Britons, English, and Dutch

As a follow up to the previous post I've spent some of this weekend looking for the results which might shed some more light on the genetic impact of Germans on the British landscape between ~500-600 A.D. There are some problems here even assuming all other conditions are met: Northwest Europeans are already genetically rather close. This does not mean you can not distinguish an Irishmen from a German, but, once you take into account the clinal variation in gene frequencies due to isolation-by-distance models it becomes somewhat difficult to ascertain admixture in the spaces in between. After all, populations spatially between northern Germany and Ireland, the Brythonic Celts, are presumably going to be genetically between these two populations as well. That being said, space is not the only variable. Culture is another. The Celtic dialects spoken in Ireland and Britain are extremely distinctive, being of two branches of the broader language family, but there was still a clear resemblance between the two cultures (e.g., druids and other aspects of religion). In other words, the Celtiberians of Spain, the Galatians of Anatolia, the Gauls, and the various peoples of Britain in Ireland, all traded in a common cultural currency. Not only are they likely to have had some common ancestors, but there is going to be a dialect continuum across much of this cultural zone, facilitating continuous gene flow. And speaking of continuity, the fact that