Speculation and at least one person's educated conclusion is that this group, not now dominated by Sardinians, was among the group that repopulated extreme Western Europe.
What does that mean? What is extreme Western Europe actually? The definition of that varies but some DNA population experts feel that is Western Scandinavia, Ireland, Scotland and the Germanic area which faces the UK.
DNA Tribes who has done my autosomal include Celtic speaking area of the Atlantic facade and the Northwest area of the Continent including the Germanic speaking areas of Scandinavia and lands and territories invaded by the Vikings. Lands that are linked by the North Sea and the Irish sea.
Our Faunt family as typified by Walter L'Enfant as early as 1290 in Ireland here:
John de Saunford, Archbishop of Dublin, on July 7, 1288, was appointed by the King's Council 'Keeper of Ireland until the king should otherwise decide ' : Cal., vol. iii, no. 559. William d'Oddingeseles and Walter l'Enfant were his deputies in 1290 in some operations against O'Melaghlin of Meath : ibid., p. 270.( from Ireland Under the Normans)
Irish records that I have pulled indicate to me that at least my one line back to 1730 married predominantly of the same "Cultural group" as themselves..Anglo-Normans.Cunningham, Slattery,Lynch,Hannon,Butler,Hickey.
Curiously, Joe Wearing a Fant cousin whose Grandmother descends from the Faunt family in Westmeath is very close to us ancestrally on this I21a haplogroupeven though on different lines.
Joe's Wearing ancestor (actually Waring or Berry) on his Y line side as well as his Faunt side share this hapoltype although a variant. Here is a link to a goup that Joe and Fran and James belong to:http://www.familytreedna.com/public/I2aHapGroup/default.aspx
The Clade is divided into smaller groups here:
Joe Wearing on his Waring/Berry ancestor is in I-M26C..almost as small as ours is.
There is a predictor that was used to place us there..
Here is a predictor by Ken Nordvedt on the estimation of age of this group:
6,000 12,000 18,000 24,000 years
200 400 600 generations
Since we are M26 which apparently arose 7500 years ago I think that means we ( our men) did not actually live in Sardinia..
we shared an ancestor at that point..Joe's kinsman who later became Berry and our man who later became Fant were brothers or cousins..c 7500 and they at that point in time were founders of the Culture that settled extreme Western Europe
That is how I understand it..
and I am a non-scientist