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chimney.
This is how I got to know the data. Thanks to a mapping program written by a colleague, I
could quickly place any selection of DNA sequences on a map of the Isles. As I did this I soon
noticed that some DNA sequences were found in all parts of the Isles, while others were very
localized. For instance, I had found one particular mDNA sequence in the clan of Tara four times in
Skye, once in Lewis in the Western Isles and once in Glasgow – and nowhere else in the world.
When I looked up in my records where on Skye the four people lived, I saw they came from
different parts of the island. But all traced their maternal ancestry back to the Isle of Rona.
Drive to the north end of Skye past the eroded cliffs and pinnacles of Trotternish, high above
the sea, and Rona is the low rocky island on your right, lying 5 miles offshore. It looks as if it is
connected to the longer, higher island of Raasay to the south, but it is not. A hidden sea channel
separates the two islands. Rona is deserted now, but once held a few crofting families who fished
in the dark blue seas. Their houses have been abandoned and only the lighthouse, white against the
rocks, is visible from Skye.
What must have happened on Rona to account for the unusual DNA I had found on Skye was a
mutation, a slight change in the DNA of one of the ancestors. Silent, unnoticed and with no effect at
all on the woman in whom this event had occurred, just one DNA base, one bead on the chain, had
changed. The new sequence was unique, never seen before in the history of the world. If this
woman had been childless or had only sons, it would have died with her. No one would ever know
it had been created. But she must have had children, and at least one of her children must have been
a girl for her mDNA to be passed on. Through this girl, or her descendants, this new sequence left
the island of Rona and found a home on nearby Skye, where it still remains. From there, perhaps
one of the daughters in the next generation went to live on Lewis while another travelled down to
Glasgow. I cannot tell exactly when this happened, but the journeys have been recorded by the
genes of the descendants. I have not found this particular sequence of DNA letters anywhere else.
Nor has anyone as far as I am aware. That doesn’t mean it isn’t there in other parts of Scotland, or
Ireland, or Wales, or England. Just that we haven’t found it. That is always the way, and always
will be. We will never know everything there is to know about this new gene and what happened to
it. We can only piece together something of its journey from the scraps of information that have both
survived to the present day and that we have found in the cells of people we have tested.
This is a little story of one particular gene, a new version that has changed very slightly. If we
ever do come across it again in the future, we will know it has travelled from Rona. It is a
fragment, like a piece of pottery or a flint tool, and just as reliant on the twin necessities of survival
and discovery as any archaeological remains. This is how I would build the genetic history of the
Isles, by sifting through the thousands of fragments, trying to make sense of them. I would treat them
as if they were the scattered shards of broken pottery and do what I could to understand what they
meant. This was the point at which I decided to become a genetic archaeologist. I would work with
fragments of DNA, perfectly preserved in the bodies of descendants, to reconstruct the travels of
their ancestors with the same discipline that an archaeologist would use when excavating a site.
Collect, examine, record, compare, interpret. In my mind’s eye, even though they were in reality
stored on my computer, I began to think of them as, literally, a pile of fragments, pottery perhaps or
maybe coins. Yes, coins would be an even better metaphor. Through Chris Howgego, a friend and
colleague from Oxford, I had been allowed to examine the Ashmolean Museum’s collection of