100% Irish: Generational Isolation
Photo by Abigail Mason
Back in 2019, I watched a Stephan Colbert interview of Conan O’Brien where O’Brien discussed his recent findings that he is 100% Irish. I remember, at the time, thinking about how weird it was to have DNA from just one region, and O’Brien’s doctor echoed this surprise. He stated that he had been conducting DNA tests for ten years but had never seen a result like that. My DNA results were like many others of European ancestry—a smattering of English, Irish, Scottish and Welsh, with the more exhilarating spice of German, Norwegian and Swedish DNA. This was not a surprise to me, or anyone else.
Is it truly possible to have 100% of your DNA be from one region? I remember my anthropological senses tingling at the time, but I soon forgot about the interview until last year, when my fiancé received back the results of his DNA test: 100% Irish.
It wasn't until I traveled to County Mayo, on the rural west coast of Ireland, that I began to understand the reasons for this result—generational isolation. County Mayo, the boundaries of which were established in 1585, is home to approximately 137,000 people who are spread out over 2,158 sq miles. The terrain is rugged and the weather is extreme. Evidence of human presence in County Mayo dates back to prehistory, with ancient villages from the Mesolithic Age giving contemporary anthropologists a plethora of information about the ancient hunting and gathering way of life. The expansive coastline of County Mayo (21% of the coastline of Ireland) allowed for the development of a successful fishing way of life—an industry that remains critical to the economy of the county.
The mountains of Mayo drop off at the coastline, resulting in a range of steep cliffs. Small single-family owned farms scatter the cliff tops, adding to the rural feel of the area. Many of these families have been in the county for generations—as far back as their family records show. Even before my fiancé received his DNA results, he would often say that his family had been in Ireland forever. They have no records of a time when they weren't—and his DNA results reflect this.
Obviously, it is impossible for his ancestors to have been in the west of Ireland forever. Geneticist David Reich explains that “no population is, or ever could be, pure.” He continues, stating that “Ancient DNA reveals that the mixing of groups extremely different from each other is a common feature of human nature.” No one is actually 100% Irish. These rare few have just had ancestry in one place, for a length of time that exceeds the limited parameters of DNA testing as they currently exist. Because of the sheer isolation of the region, these Irish people married and had children with others in the county or adjoining counties—and this continued for hundreds of years. It is a DNA result that has been entirely influenced by geographic isolation.
My assumption is that as DNA testing continues to advance and improve in accuracy, this result will change. But for now, yes, it is possible to be “100% Irish”.
