Unexplainable - Why do we yawn?

Episode Date: July 10, 2024

People yawn when they’re bored, right? So then why do athletes yawn before races? And why do so many animals yawn? … And why does reading this paragraph make you more likely to yawn? (Updated from 2022) Guest: Dr. Andrew Gallup For show transcripts, go to vox.com/unxtranscripts For more, go to vox.com/unexplainable And please email us! [e-mail] We read every email. Support Unexplainable by becoming a Vox Member today: vox.com/members Please take a second to help us learn more about you! vox.com/podcastsurvey Learn more about your ad choices. Visit podcastchoices.com/adchoices

This episode is brought to you by Defender. With a towing capacity of 3,500 kilograms and a waiting depth of 900 millimeters, the Defender 110 pushes what's possible. Learn more at landrover.ca. Okay. Can I give you some full disclosure? Yeah. I got less than an ideal amount to sleep last night.

Okay. And I know this episode is about yawns. So I'm kind of scared. If you don't keep me interested in yawns, you might lose me. So this is your challenge. Okay, okay, challenge accepted. So let's just reset for a second. I'm Noah, you're Brian.

Hey, it's unexplainable. And this whole episode actually started because we got this email from a listener named Chris all about yawns. Here's what he said. When I was in college, I had a professor in my physiology classes that offered extra credit to anyone that could provide a scientific paper or documentation that identified why we yawn and why yawning is contagious. He claimed that no one was ever able to provide a satisfactory paper or answer. Really stingy on that extra credit, that professor. Really stingy on the extra credit. So I thought maybe it would be a good thing to look into

yawns, see if we could get some extra credit for the show. And the more I looked into it, the more I realized how much I'd kind of fundamentally misunderstood yawns for my entire life. So what do you think makes people yawn? I think it's probably related to attention. So like when your motivation to pay attention is waning, like you yawn and it kind of, I don't know, gets you sleepier? Kind of like, I'm like, okay, I can go to bed now.

Yeah, so this is exactly what I thought about yawning. You basically said it's about attention, sleepiness, you know, we could say boredom. And I found this video from a few years back of this college professor who seemed to agree. Like, yawns are about boredom. Not the extra credit guy.

Not the extra credit guy. So basically, all the students are sitting in this big lecture hall. One of them yawns. Who just did that? No, I want to know. Stand up. And the professor is not happy.

If I hear one more of these overly loud yawns, get up and walk that. hell out. Yon outside. Yeah. Yon outside. Maybe we shouldn't yawn inside. Like, I don't know. So this is a professor who is so offended by yawning because he is so certain that yawning means someone is bored and disrespectful. And he's not the only one who thinks that. A judge was sentencing Clifton Williams Jr.'s cousin on a drug charge. When Williams stretched out his arms and yawned. The judge cited him for criminal contempt and ordered thrown in jail for six months. So yawns like have consequences. Right. And the reason I think these can have consequences

is because people feel very confident that they know what it means. Okay. But yawns are a lot more complicated than just boredom. Let me show you some pictures of a few athletes here. This is an Australian hurdler. It looks like she's yawning or like making a big O with her mouth? She's definitely She's definitely yawning. Or here's like a Venezuelan water polo player. Yeah, his mouth is super wide open. Teeth, teeth are out. Yeah, yeah.

And here's like a football player for the Chargers. I love this yawn. Oh, this is the widest open mouth yet. He's just like standing there like unhinging his jaw. Yeah, like huge gaping yawns, right? And then the most famous one, this is speed skater Apollo Ono. And he's like known for yawning. before all of his big races.

Does his coach yell at him to go yawn outside, not yawn in here? I don't think his coach yells at him. And it seems pretty clear that Apollo Ono is not bored before his speed skating meets. And it turns out that scientists just aren't really sure why we yawn. There's no grand unified theory of yawning. There's no grand unified theory of yawning yet. Uh-huh. And that's exactly what I want to get into on this week's show.

Okay. How could scientists know so little about something so fundamental? Essentially, why do we yawn? Okay, so Brian, to start, I want to introduce you to Andrew Gallup. When I speak about yawning in public settings, I often say, please, feel free to yawn that you don't need to inhibit this behavior at all. He's a yawn scientist. That's not his technical title, but he's basically a psychology professor at the State University of New York Polytechnic Institute. and he's obsessed with yawns.

I began studying yawning as an undergraduate, and my advisor at the time suggested, well, I could study why we yawn because no one knows. He just couldn't believe it. How could it be with a behavior that is so common that we do multiple times a day, how do we not know what the purpose of this action is? And the first thing I asked him was just, you know,

what is a yawn? A yawn can be characterized by a powerful gaping of the jaw You open your mouth really big. That's accompanied by a deep inhalation. You breathe in air. And that's followed by a period of peak muscular contraction. You stretch your jaw, and then subsequently a more rapid closure of the jaw. You breathe out, an expiration of air.

And yawning is way more common than I initially thought. So first off, humans start doing it really early. Like fetuses actually yawn as early as 11 weeks. So just like breathing movements can be seen in the womb among growing big. baby's yawning actions can be as well. But it's not just us. Like, tons of animals do it, too. Like, I'm sure you've seen animals yawn.

Oh, I've seen dogs do it. I have a dog in my house right now, not mine, and she's just really lazy and makes a lot of yawny noises. Right, so dogs yawn. But this kind of blew my mind. Apparently pretty much all vertebrates yawn. Little frogies yawn. Like, basically every vertebrate.

So fish, amphibians, reptiles, birds. worm-blooded, cold-blooded, and mammals. It suggests that, like, yawning was this really early evolutionary trait. That it did evolve via natural selection, and that it continues to be present because it serves an important biological function. And this isn't a new idea. Like, Darwin actually wrote about this. He said, seeing a dog and horse and man yawn makes me feel how much all animals are built on one structure. I need to see these animals yawn.

Yeah, so I have a bunch of yawns to show you some animal yawns. Please. So I want to play you some of the best sounding yawns. So here is a llama. That yawn is like... It's a great lava. It's a giant llama, but it's making the sound like a baby might make when they're first learning that they can make sounds. That's amazing.

It feels very relaxing. Here is a little cat. And I think this one is my favorite. It's a Tasmanian devil. This Tasmanian devil needs an exorcism. It's a completely insane yawn. Yeah, that is a voice from some netherworld. Yeah, so this is a really evolutionarily fundamental thing.

And in order to have, like, made it this long, it's probably pretty important. And somehow scientists still don't know exactly why we all do it. What are some of the ideas out there of why we or why would a, you know, goldfish do this? So when Andrew got to college, there weren't all that many accepted hypotheses about yawns. Okay. The main one was about getting more oxygen in the blood, which was mainly because yawning, you know, makes you take these big breaths. And I think for a long period of time, that was just assumed. So the scientist Robert Provine put it to the test.

He passed away a few years ago, but he was this. neuroscientist who is a huge yawn expert. And he basically tested this by putting people in an environment with more or less oxygen and carbon dioxide. So, for example, if yawning is a mechanism to increase oxygen in the blood, we would expect that breathing increased levels of oxygen would diminish yon frequency. You'd assume yawns would go down. And they don't.

They don't. We found that these manipulations had no effect on the rate of yawning. Plus, goldfish are clearly not getting oxygen when they yawn. Yeah, they got the gills to do that. Exactly. But Andrew says that even though the evidence is pretty clearly stacked against this theory, a lot of people still think it's the way to go. Sadly, it's sometimes when hypotheses are falsified,

they don't get the same recognition as when they are supported. And this is a good example of that. Is there a better idea here? So Andrew thinks it's got something specifically to do with the brain. Okay. He basically says, don't look at all the breath going in the mouth. Yeah, maybe we're getting too focused on this idea of oxygen. Exactly.

Look at the other things the yawn is doing. So it's stretching the muscles around your jaw and letting more blood flow to the brain. Increasing blood flow to this area would suggest that yawning may be tied to some neurological function. So in some ways, this is actually kind of like a brain stretch. And if this stretch is doing something important for the brain, you know, a bigger brain might need a bigger yawn or a longer yawn. So we predicted that animals with larger brains should be tied to the length of yawns. And when he tested it, that's exactly what he found. So then animals with larger brains and more complex brains show longer yawns than animals with smaller brains, uh, brains with fewer.

neurons. But it obviously leaves open the question, what is it doing to the brain? Well, what is it doing to the brain? Right. So, there's a bunch of hypotheses here, but Andrew specifically thinks that yawning has to do with the temperature of the brain. In my research, I propose that the motor action pattern of yawning may have a brain cooling function. Blood further from your brain is cooler. So if you send more blood to your brain, it cools the brain. Andrew also says that if you breathe in, the oxygen is cooling the blood near your lungs, that blood is going to the brain,

which starts bringing down brain temperatures when you're yawn. That's right. We're increasing blood flow and cooling that blood as it is traveling to the brain. Andrew actually had this great analogy to explain this. He basically said, yawning sort of functions like a car radiator. What it does, how it cools the engine,

is it circulates coolant. As that coolant is circulate, it's then introduced into the front of the radiator where heat is allowed to dissipate from it, and the wind is then cooling that fluid. And that's basically what it seems like Andrew thinks yawns do. The radiator serves to circulate fluid in the engine and cool that fluid simultaneously. Okay, so that sounds like a neat idea. It's very, you know, makes sense to me, but it makes as much sense as needing more oxygen in your body.

Exactly. You prove that? Is that the correct idea? Yeah, so he's got a bunch of really cool evidence. First of all, he did these experiments on rats. So what we did is we performed intracranial surgeries on these rats and implanted probes in their brain to monitor moments to moment to moment changes in brain temperature. This is a lot of research on yons for a lot of intensive. Yon research. But they watched these rats and they saw when they yawned, and then they, they were.

looked at the temperature changes in their brain. Yons were routinely preceded by rises in brain temperature and then subsequently followed by these corresponding decreases in temperature. Okay, that's, that seems pretty neat. Right, but that's just correlation. Andres team also showed causation by studying people. We tried to manipulate brain temperature by having participants hold cold compresses to their forehead or warm compresses or room temperature. And they noticed that that when people held cold compresses to their forehead, yawning went down a ton. They also know that breathing through your nose tends to cool down the brain. So they tested that too. Similarly, conditions in which participants were nasal breathing exclusively, they were less likely to yawn

as well. They also did a much bigger study looking at a couple populations around the world, and they found that yawns are most likely to happen at room temperature, and then the colder it gets, the less likely yawns are to happen. Yeah, and then if it's like super hot out, do yawns still work to cool your brain down? So actually, once the outside temperature gets hotter than the brain, yons fall off pretty dramatically. Like, they're not actually helping your brain cool down. Oh, so if it's super hot outside, the yawn's not going to help. Exactly.

And then finally, there's this one example that I thought was super fascinating. Basically, Andrew was contacted by a woman who had, like, repetitive excessive yawning, these, like, yawning attacks that happened. They wouldn't go away for a really long time. she couldn't do her work normally. But then Andrew was like, okay, what if you, when you sense it coming on, take your temperature. And then after the yawn, take your temperature.

Okay. And they found that before the yawns, her temperature was higher, and after the yawns, her temperature was lower. So what's the point of having a cooler brain? Well, like any machine, the brain works best at an optimal temperature. If it's too hot, it's just not going to run well. So, you know, when Apollo, oh, no,

the speed skater when he yawns before a race, it seems like he might just be trying to get his brain into like peak racing shape. These yawns were occurring right before the most important races of his entire life, and were likely tied to anxiety and stress. And the yons, in this case, we're likely preparing Apollo Ono for the subsequent race. We know that stress and anxiety are things that increase brain temperature. Oh.

Yeah. So when Ono yawns before a race, he's getting more blood to his brain. It's cooler blood because of the oxygen that he breathed in. And then overall, the idea is that, like, a cooler brain might be a less anxious brain. Ono actually says that he does this before races to help get the nerves out. So it seems like he understands what this is doing for him. Yeah, it seems like he gets the power of yawns. So what's wrong with this picture?

Why isn't this, oh, we've solved yawning? Because yawning isn't just about helping you focus or get the nerves out. It's also something that happens when you're winding down to go to sleep. So in the evening, when we are tired and about to fall asleep, our brain and body temperature are at their highest point throughout the 24-hour cycle. And that sleep onset actually initiates a really steep decline in brain-and-body temperature. So yawning at night could be facilitating this change. But then we also know that we yawn in the mornings after we wake up.

That change, that transition from sleeping to waking is associated with the most accelerated increases in brain and body temperature. We're up, we're moving around, and yawning might sort of be like us pumping the brake a little bit, you know, when we're dealing with this super accelerating temperature in the morning. So our highest frequency yawning events are tied to periods of time in which our brain and body temperatures are at their highest point, or they're increasing the most rapidly.

So it's kind of weird, right? Like, yawning seems to get us aroused when we're bored, and it focuses us when we're stressed. But it also allows us to go to sleep at night and then also help us wake up more gradually in the morning. We know yawning can do all of these things, which is why some researchers have focused on the more general idea that yawning is just about state change,

you know, going from waking to sleeping or going from boredom to... focus. But it's not totally clear how yawns can really accomplish all these different outcomes. Yawning may be multifunctional. It may help promote arousal and alertness and activity in certain contexts while facilitating downregulation in those states and other contexts. I mean, like when I was talking to our senior producer Meredith about this, she raised this interesting point of just like, of course, yons would be multifunctional, like they're so freaking old. Why would we think they're doing one thing? They've been with us from

fish to now, and I thought that that was such an interesting idea, too. Just like how kind of sleep performs different functions for different animals at different times. Right. Andrew is pretty sure that yawning does all of these different things through brain cooling. But other scientists think yawning might just be delivering more oxygen or activating certain brain networks. Like, ultimately, all of these behaviors are just really, really complicated and kind of more unknown than you would think. You know, more recent. More research needs to be done. Yeah, what kinds of places could this research take us?

Well, one thing Andrew told me was that more research could actually help us with diseases. So increased yawning has been documented as a side effect of a number of different conditions such as multiple sclerosis, epilepsy, and therefore we could potentially more closely examine changes in yawning behavior, potentially uses a diagnostic indicator in some cases. for certain types of medical conditions. And the other thing that needs more research is just the enormous yawn mystery we haven't talked about yet. If yawning is about brain cooling and state change, why do you yawn when you see someone else yawn?

Oh, that does happen. That is definitely the contagious yawns. I've experienced those. As much as, or perhaps arguably, as little as we know about spontaneous yawning, we know even less about contagious yawning. Contagious yawning is where this whole thing gets even weirder and more complicated and maybe more powerful? I'll tell you after the break.

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I was just stretching my throat. Okay, unexplainable. We're back. Hey, Brian. Hello. When we left off, we went through all these various theories of why we yawn. We talked about brain cooling about how, you know, yawning could help you focus when you need to operate at an optimal temperature, how it could help you transition to sleep, where your brain is cooler, how it could help you pump the brakes on waking up when you're transitioning back to waking. But there's still this huge mystery of why you yawn when someone else yawns.

And is it like your brain is at some temperature? And mine's at some temperature, too. Like, why would I need to reset my brain temperature if you are resetting your brain temperature? That is a very good question. And it's the exact question that people are trying to figure out. Yeah. But to start, I just wanted to double check that this was like a real thing, that it's not, you know, a myth. Contagious yawning has been studied scientifically and is a response that we can reliably elicit.

seeing or hearing or even thinking about yawning increases the tendency to yawn, and that's very well documented. I would guess that people listening to this episode have had a few yawns so far, and I'm hoping it's not just because they're bored. Yeah, please keep listening. Is it like cross species too? So we talked about different animals that can yawn if I see a dog yawn. Is that contagious or is it just limited to us? Well, humans don't normally yawn when they see dogs yawn. But lots of animals do contagiously yawn. Humans, chimpanzees, orangutans, they all yawn contagiously. Domesticated dogs will yawn when they see a person yawn,

but they actually won't yawn when they see another domesticated dog yawn. So it kind of tells you something about the particular kinds of relationships that can end up causing contagious yawns. We also find that contagious yawning occurs in very unrelated species to humans. There's evidence for contagious yawning among lions, pigs, among rats. Those are really quiet. And even contagious yawning among some bird species. Also pretty quiet.

But it's not like we're born with this ability to contagiously yawn. Research shows that among humans, contagious yawning doesn't occur until about early childhood. You know, this is around when you're developing theory of other minds. Yeah. You know, around when you're being more social. And then interestingly, near the end of life, contagious yawns decrease a bit too. And in that middle range, there's also a lot of variation.

Like, people tend to yawn more when they see their friends and family yawn. And that sort of led to what's kind of been the default theory of the field for a long time, which is that contagious yawning is about empathy. Empathy can be defined by the ability to be affected by and or share the physical or emotional states of others. So if we yawn in response to seeing another person yawn, that may represent kind of a basic form of empathic processing. And scientists studied it.

They basically had a bunch of people take empathy tests. You know, you can take a test that's supposed to measure your empathy. You can get various scores. And then the scientists show them videos of people yawning. And some of these initial studies found that those that were more susceptible to yawn contagion score really high on these empathy measures. And there was another influential study on this where they studied contagious yawning in children on the autism spectrum who might struggle to pick up social cues.

So the prediction would be that this population would show reduced contagious yawning. And in fact, the study found that those with autism spectrum disorder were much less likely to yawn contagiously. But the more people have studied this, that the more people have studied this, that the more this idea of empathy and contagious yawning has started to be a little suspect. More and more studies coming out failing to demonstrate this association with empathy as previously described.

Andrew raised this really interesting point to me, which is like, when people yawn, when they see friends, it may not be because they're more empathetic to those people. It may be because they tend to look at those people more. If you were to just look directly at a complete stranger in front of you,

that's kind of an awkward scenario that you tend to avoid doing, you look away from them and you mind your own business. So as a result, you're less likely to even detect whether they yawn in the first place. And Andrew specifically highlighted some follow-up work on the autism study that I thought was particularly fascinating. The researchers did another study with eye-tracking

where they told the kids to focus on the people who were yawning. And once their attention was directed toward the stimuli, there was no difference in the rate of yonning. contagion. Hmm. Okay. And so we're just repeating things that we're paying attention to. Exactly. Exactly. And that is something that happens across tons of species. Like this type of mirroring behavior, right? Yeah. You tend to mirror itches. You can mirror laughter. You can mirror...

You start tapping your foot. Someone else starts tapping their foot. Right. And this could be just sort of like basic mimicry. It's not any kind of higher level emotional thing like empathy, where you're understanding, you know, another person's interstate. This is just like you pay more attention to people in your own group and you tend to mimic them. But so why? Why would I mirror what I'm paying attention to? Is this an important thing we do? Right. So this gets into a lot fuzzier territory just to state that up front. Andrew has this idea that, okay, maybe if yawns promote attention and arousal and vigilance. The spreading of that action pattern through contagion might help to serve to increase overall group alertness.

So Andrew did this study where he showed people pictures of friendly animals and snakes. Apparently, like, people do this all the time, that humans have a very clear evolutionary adaptation to, like, recognize snakes in particular. What we found is that following, seeing other people yawn, the tendency to detect snakes increases. So just seeing other people yawn improves vigilance towards these threatening animals. Connect that for me. Why would that? Either the seeing of the yon could promote you to yawn, which could then help you focus, or seeing the yon could just make you focus because of seeing it. And if that cue also elicits contagion, that serves to basically amplify this signal among the group members,

which is going to further improve the vigilance of the... members in that group. That kind of makes sense if one member group is like, ooh, time for vigilance or time to like shake you out of like that sleepy feeling. That makes sense to share that signal. Exactly. So this is plausible.

Okay. So just to stay clear, like this is plausible. This is not like a definite reason why contagious yawning exists, but it does give us a reason for why I would want, you know, if I'm like a pride of lions, why I would want that yawn to spread around my group. So like everyone in my

is like a little bit more vigilant, you know, and over millions of years, maybe that difference can be the survival of a species. Is it like some sort of like handshake or like some sort of like, I want to say it sounds like a little bit like a language of like, oh, hey, hey. Well, Andrew does say that there's recent evidence pointing to the fact that yawning might not just promote vigilance, but it might promote what he calls synchronizing of activity. So there's a study conducted on African lions. And this study. documented for the first time that these lions yawned contagiously in response to other lions.

And also went a step further in showing that individuals that yawned contagiously were more likely to synchronize their movement behavior with the individuals that triggered those contagious yawns. So if the lion yawned and then went to sleep, the next lion was more likely to go to sleep. And if the first lion yawned and then went on a hunt, the next line was more likely to go on hunt. So if yawning precedes changes in state and movement behavior, the spreading of yons within a group via contagion might basically initiate collective changes in state and synchronize group movement. So to your question of like, is this almost like language, there's a sense in which,

again, not proven, but it could be one of many, many, many things that helps sustain a group and helps keep people together. So there seems to be a lot of research on contagious yawning and what it's for. Where does this all land? Yeah, so contagious yawning is a lot fuzzier than spontaneous yawning. It's harder to study. There's lots more variables because it's a social thing. There honestly just haven't been as many studies so far. But we know it's got, you know, something to do with group dynamics, probably. It might be about vigilance. But it also just might be something that was valuable at one point, you know, a long time ago, and it's just sort of a random quirk of our behavior at this point. Okay, so we've learned a lot about yawning here. Maybe it's like a

way to like shake you out of something, kind of change your brain state. Maybe it's like this kind of mental program to kind of share your brain state. But like I'm kind of thinking about that, that video you showed me of the professor getting really really angry at the yawner in their class. Yon outside! Having learned all of this, should we see that in a different way now?

I definitely think we should. I actually asked Andrew, like, what would you say to that professor if you could talk to him? Or what would you say to that judge? Yeah, I mean, I'd say they're... They need to read up on what we know about this behavior

and that their views are very outdated, and unfounded. He basically wants people to embrace the yawn. My oldest daughter has told me that some of her past teachers have discouraged yawning in the classroom. And I take exception to that. There is absolutely no reason

to discourage yawning among students. Yawning, if anything, is a mechanism that is only going to improve their attention and alertness in that setting. Stifling a yawn is likely to decrease your ability to pay attention thereafter. So it's contrary to what we would want to happen, right? If the idea is that don't yawn because that's an indicator that you're not paying attention, no, in fact, that yawn can help promote attention. It might serve that outcome. And having people

stifle it is going to decrease their ability to pay attention. I'm going to think about that next time I yawn. Like, don't stifle this. Let the yon complete itself, you know, get the full benefits of my own yawn. That's right. Yeah, so not only does the individual benefit, but even those around the yawner could benefit. So it's a... Do your part. That's right. Do your part, complete your yawn.

That's right. This sounds like you're gearing up to like, we need to like put out a PSA. We do. We need to make a PSA. Yawning isn't rude. It's all these other things. Right. Yawning is good for you.

Yawning is the new vegetables. Now you have to make a PSA. A yawn. One simple action connects you across species, across millions of years of history. You are an iguana, an elephant, a gopher, a barracuda. Because yawning is a secret superpower. You can change the temperature of your own brain. And if you're feeling distracted, a yawn might be just what you need.

So stop stifling your yawn. Oh, God. Open wide and yawn with pride. Don't just... Yon outside. Yon inside, too. And don't hog all the yawning for yourself. I can't stop.

I can't stop. Share your yawns with your family, with your friends. Yon at your teachers. Who just did that? Get your teachers yawning back at you. Start an infinite loop of yawns. We will not go close. quietly into the night. We will not vanish without a fight. Today, we celebrate our Yon Dependence Day.

Hey, Chris. Hey, how's it going? It's going good. So you wrote us this email about Yons and your professor and some potential extra credit that he might have offered to give for explaining them. So I got to ask, do you think we get any extra credit? You know, I think I would probably give you the extra credit. I think he was a little bit stingy, so I don't know if he gave it to you. I think he really enjoyed the fact that he never had to give out the extra credit. But I would 100% give it to you. I thought it was a great episode. Well, Chris, I hope next time you yawn, you can embrace the superpower of being able to change your own brain temperature. And my attentiveness and that of everyone around me. So I should yawn and then make everyone thank me.

This episode was reported and produced by Noam Hassamfeld, who wrote the music too. It was edited by Catherine Wells and Brian Resnick, with help from Meredith Hodnott and me, Bird Pinkerton. Fact-checking from Richard Zima and mixing from Christian Ayala and Afim Shapiro, who gave us his best impression of the president from Independence Day in that Yon's PSA. And Manning Munn is now officially a splunger, I think, So you should stay tuned for some spulunking in the near future. We made this episode because of a suggestion that we got from a listener. Thank you so much, Chris.

And we'd love to make more of these. So you can submit an idea at our website, which is fox.com slash unexplainable. Or you can just email us. We're at Unexplainable at box.com. We read every email. Unexplanable is part of the Vox Media Podcast Network. And we will be back.

next week.