Evolutionary origins of laughter
Posted: Tuesday, October 7, 2003
2 October 2003 13:00 GMT
by Laura Spinney, news.bmn.com
Bonobos laugh just like babies, say German researchers who believe their findings indicate that the rules for how emotion is encoded behaviorally were laid down in the common ancestor we share with our closest ape relatives.
Eight years ago, Birgit Förderreuther meticulously recorded the laughter of an infant bonobo from Wuppertal Zoo, Germany from birth to one year, in response to tickling. But before she was able to analyse the recordings, she fell ill and had to abandon the project.
Now her colleague Elke Zimmermann of the Institute of Zoology at the Tieraerztliche Hochschule in Hanover has picked up where she left off and compared sophisticated spectrographic analyses of the bonobo sounds - that is, computer-generated graphs showing variation in energy and frequency over time - with sounds made by human infants, also in response to tickling.
Zimmermann finds that, like babies, bonobos combine the visual gesture of a "relaxed open-mouth display" with vocalizations, and that these vocalizations follow broadly the same spectrographic pattern as that of infants - though bonobos laugh at higher frequencies.
She believes that her findings confirm the hypothesis that laughter originated in primates before humans, and that it represents a universal signal of wellbeing in a playful situation. In that way, it helps to regulate social interactions.
A pre-human evolutionary origin for laughter could also explain why it is still present in deaf and blind infants, and why it fulfils the same role - and sounds the same - in people from different cultures.
Robert Provine, a psychologist at the University of Maryland, Baltimore County who has studied the laughter of common chimps, thinks this field of research has a bearing on other big questions, such as the evolution of speech.
In chimps, he says, laughter is a breathy, panting sound involving both inhalation and exhalation, while the human laugh is a single, "chopped" exhalation. "That indicates why we can talk and chimpanzees can't," he said. "People have shown that chimps have symbolic capacity in that they can sign. Although chimpanzees can recognise many spoken words, they can't produce the sounds."
Provine believes that the difference was driven by the evolution of bipedality in humans. "Walking upright provides independence between breathing and running, which does not exist in other animals. All quadrupedal animals have a one-to-one relationship between breathing and running." And that, he says, is why chimps laugh as if they had been running and were out of breath.
But when bonobos stand, they straighten up more than chimps, and their posture more closely resembles that of humans - which could explain why their laughter is also more similar.
The findings was presented at a meeting of the German Primate Society in Leipzig, Germany at the beginning of October.
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