The British: A Genetic Journey by Alistair Moffat Birlinn, 2013, 288 pages, $39.99 The Scots: A Genetic Journey by Alistair Moffat & James F. Wilson Birlinn, 2012, 256 pages, $29.99   History, or more often pre-history, starts to seem more like astronomy or merchant banking when you get into the thousands of years. These two racily written books are a progress report on British—and occasionally Irish—pre-history and the dawn of written history, when documentation was still very scarce. They go back many thousands of years to the earliest human habitation there and take it through to Norman times a mere…