Chimpanzees, our close primate relatives, produce vocalizations remarkably similar to human laughter. This has long fascinated scientists, prompting extensive research into these sounds. The study of chimpanzee laughter provides insights into the evolutionary origins of this complex behavior, suggesting a shared biological heritage. Researchers have analyzed these vocalizations, exploring their acoustic properties, contexts, and social significance.
The Unique Sound of Chimpanzee Laughter
Chimpanzee laughter possesses distinct acoustic properties that differentiate it from human laughter. It is described as a breathy, panting sound, unlike the clear, voiced “ha-ha” of humans. This difference arises because chimpanzees produce these sounds during both inhalation and exhalation, creating an alternating “huh-ha-huh-ha” pattern. Adult human laughter is predominantly produced during exhalation.
Physiological mechanisms include rapid breathing, 10 to 15 times faster than their normal respiration rate. This rapid airflow contributes to the characteristic panting quality. While humans rely heavily on vocal cord vibrations for voiced laughter, chimpanzee laughter often involves less regular vocal fold vibration, resulting in a noisier sound. Despite these differences, accompanying facial expressions, such as an open mouth, can be similar to human “laugh faces.”
Why Chimpanzees Laugh
Chimpanzees typically produce laughter-like vocalizations in specific social contexts, primarily during play interactions. These include rough-and-tumble play, wrestling, chasing, and especially tickling. Tickling, in particular, is a common trigger, and chimpanzees, like humans, have ticklish areas such as the armpits and belly.
The laughter serves as a clear signal of positive social engagement, indicating enjoyment and excitement. It acts as a social lubricant, helping to maintain playful interactions and prevent them from escalating into aggression. Studies show that play sessions tend to last longer when laughter is involved, suggesting its role in promoting continued interaction. Furthermore, chimpanzees can produce responsive laughter, echoing the laughter of others, which may help solidify social bonds and and alliances, particularly in newly formed groups.
Comparing Chimpanzee and Human Laughter
Comparing chimpanzee and human laughter reveals both shared evolutionary roots and distinct adaptations. Research suggests that laughter-like vocalizations have existed in great apes for at least 10 to 16 million years, tracing back to a common ancestor shared with humans.
Despite these commonalities, human laughter has evolved to be acoustically distinct, becoming more voiced with regular vocal cord vibrations and predominantly egressive airflow (exhalation). These changes may be linked to the evolution of human speech, which requires precise breath control. While chimpanzees can make various “laugh faces,” human laughter often involves more pronounced facial movements, such as the formation of “crow’s feet” around the eyes, which are less common in chimpanzees. The ability of human infants to laugh on both inhalation and exhalation, similar to chimpanzees, suggests that the exhaled-only pattern in adult humans is a developmental acquisition.