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Does a common ancestor become less relevant with distance?

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  • Does a common ancestor become less relevant with distance?

    How far back does one need to go until, in your opinion, a segment from a shared ancestor becomes largely irrelevant?

    I mean if one shares a segment of DNA with a 14th cousin from a 16th century ancestor, does not the sheer distance and greatly reduced size of population back then make this shared DNA virtually indistinguishable from the general population?

    I'm reminded of the theory, based on mathematical probability, that virtually every European is descended from Charlemagne. What of genetic matches from later on but still a long time ago, such as 500 years back?
    Last edited by Matt62; 7 July 2015, 11:34 AM.

  • #2
    I would think it depends on the type of DNA test. Family Finder is limited in the number of generations you can find matches for. yDNA would be limited by only looking at your direct PATERNAL path... therefore, if you had a direct male line from say Charlemaigne to yourself, then you should be able to trace that route (given papertrails you can confirm with. Likewise, mtDNA is your direct MATERNAL path... so your mother's mother's mothers.... path can be traced by DNA for many MANY generations. Sadly, the papertrail to confirm who is who is often lacking in both scenarios.

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    • #3
      Charlemagne...

      Let's skip him when talking about genetics of populations. For centuries in Europe, populations did not mix, the same way they did later, due to geography (mountains, rivers, forests etc.). Charlemagne is not in ancestry of most Europeans, and surely not for virtually every European...

      For an estimate on his descendants, please go to http://roglo.eu/roglo?lang=en

      Search for Charlemagne. His page is a long one, just go to the bottom.

      Select Descendants. You will see that so far only more than one million were found.

      W. (Mr.)

      P.S.
      The interface can be switched between many languages, but the entries in the database are in French. You may want to enlist aid from http://fr.wikipedia.org/ when navigating to his descendants.

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      • #4
        Originally posted by dna View Post
        Charlemagne...

        For an estimate on his descendants, please go to http://roglo.eu/roglo?lang=en

        Search for Charlemagne. His page is a long one, just go to the bottom.

        Select Descendants. You will see that so far only more than one million were found.
        That list is FAR from complete though - for example it doesn't go past King John (Lackland) of England, and includes none of his children or descendants even though he is known to be an ancestor of a great number of British nobility. (and probably a lot of modern non-nobility)

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        • #5
          Originally posted by Adam Nisbett View Post
          That list is FAR from complete though - for example it doesn't go past King John (Lackland) of England, and includes none of his children or descendants even though he is known to be an ancestor of a great number of British nobility. (and probably a lot of modern non-nobility)
          Actually, it is the opposite. John I Lackland Plantagenêt (Jean sans Terre) is listed there with 856773 descendants (as of today). That means the bulk of Charlemagne descendants are through King John.

          There is a limit of generations that can be displayed through a single query by guest users of the roglo database.

          W. (Mr.)

          P.S.
          If you know about people who could be added to that database, the researches behind roglo would be extremely happy to add them.

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          • #6
            That is interesting DNA.

            The reason I bore this belief regarding Charlemagne, is that I have read numerous articles which claim that since we would have something like trillions of ancestors at the 35th generation (aka Charlemagne in the ninth century) and the European population at the time would only have been in the relatively low millions, this indicates that practically everybody back then from whom lines of descent can be connected can be expected to be an ancestor of every Western European alive today, even if many cannot get an actual paper trail connection.

            FYI I think I can trace a line of descent directly to Charlemagne through Robert the Bruce's daughter Matilda. I've conclusively got back to the Bruce anyway through my Carstairs line (Sir John Carstairs of Kilconquhar born 1605). I feel, rightly or wrongly, that almost anyone with Western European ancestry and a decent pedigree on at least one line could connect themselves to minor nobility around 1500-1600, then to major nobility, then to royalty and presumably through inter-breeding among royals to the man himself.
            Last edited by Matt62; 10 July 2015, 06:56 AM.

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            • #7
              I should note that I am referring to purely genealogical ancestral descent, not genetic, when I speak of Charlemagne's living descendants. I imagine that Charlemagne's DNA has probably long since died out or at the very least been chopped to smithereens through so many recombinations.
              Last edited by Matt62; 10 July 2015, 07:10 AM.

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              • #8
                Originally posted by Matt62 View Post
                That is interesting DNA.

                The reason I bore this belief regarding Charlemagne, is that I have read numerous articles which claim that since we would have something like trillions of ancestors at the 35th generation (aka Charlemagne in the ninth century) and the European population at the time would only have been in the relatively low millions, this indicates that practically everybody back then from whom lines of descent can be connected can be expected to be an ancestor of every Western European alive today, even if many cannot get an actual paper trail connection.

                FYI I think I can trace a line of descent directly to Charlemagne through Robert the Bruce's daughter Matilda. I've conclusively got back to the Bruce anyway through my Carstairs line (Sir John Carstairs of Kilconquhar born 1605). I feel, rightly or wrongly, that almost anyone with Western European ancestry and a decent pedigree on at least one line could connect themselves to minor nobility around 1500-1600, then to major nobility, then to royalty and presumably through inter-breeding among royals to the man himself.
                Oh, that argument

                Whoever the original author was, she or he did not take into account pedigree collapse
                http://en.wikipedia.org/wiki/Pedigree_collapse
                http://www.isogg.org/wiki/Pedigree_collapse
                http://www.familytreedna.com/learn/a...any-ancestors/

                W. (Mr.)

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                • #9
                  Originally posted by dna View Post
                  Oh, that argument

                  Whoever the original author was, she or he did not take into account pedigree collapse
                  http://en.wikipedia.org/wiki/Pedigree_collapse
                  http://www.isogg.org/wiki/Pedigree_collapse
                  http://www.familytreedna.com/learn/a...any-ancestors/

                  W. (Mr.)
                  Thanks for that, I'm still trying to wrap my head around all this!

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                  • #10
                    What should I make of this article from National Geographic. It contends that ALL Europeans alive 1000 years ago, who have any descendants living today, are direct ancestors of ALL Europeans living today, apparently using pedigree collapse to substantiate it:

                    http://phenomena.nationalgeographic....ersal-royalty/



                    It is much more fun to think that I am a bloodline descendant of Charlemagne. And in 1999, Joseph Chang gave me permission to think that way.

                    Chang was not a genealogist who had decided to make me his personal project. Instead, he is a statistician at Yale who likes to think of genealogy as a mathematical problem. When you draw your genealogy, you make two lines from yourself back to each of your parents. Then you have to draw two lines for each of them, back to your four grandparents. And then eight great-grandparents, sixteen great-great-grandparents, and so on. But not so on for very long. If you go back to the time of Charlemagne, forty generations or so, you should get to a generation of a trillion ancestors. That’s about two thousand times more people than existed on Earth when Charlemagne was alive.

                    The only way out of this paradox is to assume that our ancestors are not independent of one another. That is, if you trace their ancestry back, you loop back to a common ancestor. We’re not talking about first-cousin stuff here–more like twentieth-cousin
                    . This means that instead of drawing a tree that fans out exponentially, we need to draw a web-like tapestry.

                    In a paper he published in 1999 [pdf], Chang analyzed this tapestry mathematically. If you look at the ancestry of a living population of people, he concluded, you’ll eventually find a common ancestor of all of them. That’s not to say that a single mythical woman somehow produced every European by magically laying a clutch of eggs. All this means is that as you move back through time, sooner or later some of the lines in the genealogy will cross, meeting at a single person.

                    As you go back further in time, more of those lines cross as you encounter more common ancestors of the living population. And then something really interesting happens. There comes a point at which, Chang wrote, “all individuals who have any descendants among the present-day individuals are actually ancestors of all present-day individuals.”

                    In 2002, the journalist Steven Olson wrote an article in the Atlantic about Chang’s work. To put some empirical meat on the abstract bones of Chang’s research, Olson considered a group of real people–living Europeans.

                    The most recent common ancestor of every European today (except for recent immigrants to the Continent) was someone who lived in Europe in the surprisingly recent past—only about 600 years ago. In other words, all Europeans alive today have among their ancestors the same man or woman who lived around 1400. Before that date, according to Chang’s model, the number of ancestors common to all Europeans today increased, until, about a thousand years ago, a peculiar situation prevailed: 20 percent of the adult Europeans alive in 1000 would turn out to be the ancestors of no one living today (that is, they had no children or all their descendants eventually died childless); each of the remaining 80 percent would turn out to be a direct ancestor of every European living today.

                    Suddenly, my pedigree looked classier: I am a descendant of Charlemagne. Of course, so is every other European. By the way, I’m also a descendant of Nefertiti. And so are you, and everyone else on Earth today. Chang figured that out by expanding his model from living Europeans to living humans, and getting an estimate of 3400 years instead of a thousand for the all-ancestor generation.

                    Things have changed a lot in the fourteen years since Chang published his first paper on ancestry. Scientists have amassed huge databases of genetic information about people all over the world. These may not be the same thing as a complete genealogy of the human race, but geneticists can still use them to tackle some of the same questions that intrigued Chang.
                    Last edited by Matt62; 10 July 2015, 07:44 AM.

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                    • #11
                      Someone beneath the article makes an interesting point:

                      There must be few factors that are not known and considered in those maths . In our family tree I could trace back most branches on average until around 1600 -1700. Many go much further , and some go to noble ancestors , and also to Charlemagne...But the thing is, I have found until now around 2500 direct ancestors of which maybe I roughly estimate at around 1650...So that’s about 350 years back in time. How many would that be around 800 AD? A couple of thousand ancestors at that time? Maybe 10,000? Now consider this from Wikipedia:http://en.wikipedia.org/wiki/Medieval_demography “Estimates of the total population of Europe are speculative, but at the time of Charlemagne it is thought to have been between 25 and 30 million, and of this more than half were in the Carolingian Empire that covered modern France, the Low Countries, western Germany, Austria, Slovenia, northern Italy and part of northern Spain.[1] Some medieval settlements were more than relatively large, with agricultural land and large zones of unpopulated and lawless wilderness in between” So how much chance is their to be an ancestor than of Charlemagne?

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                      • #12
                        Such factors are known, and here are some of them.

                        General tendency to marry within a fairly limited geographical area. It used to be within a daily walking distance, nowadays it is probably within a daily driving distance .

                        Geographical barriers like forests, lakes, mountains, rivers, swamps.

                        Language differences.

                        Taboos against marrying from another cast (or just another social strata), religion, tribe etc. Customs between adjacent tribes can vary enough that either a female or a male would find it very difficult to start living anew in another tribe. And different social strata still seldom intermarry (today that would be welfare recipients not marrying business leaders...).

                        These are almost universal restrictions and they are applicable to populations.

                        On the other hand, as I keep writing in the forum, it is next to impossible to predict someone's deep ancestry since centuries ago an individual could have travelled (or was moved) quite a large distance as a craftsman, merchant, performer, seasonal worker, servant, slave, soldier, teacher etc.

                        Can the above be easily modelled? So far not , but it does not mean that an oversimplified theory should be used to reach invalid conclusions.

                        Mr. W.

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                        • #13
                          Originally posted by dna View Post
                          On the other hand, as I keep writing in the forum, it is next to impossible to predict someone's deep ancestry since centuries ago an individual could have travelled (or was moved) quite a large distance as a craftsman, merchant, performer, seasonal worker, servant, slave, soldier, teacher etc.
                          With the age of exploration, sailors could jump ship almost any where in the world or at least leave their DNA. Some people seem to be surprised when evidence of this shows up.

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                          • #14
                            Originally posted by georgian1950 View Post
                            With the age of exploration, sailors could jump ship almost any where in the world or at least leave their DNA. Some people seem to be surprised when evidence of this shows up.
                            Populations are somewhat predictable, but any individual has genetic history that needs to be researched by performing DNA tests. It cannot be just inferred based on her or his paper trail from recent years (or even recent centuries).

                            An example. We can say that the francophone population of Quebec has French roots, but a French speaking individual from that population could have Russian DNA from all four of his grandparents who migrated to Canada after the October revolution. (And they had a higher chance of knowing French, than English...)

                            W. (Mr.)

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                            • #15
                              Originally posted by Matt62 View Post
                              Someone beneath the article makes an interesting point: "There must be few factors that are not known and considered in those maths . In our family tree I could trace back most branches on average until around 1600 -1700. Many go much further , and some go to noble ancestors , and also to Charlemagne...But the thing is, I have found until now around 2500 direct ancestors of which maybe I roughly estimate at around 1650...So that’s about 350 years back in time. How many would that be around 800 AD? A couple of thousand ancestors at that time? Maybe 10,000? Now consider this from Wikipedia:http://en.wikipedia.org/wiki/Medieval_demography “Estimates of the total population of Europe are speculative, but at the time of Charlemagne it is thought to have been between 25 and 30 million, and of this more than half were in the Carolingian Empire that covered modern France, the Low Countries, western Germany, Austria, Slovenia, northern Italy and part of northern Spain.[1] Some medieval settlements were more than relatively large, with agricultural land and large zones of unpopulated and lawless wilderness in between” So how much chance is their to be an ancestor than of Charlemagne? "
                              I think this person either is assuming an enormous pedigree collapse or is not taking into account the exponential nature of ancestry. 1650 is roughly 400 years ago. 800AD is 1200 (3 times as far back) However, the number of ancestors DOUBLES in every generation that of the previous generation (until pedigree collapse mitigates that) To assume a number of ancestors at 800AD around 10,000 (only 4x the number they were assuming for 1650) basically says that pedigree collapse can reduce an exponential rate to a linear one. If you go far enough back then yes, pedigree collapse becomes dominant enough to do that, but I'm hesitant to think it would reach that point before you reach a point where virtually all the members of a population are one's ancestors.

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