While a sense of humor is a key component of being human, laughter isn’t a pastime of Homo sapiens alone. Other primates laugh, too, though their laughter differs from ours in a fundamental way. The weird thing is, as scientists recently discovered, the laughter of human babies is a lot more similar to that of primates than that of adult people.

At a meeting of the Canadian Acoustical Association in Victoria, Canada, on Monday, a team of phoneticians and psychologists presented evidence that the laughter of especially young babies is more analogous to that of nonhuman primates, such as chimps. Their conclusion hinges on a key aspect of baby laughter: When babies laugh, they both exhale and inhale. The laughter of adults, on the other hand, is primarily produced on the exhale.

That exhalation has been thought to be the one way in which human laughter differs from that of primates. However, this new research — for now, only presented as a conference abstract — demonstrates that at the start of our lives we laugh like other primates. You can listen to the inhalation-exhalation of a baby’s laugh in the video above.

baby
While adults laugh on the exhale, babies laugh as they both exhale and inhale.

“Adult humans sometimes laugh on the inhale, but the proportion is markedly different than that of infants’ and chimps’ laughs,” co-author Disa Sauter, Ph.D. a psychology professor at the University of Amsterdam, said Monday. “Our results so far suggest that this is a gradual, rather than sudden, shift.”

As of now, Sauter and her team don’t know why the process of laughter changes as children age. After studying laughter recordings taken from 44 infants and children between 3 and 18 years of age, it became clear to the 102 participants who evaluated the sounds of laughter that the youngest babies commonly laughed on both the inhalation and exhalation. But what wasn’t clear was whether the change in laughter was timed with any developmental milestones.

chimpanzee
Babies laugh more like chimps than humans. 

One hypothesis that needs to be evaluated further is that, perhaps, the way humans laugh changes once we develop the ability to speak. The team also plans on following up this study with another trial in which specific types of laughter are evaluated: Babies, like nonhuman primates, laugh because of physical play like tickling. It’s possible that laughter caused by other stimuli could emerge differently.

While there are certain mysteries underlying this discovery, it adds further evidence to a united bond between humans and other primates. Scientists believe the common ancestor between these two groups likely started laughing at least 10 million years ago, and previous research has found that chimps, like humans, use laughter to convey how much fun they are having. Although we may not know yet why babies laugh more like chimps than their adult parents, we do know that all groups are bonded by the joy of laughter itself.