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5–10 per cent higher than in the surrounding areas. It is known that Henry I forcibly transferred a
colony of Flemish refugees fleeing political repression in Holland and Belgium to the area in the
early twelfth century. The high levels of blood group A have been attributed to this historical influx
and are often quoted in popular accounts as a classic success of blood grouping confirming history.
This is despite the levels of blood group A in the Low Countries not being particularly high.
However, a very different explanation was favoured by the Welsh scientist Morgan Watkin, the man
who originally noticed the high proportion of group A in parts of Pembrokeshire. He put it down to
a substantial Viking settlement in the region, despite the fact that there is very little in the way of
archaeology or place-names to support it. But the fact remains that, even after thousands of blood
samples from Wales and hundreds of thousands from all over Britain and Ireland, it is still
impossible to decide whether the unusual blood-group composition of this part of Wales was
caused by rampaging Vikings or by a few cartloads of Belgians.
The root of the problem is that, despite there being vast amounts of very reliable data, blood
groups just do not have the power to distinguish these two theories, nor the power to propose new
ones that might fly in the face of historical or archaeological evidence. Blood groups, despite the
advantage of objectivity, are a very blunt instrument indeed with which to dissect the genetic
history of a relatively small region like the Isles. Fortunately, we can sharpen our genetic scalpel.
Now we can do something that William Boyd, Arthur Mourant and the others could not. We can
move to the next stage and take the last step towards the final arbiter of inheritance. We can move
to the DNA itself.