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Thread: Barriers to crossbreeding with Neanderthals and Denisovans -discussion

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    Barriers to crossbreeding with Neanderthals and Denisovans -discussion

    We overlapped with Neanderthals for thousands, in some places maybe tens of thousands of years. Probably interacted on territorial borders with them for as long. And yet still, we only seem to have produced successful hybrids with a single line or tribe of Neanderthals. Although apparently multiple times with that particular group over a timespan of thousands of years.

    And I am unsure how long we overlapped or interacted with Denisovans, but it seems reasonable to suppose that it was for a long time and over quite a large area too. Yet still, Denisovan genes are mostly confined to limited groups of people, generally in southeast Asia and the pacific. American Indians completely lack Denisovan DNA. Both hint that the Denisovan introgression was quite late, although I expect not being in the initial Out-of-Africa wave meant no founder effect for the Denisovan DNA.

    However, in both cases, there seems to have been serious barriers to interbreeding. An I would postulate that they are unlikely to have been cultural or behavioral in nature, at least on our side. Humans tend to... have a very wide preferences in terms of sex-partners, to put it mildly. We are not, as a rule, a choosy people. If we live next to another people for any amount of time, fornication will occur. Given that we overlapped for thousands of years with the other peoples, and that such overlap was therefore likely to involve multiple human cultures and behaviors, I doubt the barriers can have been cultural.

    It seems possible that the barriers were biological. But the length of separation with the others -maybe 26 000 generations- seem short for us to develop such barriers. And the whole "There was one lot we had kids with a number of times -but no-one else" just seems downright peculiar.

    Any thoughts?

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    Quote Originally Posted by Gnarl View Post
    We overlapped with Neanderthals for thousands, in some places maybe tens of thousands of years. Probably interacted on territorial borders with them for as long. And yet still, we only seem to have produced successful hybrids with a single line or tribe of Neanderthals. Although apparently multiple times with that particular group over a timespan of thousands of years.

    And I am unsure how long we overlapped or interacted with Denisovans, but it seems reasonable to suppose that it was for a long time and over quite a large area too. Yet still, Denisovan genes are mostly confined to limited groups of people, generally in southeast Asia and the pacific. American Indians completely lack Denisovan DNA. Both hint that the Denisovan introgression was quite late, although I expect not being in the initial Out-of-Africa wave meant no founder effect for the Denisovan DNA.

    However, in both cases, there seems to have been serious barriers to interbreeding. An I would postulate that they are unlikely to have been cultural or behavioral in nature, at least on our side. Humans tend to... have a very wide preferences in terms of sex-partners, to put it mildly. We are not, as a rule, a choosy people. If we live next to another people for any amount of time, fornication will occur. Given that we overlapped for thousands of years with the other peoples, and that such overlap was therefore likely to involve multiple human cultures and behaviors, I doubt the barriers can have been cultural.

    It seems possible that the barriers were biological. But the length of separation with the others -maybe 26 000 generations- seem short for us to develop such barriers. And the whole "There was one lot we had kids with a number of times -but no-one else" just seems downright peculiar.

    Any thoughts?
    Contacts between modern humans and Neanderthals must have been multiple.
    The DNA we have from Neanderthals has been purified to a level of ca 2 % and it is from interbreeding during a restricted period (ca 55 ka) in a restricted area (SW Asia).
    So modern human-Neanderthal hybrids were not very succesfull, biologically.
    And the number of interbreeding events were not many, probably there was not very much sexual attraction between both species.
    I guess it only happened when there were not many mating partners to chose from.

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    ^^Or the contact wasn't consensual.

    I guess I'll be the politically incorrect one, and say I can understand it.

    I'd also say (sorry, gentlemen) that it's the male of our species who isn't very "picky". I think women are far more discriminating in these matters, and far less likely even to cross "racial" lines within our species, and the papers seem to bear that out, despite urban legends to the contrary.


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    It could be that the rapid expansion of our ancestors began from a point deep within the modern human range, and our relatives nearer the Neanderthal borders didn't fare any better in the way of the steamroller than the Neanderthals did themselves.

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    Quote Originally Posted by Angela View Post
    ^^Or the contact wasn't consensual.

    I guess I'll be the politically incorrect one, and say I can understand it.

    I'd also say (sorry, gentlemen) that it's the male of our species who isn't very "picky". I think women are far more discriminating in these matters, and far less likely even to cross "racial" lines within our species, and the papers seem to bear that out, despite urban legends to the contrary.
    The evidence for Neanderthal introgression in to modern humans suggests the opposite. Interbreeding between Neanderthals and modern humans was sex biased, with Neanderthal male+sapiens female pairings being the predominant coupling that produced modern non-Africans. Modern human mtDNA lineages are also present in Neanderthal fossils -- so far no modern human Y-DNA in Neanderthals or mtDNA in modern humans.

    Denisovan+modern human couplings were also predominantly Denisovan male+modern human female.



    Why did geneflow between Denisovans
    and modern human populations occur pri-
    marily east of Wallaces Line and not on
    the Asian mainland? Given that intentional
    dispersal to Wallacea required the use of
    watercraft, the fi rst modern human groups
    encountering the established Denisovan
    populations were likely to have been of very
    limited size. Either interbreeding may be
    more likely under these circumstances, or
    any interbreeding that does occur is more
    likely to be preserved as a signal in descen-
    dants. The genomic evidence suggests that
    gene fl ow from the Denisovans may have
    been largely male-mediated, providing some
    clues about the nature of the interactions
    ( 4).

    Probably, modern human women found the Neanderthal men more attractive because they were more handsome, physically stronger and more intelligent and has more resources and better skills than modern humans (it is known for instance they mastered dry distillation of birch bark 80,000 years ago).

    The Neanderthal+modern human hybrids were the most successful humans to ever walk the Earth; the majority of human beings alive today are Neanderthal+modern human hybrids. Non-Neanderthal hybrids (subsaharan Africans) have suffered immensely at the hands of Neanderthal-modern human hybrids for thousands of years. The decrease in Neanderthal ancestry over time is a natural consequence of the fact that they had much smaller populations than modern humans.

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    I was going to post multiple links including the source of my quote ("Did Neanderthals cross Wallace's line?" by Alan Cooper+Chris Stringer) but unfortunately I am given a message informing that I must have 10 posts to post links. So many hurdles in life we must qualify for the opportunity to jump over.

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    [QUOTE=Punish Modern human mtDNA lineages are also present in Neanderthal fossils -- so far no modern human Y-DNA in Neanderthals or mtDNA in modern humans.
    [/QUOTE]

    specific details please
    if I remember well, these Neanderthal fossils were older than the 55 ka admixture event between our ancestors and Neanderthals

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    Quote Originally Posted by Angela View Post
    ^^Or the contact wasn't consensual.

    I guess I'll be the politically incorrect one, and say I can understand it.

    I'd also say (sorry, gentlemen) that it's the male of our species who isn't very "picky". I think women are far more discriminating in these matters, and far less likely even to cross "racial" lines within our species, and the papers seem to bear that out, despite urban legends to the contrary.
    our ancestors were ostracised by their tribe and were roaming the desert
    they were lacking females and obducted some when they meat a Neanderthal tribe
    they were not just rapists, because they also helped raising the offspring
    happy end?

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    Quote Originally Posted by Punish Them 911 View Post


    Probably, modern human women found the Neanderthal men more attractive because they were more handsome, physically stronger and more intelligent and has more resources and better skills than modern humans (it is known for instance they mastered dry distillation of birch bark 80,000 years ago).

    The Neanderthal+modern human hybrids were the most successful humans to ever walk the Earth; the majority of human beings alive today are Neanderthal+modern human hybrids. Non-Neanderthal hybrids (subsaharan Africans) have suffered immensely at the hands of Neanderthal-modern human hybrids for thousands of years. The decrease in Neanderthal ancestry over time is a natural consequence of the fact that they had much smaller populations than modern humans.
    if this were so, we would have more than 2 % Neanderthal ancestry today

    the Neanderthals were not so intelligent, they never made blade tools
    but the Denisovans were, judging from the findings of needles and the bracelet

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    Quote Originally Posted by bicicleur View Post
    if this were so, we would have more than 2 % Neanderthal ancestry today
    Wrong. We can't have more than 2% because Neanderthals were never even 4% of Earth's population and have been gone as a pure population for 40,000 years.
    the Neanderthals were not so intelligent, they never made blade tools
    but the Denisovans were, judging from the findings of needles and the bracelet
    The Levallois core method requires far more intelligence and is a far superior design to blade cores. There are very few experimental archaeologists who can reproduce Levallois flakes (due to the cognitive challenges presented -- most people are too stupid), but the majority can produce blades. Flakes provide superior plano-convex edges and a far greater efficiency as they have more capacity for retouch than blades, which dull quickly.

    https://journals.plos.org/plosone/ar...l.pone.0029273


    Furthermore, the Wadi Amud cave complex in Israel does present blade technology produced by Neanderthals, so they sometimes made blades. Evidence of needles among Denisovans isn't evidence of blade technology. Denisovans used flake core technology.

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    https://www.sciencedirect.com/scienc...47248408001395

    It is widely believed that the change from discoidal flake production to prismatic blade-making during the MiddleUpper Paleolithic transition in Europe led to enhanced technological efficiency. Specifically, blade-making is thought to promote higher rates of blank production, more efficient and complete reduction of the parent core, and a large increase in the total length of cutting edge per weight of stone. Controlled replication experiments using large samples, computer-assisted measurements, and statistical tests of several different measures failed to support any of these propositions. When resharpened, the use-life of flake edges actually surpasses that of blades of equivalent mass because the narrower blades are more rapidly exhausted by retouch.

    Basically blade technology emerged as the easier, less efficient, less thought-out and less aesthetic substitute to Levallois flake technology, likely by early modern humans who lacked a sufficient amount of key Neanderthal intelligence genes necessary to produce Levallois flakes. Recent genetic analysis has confirmed that Neanderthal alleles are rich in areas of the human genome that code for brain architecture and intelligence. They were far more gifted than moderns, particularly in regards to visual-spatial mastery and abstract thought (as evidenced by the dry distillation of birch tar 80,000 years ago, the superior Levallois flake method, etc).

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    Quote Originally Posted by Angela View Post
    ^^Or the contact wasn't consensual.

    I guess I'll be the politically incorrect one, and say I can understand it.

    I'd also say (sorry, gentlemen) that it's the male of our species who isn't very "picky". I think women are far more discriminating in these matters, and far less likely even to cross "racial" lines within our species, and the papers seem to bear that out, despite urban legends to the contrary.
    It is possible that the contact wasn't consensual in general. Of the three species, humans appear to have been the least well-equipped physically and strength-wise. And that would skewer DNA transfer towards Neanderthal and Denisovan males introgressing into human lines. However, given the length of our overlap with them, I find it hard to imagine that all the contact was violent. Humans vary too much behaviorally, and we know there was variation in Neanderthal breeding habits too.

    However, in my experience the human girls are at least as bad as the human boys. They are just socially expected to be less obvious about it, and often far more heavily socially sanctioned. All that supernatural romance about hairy werewolves, twisted demons, dangerous vampires etc, etc. thats being churned out by the ton -its not the boys buying it.

    A thing that puzzles me though, is that the out-of-Africa group seem to have encountered Neanderthals early on in the expansion process, interbred, and then kept expanding. At this point in time, the human wavefront appears to have had a pretty high Neanderthal component, before purifying selection cut it down. But this already admixed population would no longer breed with Neanderthals? How would that work?

    Is it possible that the hybrids had such low fitness that only a few managed to reproduce and that only during an unusually beneficial period ? (Few competitors etc)

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    0 out of 2 members found this post helpful.
    People keep bringing up this topic of fitness. There is no evidence at all that Neanderthal-modern human hybrids were less genetically or physically fit than unadmixed moderns. Neanderthal-modern human hybrids didn't take over the world after Neanderthals vanished for no good reason.


    There is no evidence of "purifying selection" in modern humans. What there is evidence for is that the number of Neanderthals on planet Earth was always exceedingly low, and the number of modern humans/Neanderthal hybrids exceedingly high relative to Neanderthals. Neanderthals in Europe couldn't have made a big dent in in the population of modern humans who migrated there.

    Since no Neanderthals have been around for ~40,000 years, while population exodus to and from Africa has only increased, Neanderthal ancestry cannot increase; but that doesn't mean Neanderthal ancestry is being selected against or somehow harmful. It's just a reflection of the fact that Neanderthal-modern human introgression took place between two unbalanced population sizes, tens of thousands of years ago.

    This is the most ridiculous theory I have ever heard.

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    I don't think you understand how population mixing happens, or genetics.

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    Quote Originally Posted by Punish Them 911 View Post
    https://www.sciencedirect.com/scienc...47248408001395



    Basically blade technology emerged as the easier, less efficient, less thought-out and less aesthetic substitute to Levallois flake technology, likely by early modern humans who lacked a sufficient amount of key Neanderthal intelligence genes necessary to produce Levallois flakes. Recent genetic analysis has confirmed that Neanderthal alleles are rich in areas of the human genome that code for brain architecture and intelligence. They were far more gifted than moderns, particularly in regards to visual-spatial mastery and abstract thought (as evidenced by the dry distillation of birch tar 80,000 years ago, the superior Levallois flake method, etc).
    I meant the blade tools that emerged ca 50 ka and spread over almost all Eurasia in a very short time replacing most of the blade tools made by Levallois technique.

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    Quote Originally Posted by Punish Them 911 View Post
    People keep bringing up this topic of fitness. There is no evidence at all that Neanderthal-modern human hybrids were less genetically or physically fit than unadmixed moderns. Neanderthal-modern human hybrids didn't take over the world after Neanderthals vanished for no good reason.


    There is no evidence of "purifying selection" in modern humans. What there is evidence for is that the number of Neanderthals on planet Earth was always exceedingly low, and the number of modern humans/Neanderthal hybrids exceedingly high relative to Neanderthals. Neanderthals in Europe couldn't have made a big dent in in the population of modern humans who migrated there.

    Since no Neanderthals have been around for ~40,000 years, while population exodus to and from Africa has only increased, Neanderthal ancestry cannot increase; but that doesn't mean Neanderthal ancestry is being selected against or somehow harmful. It's just a reflection of the fact that Neanderthal-modern human introgression took place between two unbalanced population sizes, tens of thousands of years ago.

    This is the most ridiculous theory I have ever heard.
    Neanderthals had plenty of time to expand, if their population remained low, it was because they were not inventive enough in exploiting resources nature offered.

    The actual number of modern humans coming 'out of Africa' was very low as demonstrated by both Y- and mtDNA of which there are very few specific Eurasian clades (C, D and FGHIJK in Y-DNA). Expansion happened within Eurasia.

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    911, population mixing does not lead to fixed amounts of genes holding the same proportions for generations after mixing anyway.

    For a well-known example close to the modern age I give you -Djengis Khan! When born, he was one of 200 million male humans alive.Today, 0.5 % of human males descend from him and carry Y-chromosomes directly descended from him. So its gone from 1 in 200 000 000 to 1 in 200 over 800 years. His genes have increased their amount in the population more than millionfold.

    The reason that happened is that he had more children who lived than his contemporaries, and they had more children etc.

    During most of human history, the population was in equilibrium or close to it. Population growth, when it occurred was generally slow. That means almost as many kids dies as the number who lived to reproduce. So for example: if we have a F1 Neanderthal-Human hybrid who is 50 % of each species, he might have two kids who live to breed, and so the next generation will contain two 25 % Neanderthal individuals. But if the Neanderthal genes give a competitive advantage, he might have 3 kids who survive to reproduce. That means that the number of Neanderthal genes in the second generation is larger than the number in the first generation.

    Over thousands of years, even very small statistical advantages in reproductive fitness can cumulate to very large sweeps of genes, as genes which give an advantage sweeps in to replace those who didn't. This is a process known as... evolution.

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    Quote Originally Posted by bicicleur View Post
    our ancestors were ostracised by their tribe and were roaming the desert
    they were lacking females and obducted some when they meat a Neanderthal tribe
    they were not just rapists, because they also helped raising the offspring
    happy end?
    Well, that's looking on the bright side, I must say.

    Why not a Neanderthal male raping a human female? Although I suppose giving birth to a half Neanderthal child might have killed her.

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    Quote Originally Posted by Gnarl View Post
    It is possible that the contact wasn't consensual in general. Of the three species, humans appear to have been the least well-equipped physically and strength-wise. And that would skewer DNA transfer towards Neanderthal and Denisovan males introgressing into human lines. However, given the length of our overlap with them, I find it hard to imagine that all the contact was violent. Humans vary too much behaviorally, and we know there was variation in Neanderthal breeding habits too.

    However, in my experience the human girls are at least as bad as the human boys. They are just socially expected to be less obvious about it, and often far more heavily socially sanctioned. All that supernatural romance about hairy werewolves, twisted demons, dangerous vampires etc, etc. thats being churned out by the ton -its not the boys buying it.

    A thing that puzzles me though, is that the out-of-Africa group seem to have encountered Neanderthals early on in the expansion process, interbred, and then kept expanding. At this point in time, the human wavefront appears to have had a pretty high Neanderthal component, before purifying selection cut it down. But this already admixed population would no longer breed with Neanderthals? How would that work?

    Is it possible that the hybrids had such low fitness that only a few managed to reproduce and that only during an unusually beneficial period ? (Few competitors etc)
    At least one of the papers proposed that the male hybrids were sterile. As someone pointed out, the major "cleansing" of their dna was in the testes and the brain,and interestingly enough, in the brain a lot of it was in the areas controlling verbal processing. There's absolutely no doubt in my mind that they were more primitive.

    As for your comment about women every paper I've ever seen says you're incorrect, as does my own knowledge of women and how they think, but that's for another thread.

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    Both of your posts can be the case. Girls desire men like Edward Cullen since they project traits that are "high quality" in males (tall and fit without being grotesque, clean and good smelling, a good provider, etc.).

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    Quote Originally Posted by Alyan View Post
    Both of your posts can be the case. Girls desire men like Edward Cullen since they project traits that are "high quality" in males (tall and fit without being grotesque, clean and good smelling, a good provider, etc.).
    Personally, he gives me a gay vibe. I like the werewolf one. :) I think for most women it's an age thing. Teenage girls like non-threatening, girlish men. Tastes change as you age. In my own case, however, even as a young girl, I always liked very masculine looking men. I spent my teens watching old movies to learn English.

    My teenage crush:



    Strong jaw, strong cheekbones, strong chin and nose, big head, big body...I think I fell in love with my husband at first sight because he looks a lot like this.

    However, the point is not about what attracts women; it's whether they are, on average, as naturally promiscuous as men, as apt to divorce sex from feeling. The answer, from science as well as personal experience is emphatically no.

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    Why not a Neanderthal male raping a human female? Although I suppose giving birth to a half Neanderthal child might have killed her.
    This is the most plausible scenario to explain why human mitochondrial DNA shows no indication of Neanderthal–human admixture because of a sex bias towards Neanderthal male and human female pairings. Admixed offspring remained with their human mothers and thus introgressed Neanderthal alleles survived only on the X chromosome.
    Давайте вместе снова сделаем мир великий!

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    Quote Originally Posted by Gnarl View Post
    It is possible that the contact wasn't consensual in general. Of the three species, humans appear to have been the least well-equipped physically and strength-wise. And that would skewer DNA transfer towards Neanderthal and Denisovan males introgressing into human lines. However, given the length of our overlap with them, I find it hard to imagine that all the contact was violent. Humans vary too much behaviorally, and we know there was variation in Neanderthal breeding habits too.

    However, in my experience the human girls are at least as bad as the human boys. They are just socially expected to be less obvious about it, and often far more heavily socially sanctioned. All that supernatural romance about hairy werewolves, twisted demons, dangerous vampires etc, etc. thats being churned out by the ton -its not the boys buying it.
    The average Neanderthal male would have presented a formidable physical challenge. Even a Neanderthal female would have been hard to handle. Their disadvantage was not physical, but numerical. Adapted to colder ice-age conditions, they specialized in hunting/trapping larger game. But the climate warmed and modern humans, who were more omniverous and thus able to support larger populations within a given area, simply outnumbered them. If Neanderthals also had speech, communication, and/or language deficits compared to modern humans, that would have made it more difficult for them to coordinate resistance to human incursions.

    DNA transferal between Neanderthals and humans was one-way: from Neanderthal males to human females, likely due to force (capture, kidnapping, rape, etc.):

    Humans and Neanderthals share a small percentage of nuclear DNA. However, humans and Neanderthals do not possess the same mito­chondrial DNA. In mammals, mitochondrial DNA is exclusively maternally inherited. Taking into account an understanding of interspecific hybridity, the available data leads to the hypothesis that only male Neanderthals were able to mate with female humans. If Haldan's Law applied to the progeny of Neanderthals and humans, then female hybrids would survive, but male hybrids would be absent, rare, or sterile. Interbreeding between male Neanderthals and female humans, as the only possible scenario, accounts for the presence of Neanderthal nuclear DNA, the scarcity of Neanderthal Y-linked genes, and the lack of mitochondrial DNA in modern human populations.
    https://www.researchgate.net/publica...-human_hybrids

    A thing that puzzles me though, is that the out-of-Africa group seem to have encountered Neanderthals early on in the expansion process, interbred, and then kept expanding. At this point in time, the human wavefront appears to have had a pretty high Neanderthal component, before purifying selection cut it down. But this already admixed population would no longer breed with Neanderthals? How would that work?

    Is it possible that the hybrids had such low fitness that only a few managed to reproduce and that only during an unusually beneficial period ? (Few competitors etc)
    Or perhaps because Neanderthal populations had been decimated by, and were fleeing from, the onslaught of more numerous modern humans. There would have been less interbreeding events simply because there were many fewer Neanderthals.

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    Quote Originally Posted by bicicleur View Post
    I meant the blade tools that emerged ca 50 ka and spread over almost all Eurasia in a very short time replacing most of the blade tools made by Levallois technique.
    That is exactly the kind of blade tool that I and the paper I link to am talking about. That's an inferior technique and "replacing" something doesn't make it better.

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    Quote Originally Posted by bicicleur View Post
    Neanderthals had plenty of time to expand, if their population remained low, it was because they were not inventive enough in exploiting resources nature offered.

    That isn't true at all. Reproduction rates aren't connected to inventiveness; they're often negatively correlated. Less inventive, less competent populations breed more than more intelligent populations, as you in Europe are finding out.



    The actual number of modern humans coming 'out of Africa' was very low as demonstrated by both Y- and mtDNA of which there are very few specific Eurasian clades (C, D and FGHIJK in Y-DNA). Expansion happened within Eurasia.
    That's a load of BS, you can't use the limited understanding that fossil DNA evidence provides to show anything. Everyone agrees the expanding homo sapiens population was several times larger than the Neanderthal population.

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