I’ve had a bit of an epiphany regarding the pre-history of the Celts and Ireland.
I had always been attracted to the idea of invasions being the primary driving force of cultural change in England and Ireland.
However, the recent research of Daniel G. Bradley (discussed in the latest Irish Echo) and the aforementioned work on the evolution of the Celtic languages by Peter Forster * and Alfred Toth has changed all that.
Bradley’s work is on the inheritance of the Y chromosome. This piece of DNA is inherited by sons from their fathers. Bradley finds that 98% of men with Gaelic surnames from Connaught share a similar DNA sequence. He predicts that these men must be descendant from a single man that lived 4,000 to 6,000 years ago. The Basques of Spain show the same pattern. Incidentally, another study (http://www.nature.com//nsu/030616/030616-15.html
suggests that this sequence is relatively high in England, even where the Anglo-Saxons were politically ascendant.
So probably these Connaught families came to Ireland soon after the end of the last Ice Age (8,000 years ago) when Ireland thawed out. Fantastic!
But this is long before the arrival of Celtic culture to Ireland. I’ve heard all different dates for that. So it seems that the Irish language came in without large-scale immigration or death and destruction.
Where did it come from? Well, if Foster and Toth are right, and the insular Celtic languages form a group, then Celtic languages spread from England to Ireland or vice versa.
For comparison’s sake you could compare this work on Ireland’s history to that on South America and compare the Y chromosome to mitochondrial DNA. Mitochondrial DNA is only given to children by their moms. Many South Americans (was it Columbia?) have European Y chromosomes but indigenous mitochondrial DNA. This is evidence of a past war and invasion in which the indigenous males were killed and the invaders took indigenous mates.