All genius is inexplicable, but some kinds of genius are more inexplicable than others. George Gershwin falls into the latter category. The second son of a Russian Jewish family in New York, he was a genius of the natural kind—his mother had no special interest in culture or talent for music; his father ran bakeries, Turkish baths, a cigar store and a pool parlor, and was briefly a bookie—but Gershwin had only to sit down at a piano in his boyhood to realize that in music lay his destiny.

Like many vastly talented people, he...