Young babies laugh like apes
Young babies laugh like adult apes do: producing sounds while inhaling and exhaling. Adult humans produce sounds on the exhale only. Cognitive psychologist Mariska Kret and colleagues have published an article about the development of human laughter in the journal Biology Letters.
You hear it immediately if you listen to the laughs of a four-month-old baby and an eighteen-month-old toddler: they are completely different. This first began to intrigue Mariska Kret, Associate Professor of Cognitive Psychology, when she attended a lecture by primatologist Jan van Hooff in 2016.
Silence between the ‘ha ha ha’ sounds
Van Hooff explained how primates laugh differently from humans. We humans produce a laugh sound while exhaling and inhale silently between the ‘ha ha ha’ sounds. But when something has made a chimpanzee laugh, for instance, it produces a sound while inhaling as well. Kret: ‘I was there with my best friend and she said: “My baby laughs just like an ape. Look at this film.”’
This led Kret to the research that has now been published in Biology Letters. Around 115 people, 15 of whom were sound experts, listened to dozens of sound fragments of laughing children aged between three and eighteen months. The experts and laypersons were unanimous: the young babies produced laughter sounds when inhaling much more often than the somewhat older children did. The latter hardly did this at all.
Infectious or not
The way we laugh therefore starts off like apes do and then changes. Kret: ‘We don’t really know why this is. It’s probably a combination of anatomy, increasing control over your muscles and social learning.’
The researchers also asked the test participants about their perception of the laughter. They preferred the laughs of the older children, who only produced a sound when exhaling, and found these laughs more infectious. That was to be expected: someone who laughs in a snorting or otherwise strange fashion generally causes vicarious embarrassment in others.
Bokito wasn’t smiling
On the subject of ‘laughing’ apes, watch out for deadly misunderstandings. In 2007 gorilla Bokito escaped from its enclosure in Rotterdam Zoo when he once again stood eye to eye with a regular visitor who thought she had a special relationship with him. He grabbed the woman and dragged her around. ‘When I smiled at him, he smiled back,’ the woman said. She was left with a crushed hand and over a hundred bites.
Kret: ‘With apes, just like with us, there is a difference between laughing and smiling. With a smile, or a bared teeth display as it is known, an ape is more likely to be scared. People often smile when they’re nervous too. With an open mouth display, an ape is laughing, its mouth wide open. This generally happens during play. I often see this play face in my own toddler too.’
How we express and process emotions
Kret does a lot of research into emotions and how we express them. ‘How do we process our own emotions and those of others? I look at what can go wrong, for instance in people with autism, and at the origin of the expressed emotion. Primates are interesting for that.
‘People sometimes ask if we humans are unique in the way we express emotions,’ says Kret. ‘That’s what we want apparently. I think that all species are unique, but we have now discovered that there are similarities between how babies laugh and how apes do.’
Mariska Kret’s book Tussen glimlach en grimas - Uitingen van emoties bij mens en dier (Between a smile and a grimace - expressions of emotions in humans and animals) will be published by Atlas Contact in November.
Text: Rianne Lindhout