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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 they are so much more than adults, but it's also because of the exhale, as it was described by the research team at the Acoustical Society of America's 176th Meeting.
Babies have that pattern in common with non-human primates, like chimpanzees, who also laugh when they're inhaling and when they're exhaling. Adult humans, on the other hand, laughing almost exclusively on the exhale.
You can listen to (extremely delightful) examples of this inhale-exhale laughter from babies below:
Now compare these 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 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 was decreased, according to the initial findings. "Our results so far 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 can be said to be more likely to be heard by people who have heard of it. Sauter said it's possible that they start to laugh.
So, the next time you are lucky enough to witness a baby laugh, see if you can pick up on those primate-like, inhale-exhale giggles.
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