 What's the genetic history of Ireland? And what impact did events such as the Viking invasion and the Ulster plantation have on its genetic maker? A study called the Irish DNA Atlas, revealing fine-scale population structure and history within Ireland, looked at these precise questions using samples from almost 10,000 individuals across Ireland, the British Isles and Europe. The study notes that the Irish modern genetic landscape was established around 3,500 years ago during the Irish Bronze Age, and they sought to understand how invasions and plantations have changed this genetic landscape. A central finding of the study was that the Irish population can be divided into 10 geographically stratified genetic clusters, seven of which are of Irish Gaelic ancestry and three of which are of Irish British ancestry. Unsurprisingly, the Gaelic Irish clusters had the least amount of Germanic influence of all in the analysis, with Orkney having the second least and England having the highest. Interestingly, the study also found that Ireland had a large presence of Norwegian ancestry, a clear signal of the Norse Viking presence in Ireland. In fact, the Irish DNA Atlas study found that Ireland had the second largest of Norwegian influence on its genetics, second only to Orkney, which is not surprising, given the history of links between the Vikings and Orkney, and the Norwegian ownership of Orkney for periods in its history. The study showed that the Norse influence extended beyond areas of Norse settlement, such as Limerick and Dublin, and across the whole of Ireland. The study also found that there was high levels of Norwegian ancestry in the Scottish clusters, whilst there was a relatively low Norwegian influence in England and Wales. Another finding of the study was that there was a notable French influence derived from a single French cluster of high Northwestern French membership. The Northwest of France has previously been shown to have strong genetic links with many Celtic peoples of Britain. Therefore, the notable French signal that this study found could reflect the fact that Ireland could potentially be a sync of Celtic ancestry, given its isolation from other groups in Britain. Considering the links between the Northwest of France and other Celtic groups, this study did not interpret this as a norm in presence. The study also found groups that have shared Irish and British ancestry, and they note that there was an admixture event from the 17th and 18th century. The main reason posited for this is the Ulster plantation. Other events could have contributed to this mixing, however, with the Gallaglass mercenary families being one. Other findings of the study is that there are links between people in the North of Ireland and the West of Scotland, hardly surprising given the history of the Gaels. The study also found that the Ulster cluster had the greatest genetic distance from Britain, despite its geographical proximity. In general, the study found that any genetic differentiation between Ireland and Britain is subtle, and that the greatest genetic distance of all the clusters in the study was when they looked at Orchidian clusters versus non-Orchidian clusters, i.e. the people of Orkney are the most genetically distinct of all the groups in Britain and Ireland.