23andMe’s Take on Irish Trivia

by Samantha Ancona Esselmann, Ph.D., product scientist at 23andMe


Where our Irish Ancestors Lived

Millions of 23andMe customers have some Irish ancestry, so this year we decided to investigate where in Ireland their ancestors have called home. 


Many customers reported grandparents born in Cork, Mayo, or Galway counties in The Republic of Ireland. Unsurprisingly, many customers also have grandparents from Belfast and Dublin:  Northern Ireland and the Republic of Ireland’s largest cities. 

The darker the shading on this map, the more customers who report grandparents from that region.

Where in the US Do Our Customers with Irish Ancestry Live?

As a result of the Irish potato famine between 1845–1849, Ireland experienced a sustained exodus of people — and to date, the island’s population has not recovered to pre-famine numbers


Last year we looked at where in the United States many of these immigrants wound up. We did this by looking at data from customers with grandparents from Ireland. Sure enough, we saw higher concentrations of people with recent Irish ancestry in the Northeast, particularly New York, Massachusetts, and Connecticut.  


Studies of Irish Ancestry reveal unexpected connections

In a number of recent studies (7, 8, 9), researchers identified distinct genetic clusters within the island of Ireland. While Irish people tended to be genetically similar to each other, there were a few regional differences the study was able to identify within the DNA. 


For example, southern Ireland was the most genetically distinct from the rest of the island, followed by Northern Ireland and central Ireland (which split rather unexpectedly into a northern half and a southern half). 


Why unexpected? 


Historically, there were four traditional Irish provinces: Ulster in the North, Munster in the South, Connacht in the West, and Leinster in the East. According to the DNA, It seems that people migrated between East and West in Central Ireland over time, obscuring some of these traditional borders.  

Why “British & Irish” ancestry peaks in Ireland


Our own researchers were able to explore the impact of ancient and historical migration from mainland Europe into the British Isles (1, 2, 3, 4, 5, 6). There are clear geographic differences in our customers’ average ancestry percentages. Customers with four grandparents born in Ireland tend to have more British & Irish ancestry than customers with four grandparents born in Great Britain.


You can clearly see that French & German ancestry reaches over 25% in England’s Southeast, where British & Irish ancestry hovers around 50%. Compare that to more than 90% British and Irish ancestry in western Ireland, or more than 75% in western Wales and northern Scotland. 

What’s the “Celt Belt” and where did Celtic languages come from? 

Celtic languages and culture first appeared in Central Europe, extending from the British Isles to the Black sea by the 3rd century BCE. But, the rise of the Roman Empire spelled the downfall of a Celtic-speaking Europe. 

Today, while Celtic languages can only be found along the “Celtic Fringe” or the “Celt Belt” along the far western periphery of their former territory, Celtic cultural heritage remains deeply meaningful to millions of people around the world.

Genetic Origins of the “Celtic Curse”

Bagpipes, intricate metalwork and red hair are often associated with Celtic heritage, but less familiar is the link between “Celtic-like” ancestry and hereditary hemochromatosis. Hemochromatosis is a condition characterized by the absorption of too much dietary iron, which can cause damage to the joints and certain organs.


Today, the DNA variants associated with this condition are common in Ireland, leading to the nickname, “The Celtic Curse,” as it’s commonly known in the scientific and hemochromatosis communities. However, most evidence points to a central European origin of the most common variant (HFE C282Y), which was likely carried to the British Isles thousands of years ago and further spread by medieval Viking migrations. Some scientists have proposed that the C282Y variant may have protected our farming ancestors from iron-deficient diets, but the evidence for this “protective” role is limited.

If you’re a Health + Ancestry customer, your Hereditary Hemochromatosis (HFE-related) report is available here.

(See references 10, 11, 12, 13, 14, 15, 16, 17, 18, 19).