 The authors assumed that populations with large proportions of haplogroup I originated from northern Germany or southern Scandinavia, particularly Denmark, and that their ancestors had migrated across the North Sea with Anglo-Saxon migrations and Danish Vikings.The main claim by the researchers was

that an Anglo-Saxon immigration event affecting 50–100% of the Central English male gene pool at that time is required.We note, however, that our data do not allow us to distinguish an event that simply added to the indigenous Central English male gene pool from one where indigenous males were displaced elsewhere or one where indigenous males were reduced in number … This study shows that the Welsh border was more of a genetic barrier to Anglo-Saxon Y chromosome gene flow than the North Sea … These results indicate that a political boundary can be more important than a geophysical one in population genetic structuring.