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Thread: How can there be such great genetic distances between ancient west Eurasians?

  1. #1
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    How can there be such great genetic distances between ancient west Eurasians?

    Example: Barcin and Ganj Dareh, symbolizing Anatolian neolithic farmers and Iranian neolithic farmers respectively. The distance between them on nMonte is massive:

    1 Ganj_Dareh_N:Average 37.1502 Open Map 100


    This is greater than the difference between a German and an Uyghur. How can this be, when the Uyghur is heavily East Eurasian?

    1 Uygur:Average 31.9504 Open Map 100

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    Quote Originally Posted by Censored View Post
    Example: Barcin and Ganj Dareh, symbolizing Anatolian neolithic farmers and Iranian neolithic farmers respectively. The distance between them on nMonte is massive:

    1 Ganj_Dareh_N:Average 37.1502 Open Map 100


    This is greater than the difference between a German and an Uyghur. How can this be, when the Uyghur is heavily East Eurasian?

    1 Uygur:Average 31.9504 Open Map 100
    There must be a barrier of some kind between these populations once they drifted away from each other, water, desert, mountains, language, religion, cultural etc. for a long long time.
    Last edited by Jatt1; 03-02-2019 at 08:47 AM.

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    Phylogenetically, Iran_N and Anatolia_N have a common Western Crown Eurasian + Basal Eurasian origin, but they were still highly differentiated populations, as were EHGs and WHGs. In fact, many of these ancient Western Crown Eurasian and proto-West Eurasian groups were, by FST anyway, as genetically distant from one another as modern Europeans are from East Asians. In many cases, we're talking pairwise FSTs from ~0.08 to over 0.1! To put things in perspective, modern West Eurasian FST values are nowhere near so dramatic (e.g., Finn-North African FST is something in the range of 0.03-0.04!)

    Cautionary tale: FST can be a misleading way to gauge relationships in the case of highly isolated groups. The Karitiana and Surui, for instance, are Amazonian Amerinds living right next to each other, but if you looked at their pairwise FSTs, they look like they belong to two different races:

    The Surui and Karitiana have an unusually high pairwise FST. In fact, the Karitiana are as diverged from the neighboring Surui in terms of FST as they are from the Mongola on the other side of the world (Table 1, Figure 3, and Figure S6). Moreover, FST actually decreases initially with distance from the Amazon, from 0.13 between the two Amazonian tribes, to 0.08-0.1 between Amazonians and Colombians, further decreasing to 0.07-0.09 between Amazonians and the more distant Maya. Remarkably, the highest FST among all HGDP Native American populations is between the two geographically closest populations, the Surui and Karitiana. These apparent anomalies can be explained by the inflation of FST in genetic isolates. FST between pairs of isolates can be nearly twice as high as between either one of the isolates and a more cosmopolitan population, as pairwise FST reflects the combined isolation of both populations. Since the Surui and Karitiana are both isolated, their pairwise FST is nearly double that between any one of them and a larger, less isolated population such as the Maya. In other words, the Maya’s contribution to the pairwise FST is dwarfed by that of the Amazonians.
    https://www.biorxiv.org/content/bior...33852.full.pdf
    Last edited by Michalis Moriopoulos; 03-02-2019 at 07:34 AM.
    Ελευθερία ή θάνατος.

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    Quote Originally Posted by Michalis Moriopoulos View Post
    Phylogenetically, Iran_N and Anatolia_N have a common Western Crown Eurasian + Basal Eurasian origin, but they were still highly differentiated populations, as were EHGs and WHGs. In fact, many of these ancient Western Crown Eurasian and proto-West Eurasian groups were, by FST anyway, as genetically distant from one another as modern Europeans are from East Asians. In many cases, we're talking pairwise FSTs from ~0.08 to over 0.1! To put things in perspective, modern West Eurasian FST values are nowhere near so dramatic (e.g., Finn-North African FST is something in the range of 0.03-0.04!)

    Cautionary tale: FST can be a misleading way to gauge relationships in the case of highly isolated groups. The Karitiana and Surui, for instance, are Amazonian Amerinds living right next to each other, but if you looked at their pairwise FSTs, they look like they belong to two different races:


    https://www.biorxiv.org/content/bior...33852.full.pdf
    So due to high amounts of drift and isolation, these groups appear further from each other than they should, and comparing modern cosmopolitan/heterogeneous populations to ancient isolated ones is like apples and oranges?

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    Yeah, PCA distances can be skewed in the same way as FST distances. But, paradoxically, this actually helps in modeling ancestry in many cases, especially recent ancestry.

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    Quote Originally Posted by Generalissimo View Post
    Yeah, PCA distances can be skewed in the same way as FST distances. But, paradoxically, this actually helps in modeling ancestry in many cases, especially recent ancestry.
    So what is the best way to determine actual relatedness?

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    Quote Originally Posted by Censored View Post
    So what is the best way to determine actual relatedness?
    It depends what you mean by that.

    If you want to check overall (but in large part coincidental) affinity via all drift paths then use basic formal stats. If you want to analyze more direct relationships then use Fst and mixture modeling. And for more recent genealogical ties use IBD.

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