Without a study that takes samples on a time line, how is it possible to know when a strain of DNA arrives. I don't think Iceland had any cities in the Hanseatic League, but as an island nation I have to think that it was served by the merchants, a quite mobile slice of Europe's population. Many of the merchants transplanted their whole families & original sources show a large percentage of populations originating from other league cities.
Other than an extensive sampling on a time line, how would it be possible to know that a strain of DNA arrived in the tenth century rather than the seventeenth or eighteenth?
Exactly — it wouldn’t be. The weakness of such studies is that they use the DNA samples which have mananged to survive — something largely the work of chance, give or take ancestral lines who managed to get busy. ;’)