Irish != Celts
The Irish are not Celts, say experts 05 Sep 2004 The Sunday Times
THE long-held belief that Ireland’s population is descended from the Celts has been disproved by geneticists, who have concluded that they never invaded Ireland.
Apparently the genetics of the Irish didn't change that much 2500 years ago when the Celts were supposed to have invaded Ireland and wiped out all the natives (no significant Celtic genes were found in samples from modern-day Irish by Brian McEvoy et al. from TCD), but rather genes can be traced back at least 9000 years to people who migrated from Spain and Portugal after the Ice Age thawed out.