The question of whether complex human behaviors, such as laughter, exist in other species opens a fascinating window into primate communication and shared ancestry. Exploring the vocalizations of our closest relatives reveals a deep evolutionary connection. Analyzing these sounds and the context in which they occur helps trace the origins of human emotional expression back through millions of years of primate evolution.
Yes, But It’s Not What You Think
Monkeys and apes do not produce the acoustically distinct, vowel-like sound that humans recognize as “ha-ha-ha” laughter. They do, however, exhibit vocalizations tied exclusively to social play, tickling, and roughhousing, which are considered the evolutionary precursor to human laughter. These sounds serve the same social function, signaling a playful state and non-aggression during physical interactions.
The immediate context is the most important similarity, as the sounds are primarily elicited by tickling or during vigorous play sessions. Researchers trace this tickle-induced vocalization back to the last common ancestor shared by humans and the Great Apes, confirming a phylogenetic continuity of this emotional expression. The acoustic quality, not the intent or context, principally separates primate play sounds from human laughter.
The Characteristics of Primate Play Sounds
The vocalizations produced by apes and some monkeys during play are often described as “pant-hoots” due to their breathy quality. The primary difference from human laughter lies in the respiratory mechanics used to produce the sound. Human laughter is predominantly produced on a single, controlled outward breath, which allows for the extended, rhythmic “ha-ha-ha” sound.
In contrast, the play vocalizations of chimpanzees, bonobos, and other Great Apes are produced with an alternating flow of air, involving short bursts on both the inhalation and exhalation. This in-and-out panting creates a breathy, rapid, and sometimes high-pitched sound that is acoustically less resonant than human laughter. This panting sound is thought to have evolved from the auditory cue of labored breathing that naturally occurs during intense physical play.
Mapping Laughter on the Evolutionary Tree
The presence of these play vocalizations across all Great Ape species and humans suggests a common ancestral origin for the behavior, likely dating back 10 to 16 million years. This panting sound, which serves as a social signal during play, gradually adapted over time. This transformation was most pronounced after the hominin line separated from the ancestor shared with chimpanzees and bonobos, roughly 4.5 to 6 million years ago.
A significant physical change that helped shape human laughter was the development of bipedalism and corresponding changes in breath control. Standing upright freed the thoracic cavity, enabling early hominins to develop the greater respiratory capacity necessary for long, sustained exhalations. This increased control allowed the ancient panting sound to evolve into the louder, more acoustically complex, vowel-based laughter characteristic of modern humans.
Where True Laughter Ends and Play Begins
When considering the specific question about “monkeys,” it is important to distinguish them from the Great Apes, who are tailless and more closely related to humans. The most human-like forms of tickle-induced vocalizations are consistently documented in Great Apes, including chimpanzees, gorillas, orangutans, and bonobos. These species are the ones whose play sounds are most directly comparable to human laughter.
The play vocalizations of Old World and New World monkeys, such as Rhesus macaques or Capuchins, are generally less acoustically similar to human laughter than those of apes. While monkeys engage in social play and produce specific vocal signals to communicate non-aggressive intent, these sounds are often less prominent or acoustically different from the breathy panting of the Great Apes. The evolutionary trajectory shows that the vocal signal of play became significantly more defined in the lineage leading to the Great Apes and humans.