This podcast is brought to you by the Albany public library main branch and the generosity of listeners like you. God daddy these people talk as much as you do! Razib Khan’s Unsupervised Learning.
Hey everybody. Welcome to another episode of the Unsupervised Learning podcast. Today, it will just be me talking about the Out of Africa event and what we know about it as of 2023, which is considerably more than 20 years ago. And for those of you who have never gone on Apple podcasts, and given me and us a five star rating, can you do that? Or subscribe and like upvote on YouTube? Whatever you guys do, can you please do it? It's been a little trail off on that recently, because most of the people who do it without being asked obviously, have done so. So if you have never done it, please take a moment, literally 30 seconds max, I think out of your day, to upvote or like, whatever you hear here, so that, you know, we can get a little bit more distribution. So today, I'm going to be talking about the out of Africa event, which many of you know about and have heard about, and have read about I've seen documentaries about. And this is a big deal. It's been going on for, you know, we can say since the 1980s PBS in the United States, I think Horizon and the UK. Did documentaries on it Mitochondrial Eve, you know our African ancestry, Dawkins did those T shirts, we are all Africans. And you know, to a first approximation that did get out something real. What it got out is that everybody outside of Africa is nested within the lineages of Africans in the mitochondrial research that initially came out. And by this, what I mean is, I think there are seven major macro haplogroups. These are lineages of equidistant relatedness. Only one of them, I believe L3 for the mtDNA has any representatives that are substantially non African, that's M and N. But there are like I think 12 Major sub haplogroups in L3. So my point here is only a tiny proportion of the genetic variation in these family trees turn out to be non-African, but that's 85% of people. So that's a little against intuition, if you assume, you know, modern world populations and weightings were representative of the past. Well, how do you how do you solve this problem? The way you solve this problem is just posit that Africa is actually the reservoir of human variation, human diversity, and also likely human origins, which is something Charles Darwin believed in Descent of Man. And this was unpopular at the time, the reason Darwin believed this really had to do with the fact that he just observed that Africa is quite speciose for primates, especially for apes, of the great apes, all of them. You know, you know, orangutan and human are outside of Africa, obviously, and Gibbons are lesser apes. And there's a bunch of Gibbons in Southeast Asia. But you know, you have chimpanzees, you have the pygmies, you have the common chimpanzee, you have the bonobo, and you have different types of gorillas, and obviously, you have humans in Africa. So, you know, just by observing this diversity, Darwin believed that this is where humans are probably from he turned out to be right. And that logic is actually probably correct in some ways. primates, humans, apes do seem to be more tropical, warm adapted. Africa is a big continent has a lot of tropical habitat. And during the ice ages, it was pretty well shielded from the cold, and the inclement weather and I think this matters for humans as well. And I'll get into that, but But Darwin's logic was correct. And mitochondrial DNA, which is passed from mother to daughter, mother to daughter, single lineage that goes back, showed this pattern. And it wasn't just the mitochondrial DNA. There was a school of paleoanthropology, where you look at the skulls and morphometrics and the gracility, just you know how robust these individuals are. morphologically, there was the school of thought have, you know, really, really pushed forward by Chris Stringer, who's been on this podcast before in the UK, who argued that the expansion on the order of 100,000 years ago, and we're gonna get a little bit more refined with the dating shortly. The expansion 100,000 years ago, of new archaeological culture that took over the world that these were African individuals, they look more like people that have been found in Africa earlier. And also in terms of their build their very gracile, they look more tropical initially, it doesn't look to Chris Stringer, you know, in his analysis of the fossil record, and the 70s, doesn't look like modern Europeans do descend from Neandertals. Stringer argues that they descended from African population, I think at the time it was, you know, labeled Homo ergaster. And they show up the descendants of this African H. ergaster that become Homo sapiens in Africa and expand all over the world. That was Stringer’s idea in the 1970s. It turned out mitochondrial DNA in the 1980s supports him, they published a paper in Nature that illustrates the family tree, where non Africans are nested within Africans. After that, in the 1990s, people started looking at Y chromosomes, which is father to son. So this is kind of the inverse of mother to daughter. And this is the Y chromosome lineage. So you have mitochondrial Eve you have Y chromosomal Adam. And guess what, you see a very similar pattern, where more genetic diversity is within Africa than outside of Africa. And non Africans tend to be divided into a couple of distinct branches. Africans have these really deep diverged branches, same pattern you see in mitochondrial DNA. So this is telling you that the direct maternal and paternal lineage both tell kind of a similar story of high African genetic diversity, and people leaving Africa and then the diversity drops through bottlenecks, basically, through sub sampling and population bottlenecks. That's how you need to think of it. Okay. Fossils also say this, according to Chris Stringer, there's another school that kind of disagrees, stylized, you know, call them “multiregionalists” and they have different arguments about what was going on. Probably the most prominent figure here is Milford Wolpoff, I talked to him on my Insight podcast, many, many, well, not many years ago, but you know, on the order of four years ago, so you can listen to that podcast. And multiregionalist basically argued that there was some continuity between local regions and modern humans. So you know, Neanderthals may have, you know, given some ancestry to modern Europeans, even if there was Gene flow between the different groups. There's a philosophical difference here, that's cropping up. And in terms of like speciation and the Origin of Species. Multiregionalists are really operating within the framework of phyletic gradualism. So a species is gradually evolving over a huge range, interconnected genetic networks resulting in gene flow, and it's kind of a process that occurs simultaneously all over the world, okay. With the out of Africa model, it's kind of like a punctuated radiation of a very, very small lineage that replaces all other lineages. So the Out of Africa model, stylized, you know, let's say, like 30 years ago, is basically that, you know, there's a small tribe in East Africa, usually said East Africa, because that's where like, most of the, you know, finds are being, you know, are there and also, I think Omo Kibish, the site Omo Kibish in Ethiopia has the first anatomically modern, like fully anatomically modern human. And so if you look at skulls, you will know what I mean by that. High forehead, vaulted cranium, flat face, small chin, in contrast, you see a Neanderthal that has, you know, the middle of the face kind of is protruding sloping, sloping chin, sloping forehead, very long, long skull, more robust skull, so they look different. Similarly, East Asian hominins, the Dragon Man in China, which I think is probably a Denisovan, you know, you see the brow ridges are really intense, just like Neandertals it's more robust individual. And, you know, both genetics, and actually some epigenomics because that you can get epigenomic signal out of these ancient genomes now show that this was probably developmentally a very robust individual. So you know, there are these course differences, you can automatically see between the skulls and the physical characteristics, right? So you have these two stylized models going into late 1990s. And so let's say about like 20 years ago, or 23 years ago from 2023, where were we? So you know, there are books, papers, you can read everything. I am old enough to remember this period. I did read in this area, I was quite interested in it and So what was going on? What did people think? There were different thoughts within academia, then what was the external presentations within academia, there were still some scholars who thought that the out of Africa was going a little out of control. And you know, there should be some more admixture maybe between the lineages. The big the big critique was, you know, just with like a direct paternal or maternal lineage or with the skulls morphometrics, you didn't have statistical power to reject some level of admixture. So for example, in 1998, they got the first of the sequence, not the whole sequence, but first of the DNA for mitochondrial DNA, and it looked like the Neanderthals, were an outgroup. There were basil to other humans, they were totally different. Well, you know, the argument that of African people would be like this, this aligns with our thesis, it doesn't align with your thesis. But the problem is, you know, there's a random genetic noise within signal. And just by random genetic noise, it actually could have been that the mitochondrial DNA that was once present in humans was lost. But you know, you see it in this Neanderthal individual. So it's not definitive proof that the Neanderthals were distinct, separate out group, this mitochondrial DNA, it offers some probability that it's true, it supports it, it illustrates it. But it actually was not statistically nearly as powerful as people would say. I mean, Magnus Nordberg had a paper on this theory paper that just analyze this, like when the Neanderthal DNA actually came out. And he just pointed out, look, this is one single genetic locus, really one line of evidence, and you don't have enough other evidence to confirm that something, you know, might not have happened just randomly. Well, you know, that was pretty much ignored really by a lot of paleoanthropologists. Like, aside from minority like Wolpoff, his crew. You know, John Hawkes, who I’ll mentioned later, Erik Trinkaus, who thought that there was hybridization between some individuals in the data most most paleoanthropologists assume that the out of Africa without replacement just like total, with replacement, like total replacement was was what was going on. Richard Klein paleoanthropologists at Stanford, pretty prominent guy, he wrote a book called “The Dawn of Human Culture” in 2004. It's like the most extreme scenario, but I think it's representative of something that's out there. So Klein in Dawn of Human Culture basically argued that about 50,000 years ago, modern humans underwent a macro mutation, used Stephen Jay Gould idea, punctuated equilibrium. And then we basically just speciated into something totally different from what had come before. All of a sudden, we have recursive language and culture. And, you know, you could just say, stylized fact, we are genetically superior to what came before. We replaced the Neanderthals, and all the other humans really rapidly, you know, just expanding out of this small group in Africa, right? So Klein's model basically requires a small population where there's a mutation that sweeps and that population just spreads and expands rapidly, everywhere. So basically, humans arose in this model 50,000 years ago, with a particular archaeological tradition that expanded and Klein is a paleoanthropologist, he knows the bones really well. He knows the stones really well. And there's reasons he's saying this. And that's because there's something called the initial Upper Paleolithic, kind of new, more refined flexible blade technology, also the spread of symbolic culture and other things between 40 and 50,000 years ago, to some extent, this is part of what Jared Diamond and others overheard, referred to as the cognitive Great Leap Forward, when human culture really really becomes salient, creative, and starts to rapidly change. It was very protean. Whereas earlier cultures took a long time to change. So for them an Oldowan, you know, Flake blade technology was around for like a million years, something ridiculous. I think the Neanderthals tended to do something called the Mousterian. That was around for like, you know, hundreds of 1000s of years. So human cultures used to evolve very slowly and they started evolve really fast after the Great Leap Forward, cognitive great leap forward. Right. That's the theory. It's a pretty neat theory, I believed in it. I accepted it, you know, around the year 2000. Because, you know, it's neat, it's elegant as carcinomas parsimonious, right. So that just means that it's simple. And in science, you prefer simplicity to complexity. So yeah, you have a mutation, you have a genetic change, and they expand and replace everyone else because they're just biologically and genetically better in some way. And, you know, you look at the mitochondrial DNA. There's some whole genome not really genome because genomics is really a post 2000 thing for humans, but there's like genetic markers, so L L Cavalli-Sforza, who wrote “The History and Geography of Human Genes” I did a little analysis of this, and the genetic markers at these autosomal. So genome, why not just mtDNA y, also kind of show that Africans are more genetically diverse. So multiple lines of evidence are showing Africans are more genetically diverse. Okay, so we're from Africa. And you know, there was a big change 50,000 years ago, well, I mean, probably a genetic change. And maybe Neanderthals couldn't speak. You know, they didn't do much like symbolic culture, or maybe they don't think abstractly, et cetera, et cetera, you get the picture. Okay, this has changed in many, many ways, although a lot of the original facts are actually still correctly, there's nothing wrong with the mitochondrial, why chromosomal autosomal analysis, Africans are the most genetically diverse, etc, etc. Okay. But the interpretation of the facts, were not subtle, they're too extreme. And so now we have more information. And, you know, a lot of it comes from ancient DNA and genomics. So genomics basically means you can analyze the whole genome, you know, at the extreme, like more than 3 billion base pairs, whereas intra DNA means you get genetic material from something that's really old, like let's say, I don't know, more than 2000 years, you know, something like two or 3000, ancient prehistoric DNA, right? So, ancient DNA combined with genomics allows you a lot of power. And so that's what we started really happening in the in the late 2000s. So Neanderthal mitochondrial haplotype haplogroup was assigned with pre genomic techniques, but ancient DNA 98. You know, they got some markers, they fit it to like some model of relatedness. And, you know, they drew their conclusion. Well, in the late 2000s, was started happening as whole genome sequences started showing up, first of the mitochondrial DNA that reaffirms that the Neanderthals aren't out group, and then later the whole genome sequence. And so the whole genome means you can zoom here, a full Neanderthal genome with a full modern human genome and see what's going on. Okay. And I think some of you know what I'm going to say here, the first thing they noticed, which was a shock, is that everybody outside of Africa was clearly more genetically close to their Neanderthal samples than people in Sub Saharan Africa in particular. So what does that mean? It could be that there was population structure in Africa, and Neanderthals are descended from a population that was closer to the ancestors of people within Africa, that gave rise to modern humans outside of Africa, whereas the modern humans within Africa are descended from a less Neanderthal affiliated group, if that makes sense. So basically, the ancient population substructure, it doesn't require admixture. In this scenario, modern humans could still replace Neanderthals. And the ones outside of Africa would be more like Neanderthals, because the ones inside of Africa from whom they come, are more like Neanderthals. Okay, so this is probably not what's going on. What's going on is it does look like some Neanderthals were absorbed into modern humans. One thing that they immediately noticed is almost basically all modern humans that are not sub Saharan African, had about the same Neanderthal ancestry. So modern humans from New South Wales and Australia that are Aboriginal, modern humans from Ireland, modern humans from China, modern humans from the Middle East. This is 2010. There's some refinements that I'm gonna get into. But that was the initial pass. So the implication here is okay, if they're all equally Neanderthal, then probably it was a single admixture event early on. So Neanderthals occupied the whole range from Eastern east central Siberia, the Altai region all the way to Europe. So you can imagine a scenario where, you know, various populations go north and mix with local Neanderthals. But would they actually have the same proportion? Probably not. Okay. Also, like, how do Australians get Neanderthal ancestry? Australians, ancestors, Australian Aboriginals, their ancestors went, you know, in this out of Africa model, they went from the Middle East, to India, to Southeast Asia to Australia. Well, there were no Neanderthals in India. There were no Neanderthals in Southeast Asia, but where there were were there, nyan we Neanderthals? Well, there are Neanderthals in the Middle East. And neonatology pushed as far south as Israel, Monterey, Israel. So and you know, there's a Shanidar cave in northern northern Kurdistan, Iraqi Kurdistan today. We're Neanderthals bury their dead for a while. You can Google it. It's a great site, they might have done ritual burial. Okay. So what that means is probably in the Middle East, there wasn't at least an admixture that explains why there's Neanderthal admixture in China, in Australia, in Southeast Asia in India. as well as your Siberia, Central Asia, parts of the Northern Middle East where Neanderthals existed, right. So, as they get more and more Neanderthal answer genomes, so some of them are from Spain, some of them are from Croatia, some of them are from while a lot of them are from the Altai, from Denisova cave in that area. What they started seeing is Neanderthals are definitely a coherent population, but there's some variation. So the initial estimates of Neanderthal ancestry in modern humans use the Altai Neanderthal, which I think is like 120,000 years ago. It turns out that the contribution was probably from a different population, Middle Eastern Neanderthals that were genetically distinct. The samples from Croatia give a higher proportion of Neanderthal ancestry in modern humans, because it looks like the Middle Eastern Neanderthals were related to Eastern European southeastern European Neanderthals. This is reasonable. We don't have the ancestral Neanderthal population genome sequenced yet, all the Neanderthal genomes are from Europe, or Siberia, but it's probably a Middle Eastern, and probably an Iraqi Neanderthal population, something like that, you know, the uplands in the Middle East had Neanderthals for a long time. So as out of Africa, people moved out, they would encounter Neanderthals, and it looks like they absorbed a Neanderthal population. So right now, Europeans have around like, say, like 2% Neanderthal, East Asians a bit more Middle Eastern, or somewhat less, and I'll go into why that might be. But all of that Neanderthal ancestry that we can detect is from the same modern human pop, or the same Neanderthal population. So what's happening is probably the modern human tribes, plural, as they're going northward, absorb a group of Neanderthals, probably a Neanderthal tribe, not necessarily one individual, say more than more than a single individual. But definitely, it's, it's a small number of people that are absorbed by somewhat larger number of people, but not that much larger. So today, Neanderthals about like, 2%. In the genome, the earliest earliest humans, we have prehistoric modern humans say 40 45,000, they have more Neanderthal ancestry, it's more like three 4%, something like that. There's arguments about how much it might have been initially, but it looks like the Neanderthal absorption was actually considerably higher than 2% in the initially in the initial generations, and it slowly decreased over time. And so why did it slowly decrease over time? There's different arguments. The two main arguments is there was another population that mixed into some of these later populations that didn't have Neanderthal ancestry. And so it diluted that ancestry, and I'll get into that the call Basal Eurasians. And then there's another argument that natural selection slowly reduced the proportion of Neanderthal ancestry. I think both are probably true. Honestly, I don't think it's an either or. So what happens with natural selection is that basically, the gene of an outgroup goes into the population of concern. And if they're two genetically distinct, there's some like incompatibility, like hybrid incompatibilities, right? And it looks when you look at the Neanderthal genes, they tend to be and these are not actually technically genes for the general masses out there, because there's a lot of them are in intergenic regions, or they're introns. But really intergenic regions, is that Neanderthal ancestry in the genomic scale tends to be found in areas that don't code for proteins. That means that there are probably incompatibilities and natural selection. Natural selection reduces the proportion of Neanderthal ancestry within the genome over time, to the point where the fitness implications not that big of a deal. So a lot of the stuff that's left in the genome that's Neanderthal in origin, is what is called is basically what you would call junk. And so it has no fitness implication. We have a bunch of poll Neanderthal genomes from engineering mythos. So you can actually figure out really well like how much of the Neanderthal genome you can reconstruct from modern humans. And it turns out, I think, last I checked, it's about a third. So that means 1/3 of the Neanderthal genome is left in modern humans. Why is that? One reason is quite clearly, to me, natural selection has purified has removed a lot of the Neanderthal ancestry that was initially in those populations. The other aspect is basal Eurasian ancestry. And I'm gonna get into this more later when I talk about the out of Africa population structure. But basically, you have an out of Africa population out of Africa event, this branch population from the African modern humans that have been around for a long time. And some of them clearly mixed with Neanderthals on the way north and east. But does that mean that they all move north and east? Not necessarily. It looks like there was a branch of the out of Africa populations probably more south and west. Perhaps they were in Africa. Or perhaps they were In southern Arabia, or, you know, in the Persian Gulf area where that is now exposed? Well, it could be that those never those modern out of Africa, humans never mixed with Neanderthals. And you know, they're present in the Middle East for a while, probably they split off somewhere 60 to 80,000 years ago, maybe 60 to 70,000 is a better range. But I'll get into the details here. But they split off earlier before the ones that went north and east and mixed with Neanderthals. So who are the ones that went north and east, the ones who went north and east are the dominant group of, of Eurasians. And so that includes pretty much 100% of the ancestry of modern Chinese, Australians, etc, all the East Eurasians, the, you know, ancient, ancestral South Indian ancestry of Indians. They're the ones that went north, the basal Eurasian ancestry seems to have mixed back into the Middle Eastern northern Middle Eastern area, by about 20 to 30,000 years ago, there's a sample from Southern Caucasus 26,000 years ago, that has reduced Neanderthal ancestry looks like it has basal Eurasian ancestry. And so this ancestry mixed into the Middle East, out around that time. And, you know, it wasn't really present in large proportions in the European Pleistocene during the Ice Age before 11,700 years ago, told the arrival of early European farmers who depending on what your model is, are tend to like 40%, basal Eurasian, and then also the steppe herders who have a Middle Eastern component, a Caucasus component that has basal Eurasian ancestry. So the basal Eurasian ancestry in this model, and this is only a model, most people seem to believe it, but there are a minority who don't think it's necessary. Laurent Excoffier in Switzerland, I think he has some models where Basal Eurasians are not necessary. But in any case, setting that aside, the basal Eurasian ancestry spread all over western Eurasia and North Africa, the Middle East, and also because of the incursion of Iranians and then later indo Aryans into South Asia, in the Indian subcontinent. And this reduces the Neanderthal fraction, I think it also further beyond the initial reduction due to admixture. Right? So I think it was initially around like, five to 10%, probably closer to five, but five to 10%. So you know, the ratio is 20, or 10, you know, modern humans, leaving Africa, this out of Africa event mixing with the Neanderthals absorbing them, and they spread all over the world. We know the timing really well. Now, because there are genomes of modern humans from 45,000 years ago, what you can do is look at the length of the segments of Neanderthal ancestry in these genomes. And it looks pretty clear that the admixture event happened between 50 and 55,000 years ago. And that's when the segment's would be very long. And then recombination starts breaking them up, chopping them up to the point where they're just very, very hard to detect segments in modern humans today, 50,000 years later, but 5000 years after the event, it's kind of detectable, and that's what we're seeing. So the older the individual is the modern human that sequenced, the longer the Neanderthal segments are, and the higher proportion of Neanderthal ancestry they often have, probably has a natural selection. Okay. So you have this admixture event, you have another admixture event that was detected by Svante Pääbo lab at Max Plank in about the same time as Neanderthals. It is the Denisovans. So the Denisovans, just you know, are actually related to Neanderthals, they look to be coming out of the same ancestral wave that went out of Africa more than 600,000 years ago. And then they split as one group went east became Denisovans, and one group went north and west and became Neanderthals. So the issue with Denisovans, I have to say, though, is it's quite clear that there's a lot of deep structure within Denisovans and by that I mean Neanderthals are a very homogenous population that went through bottlenecks and reexpanded multiple times. They're very, very similar to each other, physically. And genetically, we don't know about Denisovans physicality because very little has been identified as indubitably Denisovan. You know, there's a skullcap here and there, there's things like that. Some teeth, but genetically, it looks like Denisovans and the North and the South were very distinct hundreds of 1000s of years distinct. I see estimates of like, okay, there could be a Denisovan bifurcation in ancestry like 400,000 years ago. Well, that's deeper than any modern human lineages. So Koi San, you know, San Bushmen in South Africa, or maybe 150 to 300,000 years diverged. Depending on who you trust, I think 150 is actually closer. So Denisovans in some ways, are like much more distinct from each other than any modern human races. And definitely Neanderthals who were very homogenous across their range. So that's it. A unique aspect to think about. Also, there are models that argue that some Denisovan populations had what's called a super archaic admixture, which is maybe like late H. erectus populations, something else going on. So have you absorbed Denisovan and then you get that. The weird thing about the Denisovan admixture is that it's detected in like 5%, like three to 5%, closer to three now, actually, after some updates in people in Papua New Guinea, and also Australian Aborigines, Melanesians. It declines in proportion to how much quote pure Australo-Melanesian you have, right? But, so it's really common in Southeast Asia. But it turns out with better estimates, and analyses, like 1.1 2.2% Denisovan ancestry is present across most of Eurasia. So in China is like close to point 1%. In India, it's closer to point 2%. But in populations that have more ancient ancestral South Indian, which is the Eastern affiliated ancestry of like, Andamanese like people, it's closer to point 2%. But in Pakistan, Pakistan, you know, in the northwest, it's like, less than point one, because that's much more Western Eurasian ancestry and Western Eurasians had no, it seems like Denisovan ancestry that we can see. Also, there was mixing between Denisovans and Neanderthals, we have an f1 girl who died, like 80,000 years ago, who’s dad was a Denisovan mom was Neandertal, Denny, it's pretty cool, you should check it out. There's also the the hobbits Homo floresiensis and H. Naledi in southern Africa. And I'm not gonna be talking much about Africa today, because we'll be talking about the out of Africa event Africa, you know, as those of you who have read my substack know, it's pretty complicated, it’s where most of human evolution happened. But I want to talk about out of Africa, because we kind of know it pretty well, the archaeology is really good in Europe, in Europe, and people have confused the out of Africa with the emergence of Homo sapiens in general. And that's actually false. And I want to kind of highlight it, just so that we know what's going on there so we can understand what's not going on elsewhere, so to speak. But in any case, there's all these other hominids, all these other human lineages, Flores hobbits, there's a small human group in Luzon, probably, there's probably late H. erectus, maybe in Java, it's kind of confused, but could they be Denisovans. Could be something else? And then there's also modern humans? Well, before the out of Africa expansion, but they're modern, the gracile they look, the teeth, you know, whatever, like fragments, you see in some of their technologies, they look more like African humans than they do like, Asian archaic, quote, unquote, archaic is like a dumb term, I mean, use it hominins, like Denisovans, and Neanderthals. So there's stuff like that. There's fines and all over Asia, and I'll get to it. But there's also another thing
that is important to understand about early modern humans before the expansion 50,000 years ago, there's evidence from Neanderthal genomes that are really high quality from Siberia, from the Altai, Western Mongolia, that they're like 3%, related to modern humans, modern human lineage that mixed in 200 to 300,000 years ago. This means they're basically genetically diverged from the African lineages to 200 to 300,000 years ago. So it's probably maybe a little bit later than the than the San Bushmen, maybe. So it's a very, very deep divergence. But it is definitely closer to modern African derived humans and Neanderthals. So Neanderthals themselves were they absorbed, it looks like an early out of Africa migration, okay. And that's, that's reasonable. Because Africa has a lot of humans. during the Ice Age, you probably had most of the humans in the world. So today, Sub Saharan Africa has 15% of humanity. You know, 100 years ago, it was like less than 5%. Like, you know, demographics have really shifted a lot. But for during the, during the Pleistocene, during the ice ages, when humans were foragers, Africa almost surely had like the largest human population. So if it has a really large human population, people leave periodically, there's overflow Malthusian conditions. And so that's what happens. It's what happened with early modern human populations that seem to have left. We have their, you know, artifacts in places like Laos and Sumatra. But we also have their genes and populations like Siberian Neanderthals, and not just the whole genome. So one of the weird things that's like come out recently, is the Y chromosome and mitochondrial DNA of Neanderthals, even though they're outgroups, and basil to modern, all modern humans today. They're probably actually from modern humans. So Denisovans have really, really diverged, wise, and mitochondrial DNA, but they're diverged in a magnitude in In terms of how far back they go in terms of, they're in line with the whole genome, and they're in line with archaeology of what we expect, like it's like 600,000 to a million years. I think it's a little deeper for the mtDNA. And a little shallower for the Y chromosome. But in any case, it's reasonable Neanderthals their y and mtDNA, diverse three to 400,000 years ago, but they diverged 600,000 years ago. Also their y and mtDNA is looks more like modern humans that it looks like Denisovans. But their overall genome is clearly much more like Denisovans. They are descended from what's called Neandersovans, a population that seems to have left Africa, more than 600,000 years ago, probably like descended from some branch of H. ergaster I think so. I don't know, like what's going on here? Well, a parsimonious explanation. Maybe we don't understand something deep, but a parsimonious explanation is the Y and the mtDNA of Neanderthals was replaced by modern humans, which is kind of weird. But that sort of stuff does happen. And it is possible whether through like elite cultural transmission or something like that, I don't know. It could be natural selection of some sort. selection for like human, modern human mtDNA. I don't know. I don't know what's going on here. But that is what we see. And so this indicates that there was a lot of contact between quote African humans and non African humans like Neanderthals or Denisovans. Well before the 50,000 years ago out of Africa event - so it's actually not that incredibly shocking that that happened. And the people left Africa because people have always been leaving Africa. Okay. So I mentioned Neandersovans. They look like to be a population of diversified Neanderthals and Denisovans. There's a site in Spain, Sima de los Huesos, I don't remember the exact term, but it goes to 400,000 years ago, clearly a proto Neanderthal population. They have, by the way, I think Y chromosome and my mtDNA that's more like Denisovans. So that kind of confirms when the replacement happened. Well, these Spanish humans, replaced another group called Homo antecessor. The interesting about Homo antecessor is its face looks more like African modern humans and not like Neanderthals. And that's probably because there are some aspects of modern human faces that are actually what is called ancestral. They're less modern. They're less adapted. There's less specialized, they're more ancient. And so there have been some protein analysis from H. antecessor. And it does look like - so, protein is much more robust than DNA. And so they got some protein antecessor, like was dominant, like from like, 1.2 million years ago to about like, you know, 700,000 like when Neanderthals proto Neanderthals replaced them. Well, antecessor looks like it's an out group to Neanderthals and modern humans. That means that the Neanderthal Neanderthals Neandersovans, clearly replaced older Eurasian human populations, just like they themselves, in turn, were replaced. And so what I'm trying to get across here is okay, we have a family tree model of replacement and expansion. And we think of these layers, but the reality is, it was a recurrent migration lattice. And, you know, populations move from here to here, and then back. So there's reciprocal gene flow like I'm describing. And then there's also the same dynamic that happens over and over again. So before H. antecessor at Dmanisi in Georgia, there's, there's an H. erectus. That's 1.9 million years old was well before H. antecessor. So H. antecessor probably did replace something else. We don't know where H antecessor from, but you know, could have been from Africa as well. So could be multiple out of Africa events that happened. And why is Africa so important as a source, and I think it's simply the large populations, when you have large populations, you have a lot of genetic diversity, you have a lot of possibilities in terms of adaptation and variation, you have a lot of freedom to play with as a evolutionary designer, so to speak. And so you know, Africa's you know, providing all these organisms, all these primates, to Eurasia, periodically, it's just like new kind of like genetic variation fodder, you know, but I want to talk a little bit more about the early modern humans before the the cognitive Great Leap Forward before 50,000 years ago. So, again, keep in mind, if you read my post, which I'll link about Africa, and what was going on, like, you know, modern humans of Africa, they were present at the latest 200,000 years ago, probably earlier. And then there might be a situation where you can't really say that they emerged anywhere. It was like a recurrent phenomenon where all across Africa hominins homo, were evolving, and one branch left, you know, and became the out of Africa people but really is out of this, like long history that goes back a million years. Okay. Okay, so, there's a site in southern Greece called in the Peloponnese called Apidima. It looks like there's a couple of skulls that day to about 200,000 years ago. Recently using computational methods they really analyze the skulls better. One of the skulls the older one is clearly, you know, it's much more like modern humans than Neanderthals. Okay. So it's, it's, it's a little bit more robust than, you know a lot of humans today, but still clearly a modern human. It postades Jebel Irhoud in Morocco, which was modern human more than 300,000 years ago, it's a little older than Omo Kibish in Ethiopia, or Omo Kabish is I think 195,000 years old, 200,000 years old, this like, more than 200,000, maybe 210,000 Okay. Then there's a Neanderthal skull also at Apidima which is dating to like close to 180,000 years ago or something like that? Well, that basically means that modern type humans, African type humans, expanded northward, and then disappeared later to be replaced by Neanderthals. And this happened in many places, okay. I'll go stay in Europe, there's a tooth in southern France from a baby. It's clearly a modern human tooth, and it tasted 54,000 years ago, this might have been an individual that didn't even have like, you know, that Neanderthal ancestry that I'm talking about. It could have been a little earlier, I don't know. But clearly a modern human. Clearly in southern France, it looks like they occupied the cave for about 40 years before there were Neanderthals, after there Neanderthals. Okay, so there's a lot of interaction going on here. 85,000 years ago, there was a cave in Laos, modern humans. This is well, well, before the out of Africa expansion. There was also a cave in Sumatra around the same time sites in China that may day to 100,000 years. The Chinese sites make a lot of sense, because where are the Siberian Neanderthals getting modern human ancestry. I mean, I suspect probably from an Asian source, because it looks like modern humans from Africa, like it warm, and they don't like to go too far north. So they probably go east more than they go north. So go East and Southeast Asia and push north with a little bit and then they run into maybe some Siberian Neanderthals there. Also in Israel 100,000 years ago, really between 120,000 to about 80,000 years ago, there were some proto modern human populations in Israel called the Qafzeh–Skhul population, humans a little bit more robust. The Cave is Qafzeh and Es-Skhul. So that's how they got their name. They were succeeded after 80,000 years ago by Neanderthals in Israel. So what what happened in the Middle East is when it got warm, and so 120 to 80,000 years ago, so 125,000 years ago was that Eemian interglacial, which was actually warmer than the current period. And that interglacial ended, but it's still stayed warmer for a long time. And I started getting really cooler after 80,000 years ago. And then, you know, the coldness really peaked at 20,000 years ago with the Last Glacial Maximum. But setting that aside, the theory is as it got colder, Neanderthals moved South replaced the modern humans that retreated. And so Qafzeh–Skhul is seen as a false dawn. But the point here is, there were anatomically modern humans in Israel, outside of Africa 100,000 years ago, but the out of Africa migration doesn't really happen until 50,000 years ago. And so by this, what I mean is, there's a genetically homogenous population, that seems to have just exploded 50,000 years ago. So it was sociate, with particular archaeological toolkit that replaced earlier archaeological toolkits. And, you know, they're gracile. So they're, like lightly built tend to be like, you know, they look kind of African, they look like they're from a warm climate, they show up in Australia like that, at least as late as 45,000 years ago. So it's really quickly, really, there's some sites, I think, that are like 49,000, something like that. There are some older possible human sites in Australia, if those sites are valid, like the ones from 65,000 years ago, that has to be earlier modern humans, and not the modern humans today. Because genetically, it's quite clear that everybody is, is descended from this wave pretty much today. And I'll go into like little subtlety there. But Europe, basically, modern humans show up around 45,000 years ago, and then really, they clean up by 40,000 years ago. So there's basically a 5000 year period where Neanderthals slowly retreat last Neanderthals a probably go extinct, like by 39,000 years ago or whatnot. They're in Gibraltar, they're in Spain. So that's, that's where they lasted the longest. In any case. So you have a situation where, in Europe, it took a little longer probably because there are humans there, Neanderthals. And some of the samples like Oase, in Romania from 40,000 years ago, actually had recently Neanderthal ancestries that was different than the one that's found today. And so the reason that that's not relevant is Oase seems to have been an evolutionary dead end and have no descendants, but it looks like the Oase individual had like a great grandparent or a great great grandparent. That was, maybe a Neanderthal or something like that. So, which, again, not shocking, you know, there's a lot of interaction going on there in China, again, is like 45,000 years. So by 40,000 You years ago, at the latest, pretty much aside from Siberia where the migration happened a little later, the old world was occupied by modern humans within Africa, we don't have enough archaeology. We don't know when H. naledi totally disappeared in South Africa. But you know, something similar was probably happening in Africa, but not nearly as as extreme. The population bottleneck is not as extreme. They're not as homogenous, they're still structure. There's still different modern human groups interacting with each other, just as they have for hundreds of 1000s of years. Right. So another thing that I need to mention is the genetic data, it makes it really clear that this these IUP initial Upper Paleolithic people, as we'll call them, or out of Africa event proper, because there were earlier out of Africa events, that these people were really isolated for a long time. And who are these people? And how many were there. Usually, I give an estimate one to 10,000 people, that's from an effective population, that means like, in terms of their genetic variation, that's like an ancestral founding group. It's usually it's really closer to 1000. So um, a recent paper that I wrote about, had like about 1000, in the ancestral population of out of Africa. But you know, there, I've seen other papers that have like, two to 3000, but probably on his lower end, which makes sense, because, you know, non-Africans are pretty homogenous, right. So if it's like a black skinned Andamanese Melanesian, you know, some black haired Chinese person, blonde Swede, you know, Native American, all these populations, they're all descended from these, Around 1000 people that expanded, you know, blew up outward. So if it's 1000, Neanderthals are probably like a tribe of maybe 50 to 100 people, you know, something like that. To be clear, these 1000 do include the Basal Eurasians. So the Basal Eurasians, who didn't go north and mixed with the Neanderthals, they're part of the dynamics that I'm talking here. It's called the standstill, there's a recent paper out that looked at Natural Selection patterns. And they present what's called the Arabian standstill model. So that basically means that there was a group from out of Africa. And there's other groups that see this in the data too, by the way, from like, you know, I think Alan Kennan had a paper like this from the late 2000s. Basically, to have this much homogeneity, you have to have a random mating population that's small and isolated for a long time. So when you have a bottleneck, a one generation bottleneck often doesn't do that much, unless it's like, you know, I don't know, your bottleneck is like 10 people something crazy, what really does the job of homogenizing a population as bottlenecked where you know, so it just removes the variation out of all the individuals is having them be in isolated breeding group alone, for a long time. So I don't know where this would have bad. You know, ideally, it's an island. But that doesn't really make any sense to me. So I think the most plausible situation is some sort of refugium in the Sahara, during the period between 80 to 50,000 years ago, or 55,000 years ago, when they went north mixed with the Neanderthals, Sahara Arabia, in these deserts. So this was a really cold period. And during much of the Ice Age, the Sahara, and the Arabian deserts were actually bigger. Sea levels were lower, so there was more land, but a lot of it was was drier. I don’t want to say hotter, obviously, but drier. And so it would be really hard for a lot of humans to make it in these areas. So maybe they found, I don't know, the the mountains of Yemen, I'm just, you know, put that out there. But whatever. They're isolated, they have enough to live on as foragers, but there's no one else around. So the model here is for 30,000 years, according to this paper, the papers role of genetic selection and climatic factors in the dispersal of anatomically modern humans out of Africa, it’s in PNAS so you should be able to find it easily, it's free. So basically, their model is they were in the Arabian Peninsula for 30,000 years before the Neanderthal admixture, which is when the northern movement happened. And this includes Basal Eurasians. So the paper, they're using selection sweeps, and they're looking at the timing of selection sweeps. And what they found is that a lot of selection sweeps, old selection sweeps are shared between people in Melanesia, and people in Ireland. So that's not common environment today, or even like 40,000 years ago, this has to be a common environment, when they were very, very small population packed together, and you see this and stuff like psmc MSMC, like these sorts of, there's a models that you can figure out by looking at patterns of genetic variation and trying to fit them to demographic models. And all of them showed all non African populations go through like this really, really tight period, around 60 to 80,000 years ago of a bottleneck. So that's the period of isolation and a small population. So again, like imagine a population of 1000s, isolated in the mountains of Yemen for 30,000 years. I mean, again, this seems a little ridiculous, but, you know, we don't know So how adventuresome, ancient people were, in any case, so they're isolated, they become very genetically homogenous. One group, probably during climatic warming period moves northward mixes with Neanderthals and then expands outward, right? And what would they have adaptations for - what they found is adaptations for basically, a lot of cold adaptations, fat storage, cilia formation, so your stomach has cilia, you know, I don't know skin physiology, so a lot of pigmentation stuff, and neural development. And the neural development, they probably say is like, Oh, well, you need new bio behavioral adaptations to colder weather. So I looked it up. And it looks like Arabian was probably like, you know, 10 degrees Fahrenheit, at least colder. Probably more on average, during the ice age. And what does that mean? Well, that would mean that I'm just looking at naively, Saudi Arabia in winter would get to freezing all the time. If it was 10 to 10, it was 10 degrees or more colder, because it regularly does get down into the high 30s 40s. But it would get to freezing I'm assuming once you hit freezing, that's a whole different next level of adaptation that was needed, just genetically culturally. And so I think a lot of stuff changed because of you know, this, this cooling that happened after 80,000 years ago. So
I have talked about, you know, the 80,000 years ago, cooling a fair amount now. And so I want to kind of really get into something related to that. And this is the Toba event, the Toba eruption and happened about like 74,000 years ago, this was the main this was like the biggest eruption in 2.6 million years. So it caused the whole quaternary which is like the Pleistocene plus the Holocene where the Holocene started 12,000 years ago. So the Toba that is Western Sumatra, there was a half foot Ashfall in India. And so you know, I think the Toba event really probably meant that a lot of modern humans in Southeast Asia and India just disappeared, the earlier group, so they were replaced later, I think it's an easy explanation. With denisovans probably the ones to the east made it like maybe in eastern Indonesia, whatever, maybe into Papua, but I don't know. And the ones to the north made it. But I think a lot of Southeast Asian Denisovans were probably hosed right. So I think that's had like a big demographic impact. A lot of people have written about stuff about how, oh, this is the original Garden of Eden, as like there was massive population crash. So the Toba event probably caused, like about a decade long winter. And, you know, this is a big thing if you're an agriculturalists. But obviously, foragers are a little bit more adept at it, probably a little more able to adapt to this. But even they have limits. And, you know, probably it was a situation where there was mass starvation, because the capacity of a lot of the world to support the amount of biomass they had probably went down because you know, you have less light, it's cold, there's less vegetation, that's just gonna affect the whole ecosystem and the trophic cascade, and so I do think that Toba that is pretty important, because I think the Toba event are kinda wiped the slate clean of a lot of hominin groups, a lot of human populations everywhere. Toba event probably is a little coincidental to me, that, you know, if you assume a 30,000 year old Arabian standstill, and you date it from 55,000 years old admixture, you get to 85k. With the kind of intervals the confidence interval we have. I wouldn't be surprised if it turned out if the Toba event was actually the seminal, you know, thing that drove this proto out of Africa, that population dropped its population, cut it off from other groups because of metapopulation, extinctions, a lot of extinction. And everywhere, this population survived in some area where there was enough, you know, there was enough sustenance for like one to 10,000 people, but they were isolated for a really, really long time. Maybe there's an island or something that we don't understand, I don't know. But they were isolated. And it was cold. It was colder than the earlier period. So they couldn't demographically expand. And so they were subject to homogenization and adaptation simultaneously. So the adaptation is because of the newer conditions. And you know, without gene flow, they can adapt. You know, I mean, adaptation can happen with gene flow. But obviously, if there's massive waves out of Africa, South and West that are coming at you all the time, you're not going to adapt as well to a cold, but if it got colder and you're isolated, that adaptation can happen. I think that that's probably what was going on here. So that's the scenario that I see for right before the out of Africa. So there are some details about that itself. That is that are interesting and it's kind of brought together by a paper called ‘The genetics and material cultural support repeated expansions of the Paleolithic Eurasia from a population hub out of Africa’. It's in Genome Biology and Evolution. And it just brings together a bunch of ancient DNA from last year. And it suggests that there were three waves it during the out of Africa event proper. So starting around 50,000 years ago, there are probably three waves out of what they call the hub, which is probably Arabia. And basically, this explains the patterns of variation that you see today. So there's an early early DNA sample from a site called Zlatý kůň in Czech Republic, probably a little bit earlier than 45,000 years ago, we got the genome, it's a modern human, it's modern human during a period when Neanderthals were probably dominant in Europe. So this is a really, really early modern human. And what that modeling, what they're showing is that this modern human is Basil to all other modern humans, that basically means that it splits off and it just disappears. This modern human is not closely related to later Europeans. It's not closely related to East Asians, not Middle Easterners, whatever. It's not closely related to anyone. Basically, this is the lineage that expanded outward, before 45,000 years ago, and probably just disappeared. Maybe Neanderthals killed it, maybe, you know, it couldn't adapt, I don't know. But this is very similar to what happened earlier, where, you know, you had situations where modern humans from Africa went north went east, and they kind of just disappeared like the Neanderthals. They got genetically stimulated, but in other areas, they probably went extinct. Like what the Toba that this is the same with Zlatý kůň This is, you know, par for the course. Now, there's a second wave in Europe that they detect, and also all across the world 45,000 After 45,000 years, so there's a site called Bacho Kiro in Bulgaria and Oase that I mentioned in Romania. And then there's also a site in central Siberia, which is Ust'-Ishim And then, there's the site in China called Tianyuan in like North Central China, by the way. Okay, so there's all these like, samples that day to 45,000 to 40,000 years ago. Well, all of these individuals they claim fit in like a broader clade. This is a little disputed. So Oase and Bacho Kiro have been said before, also to be unrelated, later Europeans or any other modern population. So another basil dead end that's an argument, looking at their graph, and their model, putting all the data together, they have created a lineage that were Bacho Kiro, in Bulgaria, and Oase in Romania, more than 40,000 years ago, are actually somewhat more closely related to Tianyuan and the Siberian Ust’-Ishim and East Eurasians. Now this is all very early, remember, like the out of Africa movement, the Neanderthal admixed one. The the earliest that they would have like diversified would be a 55,000 years ago, well, probably closer to 15,000 years ago. So this is very, very all recent. This is like the Holocene, you know, this is timescales, very short timescales for any diversification to happen. But the argument is modern Europeans, and later Pleistocene, Europeans are different from these early waves, which is more like East Eurasians. Okay. And so the argument is, there was a massive wave out of the hub, it went to Australia went to Southeast Asia, China also went to Europe. And this this, this was the first IUP wave that really made an impact everywhere, so after 45,000 years ago, so the NFL admixture happens. About, you know, 50 to 55000, the Denisovan admixture it's definitely later, the earliest, probably 50 to 45,000 years, you know, there are arguments of multiple Denisovan admixtures. And maybe I'll talk about it a little bit later, but, you know, China, South Asia, Papua, they all have different Denisovan admixtures with different populations, some of the ones in Papua could be quite late as late, Some estimates put it 30,000 years, I think it's probably too late. But, you know, Denisovans might have persisted in some areas longer. My point here is there's a second wave after an initial tentative first wave of IUP people after 50,000 years ago, and this wave is the one that really affected a change. Okay, in terms of its really started penetrating into Europe, it like took over in East Asia. Okay. But then there's a third wave where the, you know, the Goyet site, I think, in the Belgium dates, about 38,000 years ago, and it is distinct. It looks more like West Eurasian, what we would say is West Eurasian today, and it's ancestral to later European populations. Now there's some contact like what the Goyet with Eastern populations? So going out dates just 38,000 years ago and the original ancient DNA papers show Oh, well, it had it had East Asian admixture. That's weird, right? Because it's Belgium 38,000 years ago. I don't think that's what's happening. I think what's happening is, there were East Asian like populations or East Eurasian related populations out of the, in the Middle East. And in Europe that were still around, and Goyet absorbed some of those. So when I say East Eurasian, they weren't even East Eurasian, they were part of the wave one. So if you do wave wave or wave two, so if you do wave one, that was Zlaty kun disappeared, okay, wave two, modern East Asians are all wave two, and modern Europeans are very little wave two, although wave two was there initially as well, okay. And then like, you know, ancient,
ancient North Eurasians, or ancient North Asians, however, you want to call them, the Malta boy, probably 20 or 75%, wave, wave, three, and 25% Wave two the East Asian related stuff, just so you know. So a lot of wave two people were still around in Siberia, and they got absorbed as wave one people, or wave three people are coming out of the Middle East. They take over in Europe, they become the Gravettians like all of these archaeological cultures that you know about. And they go into Siberia and then obviously become dominant in the Middle East. So how is this happening? While there was structure in these original out of Africa, populations that occurred, there are different tribes, we're not going to ever get the details. And the archaeological culture is not distinctive enough, probably. But we can kind of imagine what happened in terms of multiple waves of migration that are coming out. But after the second after the third wave, there wasn't really anything that happened until much, much later in the Pleistocene in Europe. And I'm talking a lot about Europe, because we have so much archaeological data for Europe, right? So the initial waves didn't have any basal Eurasian admixture. In fact, basal Eurasian admixture didn't come into Europe until possibly the early European farmers, like you know, 9000 years ago, something like that, right. So there's Basal Eurasians are in the southern Middle East, and they mixed in later, they're not found in any of the wave two, or wave three. Basal Eurasians, are actually not part of these waves that are going out of Africa. They stay the Middle East or North Africa, and they eventually mix with populations that are wave three. And then there's later wave three migrants that go into Europe, the early European farmers from Anatolia that have basal Eurasian ancestry within this model. Again, Laurent Excoffier in Switzerland, you know, look at some of his group's papers, they don't use the Basal Eurasians they have a model of multiple different multiple different European populations with different population sizes, explaining this, you know, I'm not gonna get into it. It's like pretty technical, but it's interesting. So this is not writ. The basal Eurasian thing might not be needed. But, you know, it's, it's the current best model, so I'm putting it out there. Alright. So this is the out of Africa event. Looping back. Why now? What happened? Okay. So there's a couple of things that you need to remember. There are multiple earlier out of Africa events and the Neandersovan one the Homo antecessor one probably another earlier one, although the earliest was Dmanisi, those early Homo erectus they just went into like virgin territory. What really matters is when populations are replaced, or mostly assimilated away, it's likely that did happen. There's not like very, very deep lineages that I know Neanderthals, but maybe you could figure it out. But the point here is, it looks like Neandersovans replaced who was there mostly. And, you know, our own lineage at some point, replaced the Neandersovans, the Neanderthals and Denisovans. But the key that I want to point out is our old lineage of modern humans, and modern here just means like, look at the physical characteristics of our forehead and everything like that. We're not actually superior, necessarily, maybe we are. And there were early waves that just got absorbed or disappeared. So we are looking at the last successful expansion. So what's different? Was there a genetic mutation Did something happen? That's very attractive, and like the natural selection paper is going to make it make people think about like, ooh, neural development. What does that mean? Well, look, selection signatures are all over the place. People see them constantly so I wouldn't like really freak out about that. There's a lot of things going on and a lot of genes do a multiple different things. Okay. So I don't think that's just positive to be honest. Okay. So was technology superior? You know, I don't know archaeology well enough, but reading it, it looks like it's a little better. It's a little bit more flexible. You know, probably a better technology, probably a better culture? does this require like genetic superiority? I mean, did the Lakota Sioux were they superior once they got the horses and the guns? No, they got new technology, right? So technology can come in bursts. And genetics can also change fast, but it tends to be a little slower, a little bit more continuous, a little bit more gradual. So I would caution on the genetic angle here. It could be that they were the same people. Yes, they did get genetically homogenized, there was natural selection in Eurasia. So they had a few advantages there. They're better adapted to the cold than they would have been before. But it could be that they're on the edge of Africa. And they're interacting with all these cultural trends and movements. And so they got access to better technology. And they went with it now. After that. You need some ideology, I think I think you need you need some ideology, some social technology as Samo Burja would say, and so I think they probably had that, and we're never gonna figure it out. Because like, you know, we can't talk to them. There's no writing. But we can use other examples that are similar to think about how it happened. So Austronesians go from being in like southern Taiwan, northern Philippines 4000 years ago to being in like Madagascar, and Easter Island, you know, by, like, 1000 years ago, you know? So that's, like, pretty awesome. Were they genetically mutated? Do they change, did they become crazy, you know, whatever. No, they just something happened in their culture, we don't know the details, one thing led to another and they just expanded all over the world in a crazy way. In 1700, France had a population of 20 million, England had a population of 5 million. And now today, there's like hundreds of millions of more people in the English diaspora not just English speaking, I'm talking about like people descended from people in England than there are French why? Well, I mean, I can give you reasons relating to maritime power in the 18th century, or I could talk something about, I don't know, England's fiscal policy, and how it ran a debt and how that made it like such a great superpower. But read James Baelish’s replenishing the earth. And you know, the English expansions outward were just like kind of chaotic, and just periodically happened. And it's just hard to really predict what happened there. With proto indo Europeans, it looks like they were like, it looks as if they were one tribe, or one group that adopted pastoralism early became nomads. And that transformed everything. And now, you know, there's hundreds of millions of people are genetically, like that tribe, Bantu expansion in Africa again, like they weren't really that different. We have their genes, we have the genes that are neighbors, but, you know, they had a new cultural toolkit. And, you know, they got to South Africa within 2000 years, right, like 2500 years. It's pretty intense, pretty crazy, like, I'm assuming for 2000 BC, and then go to buy, like 500 ad, just you guys know. So, you know, we don't posit that they genetically changed. It just something happened technologically and culturally, and they just started expanding. We are obviously weird in some ways. We got to Australia, we got to the new world, we actually like poked into the interior of Siberia. Look, we are radically different. We modern humans, the descendants of the IUP out of Africa event within Africa, stuff started changing too much faster. But we don't necessarily have to think of it as like some biological change, like biology and culture co evolve. You know, as you guys know, brain size grew larger from, you know, 2 million years ago, to about 50,000 years ago, continuously. It wasn't jumps, you know, and as Luke Johnston's Sanger Institute has shown, it Neanderthals too, it occured in the Neanderthal lineage in the proto Neanderthal lineage. So this is a common thing that's happening everywhere. It's not restricted to any particular lineage, you know. And I think the way we need to think about it is that there was probably a long fuse. And it wasn't some sort of like, revolution or Big Bang. So long fuse basically means like, it's some sort of exponential maybe dynamic, where it starts out low, low fraction, and then it pops, it just increases event with exponential rate of increase. It happens really fast in a short period of time and at the end when you notice it. And so I think that this is maybe what was happening with the IUP, the initial Upper Paleolithic population, and modern humans, and we see it as a big bang, and it's great leap forward. But there were a lot of like experiments going on. And I just want to emphasize that this is part of a broader dynamic of African populations going out, you know, mostly failing, but sometimes succeeding, and then within Africa you know, some of you who have listened or who have read my substack will know that there were a lot of dynamics going on internally there too. So I think we can think of these like reciprocal lattice like, you know, phenomenologically multiregional. I don't know what I want to say, dynamics as really defining like how became, we became human over the last 2 million years. And I don't want to say here that there was no biological change. So, you know, there's some evidence of FoxP2 language gene, quote, unquote, introgression, into the Altai Neanderthals. So the Neanderthals might have changed because of gene flow from African humans, and maybe vice versa, like William Calvin's work on the ice age, and, you know, these pumps, cultural pumps, you know, biological pumps. So I think, you know, so I think, you know, there could have been a lot of interaction over time, and Gene culture coevolution that allowed us to be better cultural creatures. But it was a gradual process that just exploded. And you know, you see it even in our modern cultures. You know, we are as distant from the time of Julius Caesar, as Julius Caesar was from the Middle Kingdom of Egypt, right? So the Old Kingdom of Egypt was actually older, was further back. So Egyptians, as a continuous civilization, were out for at least 2000 years as a political unit. But even after that, until the Temple of Philae closed, Egyptian paganism persisted down to 500 ad, right. So that means
3500 years of a literate, you know, institutional structure 3500 years, like 3500 years ago, from us, is, is the middle of the Bronze Age, like we're talking before the Trojan War. So human cultures are changing faster and faster even today, even in the modern period. You know, most people that are Zoomers have some sense of what a flip phone was, but I know Gen alpha. And my kids, they don't know what flip phones are, they think flip phones are super weird. But they were super advanced 15-20 years ago. So the rate of change of certain things keeps increasing. And that doesn't mean there's any biological change. It's like there's underlying cultural cognitive processes, these ratchets that are out of our control that I think are occurring, I guess, probably what we need to understand for why the IUP out of Africa event happened 50,000 years ago, and why the whole world has transformed since then, it was actually part of a bigger context of, of dynamics that have been happening for millions of years. And I think the details are important with these, like, you know, wave one wave to wave three, because it kind of just shows how things happen. And we can use things that we know very well to infer the other things we don't know, as well as the process of uniformitarianism. You know, it's this is part of science. And so, with that, I think I'm gonna close this out, I think I made it clear what we know really well, and what we don't know really well. So the basal Eurasian stuff, just, you know, that's, I think, maybe it's true, but I moderate to weak confidence on it. But the different waves that are coming out with IUP, that's known, I am pretty confident now that there were modern humans, in parts of Asia in particular. But you know, now we know a tooth from France, well before the IUP expansion. So the differentiation between archaic and modern humans is a bit artificial. I think the Sahara, in the Middle Eastern mountains and deserts did create a major barrier between the two groups of humans that are in Eurasia versus those that are in Africa. But there was still some interaction that occurred over this time period. And the Neanderthals, and the Denisovans themselves are like the best example because they seem to have come from Africa more than 600,000 years ago. And, you know, they like establish themselves as Eurasian. Probably they have that mixture. I do believe they're super archaic admixture in Neanderthals and Denisovans. From earlier, H. erectus type populations, I that and so we probably have some of that in us a little bit, you know, 1%, of 1%, you know, not 1%, let's say 5% of 5%, it starts to get small, but still, I think that there's some of that there. Anyway, so this podcast, obviously is just so you guys know, I'm not totally aware of the timing when I'm, as I'm recording this, but there's gonna be a written piece associated with this. So just watch for that. And, again, please rate the podcast. If you've listened this far please rate the podcast, and yeah, just get the word out there but appreciate you and I'll talk to you next time.
Is this podcast for kids? This is my favorite podcast.