Broomstick: I’m gonna quibble with you 
( and no, I’m not following you around from thread to thread - see the Darkover thread in Cafe Society 
).
Incorrect. The early Celts did conquer the Picts and partially absorbed them. But Germanic penetration of northern Britain didn’t precede much farther than Northumbria/Cumbria and was incomplete even there ( Cumbrian Welsh survived for many centuries in that region ). Granted there were the Viking settlements in the north - But they were mostly concentrated in the Islands and Western Highlands, where they were eventually absorbed by the Gaels ( families like the Gunns so originated ). I made some relevant comments about the Scottish/Pictish relationship in this thread:
http://boards.straightdope.com/sdmb/showthread.php?threadid=51020
Although Gaelic came to be the dominant language of Scotland ( before the Normans arrived ), the larger part of the Lowland heritage was probably Brythonic Celt. Especially as the border region of the ‘Southern Uplands’, in particular the old kingdom of Strathclyde ( which peacefully amalgamated with Scotland through marriage ), were essentially Celtic domains. I don’t believe the later Norman immigrants ( mostly invited knights ), although they supplied many of the later ruling families, the language of government, and later the language ( in the form of Norman English ) of the common folk of the Lowlands, amounted to much, numbers-wise.
So I think you are incorrect when you say the Lowlands Scots are predominantly English in origin.
Though it’s not really germane, just to even out the discussion I might as well make mention the earlier Scottish emigration. Families that became associated with the term ‘gallowglass’ ( galloglaiches ) , like the MacSweeney’s in Tyrconnel ( Tir Conail ) and the MacQuillan’s of the Route. And a little later, a branch of far-flung Clan Donald, in the form of the MacDonnells of Antrim, leapfrogging via the Clan Donald stronghold of Rathlin Isle ( I believe that for awhile in the middle-ages, John MacDonald, 4th Lord of the Isles, meddled in Northen Irish affairs and was regarded as a bit of an independant threat by the Royal govt. in Dublin ).
- Tamerlane