I don't think modern Irish people are related to the builders of newgrange,and if they are it's been only a damline for several thousand years. Bronze age skeletons(before supposed Celtic invasion) that have been tested are more or less identical to modern Irish people. How does Shakespeare get blame for this?, first mention in history I've come across of us all being Celts was a Welsh guy called William Llys around 1700 (pre act of union propaganda?).