It would have been nice to know what part of Britain Mr. Sowell believes these cultural characteristics emerged. I can only imagine it must be Scotland as that was where my family and a significant number of those who settled North and South Carolina came from.
I recall reading something about the Scotch-Irish. BTW, it must be Scottish because many Trinidadians of Scotch and partial Scotch descent have a bit of the same culture. The Irish would come pretty close too.
I believe that he refers primarily to the 200,000-400,000 Scots-Irish or "Ulstermen" who immigrated during the 18th century to Appalachia then on into the south and west.
FWIW.
And, I believe the The History Channel had something on the English recruiting "thugs" to takeover parts of the
rural South during the revolution.
It's said the Irish settled much of the South, especially the Protestant Scots-Irish from Ulster. They had a reputation as pioneers and as brawlers. The other group was the Borderers who lived in Northern Britain and Southern Scotland. Like Northern Ireland it was a comparatively wild and remote part of Britain in the 18th century. The two groups blended together on the American frontier.
Probably it wasn't so much that such people were different from the English. You could see a lot of the same characteristics in Dickens' London or in early Australia. But the Ulstermen and the Borderers were further away from cities and the very settled and controlled life of East Anglia, where many New England Puritans came from.
David Hackett Fischer wrote a lot about this topic in his book Albion's Seed. It's worth a look. One thing he says is that the Gaelic-speaking Highlanders who settled in the Cape Fear area didn't mingle well with the Lowland Scots or the Scots-Irish. They had been on opposite sides of some conflicts in the old country, and didn't trust each other. The Highlanders had had their rebellions and been crushed mercilessly. Thus they tended to be more obedient and law abiding in the New World.
It's called, "Born Fighting", and traces the history of this culture (called the Scots-Irish in the book) from it's origins in the lowlands of Scotland, to America. My high-schooler read it as part of our American History unit. I highly recommend it.
As a lit major, I heard over and over the assertion that the Catskills dialect of today is the closest current dialect to Elizabethan English.