Ubiquitous shared ancestry:
We found that even people living on opposite sides of Europe are genealogically closely related to each other over the past thousand years. Even pairs of people as far apart as the UK and Turkey share a chunk of genomic material 20% of the time. Since the chance that two people inherit genetic material from any one shared ancestor from 1,000 years ago is incredibly unlikely (<10-10), to explain such sharing we need these pairs of individuals to share many ancestors. In fact, they need to share a number of ancestors that is far larger than the size of European population, indicating that any pair of individuals share as ancestors all of the individuals alive back at the time in Europe, each many times over.
This strange idea that everyone is everyone’s ancestor was actually predicted about ten years ago by Joseph Chang (and collaborators) using maths and simulations. In hindsight this is intuitively clear, due to the rapidly expanding number of ancestors you have as you go back further and further in time. You have 2 parents, 4 grand-parents, 8 great-grandparents, and so on doubling every generation. After k generations you have 2^k ancestors, and this number grows so quickly that just a thousand years back (~30 generations) you have roughly 1 billion ancestors, which is far larger than the population size of the Earth (let alone Europe) back then. The consequence is that anyone alive 1,000 years ago who left any descendants will be an ancestor of every European. While the world population is larger than the European population, the rate of growth of number of ancestors quickly dwarfs this difference, and so every human is likely related genealogically to every other human over only a slightly longer time period. http://gcbias.org/european-genealogy-faq/
You can be related to the same ancestor multiple times. For instance, someone could be your great, great, great, great, great grandfather on your mother’s side and also on your father’s side. Because of this, you and I can share the same ancestral individual as a common ancestor many times over. People who share more common ancestors have more overlap this degree of relatedness. We can measure this difference through degree of shared genome, since even when everyone is a common genealogical ancestor, not everyone is a common genetic ancestor.
Also keep this in mind, once you get back to a certain point, the only records kept were for the upper classes, which usually meant the nobility. It is just a matter of numbers. We all have 2 parents, 4 grandparents, 8 great grandparents, 16 great-great grandparents, 32 great-great-great grandparents, etc.
Charlemagne comes up as my 36th great grandfather. In theory, he is just one of my 274,877,906,944 36th great grandparents. Now, since there were not 274.8 billion people in the world in 775 (there are only 7 billion now), there are a lot of places where the family tree does not split. There is no doubt if you will, if you haven't already, find a lot of cousins, even first cousins, marrying.
If you are a direct descendant from some of the first settlers from England, many were members of noble families who where in positions where they would not inherit land because of their birth order or they were fleeing for religious or political reasons. Even if your tree is filled with indentured servants in the beginning, within a few generations in the new world, those distinctions of class mattered less and less and the grandchildren of indentured servants became wealthy in their own rights.
This is not an excuse to be sloppy or lazy in your own research, but it should ease your mind when you come across famous ancestors whose descendants now number in the 10s of millions.
We found that even people living on opposite sides of Europe are genealogically closely related to each other over the past thousand years. Even pairs of people as far apart as the UK and Turkey share a chunk of genomic material 20% of the time. Since the chance that two people inherit genetic material from any one shared ancestor from 1,000 years ago is incredibly unlikely (<10-10), to explain such sharing we need these pairs of individuals to share many ancestors. In fact, they need to share a number of ancestors that is far larger than the size of European population, indicating that any pair of individuals share as ancestors all of the individuals alive back at the time in Europe, each many times over.
This strange idea that everyone is everyone’s ancestor was actually predicted about ten years ago by Joseph Chang (and collaborators) using maths and simulations. In hindsight this is intuitively clear, due to the rapidly expanding number of ancestors you have as you go back further and further in time. You have 2 parents, 4 grand-parents, 8 great-grandparents, and so on doubling every generation. After k generations you have 2^k ancestors, and this number grows so quickly that just a thousand years back (~30 generations) you have roughly 1 billion ancestors, which is far larger than the population size of the Earth (let alone Europe) back then. The consequence is that anyone alive 1,000 years ago who left any descendants will be an ancestor of every European. While the world population is larger than the European population, the rate of growth of number of ancestors quickly dwarfs this difference, and so every human is likely related genealogically to every other human over only a slightly longer time period. http://gcbias.org/european-genealogy-faq/
You can be related to the same ancestor multiple times. For instance, someone could be your great, great, great, great, great grandfather on your mother’s side and also on your father’s side. Because of this, you and I can share the same ancestral individual as a common ancestor many times over. People who share more common ancestors have more overlap this degree of relatedness. We can measure this difference through degree of shared genome, since even when everyone is a common genealogical ancestor, not everyone is a common genetic ancestor.
Also keep this in mind, once you get back to a certain point, the only records kept were for the upper classes, which usually meant the nobility. It is just a matter of numbers. We all have 2 parents, 4 grandparents, 8 great grandparents, 16 great-great grandparents, 32 great-great-great grandparents, etc.
Charlemagne comes up as my 36th great grandfather. In theory, he is just one of my 274,877,906,944 36th great grandparents. Now, since there were not 274.8 billion people in the world in 775 (there are only 7 billion now), there are a lot of places where the family tree does not split. There is no doubt if you will, if you haven't already, find a lot of cousins, even first cousins, marrying.
If you are a direct descendant from some of the first settlers from England, many were members of noble families who where in positions where they would not inherit land because of their birth order or they were fleeing for religious or political reasons. Even if your tree is filled with indentured servants in the beginning, within a few generations in the new world, those distinctions of class mattered less and less and the grandchildren of indentured servants became wealthy in their own rights.
This is not an excuse to be sloppy or lazy in your own research, but it should ease your mind when you come across famous ancestors whose descendants now number in the 10s of millions.
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