You can characterize a group by its gene frequencies – which can be thought of as a point in a very high-dimensional space. Another group is a different point, and the between-group difference is a vector in that space. Ignoring linkage, assuming no substructure, etc.
There’s a vector of this sort that describes the genetic differences between the Irish and Germans, or for that matter between the Irish and the average of the human race.
For Sardinians, that point is unusually distant from other Europeans, since they’re almost-pure examples of Europe’s first farmers. The Iceman genome is like that of a Sardinian, but even more so: more like Sardinia before Sardinian soaked up some genes from the mainland. More Sardinian than the Sardinians: the vector in that high-dimensional space between the Iceman and modern Italians is like the vector between Sardinians and the mainland, in the same direction, but with a greater magnitude. You would expect that the Iceman’s phenotype differed from mainland Italians in the same way that Sardinians do, only more so. Modern admixtures have produced many examples of this: mestizos differ from Spaniards in gene frequencies and traits: Amerindians (from central America, say) differ in the same general way, only more so.
With modern genetic technology, we could make these vectors even longer, while still pointing in the same direction – longer than they are in any existing population, longer than they ever were in any population that has ever existed.
So.. we could make synthetic Irishmen that were far more Irish than anyone in the emerald Isle – so Irish that they were barely human. It has been said that the Irish excel in all the qualities that make a man interesting rather than successful – compared to our new and improved product, today’s Irish would seem a nation of shopkeepers.
“The great Gaels of Ireland are the men that God made mad,
For all their wars are merry, and all their songs are sad.”
Now square that.