Paris (AFP)

"Huh-ha-huh!"

vs. “ha-ha-ha!”: like great apes, human babies laugh a lot on inspiration, before evolving into more expiratory, more communicative adult laughter, according to a study.

The idea of ​​comparing man and animal in this unusual terrain arose during a conference given by a primatologist in Sicily, attended by a young researcher and her friend.

This professor showed how laughter, which we now think is not unique to the human species, worked in great apes (gorillas, orangutans, chimpanzees ...): sounds, caused by tickles, were emitted by both inhaling and exhaling air, similar to a "huh-ha-huh-ha".

"My friend then said to me + well, my baby laughs like a monkey +", recalls researcher Marishka Kret, professor of cognitive psychology.

"She showed me videos of her son, the resemblance was obvious! I then asked a colleague who is an expert in vocalizations to conduct a study with me," she told AFP.

A team of cognitive neuroscientists, which she heads alongside Diane Venneker at the University of Leiden in the Netherlands, is developing various experiments, the results of which were published Wednesday in Royal Society Biology Letters.

To a first group of 15 phoneticians and 102 novices (previously trained), they played recordings of laughter from human babies, aged 3 to 18 months.

Participants were asked to measure the proportion of breaths and breaths contained in the sounds, and then rate, on a rating scale, how pleasant and contagious they found these little laughs.

Both experts and non-experts have delivered the same observation: the bursts of laughter in younger babies were produced 50% when inhaling and 50% when exhaling.

An alternation of "huh" and "ha" close to non-human primates.

- "a clearer signal" -

In human adults on the contrary, explains Mariska Kret, laughter passes to 74% by exhalation: they take a deep breath before coming out of "ha-ha-ha", less and less strong.

Experience has shown that the more we advanced in the age of the babies, the more the proportion of expiration increased ... and the more the perception by the adult was positive.

This professor showed how laughter, which is now thought to be unrelated to the human species, worked in great apes TORSTEN BLACKWOOD AFP / Archives

"This is what surprised us the most: discovering that a more + mature + laugh was perceived as more pleasant and more contagious", says the researcher.

Two subsequent experiments, based on a new group of participants and new recordings, confirmed that the "ha-ha-ha" was more communicative.

"With the exhalation, the signal seems clearer. The sound is not only louder, but also more controlled, which makes it possible to signify to the other + hey, it's funny, let's continue! +", Analyzes the Pr Kret.

It remains to be understood why infants switch from "hu-ha-hu" to "ha-ha-ha".

One of the explanations would be that their vocal apparatus, poorly mastered in its early stages, gradually developed so as to adapt to complex faculties such as language.

Another suggestion: as his socialization is built, the little child learns to laugh better in order to have more response from his parents, says the researcher.

As his socialization is built, the little child learns to laugh better in order to have more support from his parents Ina FASSBENDER AFP

Because it has been shown that social interactions last longer if there is laughter, and it is shared.

It functions as a social bond, and not only in humans: "when great apes laugh at unexpected events, such as a somersault, they display a playful air that is easily imitated", she emphasizes. .

Gorillas play longer and more often if they have shared a part of the laughter, as the work of Italian ethologist Elisabetta Palagi has shown, continues the researcher.

But undoubtedly because they are not endowed with speech, their vocal organ evolves differently, and monkeys laugh all their lives like little ones.

© 2021 AFP