It is an experience within everyone’s reach and that everyone has been able to verify: “A good yawner makes ten yawn. Perhaps even the mere sight of the photo in this article triggered this curious mimicry in you, which science now seems to be able to explain. In the May edition of the journal Animal Behaviour, New York University Polytechnic Institute biologist Andrew Gallup pulled together the knowledge gained so far on this reflex to arrive at this well-supported guess. : contagious yawning, inherited from afar, originally served to protect us! But before coming to the point, we must trace the thread of evolution.
Because many animals yawn. It is estimated that the first species to have involuntarily opened their mouths were jawed fish, 400 million years ago! By studying the duration of yawning in a hundred species of mammals and birds, we came to the conclusion that the length of the action is linked to the size and complexity of the brain. “The act of yawning is strongly stereotyped, taking a similar form in various species. Yawns are always defined by an involuntary and forceful opening of the jaw, a temporary period of maximum muscle contraction and a passive closing of the jaw,” explains Andrew Gallup.
This reflex being very old, it is considered that it evolved originally as a spontaneous event, specific to the individual, without social utility, therefore. On the other hand, with specific functions such as regulating fatigue, making you more alert and cooling the brain. “A large number of comparative studies show that yawning promotes transitions from one state to another, arousal and the regulation of body temperature”, details Andrew Gallup. Contrary to a legend, yawning does not, however, serve to supply more oxygen to the blood.
And then there is the communicative yawn found in so-called “social” species. In the evolution of species, it would have appeared later and we know less about it. Until recently, studies focused either on the physiological role of yawning or on this social dimension. Andrew Gallup has therefore made it his mission to summarize all the work available on the subject: “There have been a number of important studies on yawning published in recent years. The purpose of this article was to synthesize this latest research with the existing literature to provide a unifying framework for understanding the evolution and elaboration of yawning in social vertebrates. »
And the thesis that emerges from this state of the art is astonishing: in these animals living in groups, yawning would also serve to warn that a member is tired and that they therefore need to be extra vigilant to protect themselves from predators. The contagion would be a way to communicate this signal to the whole community, so that everyone is more alert! An idea that emerged from previous work by Andrew Gallup.
In an experiment whose findings were published last year, the biologist and his colleague Kaitlyn Meyers showed 38 humans paintings with pictures of snakes, creatures that have always been considered a threat to humans, and more harmless frogs. These paintings included seven images of frogs and one of a snake, or vice versa. The goal was to see how quickly subjects identified the intruder after watching videos of people yawning. Result: their ability to identify snakes was improved after seeing other people yawn, while the speed of identification of frogs was unchanged… An ancestral reflex would therefore have been perpetuated to the present day! Note that we do not all respond in the same way to the yawn of others. However, the studies diverge, at this stage, as to the influence or not of empathy on our propensity to ape these funny mouth movements.