Will-I-Am Indian, but does it matter?

At least I’m not French … oh, wait. Mark Richards/PA

The front-page of The Times carried a story today that William could be “Britain’s first king to have proven Indian ancestry”. The story continues inside, along with an advert for the personal DNA testing company who tested William’s relatives‘ DNA and, for a fee, will test yours.

What unfolds is an engaging story of William’s great-great-great-great-great grandmother, Eliza Kewark, and her life in 19th century India. Eliza was said to be Armenian, but now genetic evidence suggests she may have been the daughter of an Indian mother.

So how did they reach this conclusion? Every cell of your body contains tiny fuel factories called mitochondria, which contain a small percentage of your DNA. This “mtDNA” is unusual in being passed down from mother to child without any input from the father, while most of the genome comes from both parents and is shuffled each generation.

This means you have near identical mtDNA to your mother, your mother’s mother, and so on, the only variation coming from occasional mutations. This means everyone in the world could be represented on a branching tree, going back though time and space to a common maternal ancestor, known as the “Mitochondrial Eve”. So by looking at what set of mutations someone has, you can find which branch of the tree they sit on. And by testing many people, you can start to imagine where in the world each branch may have originated.

Two of Eliza’s maternal-line descendants, though not William himself, were tested, and share a set of mutations that has only previously been seen in the Indian subcontinent. This strongly suggests a maternal-line ancestry that passes through that region on its long journey back to our African “Mitochondrial Eve”.

It can be interesting to get such information from your own DNA and to think about what it means, but be careful - it’s easy to write stories that you can’t really back up. Such “genetic astrology” has proven to be extremely tempting, but there is little meaning in genetic history without other evidence to complement it.

The vividness of Eliza’s story owes more to the historical record than it does to genetic tests. Without it, we are left with the statement that William’s mtDNA matches some found in South Asia.

It is also important to remember that the tree that you are being mapped onto is not a tree of the ethnic and national distinctions that we have grown up with. It is one of expansions, extinctions and parallel journeys though populations, and the identities of these populations may change or be forgotten on a relatively short time-scale.

Again, William is lucky in that he has such a rare set of mutations, but for many the picture is less clear, as similar sequences may be found over large areas of the globe. Even for rare sequences, there’s no guarantee that if more people were tested, the geographical picture would remain the same. For example, it is possible that Eliza’s mtDNA could have existed in Armenia for generations before her, arriving from India or elsewhere with one of her ancestors.

Another question to ask is: How much should I care about my maternal-line? It is true that studies based on mtDNA can reveal interesting phenomena. When looking at many people at a time, it can be used to examine how populations have moved and spread around the world.

On an individual level, variation in mtDNA can explain several nasty inherited diseases, but apart from that I don’t think it says too much about you. If you have a need for an ethnic identity, I don’t know whether it can provide you with one.

Your maternal line accounts for only one of your two parents, one of your four grandparents, one of your eight great-grandparents. Eliza was one of William’s 128 great-great-great-great-great grandparents, each with a story to tell. The number of ancestors doubles in each generation and, as people have always moved around, you don’t need to go back too far for you, William or the current monarch to have Indian ancestry.

It would be great if William’s Indian ancestry can help to bring together Britons of different colours at a time when some with more recent ancestry from the subcontinent may feel less welcome than they used to. It can be argued that this single line of descent amongst many can have little more than symbolic value, but then what is the monarchy itself except a symbol based on another of his single lines of descent?