Tag Archives: yawning

Why we yawn and why it’s contagious

We all yawn from time to time, and yet we know surprisingly little about what yawning is, why we do it, and why it’s contagious.

We’re still not sure why we yawn, but the only demonstrated function of yawning has been to help thermoregulate the brain.

What is yawning

Joseph Ducreux — Self-Portrait, Yawning (via Google Art).

Humans yawn, all vertebrates yawn, even fetuses yawn in the womb. We’ve all seen and experienced it countless times, but what is yawning, really? Technically, it’s a reflex through which we simultaneously inhale air and stretch our eardrums (which is why yawning helps when you have stuffy ears). Your abdominal muscles flex, your diaphragm is pushed down, and the air you breathe in expands the lungs to capacity. Then, you exhale. What a weird thing to do!

It’s an involuntary motion (we know it’s involuntary not only because you can’t control it, but also because we do it before even being born), and a very common one: we do it most often when we wake up or before we go to sleep, but we also do it when we’re tired. We even yawn while we sleep.

Culturally, yawning has also become associated with boredom or stress.

A yawning fetus.

Why we yawn

Since time immemorial, humans have had hypotheses about why we yawn. More than 2,000 years ago, the Greek “Father of Medicine” Hippocrates believed that yawning occurs before a disease or infection and helps to eliminate the “bad air” from the lungs.

This understanding was challenged in the 17th and 18th centuries when doctors started suggesting that yawning causes an increase in blood pressure, heart rate and oxygen in the blood. This would apparently make sense because yawning seems to be associated with tiredness and blood pressure and heart rate go down when we sleep.

However, modern studies have not found any evidence of any of these processes. To the best of our current medical knowledge, this is nothing more than a myth.

[panel style=”panel-danger” title=”Yawned already?” footer=””]A common belief is that yawning helps to increase the oxygen supply. However, research has failed to show an association between yawning and blood oxygen levels./panel]

More recently, research has found that yawning is “associated with the change of a behavioral state- wakefulness to sleep, sleep to wakefulness, boredom to alertness,” but the nature of this association is indirect.

Increasingly, studies have shown that yawning is used as a thermoregulation mechanism. In order to function properly, our organs need to have the right temperature — and the brain is particularly vulnerable to temperature changes. Although it’s relatively small, the human brain uses approximately 40% of our metabolic energy, which means it’s also more likely to overheat. When we yawn, we ingest a gulp of air that goes into contact with our nasal and oral cavities, which are directly linked to the brain through countless blood vessels. Furthermore, when we stretch our jaws, we increase the blood flow to the brain, which helps the relatively colder air slightly reduce the temperature of our brains.

So essentially, yawning could be a way to adjust the temperature of our brains.

When we yawn, we also often stretch. Image credits: jonathan sautter.

Researchers from the University of Vienna have found that pedestrians at some temperatures are much more likely to yawn. Andrew Gallup, a psychology professor at SUNY College at Oneonta, also found that holding hot or cold packs to the forehead influenced how often people yawn. A study on two women suffering from chronic, debilitating bouts of yawning also found that the symptoms can be alleviated by applying cool cloths to their forehead.

Studies on mice have also demonstrated the cooling mechanism: yawning is preceded by an increase in brain temperature, and after yawning the brain temperature decreases.

[panel style=”panel-info” title=”How often?” footer=””]Humans yawn, on average, 8 times a day, according to doctor Gallup. Gallup also found that yawning is much more common during winter than during summer — when it’s really hot outside, it wouldn’t make much sense to breathe in air to cool down.[/panel]

Image credits: Andrew Gallup.

Social yawning and contagion

The reasons for yawning might also be social. It might be a social cue that we’re tired, about to go to bed, or just got awake. It could also be an indication of boredom, that we’re not finding our current situation interesting or exciting. In evolutionary terms, yawning might be a herd instinct, and there seems to be a cultural component to yawning, since elements such as nationality and gender influence how often we yawn.

Yawning is also contagious, being potentially triggered by seeing, hearing, or even thinking about someone else yawning.

The interesting thing is that contagious yawning does not occur in species that do not recognise themselves in mirrors or in infants younger than two years old

[panel style=”panel-default” title=”Yawned already?” footer=””]There’s a good chance that by the time you’re reading this you’ve already yawned at least once — not that the article is boring (hopefully) but because simply thinking about yawning can make you yawn.[/panel]

A good way to start understanding this phenomenon is to look at those who exhibit it. If you see someone yawning next to you — even if it’s different species like your pet — you will, at least sometimes, start to yawn — unless you’re a psychopath, that is. In a recent study, which again emphasized the different roles of yawning, researchers showed that psychopaths don’t really respond to yawning contagion. This also indicates that yawning is related to empathy.

Another group that doesn’t typically get “infected” by yawning is autistic children, though in this case the cause is their lack of attention to social cues rather than a lack of empathy.

So why is it that all but a very few groups of people pass yawning around?

Empathy seems to be the crucial aspect. Studies have shown that the more empathic you are, the more likely you are to “catch” yawning. Similarly, the less empathy you have, the less likely you are to do so. Overall, yawning is contagious in 60-70% of people, even from images or other species, one study reports. However, another study found that only 42-55% of people yawned when they were shown a videotape of another person repeatedly yawning.

Furthermore, fMRI scans have shown that the posterior cingulate and precuneus light up during contagious yawning — two areas connected to how we interpret the emotions of others, undescoring the link between empathy and yawning.

Other theories

There are a few other reasonable theories regarding yawning. For instance, one postulates that animals in danger of predation need to constantly be alert, to be able to quickly avoid danger if it emerges.

Another hypothesis suggests that yawns are caused by neurotransmitters — chemical messengers released by brain cells that affect emotions, mood, appetite, and other phenomena. As more (or fewer) of these compounds are activated during the brain, the frequency of yawning increases. A piece of evidence to support this is the fact that people in opioid withdrawal tend to yawn much more frequently than normal. To further back this theory, in neuropharmacology, yawning proved to be a valuable tool for the assessing dopaminergic activity and the pharmacological properties of new drugs.

Stress is another potential cause for yawning. There is plenty of anecdotal evidence of yawning before a stressful event, even in the case of paratroopers, who were often reported to yawn right before jumping. At least one study reported that yawning might make the brain more alert.

Yawning can also be affected by medical conditions such as diabetes or stroke.

The bottom line

The precise role of yawning in human physiology remains unclear.

Overall, it seems that the myths about yawning aren’t really true. Instead, the phenomenon seems to have a multitude of potential triggers, which quite likely work together to generate yawning. There is both a biological and a social component to yawning, and most humans (as well as many other vertebrates). As for how this behavior evolved and came to be, the verdict is still out.




On the many mysteries of yawning


Credit: Pixabay.

You know the feeling. It’s impossible to resist. You just need to yawn.

A yawn consists of an extended gaping of the mouth followed by a more rapid closure. In mammals and birds, a long intake of breath and shorter exhale follows the gaping of the mouth, but in other species such as fish, amphibians and snakes there is no intake of breath.

But what’s behind a yawn, why does it occur?

In the past, people have had many hypotheses. As far back as 400 B.C., Hippocrates thought yawning removed bad air from the lungs before a fever. In the 17th and 18th century, doctors believed yawning increased oxygen in the blood, blood pressure, heart rate and blood flow itself. More recently, consensus moved toward the idea that yawning cools down the brain, so when ambient conditions and temperature of the brain itself increase, yawning episodes increase.

Despite all these theories, the truth is that scientists do not know the true biological function of a yawn.

What we do know is that yawning occurs in just about every species. It happens when an animal is tired. It can be used as a threat display in some species. Yawning can occur during times of social conflict and stress, something researchers call a displacement behavior.

And that wide-open mouth can be contagious, especially in social species such as humans, chimpanzees, bonobos, macaques and wolves.

Watching someone yawn – heck, even reading about yawns – can lead you to yawn yourself. Why?

Research on humans tell us that people who are more empathetic tend to be more susceptible to contagious yawning. When you see someone else yawn, the networks in your brain responsible for empathy and social skills are activated.

Is yawning contagious for dogs, too? In 2011, U.K. biologists tested for contagious yawning between people and man’s best friend. Although 5 of the 19 dogs they studied did yawn in response to an unfamiliar person’s yawn, the researchers couldn’t prove the yawns were contagious.

In 2013, cognitive and behavioral scientists at the University of Tokyo once again tested contagious yawning in canines while controlling for stress. This time the researchers found that dogs were more likely to yawn in response to a familiar person. They concluded that dogs can “catch” a yawn from humans and that yawning is a social rather than a stress-based behavior.

In 2014, University of Nebraska psychologists looked at contagious yawning in shelter dogs. They found that some dogs that yawned when exposed to human yawning had elevated cortisol levels – a proxy for stress. Levels of the cortisol stress hormone did not rise in dogs that didn’t yawn in response to a human yawn. This finding suggests some dogs find human yawning stressful and others do not. More research is needed to evaluate this aspect of the human-dog relationship.

So the jury’s still out on the true why of yawning. But when it comes to inter-species yawning, you can collect your own anecdotal data. Try an experiment at home: Yawn and see if your pet yawns back.

By Christine Calder, Assistant Clinical Professor of Behavior, College of Veterinary Medicine, Mississippi State University

This article was originally published on The Conversation. Read the original article.


Why do we stretch?

What is the point behind this deceptively simple act? Why do our bodies make us stretch and yawn even before we’re properly awake?


Et tu, leopard?!
Image credits Amit Patel / GoodFreePhotos.

I find that stretching after a long period of inactivity (especially after sleeping) is almost an instinctual reaction for me. It feels awesome, and it leaves me refreshed. But how can a simple stretch do that? And why does my body compel me to do it without even asking for my opinion? What does my body get out of it?

Some light pandiculation

The act of involuntary stretching while yawning is referred to as pandiculation in humans. The behavior, however, is far from unique to us. It’s been observed in many different species, particularly during transitions from periods of low to high activity. “Almost all vertebrates yawn,” Walusinski wrote in 2006, “testifying the phylogenetic old origins of this behavior”. He further adds that such behavior can be observed in infants as young as 12 weeks, and “remains relatively unchanged throughout life”.

Another paper (Rial et al., 2010) published in the journal Neuroscience & Biobehavioral Reviews discusses the possible origins of mammalian sleeping patterns in the wakefulness, sun basking, and sleeping states of our reptilian ancestors. It’s a very interesting read. In the context of what we’re discussing today, however, one point stands out: the paper suggests that stretching and yawning stems from post-basking risk-assessment behaviors:

“Post-basking behaviour always begins with a passive exploration of the immediate environment,” for things such as threats, food, or mates, the authors write. “This behaviour […] consists of the suspension of current behaviour, to be replaced by head dipping movements, eye scanning, rearing and adopting stretch attending postures.”

You likely know what post-basking behavior looks like if you have a pet reptile. If not, I’ll let Eli Fire’s two bearded dragons to give you a rough idea — Yoda (the red one) seems to be engaging in some serious post-basking, while Conan (the yellow one) seems content to just lounge for the most part.


So not only are yawning and stretching widely-seen in the animal world, they’re also probably very, very ancient habits. We pick them up early and stick with them for life. So surely they have a purpose — but what?

While we don’t know for sure, we have some pretty solid hypotheses.

Stretching as a ‘hardware reset’

Promote me to Captain Obvious here, but sleeping is a very passive ability. Our bodies are made to move, however, and such a long period of inactivity leaves them drowsy in a sense. Stretching is our brain’s way of checking if all muscles are still working properly while giving them a nudge that it’s time to get to work.

Beyond revving up muscles, stretching offers a gentle transition from sleep to wakefulness for the rest of the body as well. We’re basically bags of meat filled with fluid. During the day, fluid tends to accumulate in the legs. At night, which we usually spend lying down — for example in the supine position — gravity instead pulls these fluids towards the spine, torso, neck, or head, wrote Laura White and Douglas Bradley in the Journal of Psychology back in 2013. Stretching helps to gently push these fluids back into their usual place. It’s probable that this measure is designed to prevent fluid build-ups from injuring muscles during more strenuous activity.

It also helps work out any stiffness or tightness in your muscles and joints caused by spending an extended amount of time in a single position. In the long term, this helps maintain a wide range of mobility even if we don’t engage in such activities. In the short term, pandiculation might be a quick way to carry our bodies out of REM sleeping patterns (when motor activity is inhibited) and into a state of readiness, so we can react to any danger — just like reptiles after basking,

Stretching as a ‘software reset’

Pandiculation also helps improve blood flow and reduce stress by jump-starting the parasympathetic nervous system (PNS) — the branch of the nervous system that handles involuntary activity such as controlling heart rate, endocrine functions, or digestion. Stretching jump-starts the PNS, which, in turn, revs up all those background processes that keep you awake and alert throughout the day. The modicum of movement also increases your heart rate — which is slowest just before rising — pushing blood to the muscles in the extremities.

Stretching also offers the brain a chance to recalibrate its communication with muscles. As you stretch, the brain sends progressively stronger signals to your muscles. These contract in response to the signal, and stop as the filaments of actin and myosin they’re made of come close to their breaking point. This feedback lets the brain calibrate how strong a signal it needs to send to the muscles for various tasks, and lets it know how much strain they can safely take.

Finally, stretching simply feels good. It’s a form of progressive relaxation that helps reduce feelings of stress. Stretching feels good because it’s one of those things that satisfy our homeostatic drive: along with eating, having sex, and satisfying other bodily functions, stretching helps us stay healthy — so our brains reward it by making us feel nice.

Ok, but why?

Animal models suggest that pandiculation is regulated by the same networks in the limbic system (the ‘lizard brain’) that handle basic survival instincts. Some patients paralyzed on one side of their body due to motor cortex damage will still raise both arms when they yawn — which suggests be a function of the limbic system, rather than the motor cortex, is prompting this behavior.

This would also explain why we naturally stretch when we wake up, despite not trying to.

“Of 40 stroke patients attending a rehabilitation department, 32 (80%) had associated reactions affecting the hemiplegic arm,” reports a study published in 1982 in the Scandinavian Journal of Rehabilitation Medicine. “These involuntary movements nearly always occurred in association with yawning and less frequently with stretching, coughing, sneezing and laughing.”


The other part of pandiculation, yawning, is likely more brain-centered. Where stretching helps bring your muscles online, yawning likely does the same for our pounds of gray matter. It helps cool the brain and likely makes it more alert — we yawn when we’re sleepy in an effort to say awake, and yawn when we’re bored in an effort to keep us on the task at hand.

Here to stay

You probably enjoy pandiculating — I can’t blame you. But, even if you didn’t, chances are it’s here to stay. Not only is this behavior likely very useful for our bodies, but it’s also engrained so deep in the animal brain that almost all vertebrates do it.

So stretch your arms high, yawn with gusto, and enjoy that little shot of dopamine that comes with pandiculation.

Seagull yawn.

Trying to resist a yawn makes you more likely to yawn — because your motor cortex is wired that way

Why do we yawn when we see someone else doing the same?  And why, despite trying to shut it down, all we can manage is that stifled half-yawn? According to a new research paper looking into the origin of contagious yawning in the brain, it’s because you literally can’t resist. The behavior is hardwired so deep into our motor cortex that trying to stop a yawn actually makes us more likely to do it.

Seagull yawn.

Image via Pixabay.

We don’t really know why we yawn. Our best theory is that we do it to cool our brains down, based on the motions we go through to yawn and the observation we do it more often in winter than summer. Common wisdom says we do it when we’re sleepy, or bored — so school should be a prime yawning-spot. Which, I think we all know from personal experience, it certainly is.

There may be one other element at work here, however. Yawning is also extremely contagious. All it takes is for one kid to yawn, and it will catch like wildfire with his classmates. And this later tidbit has had scientists puzzled for a long time now. In search of answers, University of Nottingham’s Professor of Cognitive Neuroscience in the School of Psychology, Stephen Jackson, led a research effort peering into the human brain to see just what makes yawning so contagious.


Contagious yawning is not the only form of echophenomena (automatic imitation, or ‘echoing’, of words or actions) we know of, but it’s by far the most common. We do know that other animals, such as chimps or dogs, do it too, and that it somehow ties into conditions linked with conditions which mess with our brains’ excitability, such as Tourette’s, autism, or epilepsy — the occurrence of echophenomena can hint at such conditions. Finally, we know that for the behavior is highly dependent on the social setting — for a yawn to become contagious, you need to actually see and pay at least some attention someone else doing it.

We don’t know why we do it, and we don’t know what bits of our brains make us do it — which is what the team set out to discover. They recruited 36 adult participants and showed them video clips of other people yawning, instructing them to either try and stifle the yawn or let it rip. All the while, the researchers used transcranial magnetic stimulation (TMS) to poke targeted areas of their brains into action, in an attempt to gauge which areas make yawns contagious.  The participants were videoed throughout the experiment so the team could count their yawns later on, and the intensity of their yawns was continuously recorded.

Deep in the brain

Prof Stephen Jackson TMS.

Prof Stephen Jackson using TMS on a participant.
Image credits University of Nottingham.

By quantifying motor cortical excitability and physiological inhibition for each participant, the team was able to predict each participant’s propensity for contagious yawning. The fact that TMS readings of the motor cortex proved to be such accurate predictors of the behavior suggests that this area of the brain has a key role to play in the behavior, possibly in echophenomena at large.

To test out their theory, the team then stimulated the motor cortex through TMS and found that it would artificially increase participant’s propensity for contagious yawning.

“If we can understand how alterations in cortical excitability give rise to neural disorders we can potentially reverse them,” Professor Stephen Jackson said. “We are looking for potential non-drug, personalised treatments, using TMS that might be affective in modulating inbalances in the brain networks.”

“We suggest that these findings may be particularly important in understanding further the association between motor excitability and the occurrence of echophenomena in a wide range of clinical conditions that have been linked to increased cortical excitability and/or decreased physiological inhibition such as epilepsy, dementia, autism, and Tourette syndrome.”

Another surprising finding was that when participants tried to stop themselves from yawning, they further increased the ‘urge’ they felt to yawn. So the next time you feel an urge to yawn, it’s easier to just let it happen.

If you’re in school, the safest bet is probably to be inconspicuous about it. Though, trying to see how many people you can get in on the yawn plague is also a fun way to start your day.

The full paper “A neural basis for contagious yawning” is can be read on the University of Nottingham’s website.

Psycopaths aren't impressed by yawning. Image: Dexter

Yawning is contagious, unless you’re a psychopath

When someone yawns near us, we naturally feel an irresistible urge to yawn in response. Even dogs seem to yawn when humans do it. This contagious behavior has fascinated psychologists and behaviorists for many years, and while there are many reasons scientists have proposed for why people yawn (it’s a bit complicated, what we know for sure is that’s important and actually has a purpose), social cohesion might play an important role. The more emphatic you are, the likelier it is you’ll yawn in response. On the contrary, psychopaths barely register yawns and seem impenetrable.

Psycopaths aren't impressed by yawning. Image: Dexter

Psycopaths aren’t impressed by yawning. Image: Dexter


Previously, scientists found a link between empathy and yawning. This got researchers at  Baylor University thinking: “does this mean that psychopaths, who inherently show low empathy, yawn less frequently?” To answer this question, the team of psychologists asked 135 participants to take the  Psychopathic Personality Inventory-Revised (PPI-R) test. Those who ranked high on the coldheartedness scale were less likely to yawn when another person did so.

Another characteristic owing to psychopaths is fearlessness. Again, the researchers tested their participants by seeing how easily they got startled. Those persons who ranked high on the PPI-R test – which, in their defense, doesn’t necessarily make them psychopathic – were less likely to become startled, as reported in the journal Personality and Individual Differences. The same people also yawn less frequently. Previously, another study found autistic children also yawn very rarely in a social setting.

Though debatable, the main purpose of yawning seems to be cooling the brain. The researchers’ hypothesis is as follows: when you start to yawn, powerful stretching of the jaw increases blood flow in the neck, face, and head. The deep intake of breath during a yawn forces downward flow of spinal fluid and blood from the brain. In the last phase, the cool air breathed into the mouth cools these fluids. The fact that animals, including humans, contagiously yawn may be attributed as an evolutionary adaptation to keep a group vigilant.

“What this tells us is it’s a very complicated system, and there are probably many different roles for yawning,” says Gregory Collins, a researcher at the University of Texas Health Science Center in San Antonio who has identified some of the chemical processes at work in the brain.

In any event, evidence points to the fact that yawning is both triggered socially and elicits social response at the same time. Don’t get too worried yet, though. Chronically yawning around your friends to spot the psycho might not work well for you.

“The take-home lesson is not that if you yawn and someone else doesn’t, the other person is a psychopath,” Rundle cautions. “A lot of people didn’t yawn, and we know that we’re not very likely to yawn in response to a stranger we don’t have empathetic connections with.

“But what we found tells us there is a neurological connection — some overlap — between psychopathy and contagious yawning. This is a good starting point to ask more questions.”

Yawning not contagious for autistic children due to inattention to social cues – not lack of empathy

Boredom, tiredness, stress – they can all lead to a big healthy yawn; but even when none of those are present, just witnessing someone yawn can be really contagious – and this is not just restricted to humans. Dogs yawn in response to human yawns, and chimpanzees and baboons yawn in response to each other. But autistic children don’t respond to this “social” yawning, something which was long thought to be caused by their lack of empathy. However, a new research conducted by Japanese researchers claims that this isn’t the case at all.


The researchers say children with autism simply miss the yawning facial cues because they typically avoid looking at faces. In order to reach this conclusion, they set up 2 experiments.

In the first experiment, 26 children with autism and 46 controls wore eye-tracking devices while watching video clips of people who were either yawning or just standing still. Researchers asked the children to count how many people in the videos are wearing glasses, to be sure they are looking at their faces. The video showed the person yawning only when the eye tracker verified that the child was looking at the face.

In the second experiment, 22 children with autism and 29 controls watched video clips, this time counting how many of the people in the videos had beards; again, the yawning sequence began only when the eye tracker checked that the children were looking at the mouths in the video. The results of both experiments showed that about 30 percent of the children with autism yawned in response to the yawning they were watching – a rate which is similar to that of the controls. This strongly suggests that it’s not a lack of empathy involved, but rather the fact that autistic children don’t look at faces, and typically ignore social cues.

The next step is to study schizophrenic people, who also don’t react to social yawning, to better understand both the disease and contagious yawning.

Via Scientific American

Yawning fetus. (c) Durham and Lancaster Universities

Fetuses get bored too: research shows they yawn in their mothers’ womb

Previous research has shown that babies still in their mothers’ wombs regularly stretch, swallow and even hiccup. Recent observations have found another item to add on the list – yawning. The doctors involved in the research that identified yawning in fetuses believe this could serve as a new indicator for assessing an unborn baby’s health index.

I was just kidding about the bored part in the title, though fetuses might very well yawn of boredom; it’s not like they’re going anywhere and, after all, we’re talking about nine freakin’ months trapped in-utero. Why do we yawn anyway? Well, first of all, yawning is a physiological mechanism that is totally uncontrollable, expressed by all classes of mammals,  and is correlated by a variety of neurochemical changes in the brain. You’d think that such a common behavior would be fully explain by 21st century science, but the truth is, despite several theories that claim they have the answer, scientists aren’t sure what causes or what’s the purpose of yawning.

Yawning fetus. (c) Durham and Lancaster Universities

Yawning fetus. (c) Durham and Lancaster Universities

A study from 2008 published in the journal Evolutionary Psychology found that yawning is linked with body temperature, and acts a regulator. Back then the researchers of the respective paper proved their theory by raising the ambient temperature in a cage where several parrots were sited. As temperatures rose, they found that the birds were twice as likely to  engage in rapid and continuous opening and closing of the beak, which acts to flap membranes in the throat and thereby increase evaporative cooling. Back to babies, though.

Researchers from Durham and Lancaster Universities studied 15 healthy fetuses using 4D scans that render real-time snapshots of what’s going inside the womb. The image on the left clearly shows a fetus yawning, for instance, or is it? How did the researchers distinguish actual yawning from mere mouth opening? The scientists closely examined all events where a mouth stretch occurred in the fetus, and using their newly developed criteria, the research team found that over half of the mouth openings observed in the study were classed as yawns.

The studied fetuses were between 24 to 36 weeks gestation, of which eight female and seven male. The researchers found that yawning declined from 28 weeks and that there was no significant difference between boys and girls in yawning frequency.

Despite a general scientific consensus has yet to be reached on the importance and function of yawning,  the scientists  suggest that yawning could be linked to fetal development, and as such with its health.

The results of this study demonstrate that yawning can be observed in healthy fetuses and extends previous work on fetal yawning.  Our longitudinal study shows that yawning declines with increasing fetal age.

 “Unlike us, fetuses do not yawn contagiously, nor do they yawn because they are sleepy.  Instead, the frequency of yawning in the womb may be linked to the maturing of the brain early in gestation”, said lead researcher, Dr Nadja Reissland, of Durham University’s Department of Psychology,

“Given that the frequency of yawning in our sample of healthy fetuses declined from 28 weeks to 36 weeks gestation, it seems to suggest that yawning and simple mouth opening have this maturational function early in gestation.”

The video below shows a 30 week old fetus scanned with ultrasound 4D imaging.

Findings were published in the journal PLOS ONE.