Everyone has trillions of ancestors. If you’ve never thought about this before, it might come as a surprise.
Nevertheless, the number of ancestors doubles each generation back. You have two parents, four grandparents, eight great grandparents, and so on. Assuming an average of 25 years per generation, if you were born about 1950 you would have 256 ancestors in the generation born about 1750, the generation that fought the American Revolution. The number quickly increases. Going back 20 generations to the generation born about 1450, the generation that fought the Wars of the Roses, you would have over a million ancestors. Going back 40 generations to the generation born about 950, when northern Europe was converting to Christianity, you would have over a billion ancestors — more than there were people in Europe. Seventy-eight generations back, the generation born at the time of Christ, you would have some 302,231,454,903,657,000,000,000 ancestors — far more than there have ever been humans on the earth. You can play with these numbers by assuming a different average length for each generation, but you won’t change the result; inevitably you end up with a particular number of ancestors in a given generation.
It should take only a moment to understand that one implication of the large number of ancestors we have is that each of us is descended from many marriages of distant cousins, so that the number of distinct persons in our ancestry is considerably fewer than the theoretical number of ancestors. Some experts believe that the vast majority of marriages throughout history have taken place between people no more distantly related than 2nd cousins. In fact, in about one-third of all human cultures the preferred marriage is between first cousins. Another third of cultures have no preference, and the final third disfavors marriages between cousins. In European cultures, the prejudice against cousin marriages goes back to the rules of the medieval Catholic church. Despite the church’s ban on marriages between relatives, some studies of medieval villages suggest that the normative marriage was between 3rd or 4th cousins; a relationship just distant enough to be deniable.
Because of the large number of theoretical ancestors, and necessary prevalence of marriages between cousins, some statisticians argue that every person in England must be descended from William the Conqueror; every person in western Europe must be descended from Charlemagne; and every person in continental Europe, western Asia and north Africa must be descended from Mohammed. Modern scholarship has even provided some conjectural links from Charlemagne back to the Anicii of the Late Roman Empire.
It is not at all uncommon for quite average people to have documented descents from these people. From doing genealogy, I’ve known hundreds of ordinary people with proven royal descents. (I have a few myself.) At the turn of the 20th century, there were an estimated 500,000 descendants of Edward III in Britain and America, and hundreds of thousands more descendants of Edward I. These English kings had the kind of diverse ancestry I’m talking about. Not only were they descended from William the Conqueror and Charlemagne (and perhaps from Mohammed), they were also descended from the earliest Norwegian kings, who lived in the 11th century and in turn had a legendary descent through the kings at Uppsala from the god Freyr.
In a lyrical passage, the historian Henry Adams wrote about the English, “If we could go back and live again in all of our two hundred and fifty million arithmetical ancestors of the eleventh century, we should find ourselves doing many surprising things, but among the rest we should certainly be ploughing most of the fields of the Cotentin and Calvados; going to mass in every parish church in Normandy; rendering military service to every lord, spiritual or temporal in all this region; and helping to build the Abbey Church at Mont-Saint-Michel.” I think it was Alex Shoumatoff who wrote that if we (people of English decent) could have a bird’s-eye view of England and western France in the years following the Black Death (1348), we would see that we are descended from every farmer tilling his field and every lord in his hall.
It should take only one further moment to realize that each of us also belongs to an extraordinarily large group of kin, more than we could ever keep track of. One expert asserted, “no people of English descent are more distantly related than 30th cousins.” Another study theorized that white Americans whose ancestors have been in America since before about 1850 are one of the largest, most closely related groups on earth – probably no more distant than 13th cousins to one another, because of their likely descent from a relative handful of early immigrants. For example, many of them (perhaps most of them) are descended from at least one of the the 30,000 immigrants to Massachusetts during the Great Migration 1620-1630. In short, we are all part of a huge inbred and interconnected kinship network.
Not only does our ancestry link us all together, it gives us an ancestral diversity far beyond what we see from looking only at our recent forbears. A person of English descent will probably descend from all the different ethnic groups that touched that country’s history, from the Celts, the Romans, the Anglo-Saxons, the Danes and the Normans. Each of those groups had its own cosmopolitan ancestry. The Roman soldiers stationed in Britain, for example, were drawn from all over the Empire. Modern genetic testing has now begun to provide proof of what statisticians have believed for years. For example, a man in Norway has mitochondrial DNA that shows his matrilineal ancestry to have been Korean. I have no doubt that he has some distant ancestor who came across the Indian trade routes, or perhaps came in the company of the Mongols in Russia. From Russia, it would have been an easy step to Sweden in the company of Norse traders.