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Thread: Degree of heterogeneity of populations

  1. #1
    Satyavrata Maciamo's Avatar
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    Exclamation Degree of heterogeneity of populations

    When analysing the haplogroup frequencies in specific populations it doesn't always spring to mind that two populations with similar frequencies can look very different because of the way the "genetic elements" were mixed. Genetics is like cooking; you can make a lot of very different dishes with the same basic ingredients. A pancake, a French toast, a waffle, and scrambled eggs on a piece of bread are all derived from the same ingredients : eggs, milk and flour (with more or less water and sugar).

    We could also find two pictures that use exactly the same colours in the same proportions, and yet look very different. There are millions of combinations with the three primary colours (red, yellow, blue), and computer screens use a similarly basic combination (RGB).

    Imagine that three source populations merge together. To simplify things, let's say that one ethnic group is red, another is yellow and another is blue. Each make up 1/3 of the new population. If they stay side by side and never intermarry, the new population will remain 1/3 red, 1/3 yellow and 1/3 blue. If the yellow and blue intermingled to some extent, a bit or green will appear. If the red and blue have children together, there will be purple offspring.

    We could imagine a scenario where one ethnic group is the ruling dominant class, an aristocracy, and never mix with the two other groups. If it is the red one, after a while the population will look red (pure) and green (various shades, ranging from yellowish to blue green). However, if it was the blue ethnicity that became the ruling class, the overall population picture will look very different after a few centuries, with a blue group and the rest being shades of yellow, orange and red.

    But even the strictest caste systems are never perfectly impermeable, and the power of attractions between human with different genes will always lead to a certain amount of mixed offspring. Besides, revolutions happen, power changes hand, and lower class people can be elevated to nobility to thank them for the loyal services. Eventually, new admixture do take place.

    Given enough time, once the members of an isolated population have procreated with each others over hundreds of generations, the overall colour gets more uniform, homogeneous, and the original red, yellow and blue components end up in a brownish colour. If one group procreated more than the others for whatever reason these things happen (richer, better-looking, more promiscuous, more resistant to local diseases, or just more proficient at surviving), it will have a greater impact on the final colour.

    There are so many factors, and human societies and histories are so complex and full of unexpected events, that two populations starting with an identical admixture of ethnic groups will inevitably diverge the longer time passes. And I am not even taking genetic evolution (new mutations that arise at each birth) into account.

    The important lesson to learn here is that haplogroups only give one dimension of the picture. They are only the raw ingredients. The more time passes, the more homogeneous and unique the admixture will become.

    This is one it is vital to know when each haplogroup entered a given population. To make a French toast, you need to make the bread first (water + flour) then add the egg/milk admixture in the pan, then the sugar. If you mix the eggs and milk with the flour at the start, it will make a pancake. The cooking time at each step is also important. Just how homogeneous was one population when a group of foreign invaders came and settled within ?


    Here are a few concrete examples to think about :


    - Just how much had Paleolithic Europeans (hg I) mixed with Neolithic farmers (already an admixture of hg E, G, J and T) when the Indo-Europeans (a recent and uneven admixture of R1a1a, R1b1b2a1 and G2a3b1a) conquered Europe ? Did the I and E/G/J/T people live in clearly separate groups, or did they quickly merge with each others ? If they lived side-by-side, did this change after the Indo-European conquest ? Did the Indo-Europeans establish a caste system in Europe like in India ? How long did it last ? How often did they take brides within the non-IE population ?

    - How much genetic impact did foreign slaves in the Antiquity have on the population of heavily slave-dependent economies like Italy and Greece ? Did ancient Greek and Roman freemen and nobles look very different from their (imported) slaves ? Is the modern population an admixture of both, and which component is the dominant one (given that the slaves outnumbered their master sometimes to a ratio of 10 to 1) ?
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  2. #2
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    Quote Originally Posted by Maciamo View Post

    The important lesson to learn here is that haplogroups only give one dimension of the picture. They are only the raw ingredients. The more time passes, the more homogeneous and unique the admixture will become.

    This is one it is vital to know when each haplogroup entered a given population.
    this is really good point that is often overlooked....

    if an admixture is evenly spread in a population that suggest that it has entered the population in earlier times... if it has pronounced hotspots within population than hotspots are likely to be later admixtures...

    an example might be I2a2 that shows fairly even spread among Serbs in Bosnia, Vojvodina, Serbia, Montenegro, but extreme hotspots (Hercegovina, south Dalmatia) and extreme lack of it (north-west Croatia) in Croats ...

    - Just how much had Paleolithic Europeans (hg I) mixed with Neolithic farmers (already an admixture of hg E, G, J and T) when the Indo-Europeans (a recent and uneven admixture of R1a1a, R1b1b2a1 and G2a3b1a) conquered Europe ? Did the I and E/G/J/T people live in clearly separate groups, or did they quickly merge with each others ? If they lived side-by-side, did this change after the Indo-European conquest ? Did the Indo-Europeans establish a caste system in Europe like in India ? How long did it last ? How often did they take brides within the non-IE population ?
    these are tough questions...
    btw. can we be sure that most of people in Europe belonging to haplogroups I, E, G, J and T origin from pre-IE population? I am not convinced...

    Quote Originally Posted by Maciamo View Post
    - How much genetic impact did foreign slaves in the Antiquity have on the population of heavily slave-dependent economies like Italy and Greece ? Did ancient Greek and Roman freemen and nobles look very different from their (imported) slaves ? Is the modern population an admixture of both, and which component is the dominant one (given that the slaves outnumbered their master sometimes to a ratio of 10 to 1) ?
    there are lot of questions that comes to mind regarding this, e.g.:
    - was it common that slaves have famillies and leave offspring?
    - was perhaps origin of slaves, at least in earlier times, often from nearby tribes?
    - how numerous were in fact slaves in those societies?
    - where did the slaves origin from?
    - when and how did the people originating from slaves blended with people originating from previous upper castes?
    ...

  3. #3
    Regular Member Cambrius (The Red)'s Avatar
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    Autosomal DNA (full ancestry) provides a much fuller picture.

  4. #4
    aimless wanderer Mzungu mchagga's Avatar
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    Quote Originally Posted by Maciamo View Post
    When analysing the haplogroup frequencies in specific populations it doesn't always spring to mind that two populations with similar frequencies can look very different because of the way the "genetic elements" were mixed. Genetics is like cooking; you can make a lot of very different dishes with the same basic ingredients. A pancake, a French toast, a waffle, and scrambled eggs on a piece of bread are all derived from the same ingredients : eggs, milk and flour (with more or less water and sugar).

    We could also find two pictures that use exactly the same colours in the same proportions, and yet look very different. There are millions of combinations with the three primary colours (red, yellow, blue), and computer screens use a similarly basic combination (RGB).

    Imagine that three source populations merge together. To simplify things, let's say that one ethnic group is red, another is yellow and another is blue. Each make up 1/3 of the new population. If they stay side by side and never intermarry, the new population will remain 1/3 red, 1/3 yellow and 1/3 blue. If the yellow and blue intermingled to some extent, a bit or green will appear. If the red and blue have children together, there will be purple offspring.

    We could imagine a scenario where one ethnic group is the ruling dominant class, an aristocracy, and never mix with the two other groups. If it is the red one, after a while the population will look red (pure) and green (various shades, ranging from yellowish to blue green). However, if it was the blue ethnicity that became the ruling class, the overall population picture will look very different after a few centuries, with a blue group and the rest being shades of yellow, orange and red.

    But even the strictest caste systems are never perfectly impermeable, and the power of attractions between human with different genes will always lead to a certain amount of mixed offspring. Besides, revolutions happen, power changes hand, and lower class people can be elevated to nobility to thank them for the loyal services. Eventually, new admixture do take place.

    Given enough time, once the members of an isolated population have procreated with each others over hundreds of generations, the overall colour gets more uniform, homogeneous, and the original red, yellow and blue components end up in a brownish colour. If one group procreated more than the others for whatever reason these things happen (richer, better-looking, more promiscuous, more resistant to local diseases, or just more proficient at surviving), it will have a greater impact on the final colour.

    There are so many factors, and human societies and histories are so complex and full of unexpected events, that two populations starting with an identical admixture of ethnic groups will inevitably diverge the longer time passes. And I am not even taking genetic evolution (new mutations that arise at each birth) into account.

    The important lesson to learn here is that haplogroups only give one dimension of the picture. They are only the raw ingredients. The more time passes, the more homogeneous and unique the admixture will become.

    This is one it is vital to know when each haplogroup entered a given population. To make a French toast, you need to make the bread first (water + flour) then add the egg/milk admixture in the pan, then the sugar. If you mix the eggs and milk with the flour at the start, it will make a pancake. The cooking time at each step is also important. Just how homogeneous was one population when a group of foreign invaders came and settled within ?


    Here are a few concrete examples to think about :


    - Just how much had Paleolithic Europeans (hg I) mixed with Neolithic farmers (already an admixture of hg E, G, J and T) when the Indo-Europeans (a recent and uneven admixture of R1a1a, R1b1b2a1 and G2a3b1a) conquered Europe ? Did the I and E/G/J/T people live in clearly separate groups, or did they quickly merge with each others ? If they lived side-by-side, did this change after the Indo-European conquest ? Did the Indo-Europeans establish a caste system in Europe like in India ? How long did it last ? How often did they take brides within the non-IE population ?

    - How much genetic impact did foreign slaves in the Antiquity have on the population of heavily slave-dependent economies like Italy and Greece ? Did ancient Greek and Roman freemen and nobles look very different from their (imported) slaves ? Is the modern population an admixture of both, and which component is the dominant one (given that the slaves outnumbered their master sometimes to a ratio of 10 to 1) ?

    I really like what you've wrote here! Very comprehensible with good explanations and comparisons! I think this is something a layman to genetics and distribution of haplogroups -like me- should read as an introduction first before continuing further. I sometimes have the feeling many newcomers in this forum are confused with distinguishing haplogroups from ethnicities. So what about putting this article modified, as an introduction into the main genetics page?

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