>>514050070
The original people in Scotland, at the time the Romans invaded, were Picts - a Celtic people who we don't have a written record of and who mostly don't exist any more.
The Anglo-Saxons didn't really spread to Scotland and fought endless wars against the Scots, at a time when lots of the north west of England were still Celtic and there were repeated Norse invasions.
The Irish invaded Scotland around the same time period as the Anglo-Saxon invasion of England, and became what we know of the Scottish today.
Then after the Norman invasion, many Normans became landowners in Scotland and this was when Scotland really became anglicised, mostly from the top down through the land owners.
Normans are basically Norse who lived in northern France for a while and learnt French, so it's a small tight nit group of genetics in Britain.