Marian Kester Coombs writes from Crofton, Maryland.

All history is biography, it’s said, but an individual biography usually shines a mere flashlight on surrounding historical events. John Szwed’s book on Alan Lomax is more like a floodlight thanks to his subject’s centrality to so much of American 20th-century culture. Alan Lomax knew everyone, went everywhere, appreciated just about everything, and worked tirelessly to foster in all Americans his own great love for them: the people, the folk.

Imagine a world scarcely acquainted with the blues, bluegrass, work chants, gospel music and spirituals, jazz, zydeco, calypso, cowboy songs, and most of the great ballads of British and American folk music. Such a world would never have spawned rock ‘n’ roll. For some, that’s a tempting thought. But the world is richer for knowing these ancestors of rock. And for much of that knowledge we have the work of Alan Lomax to thank.

Alan’s story (1915-2002) is in many ways a continuation of his father’s. John Lomax (1867-1948) grew up near the Chisholm Trail in Texas, fascinated by cowboy culture. By fascinated I mean obsessed: a lifelong compulsive devotion. That devotion, in ever more all-embracing forms, persisted in his younger son Alan....