome code for development and how we get to how we are today, how do we have our capacities and so on, to me it sounds like at first principles, if you ask me what's a simpler problem, figuring out how to represent the natural world.
01:36:49 Speaker_01
in our brain or figuring out how to code for development. I think my cognitive bias, if you were presented ab initio this problem, would be to say it's easier to code for development than to represent the outside world in the brain.
01:37:01 Speaker_01
But this group and other groups are figuring out how to do this nearly perfectly with a readout from the brain, and we really can't read a genome and tell you how a person looks, how a person develops.
01:37:12 Speaker_01
We can begin to say what terrible diseases they have, but not even predict that so well. And so that's very depressing that we can't actually read the genome enough to actually see how that occurs.
01:37:21 Speaker_01
And we actually don't even know how evolution happens. Like, for example, does evolution happen by lots of little changes pushing in some direction? Like, for example, if we want to move toward a different positive set point for height or for
01:37:34 Speaker_01
you know, some cognitive capacity or propensity or something, you know, is this by infinitesimal change of polygenicity, many genetic variants pushing in the same direction? That's the mathematician's bias.
01:37:45 Speaker_01
Or is it like the example I told you about before with David Gochman and Liron Carmel with the voice box where everything pushes in the same direction and goes up to 100% and shifts all in the same direction in an incredibly simple and simplistic way?
01:37:57 Speaker_01
If you talk to neuroscientists and molecular biologists, their brain tends toward the latter, And this few examples suggest that maybe that's occurred.
01:38:06 Speaker_01
And so maybe this kind of polygenic paradigm of adaptation, when adaptation really matters, is that really what happens when important adaptation happens? Or is it instead something simple and simplistic and reliant on a small number of genes?
01:38:21 Speaker_01
So what I would really like to know is, can we mine the genetic data we have from modern genomes and archaic genomes. We now have Neanderthals and Denisovans.
01:38:29 Speaker_01
We now have some early modern humans who are far enough back in time that appreciable change may have occurred.
01:38:35 Speaker_01
And can we actually learn the patterns of biological adaptation well enough to actually read the code of how we change and how we adapt to new pressures? And I think that that's something that's not impossible to imagine.
01:38:46 Speaker_01
We can learn how to do, but it takes a different way of thinking.
01:38:50 Speaker_00
One thing that would also be interesting there is one big debate in trying to forecast AI is how big is the information content that describes the human brain?
01:39:00 Speaker_00
Because with AI models, we know, obviously, we can tell very easily, like, here's how difficult it is to, here's how many bits it takes to encode the parameters.
01:39:09 Speaker_00
But if you want to go back to like, how many bits is it to encode the training paradigm itself, there's obviously the training code, then there's a hyper parameters, and here's how many kilobytes that is.
01:39:19 Speaker_00
And the question is, we know that the human genome is three gigabytes, but we know only a small fraction is protein coding. And then also, how do you count the percentage that is responsible for regulation and so forth?
01:39:34 Speaker_00
But if you could only get the part that is responsible for the brain, how big would that be? Can we compare how big that is with respect to how big the trading code for a model is.
01:39:48 Speaker_00
And then it would give interesting insights into how similar those two processes are.
01:39:52 Speaker_01
So what we're beginning to be able to do...
01:39:54 Speaker_01
I don't know how important the particular class of work I'm involved in right now, but we're engaging with this in some way right now because we have incredible data from Europe in the last 10,000 years with huge numbers of samples where we can watch very small changes in frequency over 10,000 years.
01:40:10 Speaker_01
In this period of time, which is not a particularly important time in human evolution, it's well after the important stuff happened. the last 10,000 years. But it's an eventful time.
01:40:19 Speaker_01
The environments became very different, the lifestyles became very different. And so this is a period of time where we've done an experiment of nature. A push has happened against the human genome.
01:40:28 Speaker_01
There's agriculture, there's people living more densely, there's infectious disease happening in a different way, in a different type than before. And how does the genome respond to this traumatic set of conditions?
01:40:38 Speaker_01
And so you can actually watch all these little variables, all these little gene frequencies, tens of millions of them shifting up and down in coordination. And what can you learn from that? Because we now have all the measurements, right?
01:40:50 Speaker_01
We have a selection coefficient measured at 10 million positions across the genome. How do you And we know what the effect of those are on traits today, because they've been measured in large numbers of, on the order of a million people today.
01:41:02 Speaker_01
So what can you do with this data set? How relevant is this to important evolution?
01:41:07 Speaker_01
So I think that that's the type of rich data that could potentially be mined to learn something sort of qualitatively interesting, beyond the storytelling that's characterized molecular biology, beyond the Fox P2, where you say, oh, maybe it's this, maybe this is the Holy Grail, or maybe that, maybe that's the Holy Grail.
01:41:22 Speaker_01
Maybe you learn something about the process that's deep and profound. And so, I think that my million dollars goes to someone who can actually come up with a way of thinking about the process that's really kind of qualitatively profound.
01:41:38 Speaker_00
Interesting. All right. Well, I guess we need to find the million dollars first. But somebody, if you've got a million dollars, and somebody else, if you've got the idea, we can make a market here.
01:41:47 Speaker_00
One of the interesting things, we were talking about the contingency of human history and human evolution, and one of the really interesting things is not only is it contingent, but it seems to be persistent, at least across the last few thousand years, and the way that genetics have changed, culture has changed.
01:42:02 Speaker_00
So when the Indo-Europeans, the Yamnaya, disrupt, whatever, the Indus Valley civilization 4,000 years ago or something like that.
01:42:16 Speaker_00
Not only does that mean that the languages which are spoken in India today, or at least many of them, are descended from this group, but literally the actual core myths of Hinduism are descended from this initial group.
01:42:29 Speaker_00
How is it possible that for 4,000 years, that things like caste, things like basic mythology,
01:42:35 Speaker_00
can be preserved with such high fidelity, especially in an era for half of that you don't have writing, not half of that, for at least a couple thousand or two thousand years, you don't even have writing.
01:42:47 Speaker_00
How is that sort of persistent cultural heritability preserved?
01:42:51 Speaker_01
Well, you're asking me a cultural question, not a genetic one. So what you see in the genetic data from South Asia is an amazing process.
01:43:00 Speaker_01
So today in South Asia, almost everybody is on a gradient of ancestry with two poles, what we call the ancestral North Indians and the ancestral South Indians, with very few exceptions. The exceptions are people with your last name, Patel,
01:43:17 Speaker_01
And as a minor exception, but it's interesting that that's your last name. But also people from Munda speak Austroasiatic languages or are unmixed with them, or people who are Tibeto-Burman speakers.
01:43:29 Speaker_01
But most people are on a mixture between two poles, ancestral North Indians and ancestral South Indians.
01:43:34 Speaker_01
And when you look at genetic data from India, it looks like what you see today in African Americans with people with relatively higher or lower proportions of, say, European and West African ancestry.
01:43:45 Speaker_01
And so it looks like a population in the process of mixture, like African Americans who are the result of mixture in the last 10 or so generations between two, mostly two very different populations mixing in different proportions.
01:44:00 Speaker_01
But what happened in India is it froze. So the mixing started, and then it froze. And the freezing happened 2,000 to 3,000 years ago, and it froze because of cultural change. So what happens in India is you have a three-part change.
01:44:13 Speaker_01
You have an arrival of three source populations, essentially parallel to what you see in Europe. There's a local hunter-gatherer population. There's what's probably a farming population, maybe also a hunter-gatherer population initially.
01:44:25 Speaker_01
And then there are these people descended at some level from steppe pastoralists. These are the three primary ancestral populations. They come together at the end of the decline of the Harappan civilization, which ends about 3,800 years ago.
01:44:39 Speaker_01
And groups from this Harappan group, which we actually have sampled, and they're all on a different gradient, they mix with the steppe groups and with the local hunter-gatherer groups to form and coalesce to these two later groups, which we call the ancestral North Indians and ancestral South Indians.
01:44:54 Speaker_01
And then mixtures of these two mixed populations form in the gangetic plane, form people all along this gradient, and it's really a very simple mixture of two sources.
01:45:04 Speaker_01
And then the cultural change happens, which locks in the caste system, and people freeze and they stop mixing very much.
01:45:10 Speaker_01
And so what you see is instead of people collapsing to a point, which is what you see in Europe after this type of mixing process of these three sources happen in any one region, you see this gradient forming and it's stable. And because of the
01:45:23 Speaker_01
enduringness of the caste system, you actually have a snapshot going back a couple of thousand years and without this continuing change.
01:45:32 Speaker_01
And so it's kind of an amazing system genetically to look at because of people's reluctance to mix with people from very different groups in traditional communities. And so the three steps are
01:45:47 Speaker_01
coming together of very different populations, and then convulsive, profound mixing of groups that had previously not mixed, and then locking into this static system as the caste system sets in, which is documented in the early texts like the Rig Veda.
01:46:04 Speaker_01
And you can actually see the change in that discussion during the course of the Rig Veda.
01:46:07 Speaker_00
I know you warned about being too interested in yourself, but what was it about the Patels? Why are they an exception?
01:46:12 Speaker_01
So the first good genomic data from South Asians is embarrassingly from Houston, Texas. So in the Human Haplotype Map Project, there was a sample from Houston, Texas of Gujaratis and Houston Texans.
01:46:24 Speaker_00
Yeah, a lot of Patels in Houston.
01:46:25 Speaker_01
G-I-H. And if you look at them, people are actually not on this gradient, but they're in a few different places. They're clustered into groups, and there's the main gradient and there's an off-gradient group.
01:46:35 Speaker_01
And I forgot how we figured this out, but someone figured out that these people are all Patels. And Patels have their own distinctive history with different relationships to people in Central Asia.
01:46:45 Speaker_01
And it's probably some additional ancestry from Central Asia pushing them off the main gradient.
01:46:50 Speaker_00
Interesting. We've obviously talked about so many different different types of fields.
01:46:57 Speaker_00
I'm not sure where exactly in what field you started your research, but obviously now your lab is doing stuff in like genetics and you have to touch on how does your research combine with archaeological record?
01:47:10 Speaker_00
What are the inferences you can make from that? Or obviously with different kinds of history, there's so many different disciplines here. And how does one sort of like How do you start your field at a certain, researching a certain topic?
01:47:25 Speaker_00
Do you just keep expanding? Now I'm going to master archaeology. Now I'm going to master anthropology. Now I'm going to, like, how does that process work through your career?
01:47:34 Speaker_01
It's a very unstable life.
01:47:36 Speaker_01
So I think that in some areas, like in archaeology, a lot of my colleagues who I respect tremendously, the career trajectory is you learn to become an archaeologist, you dig, and you have a set of digs that you're doing for dozens and dozens of years with similar or slowly evolving techniques.
01:47:54 Speaker_01
And my work has just changed so radically. When I started doing this work, one could not sequence a whole genome. The genome was not yet sequenced. We had very little genetic variation accessible.
01:48:04 Speaker_01
The amount of data has increased by orders and orders of magnitude every few years. The types of data that we collect, the ability to collect ancient DNA beginning 14 years ago, the ability to generate the volumes of it we have.
01:48:17 Speaker_01
We had no DNA, ancient DNA, in 2009. And then in 2014, we only had a few hundred individuals with genome-scale data. We have tens of thousands of individuals with genome-scale data. We have data from places we didn't have data before.
01:48:31 Speaker_01
So it's such a destabilizing process. And so someone like me wanders into areas that I'm not expert in. I'm not South Asian. I get to be part of trying to learn about history of South Asia.
01:48:45 Speaker_01
I get to interact with archaeologists at the cutting edge of learning about ancient Southwest Pacific or ancient China or ancient Southern Europe.
01:48:58 Speaker_01
It's like an incredible privilege, but also I'm a kind of rank amateur in terms of a lot of the work I do. So one wanders from one area once an amateur into another area once an amateur and tries to learn a lot. Maybe this is a little bit like
01:49:11 Speaker_01
what it's like in Silicon Valley right now, constantly doing new things and bringing some skills to bear that are useful and hopefully trying to be respectful of the people one works with and the knowledge, the tremendous knowledge people have and to learn as much as one can and to work with other people to try to produce some joint research product that makes progress.
01:49:37 Speaker_00
How do people, so like, I don't know, somebody's doing archaeology for their entire career on a certain group in some mountain somewhere and then you come in and you were like, you know, here's a paper, we figured out what the exact genetic combination that explains all your research is.
01:49:55 Speaker_00
Is it like, is there a reaction usually? I don't know how much of this you can say, but basically, are people sometimes disappointed that you've been able to figure out the things in their field with a different technique?
01:50:10 Speaker_01
I think that a lot of people we work with are incredibly excited about being able to do this. Prehistory is a period of time we know so little about. We have such poor clues.
01:50:19 Speaker_01
True archaeologists who are truly dedicated to understanding the past are super thirsty for knowledge about the time periods. And if a new scientific technique
01:50:29 Speaker_01
becomes available that can probe these at times, the true archaeologists who are truly interested in the past get incredibly excited.
01:50:36 Speaker_01
And they embrace it as they've embraced previous scientific techniques, such as scientific archaeology, such as isotopic analysis, such as radiocarbon dating.
01:50:44 Speaker_01
And that's been my experience with people again and again in archaeology, with people who really want to know about the time periods before writing, when at some point one didn't even imagine one could learn anything.
01:50:54 Speaker_01
being excited about this new type of information. I think sometimes people are dug into particular views of the past that are challenged by the new findings that come from scientific research such as ancient DNA.
01:51:08 Speaker_01
And when the DNA is strictly in opposition to some of these models, that becomes an area of tension. And I think I have found myself to be proven wrong in a number of cases, including by my own work or by other work amongst my colleagues.
01:51:24 Speaker_01
And I hope to be someone who can welcome that. One of my idols in this field is the archaeologist Colin Renfrew, who is a British archaeologist who is responsible for the Anatolian theory of
01:51:42 Speaker_01
of Indo-European origins, the idea that farmers spread Indo-European languages, the language spoken in Armenia and in Iran and in Northern India and in much of Europe today, spread with farming after 8,500 years ago from Anatolia in all different directions.
01:51:58 Speaker_01
and that the demographic expansion and economic transformation associated with that spread farming.
01:52:02 Speaker_01
It's very plausible, and there was a debate with Maria Gimbutas and others who argued that these languages spread from the steppe north of the Black and Caspian seas, and one of the main arguments for the Anatolian hypothesis was that steppe expansions could not have been demographically significant because they were much thinner on the ground than farming expansions, and that this is why the steppe could not explain it, even though other linguistic arguments made the steppe seem more plausible.
01:52:28 Speaker_01
And so when the genetic revolution happened with regarding to our understanding of Yamnaya expansions and Indo-European origins in 2015, Colin Renfrew at some point said, I was wrong. I was wrong about this topic.
01:52:40 Speaker_01
In fact, it's the weight of evidence now suggests that in fact, demographic transformation did come from the steppe. It's kind of amazing it did. Maybe it's from disease. Maybe it's from something else. Who knows what it is?
01:52:49 Speaker_01
That's a very interesting topic, but we adapt, we learn. So I think that this is incredibly inspiring to be able to change one's opinion.
01:52:58 Speaker_00
Final question, so you mentioned these different revolutions in our ability to understand the past, like radiocarbon dating to obviously now with ancient DNA and genomic sequencing.
01:53:12 Speaker_00
Is there something that feels like the next thing along the spectrum? Because one would hope in the very future, like a thousand years from now, the future AIs are looking back on human history. And hopefully there's no lost period.
01:53:25 Speaker_00
Hopefully, literally, they know what kind of gods, the tribe in the Near East that basically settled Eurasia worship. They would know everything, right?
01:53:36 Speaker_00
Along that spectrum, we're making progress, but what is the next thing after advances in more genomic sequencing or more samples from different parts of the world?
01:53:45 Speaker_01
I think I don't know. So the discovery of the ability to extract DNA from ancient human remains was such a shock that we could even do this. We just didn't think we could do this.
01:53:59 Speaker_01
There's a section in the introduction of my book which was sort of my impression of what it was like. I had a
01:54:05 Speaker_01
conversation with my PhD supervisor about what it would be like if one somehow could open a cave or a room that was echoing still with languages that don't exist anymore, that are not yet spoken.
01:54:18 Speaker_01
And you could hear the words still echoing somehow after thousands and thousands of years and record that down. That's what ancient DNA is like.
01:54:26 Speaker_01
It's an unexpected gift from the past that this, what we thought was an incredibly delicate biological molecule, in fact is intact. And there must be other such things, just it's hard to imagine what they are.
01:54:41 Speaker_01
In ancient DNA, there is an extraordinary amount still to do. So there is systematic sampling from many, many places in the world where there has not yet been sampling.
01:54:52 Speaker_01
there is systematic sampling and the ability to sample from deep, deep into the past, up to the point where we can begin to decouple these lineages from each other.
01:55:00 Speaker_01
I think that will reveal incredible richness, and I think that that's something that we should all look forward to, the insights that come from that, both in terms of the understanding of individual places, including places like many parts of Africa and South Asia,
01:55:15 Speaker_01
and Australia and New Guinea and so on, where we have essentially no data currently in terms of ancient DNA, but also in terms of deep, deep, deep time and the deep lineages that mix together to form us, where we really have no sampling except for the Denisovans and Neanderthals right now.
01:55:31 Speaker_00
I think that's a great place to close. David, thank you so much for coming on the podcast. I highly, highly recommend your book, Who We Are and How We Got Here. I mean, yeah, just so wild.
01:55:42 Speaker_00
Just basically a lot of the stuff you learned in grade school at least needs a lot more clarification. Some of it is wrong. And the fact that that's the case is crazy.
01:55:49 Speaker_00
And I hope that, I don't know, in five years, 10 years, there's a new edition of the book or a new future book you write that all the questions we talked about today, which we don't have the answers to.
01:56:00 Speaker_00
It seems like there's a bunch of progress happening here, and I'm very eager to see what the future results look like.
01:56:04 Speaker_01
Right, yeah.