A 2017 genetic study done on the Irish shows that there is fine-scale population structure between different regional populations of the island, with the largest difference between native 'Gaelic' Irish populations and those of Ulster Protestants known to have recent, partial British ancestry. They were also found to have most similarity to two main ancestral sources: a 'French' component (mostly northwestern French) which reached highest levels in the Irish and other Celtic populations (Welsh, Highland Scots and Cornish) and showing a possible link to the Bretons; and a 'West Norwegian' component related to the Viking era.