GENEVA - "It is better to write of laughter than of tears, for laughter is the property of man," French Renaissance writer Francois Rabelais once said. Laughing, it turns out, may even be an inherent human trait, a British research team has concluded after filming babies in the womb.

Nadja Reissland from the University of Durham and her colleagues have shown the gradual appearance of several facial movements beginning in the second trimester that enable the formation of all the elements of laughter around the 30^th week of pregnancy. The researchers have just published their findings in the PloS ONE journal.

"It is the first time, to my knowledge, that this technique to measure anatomical movements of facial expressions was applied in utero," says Patrik Vuilleumier, director of Geneva University's Neuroscience Center. "These results showing the appearance of human expressions before birth are both new and very interesting," he adds.

In humans, the first facial movements appear in the 10^th week after birth and become more and more complex with time. The researchers used an ultrasound camera to film two babies in their respective mother's uterus. An analysis of the babies' facial movements using American psychologist Paul Ekman's "Facial Action Encoding System" allowed them to characterize the expressions linked to laughing and crying. In the 34^th week of pregnancy, more than one month before birth, these two expressions were clearly recognizable.

"The movements of the face were spontaneous and could not have been triggered by the ultrasound because the babies were probably not even aware of it," says Nadja Reissland. "In order to exclude any possibility of external influence, we decided to take this approach rather than studying pre-term babies."

The smile observed by researchers was therefore not a reflexive response mimicking a human, which appears very quickly once the baby's born, but rather the manifestation of an independent action.

Fleeting muscle, lasting expressions

The results did not come as a surprise for Rui Diogo, a specialist in facial muscles in the anthropology department at George Washington University in Washington, D.C. "Believing that muscles form only to serve well after birth, for example in society, is a myth," he says. "The proof is that there is at least one muscle in the baby's face that disappears later." Its fleeting appearance, argues Diogo, is linked to a necessary rite of passage in the formation of a baby's face, a brief nod to a step in our evolutionary past.

What is laughter then? What purpose does it serve? Technically speaking, it is one of the numerous facial expressions that distinguish superior primates. And yet laughter is less noticeable among orangutans and chimpanzees, even though they possess 23 pairs of facial muscles, the same as humans - with the exception of one small muscle.

If humans, therefore, produce a more varied combination of expressions, the explanation must be found somewhere in the nervous system. The expression of a smile indeed remains the essence of man according to Diogo because, among the six pairs of muscles that produce a smile, that of the risorius, which pulls the corner of the mouth outwards, is specific to human beings.

Other indicators suggest that the smile is "pre-programmed" in humans. "With certain forms of brain damage, a smile can occur without reason, and this type of spasmodic smile appears as more of a reflex than a social signal of emotion," says Vuilleumier. A smile is also an expression of universal joy, one found in all human cultures, as Paul Ekman has shown.

In his work "The Expression of the Emotions in Man and Animals' published in 1872, Charles Darwin noted that a blind and deaf person could have a normal smile, proof that it is not a product of learning. He also observed in his first child "that he can understand a smile and take pleasure in seeing one even at an age where he is too young to be able to learn it."

Does the standard movement of a smile correspond with a positive emotion? "The question remains actively debated because it is difficult to evaluate the emotions that can be felt at this age," says Patrik Vuillemier. "We are in the presence of a pre-programmed muscular behavior of which the use will then be largely a product of the culture and context."

Such is also the opinion of Nadja Reissland, who stops short of assigning effects or emotions to a fetus. "The debate is about knowing in which month the baby begins to smile in order to communicate with the people around him, mainly the mother," she says.

This does not necessarily mean a smile is useless for a newborn. Like crying, it is a primary way of establishing a link with one's surroundings and could be a vital element retained by evolution so that a baby can form attachments with those around him or her.

Read the original article in French

Photo - Worldcrunch