I have been a student of human migration over the years and was taught that the history of mankind's movements involved a series of mass replacements of entire populations. The Indo Europeans replaced the paleolithic inhabitants of Europe (except for some Basques). The Celts replaced the earlier denizens of Erin and Albion. The Anglo-Saxons drove the Celts to the fringes. You get the picture.
Recent genetic studies have not borne this out. Indo Europeans did not enter Europe in massive numbers. Their languages were adopted, but the population of Europe is still made up mostly of the descendants of the paleolithic foragers who first colonized the subcontinent. The population of the British Isles does not show any legacy of mass replacements in its genes. Everything we thought we knew about European prehistory is pretty much wrong.
I'm heartened by this. Mass murder appears to be a relatively recent innovation.
I watched "Naked Archaeologist" the other evening, and I was amazed at the lengths the host was willing to go to "prove" the historical accuracy of the Biblical accounts of King Solomon. For him, if Solomon did not build the gates at Megiddo and Gezer and some other place, as written in the Bible, then Solomon probably didn't even exist. The likely explanation that the writers of the Solomonic history concluded wrongly that Solomon built the gates in question (they date to a century after Solomon) seemed not to have occurred to him. The guy's thought processes were completely boxed in. Perhaps this is what happened with the guys who wrote the now debunked narrative of European migrations and population replacements. They had it in their heads that language diffusion was proxy for gene flow, so they interpreted everything in that light.
You know how everyone in the "Tain" rides around in war chariots? How come there haven't been any chariots dug up in Ireland? I reckon that the charioteers never made it to the Emerald Isle, just their stories.