7Even as recently as 1989, Irenäus Eibl-Eibesfeldt, one of the leading scholars of animal behavior, suggested that laughter may be an ancient form of aggression. “The rhythmic sounds,” he writes, “are reminiscent of threat and mobbing sounds made by lower primates, and the baring of teeth may be derived from an intention to bite” (Eibl-Eibesfeldt 2009).
