An estimated 10 million people born in Ireland have emigrated from their homeland over the past 300 years, making the Irish diaspora one of the biggest of any nation. Even before the Irish began charming every single corner of the world, it appears that Ireland had a long and intertwined history with the rest of Europe.

Scientists at Trinity College Dublin have taken the most extensive look at the genetics of the Irish population to date. It turns out, the genetic jigsaw of the Emerald Isle is a lot more influenced by the Vikings, Anglo-Normans, and British than we previously thought.

People have inhabited Ireland for over 10,000 years. Using a haplotype-based method of analysis, the team were able to see how the introduction of certain genes pairs up with historical records of Norse-Vikings from Scandinavia and Norman invasions from France.

"The long and complex history of population dynamics in Ireland has left an indelible mark on the genomes of modern inhabitants of the island,” study co-author Russell McLaughlin said in a statement. “We have shown that, using only genetic data, we can accurately reconstruct elements of this past and demonstrate a striking correlation between geographical provenance and genetic affinity.”

For their study, recently published in the journal PLOS Genetics, the researchers looked at the genetic variation of nearly 1,000 Irish genomes and over 6,000 genomes from the rest of Europe.

They found that there were at least 23 distinct Irish genetic clusters, where considerable groups of people from an area all shared a certain genetic heritage. This goes against previous smaller studies that found no clear genetic groups within the Irish population. The genetic clusters were most pronounced in the west of Ireland. In the most easterly regions, more waves of historical migrations appear to have flattened-out the genetic divisions even more so.

All of this also means that the genetic background of the Irish population is a lot more diverse than previously thought.

The study isn’t just an interesting insight into the migrations across northern Europe, the researchers are also hoping that this information could be used to deepen our understanding of genetic medical issues.

"Understanding this fine-grained population structure is crucially important for ongoing and future studies of rare genetic variation in health and disease," McLaughlin said.

Ross P. Byrne, who also worked on the study, added: “This subtle genetic structure within such a small country has implications for medical genetic association studies. As it stands current corrections for population structure in study designs may not adequately account for this within-country variation, which may potentially lead to false positive results emerging."