 In 2002 a paper was published by Michael E. Weale and colleagues showing genetic evidence for population differences between the English and Welsh populations, including a markedly higher level of Y-DNA haplogroup I in England than in Wales.They saw this as convincing evidence of Anglo-Saxon mass invasion of eastern Great Britain from northern Germany and Denmark during the Migration Period.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.