It is natural to associate laughter with human experience, a complex expression of enjoyment and social connection. This uniquely human trait raises a fascinating question: do other animals, particularly our closest relatives like chimpanzees, share similar behaviors? Exploring the vocalizations of chimpanzees offers insights into the ancient roots of this compelling form of communication.
Chimpanzee Play Vocalizations
Chimpanzees produce distinct vocalizations during play that researchers often refer to as “laughter.” These sounds differ from human laughter, characterized by alternating inhalations and exhalations that create a panting or breathy quality. Unlike the clear, voiced sounds of human laughs, chimpanzee play vocalizations can sound more like staccato grunts or even screeches. They are typically short, serially organized bursts of low-amplitude sound. Chimpanzees also exhibit specific facial expressions, known as “laugh faces,” involving parted lips, dropped jaws, and pulled-back lip corners.
Triggers for Chimp “Laughter”
These distinctive chimpanzee vocalizations are primarily associated with social play, tickling, and physical interactions. In both wild and captive settings, chimpanzees produce these sounds during wrestling, chasing games, or when being tickled. Laughter can be spontaneous, such as when a playmate surprises them, or it can be a responsive, shorter chuckle in reaction to another chimpanzee’s laughter. This responsive “laughter” appears to serve as a social signal, helping to prolong play and solidify social bonds within the group.
Comparing Chimp and Human Laughter
Chimpanzee and human laughter share functional similarities despite their acoustic differences. Both serve as important social signals, facilitating play, reducing tension, and fostering social bonding. The ticklish spots on the body, such as armpits and the belly, are similar between humans and chimpanzees, and both species exhibit comparable facial expressions during laughter.
However, the acoustic and physiological mechanisms behind these vocalizations differ significantly. Chimpanzee laughter involves alternating airflow during both inhalation and exhalation, creating its characteristic panting sound. Human laughter, in contrast, is predominantly produced during exhalation and involves more regular vibrations of the vocal cords, resulting in a more voiced and clearer sound. While apes primarily laugh in the specific contexts of social play and tickling, human laughter occurs across a much wider array of social situations and emotional states.
The Origins of Laughter
The similarities between chimpanzee and human laughter suggest a deep evolutionary connection. Laughter-like vocalizations are present in all modern great apes, indicating a common ancestral origin that predates the human lineage. Research suggests that the earliest forms of laughter may have emerged at least 10 million years ago, challenging the notion that laughter is exclusively a human trait.
The acoustic features of tickle-induced vocalizations across great ape species and humans provide strong evidence for a shared evolutionary path. This suggests that the distinctive characteristics of human laughter, such as its voiced quality and exhalatory airflow, evolved from pre-existing acoustic traits found in our primate ancestors. Laughter likely evolved from an ancient play signal, possibly originating from the sounds of labored breathing during vigorous play.