June 4, 2009 -- Humans aren't the world's only laughers, according to a new study that determined gorillas, orangutans, chimpanzees and bonobos all enjoy a good chuckle too.
The propensity of great apes to giggle suggests the last common ancestor of humans and non-human great apes also laughed around 10 to 16 million years ago. The ability then evolved among subsequent primate relatives, leading to distinctive ways of chuckling in each.
"Orangutans produce a short laugh series of noisy calls," project leader Marina Davila Ross explained to Discovery News. "Gorillas, chimps and bonobos produce longer laugh series and the calls are produced more rapidly."
Davila Ross, a University of Portsmouth primatologist, with colleagues Michael Owren and Elke Zimmermann, made over 800 recordings of 22 juvenile and infant apes and three human babies laughing as their palms, feet, necks and armpits were tickled.
"It is amazing to see an adolescent gorilla laugh," she marveled.
An analysis of the laughter, presented in the latest Current Biology, revealed that human laughter is most similar to that of chimpanzees and bonobos. Next in line, in terms of similarity, are gorillas, followed by orangutans and siamangs, which are lesser apes.
"These results coincide with the genetic topology of great apes and humans," Davila Ross said.
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Given how laughter has evolved over time, it appears that the first relative to apes and humans who guffawed did so in a much longer and slower fashion than we do now, Davila Ross explained. Non-human great apes to this day can laugh while inhaling and exhaling, often for a long time.
"We found that bonobos and gorillas have the ability to produce laughter while breathing out for more than 10 seconds," Davila Ross said. "This shows that they can extend their exhalation phases while vocalizing, a trait thought to be unique in humans."
She added, "The ability to produce such a vocal flow is particularly important in human speech."
Human laughter is produced more often during exhalation and has a pronounced lyrical quality to it due, in part, to regular vibrations of the vocal chords.
Jo-Anne Bachorowski, an expert on human laughter who is an associate professor of psychology at the Vanderbilt Kennedy Center, told Discovery News "the work provides a very interesting perspective on the evolution of human laughter."
Bachorowski added she would "like to see the work expanded to include non-tickle-induced sounds."
Frans de Waal, director of Living Links at the Yerkes Primate Center, said the new study puts to rest prior claims that human laughter is a unique display in the animal world.
"The primate laugh is given in playful contexts, and as such has a strong similarity to the human laugh," de Waal told Discovery News. "Tickling and wrestling are the situations in which primates laugh, and I use the term 'laugh' now advisedly because the evidence from this study is very strong that their display is evolutionarily related to the human laugh."
Is it possible then that apes, and even monkeys, have a sense of humor?
Ross doesn't rule it out, but said "it is difficult to find a method to accurately test it."
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