Babies under three months of age can already laugh out loud, but they still do it the way nonhuman primates do: with a lot of noise during inhalation and not particularly loud on exhalation as adult humans do. As children age, this percentage of inhaled decreases steadily, from more than 50 percent at three months to less than 40 at a year and a half. Surprisingly, the more children laugh on their exhale, the more adults will develop laughter. All this is evidenced by research of more than 100 videos of babies laughing between three months and a year and a half, and the assessment of that smile by panels of experts and “normal” people, led by Mariska Krett, a zoologist in Leiden. The analysis appeared in Biology Letters in early September.
Different groups of mammals laugh, except for primates too some rodents. In animals, the laughter signal, with which they indicate that they are having a good time, is issued when inhaling and exhaling. The signal may have arisen from labored breathing during physically active games.
In humans, this signal has been converted into the well-known ha-ha sound (in all sorts of variants) which is made primarily on exhalation. Laughter in humans, like animals, is an intense social activity that strengthens the bonds between them. Krit says in press release From the University of Leiden, how did she come up with the idea of analyzing early childhood laughter when she and a friend attended a lecture by the first Dutch biologist Jan van Hoof. Van Hoof became famous in the early 1970s because he demonstrated that a human smile is associated with the relaxed open-mouthed face and the cheerful gasping sound that chimpanzees and other great apes make during social play. When he showed up and heard a monkey laughing during the lecture, Crete’s friend said, “That’s how my baby laughs too.”
Laughter always arises in a social process, such as a tickle or a peek
To scientifically substantiate this observation, Krett collected videos of children laughing, 4-7 second in length, including data on the context of the laughter. No records of children’s laughter under the age of three months were found, before that time babies could not laugh out loud. It turns out that inhaled and exhaled laughter could not be automatically distinguished based on the vocal tract alone, so Krett had several teams of experts and “normal” participants to assess the laughter. They also had to clarify whether laughter was contagious.
(Audio from Mariska Crete)
Researchers believe that it is not surprising that newborns have not yet mastered the typical advanced human exhaling smile. Their throats are still very similar to that of a “normal” primate. The larynx, which is normally adapted to human speech, and which also allows for more precise control of laughter, matures only gradually after birth. From the age of seven to eight months, babies begin to “chatter” on their own, that gentle flow of sounds that actually sound like language but aren’t.
But laughter does not come naturally, not even with a more appropriate throat. Laughter always arises in a social process, such as a tickle or a peek. The authors write that imitation is the obvious mechanism for this learning process. After all, six-month-old babies already imitate all kinds of sounds that adults around them make. But they think there is another process: Young children are very sensitive to the reactions of adults to their vocal productions. Hence the greater attractiveness of an exhaling smile becomes important. When children begin to exhale better, they are immediately rewarded with a more positive response than the adults around them. They usually shoot in spontaneous exhaled laughter.
Like monkeys, laughter in humans has more to do with communicating a good feeling than laughing at something funny, as the American sociologist and neurobiologist does. Robert Provine It was already established in the nineties. People laugh more in company than when they are alone. The “contagion” of laughter is most striking: people also laugh more often because someone else is laughing more than because they hear something funny. Bruffin compares the auditory contagion of laughter to the visual contagion of a yawn, and no one “yawns” because of anything.
A version of this article also appeared on NRC on the morning of September 21, 2021
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