Ape Laughing: The Evolutionary Origin of Our Laughter

While laughter is often considered a uniquely human trait, researchers have observed similar behaviors in great apes. Scientific inquiry into these vocalizations, and the contexts in which they occur, provides a window into the emotional lives of apes. It also sheds light on the evolutionary history of our own behaviors.

Recognizing Laughter in Apes

Scientists identify ape laughter through its distinct sounds and physical actions. Unlike the rhythmic “ha-ha” of human laughter produced on the exhale, ape laughter is a breathy, panting sound. It is often produced during both inhalation and exhalation, creating a continuous, wheezing quality described as low-frequency, staccato grunts.

This sound is almost always accompanied by a specific facial expression known as the “play face.” This expression involves an open mouth with the upper lip raised and the corners of the mouth pulled back, sometimes causing crow’s feet to appear around the eyes. Researchers study these behaviors through careful observation and acoustic analysis to compare the sounds across different species and situations.

There are subtle differences among the great apes. Orangutan laughter, for instance, tends to be simpler in structure with shorter bouts compared to African apes. Chimpanzees and bonobos, our closest relatives, exhibit laughter that is more complex and variable, much like the play vocalizations of very young human infants.

Triggers and Social Functions of Ape Laughter

Ape laughter is a social phenomenon observed most frequently during physical play. Common triggers include tickling, wrestling, and chasing games, particularly among juvenile apes. Tickling is a reliable way for researchers to elicit these vocalizations, a discovery dating back to the observations of Charles Darwin.

The primary function of this behavior is to manage playful interactions. The vocalization acts as a cue that an ape’s intentions are not aggressive, even when play becomes rough. This signal helps initiate and prolong play sessions, which are important for developing physical and social skills.

This laughter also serves to build and reinforce social bonds. Researchers have observed that apes sometimes produce short, responsive chuckles after a playmate has laughed, suggesting a form of positive emotional contagion. This responsive laughter is more frequent in newly established colonies, indicating it may be used to solidify friendships and alliances in less familiar social settings.

Ape Laughter and Human Laughter: An Evolutionary Link

The parallels between ape and human laughter suggest a shared evolutionary origin. The laughter of great apes is considered a precursor to our own, indicating the behavior evolved at least 10-16 million years ago, before the human lineage diverged. This is supported by analyses of tickle-induced laughter across great apes and human infants, which found the acoustic relationships mirrored their genetic divergence.

While both are linked to play and social bonding, there are notable differences. Human laughter is produced almost exclusively during exhalation, allowing for the classic “ha-ha” sound due to greater vocal control. In contrast, ape laughter, with its alternating in-and-out breathy pants, reflects less refined muscular control over the vocal tract.

Studying these vocalizations informs our understanding of how positive emotional expressions evolve. Human laughter has expanded beyond its original play-specific function to become a sophisticated signal used in a vast array of social contexts, from humor to irony. The laughter of apes gives us a glimpse of its more fundamental form, a tool born from play that laid the groundwork for an important human social signal.