Researchers looking into the origins of laughter and its social implications have found that even apes may be fans of slapstick humor.
"The use of language-based jokes is clearly unique to humans," Robin Dunbar, a professor of evolutionary psychology at the University of Oxford, told Discovery News.
Dunbar, who co-authored the study with Guillaume Dezecache, described what non-human primates might be amused by.
"There is some suggestion that apes 'play practical jokes' or laugh at another's misfortune, such as the banana skin situation, but these are only casual observations.
"Human laughter derives from the play invitation vocalizations of Old World monkeys and apes, but this is normally confined to juveniles and adolescents; adults don't play," he continued.
"In apes, this is identifiably rather closer to human laughter," Dunbar explained, "and bonobos in particular use laughter a lot in play contexts, even among adults. What seems to have happened is that humans have taken these monkey/ape play vocalizations and tweaked them and increased the frequency of their use."
Human laughter still has an animalistic quality, in the sense that it involves a series of rapid exhalation-inhalation cycles comparable to other primate sounds; it's louder than human speech; and, like sneezing, laughter is contagious.
Although a room full of people can laugh at one comic's joke, Dunbar and Dezecache suspected that the size of bonded natural laughter groups might be limited and similar to social grooming. The latter facilitates bonding and makes individuals feel good, promoting connections between others. Laughter can function in a similar way.
For the study, the researchers studied multiple social groups in bars throughout the United Kingdom, France and Germany. They took note of conversational subgroup size and laughter subgroup size, meaning the number of individuals laughing in an obviously coordinated way.
The scientists found that laughter groups were limited to three to four individuals.
"We think laughter long predates the appearance of language in human evolution, and was co-opted from play as a mechanism to allow bonding between larger numbers of individuals," Dunbar explained.
"Laughter triggers the release of endorphins, which are the neurochemicals used in bonding in monkeys and apes. Laughter allows us to increase the size of the bonding group because several people can laugh together; whereas grooming is, even in humans, a one-to-one activity, with only the recipient gaining the benefit of the endorphins," he said.
The study has been accepted for publication in the journal Evolution and Human Behavior.