You say it like it's a bad thing.
If "typed" these folks would derive from Celts, Anglo-saxons and Vikings, mainly.
Judeo-Christian heritage. Satisfactory standard of living, good personal freedom, good education system.
What explains the penchant for violence? Has British culture accross-the-board devolved to anarchy in the barroom?
You say it like it's a bad thing.
I visited a friend in Glasgow a few years ago and was blown away. I saw a lot of fights and passed a lot of people in the streets who looked like they had been on the wrong side of a baseball bat. Lots of bruises and busted heads, etc.,etc.
The root of it all is alcohol. What you or I in the U.S. would consider stinking, obnoxiously drunk is socially acceptable there (Full disclosure: I did my best to keep up, and was falling-down drunk on several occasions). It's a pretty aggressive male society too (aforementioned progeny of Vikings, Celts, etc.), coupled with enough urban unemployment, a bit of religious intolerance, and a rough climate, and there you go.
Don't get me wrong, I had a great time there and would go back in a heartbeat, and most of the Scots that I met were wonderful, down-to-earth, and generous people. It's just that A) drinking heavily as a whole is acceptable throughout the U.K. B) Even though it does have a pretty good economy, Scotland has always sort of a red-headed stepchild of England. If anything, I got the feeling that it was WORSE back in the old days.
In other words, those Scots are some TOUGH MF's.