Why do we yawn? It’s almost certainly not for the reason you think Human biology

AAll vertebrates yawn, or indulge in a behavior that is at least recognizable as adjacent yawning. Sociable baboons yawn, but so do semi-solitary orangutans. Parrots, penguins and crocodiles yawn, and perhaps the first ever jawed fish did. Until relatively recently, the purpose of yawning was not clear, and it remains a matter of dispute among researchers and scientists. But this commonality provides a clue to what it’s really about — and it’s probably not what you expect.

“When I survey audiences and ask: ‘Why are we doing this? ” You “Do you think we yawn?” says Andrew Gallup, a professor of behavioral biology at Johns Hopkins University. Most people suggest that it has to do with breathing or breathing and may somehow increase blood oxygen. “This is intuitive because most yawning has this obvious respiratory component, this deep inhalation of air. However, what most people don’t realize is that this hypothesis has clearly been tested and shown to be false.

To test the idea that we yawn to bring in more oxygen or expel excess carbon dioxide, Studies published in the 1980s The researchers manipulated the levels of both gases in the air the volunteers inhaled, and found that as they changed an act It significantly affects other respiratory processes, and does not affect the regularity of yawning. There also does not appear to be any systematically measurable difference in yawning behavior in people with diseases related to breathing and lung function, which would be expected if yawning were related to breathing.

This, more or less, is where Gallup gets to the point. “When I was pursuing my honors thesis, my advisor at the time said, ‘Well, why don’t we study yawning, because no one knows why we do it?’ He says. “That was interesting – we knew it had to perform some basic physiological function. So I started examining the pattern of locomotor movement involved in it – this extended gap in the jaw accompanied by this deep inhalation of air, followed by a rapid closing of the jaw and a faster exhalation. It occurred to me that this could potentially have important circulatory consequences that are localized in the skull.”

In fact, this appears to be exactly what happens: Several reviews of the medical literature suggest that yawning increases arterial blood flow to the skull, and then venous return (the rate at which blood flows from the head to the heart).

“We can think of the jaw gap as a localized stretch, similar to muscle tightening in other areas of the body,” says Gallup. “In the same way that stretching helps blood circulation in those extremities, yawning seems to do the same for the skull.”

From here, Gallup and his fellow researchers began to develop the idea that yawning helps regulate temperature in and around the skull. Your brain temperature is primarily determined by three variables — the rate at which arterial blood travels to the brain, the temperature of that blood, and the metabolic heat production that occurs within the brain, based on neuronal activity — and in theory, yawning could alter the first two. When you yawn, you take a deep breath of air that moves across the moist surfaces of your mouth, tongue, and nasal passages, just like air flowing through a car radiator—carrying heat away through evaporation and convection.

Studies seem to prove this: Ambient temperature has a very predictable effect on yawning frequency, which increases when this is the case slight Very warm (when it gets very hot, the air temperature is too high for the radiator effect to work, so other cooling mechanisms such as sweating and yawning start to stabilize again) and lower when it is colder.

This also seems to explain why some medical conditions are linked to excessive yawning: either the conditions themselves, or the medications used to treat them, cause an increase in brain or body temperature. The “neural activity” explanation is also supported by animal studies: mammals and birds with more neurons in their brains yawn for longer periods, regardless of the size of their actual brains.

This does not mean that the other hypotheses have been fully established. The theory best supported by evidence is the “change in arousal” theory: Essentially, yawning helps the brain transition between states — from sleep to wakefulness, from boredom to alertness, and so on. “One possibility is that yawning helps the brain switch between using the ‘default mode network’ — areas associated with daydreaming, reminiscing, and self-reflection — and the attention network responsible for preparing the body for action,” says medical historian Dr. Olivier Valusinski, who has authored several papers on the subject. “One proposed mechanism for this is that it helps circulate cerebrospinal fluid, the fluid that surrounds and protects the brain and spinal cord.”

In fact, it may be the case that this function evolved first, with the effect of thermoregulation emerging as a beneficial aftereffect: something we will have better evidence for when studies are conducted in a wider range of animals. It is also possible that the two explanations are directly related: perhaps these state changes mean changes in brain activity and temperature, which means a need for enhanced blood flow. and Nervous cooling. This would explain why you yawn when you’re bored: your brain’s activity level may spike as it begins to think of ways to move you into a more stimulating situation, as well as your circulation needs.

Wait a minute, though: what about stomachic Yawning? We’re all aware of the phenomenon of one person in a room – or even on a TV screen – taking a gulp of air, while everyone else is doing the same thing. Some researchers have suggested that this type of contagious behavior brings groups together, perhaps because it is a hard-to-fake signal of sleepiness, boredom, or alertness — although it is unlikely to be the main purpose of yawning, since many solitary animals yawn regularly.

“It is possible that contagious yawning has no function and is merely a byproduct of advanced social cognitive mechanisms within highly social species,” Gallup says.

More simply put, many animals – including humans – have different ways to improve their empathy, including “mirror neurons”, which fire when an individual performs an action and when they see someone else performing a similar action. It may be the case, then, that seeing someone else yawn makes mirror neurons fire, prompting you to yawn yourself. But yawning is contagious maybe They also play a role in group coordination through mechanisms related to arousal change theory: helping each animal in the group switch states from relaxed to active.

one A 2021 study tested this effect on lions She found that other behaviors can be contagious among yawners, so if one lying lion yawns and then gets up for a walk, another yawner will follow.

Contagious yawning may also enhance a group’s alertness: If one baboon in a group stimulates the others to yawn, they may all become more alert. This may also work in reverse, helping to down-regulate arousal before sleep.

So, in other words: yawning is probably good for you, and may even help your brain work better. Oh, and if you’re conspicuously yawning to get a five-year-old to go to sleep, don’t stop — there’s a chance it’s actually working.