The point made is this - The SNP R-U106 is well-represented among those with "authentic" Flemish surnames. Also very telling; U106 is not well-represented in the Île-de-France or in Nord-Pas-de-Calais.
Details of the paper - "In the name of the migrant father—Analysis of surname
origins identifies genetic admixture events undetectable from genealogical records"
by M H D Larmuseau, J Vanoverbeke, G Gielis, N Vanderheyden, H F M Larmuseau
and R Decorte. You must register to receive it in full. Click this link >>
The paper acknowledges something far too many amateur genealogists won't - that family records aren't reliable before the 16th century. Then the paper points out that surnames were moving in large numbers during the demic migration from French-speaking parts of Normandy to scantily populated parts of Flanders. And I'm assuming that resulted in the densities we're seeing on the chart at Dienekes blog post.
However, what's interesting about the percentages of French among the Flemish is that most (if not all) of the St Clair / Sinclair DNA study participants were already located in the U.K. long before this demic migration took place.
Does this mean that the actual numbers of French DNA among Flemish, as well as Flemish DNA among the French, was much lower before this migration? I'm not certain yet. But the French among the Flemings is a very low percentage among modern DNA study participants.
If the St. Clair / Sinclair surname originated in France, then how and when did those with the DNA SNP called R-U106 obtain it so long ago? Especially if they were across the border in Flanders?
I think the answer is there can't be an answer yet. DNA subclade studies of the U106 SNP will lead to more answers for the Sinclair DNA study very soon. Already we're down to the Z1 SNP, and that's getting relatively recent in terms of when their common ancestor was alive in Europe.
The demic migration was certainly not the only such event. We know that William the Conqueror recruited far from the borders of Normandy for his invasion. Surely there was other mixing going on; both with large groups and smaller numbers.
We have 3 groups in our Sinclair DNA study who show U106
That's quite good data. And, while our U106 groups members show 3 distinct SNPs downstream of U106, they all share an ancestor within the last 4,000 to 4,500 years, possibly sooner. It's currently believed that all the visible SNPs beneath U106 all share a common ancestor who lived on mainland Europe, not in the U.K. So there's still a long way to go before we have clear demarkations in the groups who showed up in the U.K. versus those who stayed behind in mainland Europe.