Saturday’s coronation of King Charles III may spark excitement or indifference, but regardless of one’s opinion of the ceremony, there’s one point everyone can agree on: Charles is the one who won the crown because of his line of succession.
About 28 generations up the family tree of the current British monarch is William of Normandy, who defeated his Anglo-Saxon opponent Harold II at the Battle of Hastings in 1066 and forever changed the course of English history.
For those busy or simply intrigued by genealogy, this is an occasion to wonder just how much of the royal bloodline Charles inherited. To put the question more scientifically, how much of William the Conqueror’s DNA is present in Charles’ genome?
The answer—which may come as a surprise to non-geneticists—is almost certainly nothing.
The reason does not include any speculation as to the paternity of those who preceded Charles in the long line from William. It’s more a matter of probabilities.
This point is succinctly explained by David Reich, professor of genetics at Harvard Medical School, in his 2018 book. Who we are and how we got here.
As Prof. Reich points out, inheritance is diluted by the splitting and mixing of genes that occurs with each successive generation. You and everyone you know carry a mixture of DNA that comes from two parents. Your parents, in turn, received this DNA from your four grandparents, who received it from your eight great-grandparents, who received it from your 16 great-great-grandparents, and so on.
Going back four generations, there remains a 100 percent chance that you carry at least some DNA from all 16 of these ancestors. Going further, however, the continued fragmentation of the genome means that some ancestors have been lost in the mix. 10 generations ago, you have 1,024 direct ancestors, but only a 50 percent chance that you inherited DNA from any particular one of them. Going back 15 generations, that probability drops to just 3 percent. By 28 generations, the chance of any part of William the Conqueror’s DNA surviving molecular transmission and making it all the way to Charles is vanishingly small.
It’s certainly possible to inherit DNA from an ancestor in more than one way, said Simon Gravel, who holds the Canada Research Chair in Statistical and Population Genetics at McGill University in Montreal.
As Dr. Gravel demonstrated in a recent study of the French population of Quebec, the majority of those who today belong to this population group are genetically descended from only 8,500 individuals who came to Canada from France in the 17th and 18th th century Of these, the first 2,600 to arrive contributed about two-thirds of Quebec’s total gene pool.
Likewise, in the context of historical and modern England, it is certain that Charles has many of the same genes as William the Conqueror, who would both have been inherited from common ancestors dating back many tens of centuries.
But unless Charles descended from William in a thousand different ways, “which seems unlikely even given the high level of inbreeding in the British royal family,” writes Prof. Reich, it is implausible to imagine that the first Norman king of England was born nearly 1000 years ago left some mark on Charles today.
“My reasonable guess here would be that they wouldn’t be any more closely related than any two Brits because it doesn’t take much mixing to make everyone similarly related,” Dr . Gravel said.
The two exceptions are in mitochondrial DNA, which survives only through the maternal line, or in Y-chromosomes, which are passed from father to son. They change only gradually and can be linked back many generations. By comparing mitochondrial DNA, for example, researchers were able to determine that a skeleton found under a car park in Leicester, UK, in 2012 was genetically related to known living relatives of King Richard III.
However, since Charles is descended from the medieval rulers of England through a combination of male and female ancestors, he has no such continuous connection with those individuals, including William.
What does this mean for the legitimacy of the monarch today? Practically nothing. Legally, inheritance is based on descent, but not on exact chromosome content.
But for those fascinated by famous ancestors – whether they are a king’s or their own – it’s worth remembering that such perceived connections may be less significant than they appear.
“Some people tend to take their ancestry very seriously and are encouraged to do so by ancestry testing companies,” Dr. Gravel said. “But as a geneticist, I try to encourage people not to put too much importance on these things, because they tend to be over-interpreted.”