The DNA of two ancient occupants of Ireland has given researchers a breakthrough clue into the history of the Celtic population.
Of greatest consequence to scientists is new evidence there was a mass migration from the Middle East and Southern Europe circa 2000 BCE.
Geneticist Professor Dan Bradley said these findings had medical implications.
"Ireland has the world maximum frequency for a number of important genetic variants," he said. "They include variants that code for genetic diseases like cystic fibrosis and hemochromatosis."
Scientists from Trinity College have paired with Queens University palaeontologists for the study.
They extracted DNA from a woman believed to be among Ireland's first farmers, who lived circa 3000 BCE.
Research places her ancestors among an influx of migrants that moved across Europe, over 5000 years ago.
Her appearance was closer to that of modern Southern Europeans, with dark hair and eyes.
These physical features contrast with the typically fair modern Celtic genepool, in which fair skin and blue eyes are more prevalent.
In contrast, the DNA of a man who lived approximately 1000 years later, showed markers for disease that were not present in the woman's genes.
"When we look at the Bronze Age genomes, we again get a very strong signal of people coming in to Ireland and for the first time, we see one of these individuals was a carrier of haemochromotosis."
Dr Lara Cassidy, a researcher at Trinity College, described this form of "genetic time-travel" as the "meat and bones of history."
"Genetics in its essence is basically the science of inheritance, and... every individuals genome holds a complete wealth of information about our ancestry," she said.
In addition to discovering more about the introduction of various diseases, the research is of historical significance.
"There is a population upheaval shown, where people came into the island, and that at least is a candidate horizon for the entry of a new language," Prof Bradley said.
"Maybe he was a father, son, maybe he was a brother," Dr Eileen Murphy of Queens University said.
"It is only natural to empathise and to wonder, what would like have been for this person four thousand years ago."
