The Scots: A Genetic History by Alistair Moffat and James F Wilson
 
One very interesting fact to emerge from Alistair Moffat and James F Wilson’s research is that the large numbers of redheads in Scotland maybe the result of inbreeding between Neanderthals and modern humans; Neanderthals are thought to have had predominantly red hair. The following is an extract from the excellent review of the book by David Robinson.
 

I’m not sure how the numbers of survivors are worked out, but they are impressively small. All people that on earth do dwell – apart from those in Africa – are apparently descended from a mere 300 who made the journey out of our home continent. Again, the numbers are unexplained but a cause of wonder.

As is the peopling of Scotland. All Scots, Moffat reminds us, are immigrants, but DNA evidence allows us for the first time to be more precise about from where. It must be hard, you can’t help thinking, for any geneticist to be a racist, given that we’re all originally African. But even racist nostalgia for a once-pure bloodstock takes a battering from genetics. In Scotland’s case, for example, the people here longest were originally from either side of the Pyrenees, while most of the rest of us are basically Irish. As far as the Romans are concerned, they came, saw and conquered most of Britain, but genetically speaking, they hardly left much of a trace behind.

See http://living.scotsman.com/features/Book-review-The-Scots-A.6732585.jp?articlepage for the full review.