The Evolutionary Mystery Deepens: Scientists Split on the Origin of Laughter

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The play-signal model fails to answer an obvious morphological problem: why do humans expose their front teeth when they laugh? In almost every non-human primate lineage, retracting the lips to reveal incisors and canines serves as a threat display or an acknowledgment of raw hierarchical dominance.

Researchers championing the agonistic model argue that laughter shares deep roots with primate aggression and fear-submission displays. When an animal flashes a bared-teeth display during intense social standoffs, it exposes weapons while signaling heightened autonomic tension. Field observations of rhesus macaques and baboons document intense, rhythmic vocal hacking during group territory defenses, mobbing attacks against predators, and hostile border disputes. These vocalizations sound uncomfortably close to human mob laughter. Under this evolutionary framework, weird laughing sounds originated not as an invitation to cuddle, but as an auditory marker of group-level territorial solidarity, a collective bark demonstrating that the pack is unified and ready to intimidate an outsider.