The rhythmic patterns of laughter in humans and great apes suggest that complex forms of vocal control in primates may have begun to evolve around 15 million years ago.
Tickling a chimpanzee, a gorilla or a human child causes similar rhythms of laughter, according to an analysis of primate behavior.
O Laughter is not exclusive to humanss: is a form of vocal expression shared with its closest primate relatives, note a .
In a published on Thursday in Communications Biologyresearchers concluded that the laughter of humans and great apes follows consistent rhythmic patterns. When tickled, great apes and children between six months and seven years of age made laughing sounds separated by regular intervals.
These rhythms can reveal a more sophisticated degree of control voice engine in primates than previously thought and were inherited from a common ancestor who lived about 15 million years ago, say the study authors.
The analysis is in line with a growing body of data that suggests that our closest living relatives, the primates, and in particular the great apes, have more control over the vocal system than previously thought, says Simon Townsendresearcher at the University of Zurich, Switzerland, who studies communication between primates.
The findings also help to understand the evolutionary progression of vocal flexibility in the primate lineage, adds the researcher.
Tickling and playing
Chiara De Gregorioa primatologist at the University of Warwick, in the United Kingdom, and co-author of the study, compared recordings of four children humans playing at home with their mothers with recordings of young great apes and offspring: four orangutans (Pongo pygmaeus), two gorillas (Gorilla gorilla), three bonobos (Pan paniscus) and four chimpanzees (Pan troglodytes).
The analysis focused on 140 laugh sequences: 42 bonobos, 35 from chimpanzees, 34 from gorillas, 16 from orangutans and 13 from human children.
The researchers measured the interval between each burst of laughter and discovered that during tickling, both humans and great apes maintained a regular rhythm.
The same did not happen during social play.in which laughter was more variable. “During the game, the laughter was a little more chaoticbecause when we think of two animals or two children playing, a lot of things happen at the same time”, explains De Gregorio. “They can roll around or play fights.”
These physical movements alter breathing and make it more difficult to maintain a steady rhythm when laughing.
The team further concluded that human laughter has a faster rhythm than that of great apes. Furthermore, unlike the animals studied, humans can adapt laughter to different social contexts. “The essential difference is that humans have even more control about the sounds of laughter,” says Townsend.
De Gregorio and colleagues suggest that this acceleration may have occurred gradually over the course of hominin evolution. “Starting from orangutans, which had a slower or irregular laugh, there is a gradual evolution towards human laughter, which is faster” and more flexible, says the researcher.
The conclusions may reveal “something about laughter itself, but also, in a certain way, about the evolution of human speech“, he adds.
