Little kids aren’t just sassy monkeys – it turns out they also laugh like chimpanzees.
The researchers found that both babies and chimpanzees laugh during inhalation and exhalation, unlike adults, who laugh mostly during exhalation.
A hoarse squeaky sound may be due to the fact that babies, like monkeys, have poor control over their vocal pathways, so they laugh when they inhale.
But as we age, our laughter becomes less chimpanzee-like and more human, Dutch researchers say.
Both humans and chimpanzees are great apes (hominids), and chimpanzees are our closest animal relatives, but laughter is a behavior in which the adults of both species differ.
When an adult laughs, they first inhale and then make short “ha-ha-ha” sounds, starting loudly and then fading away, says study author Mariska Kret, a professor of cognitive psychology at the University of Leiden in the Netherlands.
‘ [non-human] the simian type is harder to describe, but there is an alternation ha ha ha ha,” she told CNN.
Both humans and chimpanzees (pictured) are great apes (hominids). The Pan genus consists of two living species, chimpanzees and bonobos.
As children get older, they begin to laugh more like adults, perhaps because such laughter elicits a better response from their parents.
“This is not a topic that has really been covered before, but every parent knows that young children are a lot like chimpanzees,” said study co-author Dr. Disa Soter of the University of Amsterdam.
“Perhaps children learn to imitate their parents, so they grow out of it.”
For the study, the researchers collected audio clips of human babies between the ages of three and 18 months as they laughed.
These audio clips were played back to 196 volunteers and 15 phonetics experts, who had to rate the extent to which laughter is produced during inhalation or exhalation, and how much they find laughter pleasurable and contagious.
As a rule, they rated the laughter produced during exhalation as more pleasant and contagious than the laughter produced during inhalation.
The older babies in the sample — those who were 18 months old — exhaled more when laughing.
This suggests that during this key developmental period of three to 18 months, babies learn to exhale when they laugh.
Exhaled laughter tends to be louder, Professor Kret told CNN, making it easier for babies to communicate that they’re having fun and want to keep playing.
As children get older, they learn about the “communicative function” of laughter and that this communication is best achieved by exhaling rather than inhaling, she said.
Perhaps children subconsciously adapt their laughter to get the best response from their parents, such as laughter, smiles, or eye contact.
Parents, meanwhile, see that their baby is actively trying to clarify something.
In another experiment, 102 people were asked to rate videos of laughing babies and adults without paying attention to their breathing.
The researchers found that they preferred more sing-song adult-style laughter, even when they didn’t think about the style of the laughter.
“This study started when our lead author was shown a video of her friend’s baby laughing and she thought it sounded like a chimpanzee laughing,” said Dr. Soter.
Of course she didn’t tell her mother! But it got us thinking, and we found these similarities that parents might want to listen to.
“It just shows that our behavioral repertoire is ancient and inherited from a common ancestor that we share with apes.”
The study, titled “The Ontogeny of Human Laughter,” was published in the journal Biology Letters.