The idea that virtually anyone with a European ancestor descends from English royalty seems bizarre, but it accords perfectly with some recent research done by Joseph Chang, a statistician at Yale University. The mathematics of our ancestry is exceedingly complex, because the number of our ancestors increases exponentially, not linearly. These numbers are manageable in the first few generations—two parents, four grandparents, eight great-grandparents, sixteen great-great-grandparents—but they quickly spiral out of control. Go back forty generations, or about a thousand years, and each of us theoretically has more than a trillion direct ancestors—a figure that far exceeds the total number of human beings who have ever lived.
In a 1999 paper titled "Recent Common Ancestors of All Present-Day Individuals," Chang showed how to reconcile the potentially huge number of our ancestors with the quantities of people who actually lived in the past. His model is a mathematical proof that relies on such abstractions as Poisson distributions and Markov chains, but it can readily be applied to the real world. Under the conditions laid out in his paper, 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. http://www.theatlantic.com/magazine/archive/2002/05/the-royal-we/302497/
In a 1999 paper titled "Recent Common Ancestors of All Present-Day Individuals," Chang showed how to reconcile the potentially huge number of our ancestors with the quantities of people who actually lived in the past. His model is a mathematical proof that relies on such abstractions as Poisson distributions and Markov chains, but it can readily be applied to the real world. Under the conditions laid out in his paper, 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. http://www.theatlantic.com/magazine/archive/2002/05/the-royal-we/302497/
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