The press, led by the Daily Mail and the New York Daily News, recently hailed the ‘remarkable discovery’ made by 12 year-old Californian genealogist BridgeAnne d’Avignon that 42 out of 43 US presidents have King John of England as a common ancestor.
King John, who ruled 1199-1216 AD, was not a particularly impressive figure in English history. Nicknamed ‘Lackland’ by his father Henry II who thought he would never inherit substantial lands, he is renowned for being forced to sign the Magna Carta in 1215, which limited the monarch’s power by law, and for losing the Crown Jewels in The Wash. But, by focussing on both male and female family lines, BridgeAnne traced an ancestral link to him that all US presidents share – bar one, Martin Van Buren.
But the most remarkable aspect of this story would be if Van Buren wasn’t descended from King John as well.
Boasting ‘royal blood’ isn’t about being born with a silver spoon in your mouth – even some US Presidents, such as Andrew Johnson and Bill Clinton, had famously humble backgrounds – it’s about mathematical probability. Andrew Millard of the University of Durham calculated the probability that anyone with Anglo-Saxon ancestry descends from King Edward III (1312-1377) to be as high as 99.997%, and conservatively estimated that Edward III has around 100 million descendants in the British Isles, Europe and former British colonies, including the USA, Canada and Australia.
The reason why US Presidents, or you and I, can claim royal ancestry is down to what genealogists call ‘pedigree collapse’. This happens when relatives (no matter how distantly related) marry, produce offspring and narrow a family tree through duplicate appearances on it. The further back you go, the more duplicates you’ll find through multiple lines of descent.
If you trace your lineage back over generations, the theoretical number of individual ancestors in your tree grows exponentially and soon exceeds the population from which your ancestors could possibly be drawn. If you go back 30 generations to the Middle Ages you would theoretically have over 1 billion ancestors on that generation line of your family tree, more than the population of the whole world at the time. If you go back a further 10 generations to the Dark Ages you would have over a trillion ancestors, at a time when the planet’s population was around 200 million. Divide your theoretical 1 trillion ancestors by the real population of 200 million, and the average ancestor would appear on your family tree 5,000 times. This assumes of course that all of the 200 million alive in the Dark Ages were capable of producing children – many didn’t and so wouldn’t appear on anybody’s family tree, meaning that your more prolific ancestors would actually appear many more than 5,000 times.
Demographer Kenneth Wachter first illustrated this in his 1980 book Ancestors at the Norman Conquest, which calculated that in 1977 an average Englishman born in 1947 would have had 32,768 theoretical ancestors 15 generations ago (at 30 years between generations), around 1527 AD; of these, 96% would have been ‘real’ and 4% duplicates. Going back 20 generations to 1377 AD and he would have over 1 million theoretical ancestors, 40% of which would be duplicates. 25 generations ago, around 1227 AD – not long after the reign of King John – he would have over 32 million theoretical ancestors, 94% of which would be duplicates and only 6% ‘real’, i.e. 2 million, or 80% of the estimated English population of 2.5 million at that time.
I’ve found an instance in my family tree where one individual, Nicholas Rimmer (1657-1717), features twice as an ancestor; once as my 8 x great grandfather through my direct paternal line, and again as my 8th x great grandfather through the lineage of a 4 x great grandmother. My case of pedigree collapse is very mild compared to that of Alfonso XIII of Spain (1886-1931), who only had 4 great-grandparents instead of the expected 8 because of royal inbreeding.
Your true family tree is therefore diamond-shaped rather than an inverted pyramid. The further back you go, the number of ancestors in each generation increases steadily up to a point, then slows, stops, then reduces. And as there are fewer people to put on the branches of the 7 billion family trees of people living today, it is a mathematical certainty that, at some point, there will be an ancestor who appears at least once on everybody’s tree – the ‘most recent common ancestor’ of all humans currently alive. A team led by Joseph Chang, a Yale professor of statistics, produced a complex computer model to estimate that this point was likely around 2,000 to 3,000 years ago.
The model accounted for complexities such as social barriers, physical barriers of geography and migration, and the impact of known events within the last 20,000 years. It also introduced the ‘identical ancestors point’, between 5,000 and 7,000 years ago, where everybody living today has exactly the same set of ancestors. In other words, every person who was alive at that time is either an ancestor to all 6.5 billion people living today, or their line died out and they have no remaining descendants.
This worldwide genealogical web is not so difficult to spin. If the history of mankind has one common theme, it is our ability to get around the planet, whether it is the migration of the first Siberian hunter gatherers into North America; the conquering armies of Julius Caesar and Alexander the Great; the raping and pillaging hordes of Vikings, Mongols, and Huns; the Empire builders of Spain, Portugal and Britain; the refugees of the Irish Potato Famine; or even the odd shipwrecked sailor. It takes just one ancestral link to a ‘foreign’ cultural group among your millions of ancestors, and you share ancestors with everyone in that group. Through this, some geneticists estimate that everybody on Earth is at least 50th cousin to everybody else.
As Joseph Chang’s team concluded, “No matter the languages we speak or the colour of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who laboured to build the Great Pyramid of Khufu.”
Or as statistician Jotun Hein of Oxford University remarked, “Had you entered any village on Earth in around 3,000 BC, the first person you would have met would probably be your ancestor.”
None of this should downplay the commendable work of a 12 year-old amateur genealogist in claiming that 42 out of 43 US Presidents descend from King John. But it’s not a remarkable coincidence that suggests a genetic ‘quest for power’. The remarkable bit is the statistical certainty which makes it so. And consider this: 2,000 years from now it is likely that everyone on Earth will be descended from most of us; and if you have a line of descendants that doesn’t die out, you will also eventually become an ancestor of the whole world.