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FTDNATiP™ & Generation length

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  • #16
    Same here

    I have to agree on the use of about 30 years per generation. My own genealogical tree shows it. I haven't calculated an average, but if I would, it would give me a number around 30. The shortest was about 20 for males and 16 for females. On the higher end, it would reach 50 and 30+, respectively. So 30 for male and 25 for female would make sense to me.

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    • #17
      Originally posted by T E Peterman
      Jim,

      You are missing my point. True, a thousand or 10,000 years ago, without the rituals of school & other passings that lead to adulthood today, the average man probably married (or began to sire children) at a younger age. True, way back then, for the average man, 35 was old.

      However, thanks to natural selection (which could be called the "law of differential reproduction"), none of us living today are descended from the average man. We are descended from that small minority that were exceptionally good reproducers. They may have begun siring children when they were young, but they continued until they were quite old. The average age of fatherhood for this small minority of men was probably 30 to 35 in agricultural times & may have been 25 to 30 in prehistoric times.

      If geneticists like Spencer Wells would factor in the longer generation length for men, they would probably resolve the discrepancy between the suggested dates of departure from Africa for non-African men & women. Mtdna suggests 80,000 years ago. Y-dna, according to Wells, suggests 55,000 to 60,000 years ago.

      Timothy Peterman

      Tim i dont think the people in niger and the rest of africa would agree or india and china where they kill extra children
      in the west yeah maybe

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      • #18
        Years/generation

        The formula used in the S*RM*N DNA Project is to take the earliest recorded, or circa, baptism and the last and divide by number of generations. The results range from 27 years/generation to 41.7


        Maureen Surman
        ============
        S*RM*N = SERMAN thru to SURMON

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        • #19
          Prior to the advent of farming about 15,000 years ago, humans would have been much more mobile. I have read that they had fewer children and probably lived older than was previously thought.

          Since most of our history is before farming, I wonder what the generation gap was back then.

          I think it is important to separate FTDNAtip and estimating relationships for the last 1000 years, from deep ancestry which may have been very different.

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          • #20
            I recently picked up a copy of Cavalli-Sforza's book on consanguinity in Italy. As part of the research they calculated, using church records, the average age of men and women from Parma at the birth of their children.

            For men it was about 33 years, and for women it was about 28 years.

            I think the time period was 1815 to present.

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            • #21
              The Probability Distribution of Mutations

              The FTDNATIP report gives the probability (converted to a percent) that two individuals share a common ancestor within a stated number of generations. For example, 33.57% that the commom ancestor is within 4 generations, 55.88% that the commom ancestor is within 8 generations, etc.

              I understand how they determine the rate of mutations, but to calculate these percentages, they must make some assumption about the probability distribution of the mutations. Obvious choices are the normal, the negative bionomial, or the Poission distributions, but I cannot find where they identify the distribution they use.

              Can anyone give me a clue or a reference?

              Jim Gates

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              • #22
                I'm not a mathematician...

                but anecdotally - in my case - Mr. Peterman is correct. average age of forefathers for last few hundred years in the low-mid thirties.

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                • #23
                  Even longer ago . . . .

                  Using data from the 1427 tax census of Florence, Italy I calculated the median age of male heads of households. It is 45 years, and the distribution of ages is shown in the graphic I attached to this message. Interestingly, there are more 70 year old household heads than 20 year old ones.

                  And the age of the household head is not at all correlated with the tax assesment, implying that people in Florence did not die notably younger if they were poorer.

                  The spike in frequency of 80 year men is likely to correspond to an uncertainty of age: "old" men were likely said to be 80 years old, which is telling in its implication for expectations of mortality.

                  The data do not directly demonstrate fertility, but the implications are clear and certainly suggest that nearly six centuries ago men routinely lived long enough to father children well into their fifties, making the emerging estimate of 30-35 years more likely for the generational duration than the earlier 25 year estimate.

                  http://chnm.gmu.edu/worldhistorysources/r/89/whm.html
                  Attached Files
                  Last edited by vineviz; 31 July 2006, 06:33 PM.

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