For five years, Henry Alford signed up for everything from pas de deux classes and a swing dance conference to tap lessons with Alvin Ailey and a “contact improv jam.” He researched the lives of the greats — Isadora Duncan, Martha Graham, Bob Fosse, Arthur Murray, Mikhail Baryshnikov — and includes anecdotes about each. For example, in the early 1960s, Martha Graham told a roomful of Texas college students that “all great dancing stems from the lonely place.” “Where is the lonely place?” asked a girl in the audience. “Between your thighs,” Martha told her. “Next question?”