The world is bad, but babies remain good.
Babies are especially good when they are laughing, which they start to do at around three and a half months old. Babies laugh when other people do things, like tickle them or play peek-a-boo, or when other people are laughing.
The laugh of a human baby is distinct from (and significantly more excellent than) the laugh of a human adult. That’s because babies are much cuter than adults, but it’s also because, unlike adults, babies laugh both on the inhale and on the exhale, as described by new research presented at the Acoustical Society of America’s 176th Meeting.
Babies have that pattern in common with non-human primates, like chimpanzees, which also laugh both when they’re inhaling and when they’re exhaling. Adult humans, on the other hand, laugh almost exclusively on the exhale.
You can listen to (extremely delightful) examples of this inhale-exhale laughter from babies below:
Now compare those chortles to the sound of a gorilla being tickled:
Disa Sauter, a psychologist and associate professor at the University of Amsterdam in the Netherlands, and her team studied recordings of laughter from 44 children between the ages of three months and 18 months. Student listeners coded the recordings, noting when the laughter was on an inhale versus an exhale.
As the babies got older, the proportion of their laughter that was on the inhale decreased, according to the initial findings. “Our results so far suggest that this is a gradual, rather than a sudden, shift,” Sauter said in a statement. However, she noted that professional phoneticians are re-checking the results to confirm that the transition was actually happening.
It’s not clear why babies and chimpanzees laugh in this way. But laughter and laugh-like vocalizations in humans and non-human primates both probably evolved from common ancestry. Selection for traits that allowed humans to talk might have pushed humans towards a more speech-related laugh sound—and Sauter said it’s possible that babies start to laugh more like adults as they start to learn to speak.
So, the next time you are lucky enough to witness a laughing baby, see if you can pick up on those primate-like, inhale-exhale giggles.