Humor seems uniquely human, but it has deep biological roots. Laughter, the best evidence suggests, derives from the ritualized breathing and open-mouth display common in animal play. Play evolved as training for the unexpected, in creatures putting themselves at risk of losing balance or dominance so that they learn to recover. Humor in turn involves play with the expectations we share-whether innate or acquired-in order to catch one another off guard in ways that simulate risk and stimulate recovery. An evolutionary approach to three great literary humorists, Shakespeare, Nabokov and Beckett, shows that a species-wide explanation not only cuts deeper but in no way diminishes individual difference.