In the '30s, brother duets were common in country music: Among the better known were the Monroes, the Delmores, the Dixons, and the Carlisles. Bill and Earl Bolick, who in 1936 were ready to make their first recording, followed their producer's suggestion that they should be different by avoiding the word "brother." From "Blue Ridge Mountains, Land of the Sky" they took two words and named their act. But the Bolicks would have been different without the new name. Their intricate yet simple harmonies, their perfectly matching voices, and their unadorned mandolin and guitar inst...