Before revision:  Some evidence for RAR includes physiological similarities between hyperventilation and laughter and the fact that smiles often indicate negative affect in non-human primates (e.g. fear grimaces where teeth are exposed as a kind of inhibited threat display , as suggested by Michael Graziano). If humor reliably indicates conditions of a) anxiety induction, b) anxiety reduction, and c) the time-course relating these things--so productively constraining inference spaces regarding latent mental states--then we know a great deal about the values and capacities of the persons experiencing humor.
After revision:  Some evidence for RAR includes physiological similarities between hyperventilation and laughter and the fact that smiles often indicate negative affect in non-human primates (e.g. fear grimaces where teeth are exposed as a kind of inhibited threat display ). In accordance with Benign Violation Theory, if humor reliably indicates conditions of a) anxiety induction, b) anxiety reduction, and c) the time-course relating these things--so productively constraining inference spaces regarding latent mental states--then we know a great deal about the values and capacities of the persons experiencing humor.