I don't know if you are familiar with the latest developments in population genetics/genetic genealogy, but in recent times a researcher by the name of Professor Ken Nordtvedt has identified a haplogroup which he associates with some of the very earliest settlers to the British Isles including Ireland in the post-LGM period. He calls this clade of haplogroup I2a2 [old I1b1], 'I2a2-Isles'. He has managed to divide the clade up into 8 separate subclades; A1, A2, B1,B2, C1, C2, D1, and D2.
This may be of interest to you because I think we may have a possible [I say that cautiously..] link with the Cruthin here. Nordtvedt conjectures that I2a2-Isles, at least the oldest clade [B1] has been in the isles almost 6,000 years and was probably founded on the north German plain. The clades came to our isles before the Iberian-founded R1b haplogroup which accounts for around 80% of Irish men [and roughly 90% in parts of Connaught]. Its distribution suggests possible Cruthin connections - more the west and Ulster than anywhere else. The haplotypes are also found to a lesser extent in England and Scotland.
I was most interested in your comments on the Pretani (a). I use the word Cruthin rather than Cruithin according to the convention of O Rahilly and Byrne (b) and am particularly interested in the Creenies or Cruthin who migrated to South West "Scotland" and would have migrated back again in the Plantation and other periods.
Just a couple of [further] points.. Ptolemy (c AD 135-50) used the term Ivernia as part of the Prettanic Isles but also referred to Ireland as Little Brettania, Albion, of course, being Great Brettania.
And don't forget the Carthaginians ... Gaelic is a complex language with Semitic and Hamitic influences. According to Ayllet Sammes (1676), a scholar from Christ's College, Cambridge, Britannia was originally called Bretanika by the Greeks after the Phoenician word Bratanac, or Barat-anac (Country of Tin), the equivalent of the ancient name Cassiterides.
In Phoenician Ierne, Ivernia or Ireland would merely mean "the Farthest Island". One thing is certain, it is not Celtic in origin.
T. F. O'Rahilly in Early Irish History and Mythology first drew attention in modern times to the Cruithin as a population element in Ireland.
On Cruthin/Cruithin: Irish Gaelic classifies all vowels and consonants into 'slender' and 'broad' categories. In its written form, there is the convention that a slender consonant must have a slender vowel on either side, and likewise for a broad consonant. This accounts for the insertion of a large number of silent vowels in written Irish. The extra 'i' may derive from this. [The convention reminds one of the Hungarian principle of "vowel harmony".]
I'd plan to add some further comments of mine separately.
Dr Adamson's colleague and informant, Dr Tim Owen of Southport, Lancashire, comments;-
I think, as time goes by and the databases start to fill up, we may see more evidence for the I2a2b-Isles-Cruthin link. The clade is very low level, but as Aiden Mulvihill's map shows, there is enough distribution to make the link in Britain/Ireland. Also, more continental members are emerging with Germany predominant.
I imagine that the Cruthin probably carried some other varieties of I haplogroup, and Bradley and McEvoy's study [sponsored by Patrick Guinness] suggested a link between the Maguinness clan and I2b1 [old I1c]. The M22 variety of R1b haplogroup certainly dominates Ireland though. There is a high incidence of I2a2b-Isles in the O'Driscoll clan, which suggests to me that they might have been somehow 'cut off' from the rest of the pre-Gaelic stock as the R1b-predominant Gaels, ultimately of Iberian stock, colonised the island by force.
I wonder if the oldest clade [B1] entered Scotland first [travelling from its north German place of foundation] via Doggerland, going on to parts of Ireland to 'give birth', so to speak to the 'younger' clades? I suspect that we could find a link between I2a2b-Isles and the narrowblade culture of the late Mesolithic, which replaced the broadblade culture, and ultimately to the Cruthin.