I recently read articles (and I've been struggling to find them, the one below is a bit older) that used DNA to show that the peoples of Great Britain and Ireland have almost the exact same DNA. They stress that none of the Celtic, Roman, Anglo-Saxon, Viking or Norman invasions significantly displaced the population at all.
I haven't done near as much reading on this as you guys have though, so by all means, let me know what you think. It IS interesting to think that the majority of British and Irish peoples (including my ancestors, most of whom come from various areas of Britain) were originally from the Basque region!http://www.prospectmagazine.co.uk/2006/10/mythsofbritishancestry/
Here's a salient (and looooong) quote:
"What is more, new evidence from genetic analysis (see note below) indicates that the Anglo-Saxons and Celts, to the extent that they can be defined genetically, were both small immigrant minorities. Neither group had much more impact on the British Isles gene pool than the Vikings, the Normans or, indeed, immigrants of the past 50 years.
The genetic evidence shows that three quarters of our ancestors came to this corner of Europe as hunter-gatherers, between 15,000 and 7,500 years ago, after the melting of the ice caps but before the land broke away from the mainland and divided into islands. Our subsequent separation from Europe has preserved a genetic time capsule of southwestern Europe during the ice age, which we share most closely with the former ice-age refuge in the Basque country. The first settlers were unlikely to have spoken a Celtic language but possibly a tongue related to the unique Basque language.
Another wave of immigration arrived during the Neolithic period, when farming developed about 6,500 years ago. But the English still derive most of their current gene pool from the same early Basque source as the Irish, Welsh and Scots. These figures are at odds with the modern perceptions of Celtic and Anglo-Saxon ethnicity based on more recent invasions. There were many later invasions, as well as less violent immigrations, and each left a genetic signal, but no individual event contributed much more than 5 per cent to our modern genetic mix."