Phylogeny Of Laughter

Laughter is estimated to be 7 million years old. Like other vocalizations, such as moaning, sighing, and crying, laughing is thought to have preceded speech and, like these vocalizations, it may also have a communicative function.

Although laughter is often claimed to be unique to humans, behaviors similar to human laughter have been observed in other primates and something akin to laughter has even been argued to be present in rodents. In 1997, Signe Preuschoft and Jan van Hooff examined variations in the contexts and social functions of bonding displays in various primate species, including Old World primates, macaques, baboons, great apes, and humans. They noted a silent bared-teeth display (also called a grin, grimace, or smile) associated with inhibited locomotion, evasive and protective body movements and postures, and grooming and embraces. This display was observed in all macaque and baboon species and humans. A relaxed, open-mouth display ("play face''), marked by a widely opened mouth but without pronounced baring of the teeth, was observed in all macaque and baboon species, in each of the great apes, including the chimpanzee, bonobo, orangutan, and gorilla, in humans, and in more distant species such as vervets and squirrel monkeys.

One variant of the play face noted in some species was an open mouth, bared-teeth display with associated staccato breathing and bursts of vocalization. This latter display, which Preuschoft and van Hoof termed the "laugh face,'' appeared strikingly similar to human laughter. It was accompanied by boisterous body postures, brusque movements, mock biting, playful chasing, and evasive, repetitive glancing movements rather than a tense gaze. The laugh face was found only in certain macaques, mandrills, geladas, the orangutan, the bonobo, and, of course, humans, and it occurred primarily in social play contexts, although in some cases it was observed to accompany solitary play, but in these cases it occurred only when conspecifics were near. The presence of an audience thus appears to be at least facilitative, if not necessary, for releasing the laugh face display.

In 1987, Preuschoft and van Hooff proposed a functional significance of play that is relevant to the current analysis. They noted that in bonding behaviors (i.e., those involving care, sex, and affiliation), it is important to deemphasize competition and focus on shared interests. Play is one form of bonding behavior. An important element of play is the partner's unexpected performance of an expected behavioral act. Preuschoft and van Hooff suggested that the "essence of play seems to be to actively bring about incongruous and unexpected behaviors and to interpret them as nonthreatening.'' This, they argued, allows for affective and cognitive mastery of incongruous situations.

Whereas laughter in nonhuman primate species is found principally in play contexts and primarily occurs in the young of the species, laughter in humans occurs in a variety of social contexts throughout the life span. Moreover, there is no evidence that nonhuman primates have anything comparable to the human ability to produce, comprehend, and enjoy humor.

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