Few sounds encapsulate the feeling of pure, undiluted joy better than a baby’s giggle. But as babies mature into toddlers and inevitably veer closer to adulthood, their laughter loses some of this intangible charm. (Unfortunately, we can’t all be like Peter Pan, the perennially youthful boy who refused to grow up.)
Now, researchers say there’s a scientific explanation for the shift: Although most humans only laugh while exhaling—a practice that separates us from other primates—babies let loose while inhaling and exhaling, making their laugh patterns surprisingly similar to that of chimps and gorillas.
The team’s findings were presented this week at the Acoustical Society of America’s 176th Meeting in Victoria, British Columbia. Lead researcher Disa Sauter, a psychologist at the University of Amsterdam, tells Newsweek’s Aristos Georgiou that the project, which has yet to be published in a scientific journal, was inspired by the realization that baby laughter sounded “a bit” like chimp laughter.
To investigate the issue further, Sauter and her colleagues compiled a database of laughs produced by 44 infants and children between the ages of three to 18 months old. (The giggles came from online videos of babies laughing—a robust, if eclectic, YouTube genre.) Next, the team recruited 102 psychology students, who were asked to listen to the recordings and judge whether a laugh occurred on an inhale, exhale or both.
Older children included in the sample showed a marked decrease in giggles produced on the inhale, Nicole Wetsman reports for Gizmodo. Comparatively, the youngest infants laughed with reckless abandon, chortling their way through both the inhale and exhale.
Preliminary findings point toward a rather random transition from chimp-like laughter to mundane adult laughter. The researchers, according to Inverse’s Sarah Sloat, were unable to identify any connections between the switch and key developmental milestones.
“Adult humans sometimes laugh on the inhale, but the proportion is markedly different from that of infants' and chimps' laughs,” Sauter says in a statement. “Our results so far suggest that this is a gradual, rather than a sudden, shift.”
Sauter tells Newsweek the change is most likely linked to young children’s burgeoning speech abilities. As humans learn to control their vocal chords, they may adopt a new method of laughing. It’s also possible that the context in which laughter is produced—infants tend to respond to physical cues, such as tickling, while older individuals are better attuned to humor arising during social interactions—affects the laughing process.
For now, the researchers are focusing on confirming the student-led analysis with professional phoneticians. According to the statement, potential paths forward include seeing whether the findings prove true with vocalizations besides laughter and adding to the body of scholarship surrounding children with developmental disorders.
Sauter explains, “If we know what normally developing babies sound like, it could be interesting to study infants at risk to see whether there are very early signs of atypical development in their nonverbal vocalizations of emotion."