Although it might not help your family history research all that much, this is a fascinating survey of where Scottish people have come from, using DNA, archaeology and recorded history. It’s also very well written, so though full of “science” it’s not too hard to read. It starts with the end of the ice age, more or less, as there weren’t humans that anyone knows about in Scotland before then, and works forward in time, right up to the incomers of more recent times.
Particularly impressive is how genetics is interwoven with an interesting telling of Scotland’s history and an analysis of it languages. But in brief, if you’re Scottish, or descended from Scots, you’ve probably got a largish dose of Irish in you.