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The number of Ancestors

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  • Rebekah Canada
    Hi, The walk through on the number of ancestors anyone has goes something like this. Say that the average number of years per generation is 25. Now we know
    Message 1 of 4 , Jun 14, 2008
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      Hi,
       
      The walk through on the number of ancestors anyone has goes something like this. Say that the average number of years per generation is 25. Now we know that the number of ancestors grows exponentially each generation: two parents, four grandparents, eight great grandparents.
       
      Here then are the generations, number of needed ancestors, and year for each generation going back.
       
      1 2 1950
      241925
      381900
      4161875
      5321850
      6641825
      71281800
      82561775
      95121750
      1010241725
      1120481700
      1240961675
      1381921650
      14163841625
      15327681600
      16655361575
      171310721550
      182621441525
      195242881500
      2010485761475
       
      The number of needed ancestors rapidly exceeds the historic population. For most of us it turns out that our ancestors were marrying cousins from a limited number of towns. Depending on the norms of the day they might have been 2nd cousins or 10th cousins.
       
      If we could all get all of our lines back even 15 generations then we would see the same names cropping up time after time.
       
       
      Regards,
      Rebekah
    • Chet
      After 9 or 10 generations you far exceeds the average population of the Shtetl, and you d have to figure that the original population of Ashkenazim in northern
      Message 2 of 4 , Jun 14, 2008
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        After 9 or 10 generations you far exceeds the average population of
        the Shtetl, and you'd have to figure that the original population of
        Ashkenazim in northern France could not have been more than a few
        hundred families. That and the prevalence of genetic disorders among
        the Ashkenazim, one could speculate that there must be more than one
        bottleneck in the family tree. That and I am my own grampa.




        , --- In Ashkenazi-Q@yahoogroups.com, "Rebekah Canada"
        <rebekahthorn@...> wrote:
        >
        > Hi,
        >
        > The walk through on the number of ancestors anyone has goes
        something like
        > this. Say that the average number of years per generation is 25. Now
        we know
        > that the number of ancestors grows exponentially each generation: two
        > parents, four grandparents, eight great grandparents.
        >
        > Here then are the generations, number of needed ancestors, and year
        for each
        > generation going back.
        >
        > 1 2 1950 2 4 1925 3 8 1900 4 16 1875 5 32 1850 6 64 1825 7 128
        1800 8
        > 256 1775 9 512 1750 10 1024 1725 11 2048 1700 12 4096 1675 13 8192
        1650 14
        > 16384 1625 15 32768 1600 16 65536 1575 17 131072 1550 18 262144 1525 19
        > 524288 1500 20 1048576 1475
        >
        > The number of needed ancestors rapidly exceeds the historic
        population. For
        > most of us it turns out that our ancestors were marrying cousins from a
        > limited number of towns. Depending on the norms of the day they
        might have
        > been 2nd cousins or 10th cousins.
        >
        > If we could all get all of our lines back even 15 generations then
        we would
        > see the same names cropping up time after time.
        >
        >
        > Regards,
        > Rebekah
        >
      • NADENE GOLDFOOT
        Right, Rebecca, I ve seen this happen in American families from the 1600 s, 1700 s, etc. There was a limited amount of people to choose mates from, and they
        Message 3 of 4 , Jun 14, 2008
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          Right, Rebecca,
          I've seen this happen in American families from the 1600's, 1700's, etc.  There was a limited amount of people to choose mates from, and they often married cousins.  I've seen this on my own Jewish families.  It's interesting to see just in my city the new immigrants marrying each other and the tree will have branches throughout showing they are marrying each other at different generations.  After all, transportation was limited.  I've seen the same names cropping up on my trees.  That's when it gets interesting.  The more your tree branches out, the more you get a chance to see the connections.
          Nadene
          ----- Original Message -----
          From: Chet
          Sent: Saturday, June 14, 2008 2:09 AM
          Subject: [Ashkenazi-Q] Re: The number of Ancestors

          After 9 or 10 generations you far exceeds the average population of
          the Shtetl, and you'd have to figure that the original population of
          Ashkenazim in northern France could not have been more than a few
          hundred families. That and the prevalence of genetic disorders among
          the Ashkenazim, one could speculate that there must be more than one
          bottleneck in the family tree. That and I am my own grampa.

          , --- In Ashkenazi-Q@ yahoogroups. com, "Rebekah Canada"
          <rebekahthorn@ ...> wrote:
          >
          > Hi,
          >
          > The walk through on the number of ancestors anyone has goes
          something like
          > this. Say that the average number of years per generation is 25. Now
          we know
          > that the number of ancestors grows exponentially each generation: two
          > parents, four grandparents, eight great grandparents.
          >
          > Here then are the generations, number of needed ancestors, and year
          for each
          > generation going back.
          >
          > 1 2 1950 2 4 1925 3 8 1900 4 16 1875 5 32 1850 6 64 1825 7 128
          1800 8
          > 256 1775 9 512 1750 10 1024 1725 11 2048 1700 12 4096 1675 13 8192
          1650 14
          > 16384 1625 15 32768 1600 16 65536 1575 17 131072 1550 18 262144 1525 19
          > 524288 1500 20 1048576 1475
          >
          > The number of needed ancestors rapidly exceeds the historic
          population. For
          > most of us it turns out that our ancestors were marrying cousins from a
          > limited number of towns. Depending on the norms of the day they
          might have
          > been 2nd cousins or 10th cousins.
          >
          > If we could all get all of our lines back even 15 generations then
          we would
          > see the same names cropping up time after time.
          >
          >
          > Regards,
          > Rebekah
          >

        • Rebekah Canada
          Chet, Things don t get as bad as being your own grampa. :-) But you can see how with a small starting population like 25,000 in the thirteen hundreds
          Message 4 of 4 , Jun 14, 2008
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            Chet,

            Things don't get as bad as being your own grampa. :-) But you can see
            how with a small starting population like 25,000 in the thirteen
            hundreds intermarriage was necessary. There are other factors. Social
            structure would have played a part too. So there might have been
            social groupings that would necessitate looking to another Shtetl for
            a spouse.

            I have uploaded a copy of 'A genetic profile of contemporary Jewish
            populations' by Harry Ostrer. It is mentioned as a source in some of
            Dr. Behar's papers. I think that the links between diseases in
            different Jewish populations is interesting and can help us understand
            movements between the groups. With small populations it only would
            take one or two people with a recessive trait like one of these
            diseases or even blue eyes. Within a few generations it might be
            spread throughout the Shtetl and into surrounding ones. Those
            recessives may well have been carried into Germany by the
            pre-Ashkenazi population.

            Finding the connections is important then. As Nadene mentioned,
            tracking cousins helps show the big picture.

            --
            Peace and Light,
            Rebekah
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