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Britain and specialized in capturing and then ransoming high-ranking hostages, hence his
soubriquet. His most famous captive was one Succat, who went on to become St Patrick. Niall’s
military exploits carried him over the sea to Scotland, where he fought the Picts who were trying to
retake the recent Irish colonies of Dalriada. It was during a raid even further afield, in France, that
an arrow from the bow of an Irish rival killed Niall on the banks of the River Loire in AD 405.
Niall was succeeded in the High Kingship by his nephew, Dathi, his brother’s son. This was
typical of the Gaelic tradition of derbhfine, the rules of inheritance that chose the new king from
among the direct male relatives of the old. This served to ensure the patrilineal inheritance of the
High Kingship itself and of the whole clan of Ui Neill. Their hold on the High Kingship was
remarkably durable, lasting from the seventh to the eleventh century AD. Brian McEvoy’s and Dan
Bradley’s Y-chromosome tests on the Irish showed that a high proportion of men with Ui Neill
surnames – names like Gallacher, Boyle, Doherty, O’Connor and even Bradley, as well as O’Neill
– shared an identical or very closely related Y-chromosome signature, strongly indicative of direct
descent from Niall himself. In the parts of Ireland most strongly associated with the Ui Neill,
mainly in the north-west, the proportion of these Y-chromosomes reaches almost one quarter of the
male population.
These bursts of Y-chromosome success over a few generations are something to be aware of in
our interpretations of the genetic evidence from the Isles. The predictable effect will be to distort
the Y-chromosome profile of a region in favour of the local chieftains and also to exaggerate the
differences between the regions. We have already seen how this may be happening in that Y-
chromosome similarity scores between regions are usually lower than the same comparative score
for mitochondria. The only regions that we have so far encountered where the Y-chromosome
similarity score is almost as high as the mitochondrial are the two Pictland regions of Tayside and
Grampian. If inheritance and succession really were matrilineal, then this practice would indeed
neutralize the Genghis effect, since no Y-chromosome could be linked to wealth and power for
generation after generation. Another effect will be to reduce the age of a patrilineal clan. If one or a
few Y-chromosome signatures come to predominate in a region due to the Genghis effect, they can
do so only at the expense of others. These, it follows, are eliminated either because the men who
carry them are actually killed, as was the case in the Mongol Empire, or because they do not have
their fair share of children, since the Genghis male monopolizes the women in one way or another.
The Genghis effect can substantially reduce the variety of Y-chromosomes, so the normal way of
estimating the age of a clan in a region by averaging the number of mutations will be distorted. The
fewer different Y-chromosomes there are, the fewer mutations will be found, the average will
drop, and the age estimate will become artificially younger. The more pronounced the Genghis
effect, the greater the distortion and the greater the difference between the true age of a clan and the
estimate. To take things to extremes just to illustrate the point, were Genghis Khan’s Y-chromosome
the only one to have survived from thirteenth-century Mongolia, only the mutations along his line
would have accumulated and the age estimates of Mongolian Y-chromosomes would come out
around 800 rather than thousands of years.
Scotland has shown us a bit of everything. Vikings, Picts, Celts, the erratic effects of patrilineal
kingship and the ancient bedrock of maternal ancestry. We have discovered that the Viking
settlement of Orkney and Shetland was very substantial but also much more peaceful than was
previously thought, with as many Norse women as men among the settlers. We now know how to