Why is yawning contagious?

Summary

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Podcast Summary: "Why is yawning contagious?"

Podcast: What's That Rash? – ABC Australia
Air Date: May 5, 2026
Hosts: Dr. Norman Swan, Sandy, Mandy
Episode Theme: Exploring the fascinating science of yawning: why do we yawn and why is it contagious?

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Episode Overview

This episode dives into the curious phenomenon of contagious yawning—why seeing or even hearing about a yawn can make us yawn ourselves. Hosted live at the World Science Festival, Brisbane, the discussion explores what yawning is, its evolutionary roots, the science behind its contagiousness, and the social aspects that make it so uniquely human (and animal!). The hosts take on a listener’s question, share research findings, invite audience participation, and even spark a “yawn tally.”

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Key Discussion Points & Insights

1. What is Yawning?

• Definition: Yawning is an inhalation followed by a wide stretching of the jaw ("mandibular gaping") and then a forceful exhalation.
• Plesiomorphic Behavior: Yawning is a behavior that crosses species lines, much like handedness; it’s deeply ancient in evolutionary terms ([02:01–02:23]).
• Chasmology: The science of yawning is called "chasmology," from the Latin for yawn and gaping. The same root gives us words like "chasm" and even "chaos," linking the physical act to a sense of existential void ([02:25–03:00]).
• Prenatal Yawning: Babies have been observed yawning in the womb, indicating how fundamental and old the reflex is ([03:00–03:13]).

Memorable Quote:
"My name's Claire. What is yawning?" – Norman Swan playfully roleplaying a listener ([01:21]).

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2. Why Do We Yawn?

• Old Theory (Oxygenation): Early scientists thought yawning increased oxygen in the blood. However, experiments showed that raising carbon dioxide levels in the air does not make people yawn more ([03:37–04:17]).
• Prevailing Theory (Brain Cooling): Current research leans towards yawning as a mechanism to cool the brain, supported by studies showing that animals yawn less when their brains are externally cooled. Larger-brained mammals tend to have longer yawns ([04:17–04:57]).
• Evolutionary Roots: Yawning is found throughout the animal kingdom—even in fish—suggesting it's one of the oldest vertebrate behaviors ([04:57–05:30]).

Memorable Moment:
"Does that mean we yawn less in cold weather than in hot weather?" – Norman, questioning the logic of brain cooling ([05:32–05:38]).

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3. When and Why Is Yawning Contagious?

• Social Nature: The contagious aspect of yawning is closely linked to social behavior. Contagious yawning is far more common in social animals (humans, primates, dogs) than in less social ones ([08:13]).
• Mirror Neurons & Empathy: The brain’s mirror neuron system is activated when we see someone yawn, reflecting our evolved tendency to imitate and empathize with others (theory of mind, default mode network) ([06:16–08:13]).
• Not Uniform Across Species: While yawning is widespread, contagious yawning is mostly seen in social species.

Researcher Highlight:
Andrew Gallup, dubbed "Professor Yawn," studies yawning and notes that researchers themselves can become habituated to contagious yawning after prolonged exposure to yawning stimuli ([08:13–09:18]).

Quote:
"Because we're mirroring other people and we want to copy you. We want to learn from you. It's part of you being a social being." – Dr. Norman Swan summarizing the contagiousness of yawning ([09:26]).

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4. Audience Experiment: The Yawn Tally

• Host Norman invites the audience to tally their yawns during the discussion.
• Result: About two-thirds of the room yawned at least once; some reached 12 yawns! This playful moment underscored the topic’s direct, immediate impact and entertained the crowd ([09:33–10:32]).

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5. Live Audience Q&A: Grip Strength and Dementia

Segment Starts: [11:18]

• A listener asks about the link between grip strength and dementia, as well as its impact on heart health.
• Dr. Norman Swan: Grip strength is a proxy for overall physical robustness and frailty, not a sole predictor of dementia or heart health. Exercising grip strength alone isn’t sufficient; it reflects general fitness ([11:44–13:26]).
• Cardiac rehab after a heart attack is about comprehensive physical fitness, not just grip strength ([13:26–13:58]).

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6. Mailbag: Left-handedness in Life & Dentistry

Segment Starts: [14:04]

• Listeners share challenges faced as left-handers in predominantly right-handed societies, especially in professions like engineering and dentistry ([14:04–17:32]).
• Cultural & Linguistic Notes: Russian language and culture also reflect a right-handed bias, with positive words rooted in "right" and negative connotations for "left" ([16:00–16:28]).

Quote:
"It's a rough world out there for us, left-handed Norman." – Sandy, in response to challenges faced by left-handed professionals ([17:31]).

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Notable Quotes & Memorable Moments

• On Chasmology:
  "The science of yawning is called chasmology, as in a yawning chasm." – Norman Swan ([02:25])
• On Theory of Mind:
  "It's about social cognition and it's about us recognizing ourselves as self and others as other." – Dr. Norman Swan ([06:16])
• On Empathy and Imitation:
  "We want to be like you, or I want to imitate you, or I want to learn from you." – Dr. Norman Swan ([07:09])
• On Real-Life Science:
  "If it means that you go off and do chin ups at the gym when you're 85 years old, good on you." – Dr. Norman Swan ([12:59])
• On Left-Handed Dentistry:
  "Dental chairs are designed for right handed dentists and dental assistants are trained to sit on the left side of the chair." – Sandy ([16:42])

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Recommended Listening Sequence (Timestamps)

| Segment | Timestamps | Content Summary | |-----------------------------------|-------------|---------------------------------------------------------------------------------| | What is Yawning? | 01:09–03:37 | Definition, chasmology, etymology, ancient origins, prenatal yawning | | Theories Behind Yawning | 03:37–04:57 | Oxygenation vs. brain cooling, cross-species yawning | | Contagious Yawning & Social Roots | 06:00–09:26 | Theory of mind, mirror neurons, social cognition, empathic connection | | Audience "Yawn Tally" | 09:33–10:32 | Interactive count of audience yawns | | Audience Q&A: Grip Strength | 11:18–13:58 | Relation between grip strength and dementia/cardiac health | | Mailbag: Left-handedness | 14:04–17:42 | Listener experiences of handedness bias in life and professions |

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Tone and Style

The hosts blend scientific detail with humor, audience participation, and relatable anecdotes, keeping the episode light, lively, and conversational. Running jokes about yawning contagion and left-handed woes make the scientific discussion friendly and fun.

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Final Takeaway

Yawning is a deeply ingrained behavior, both ancient and cross-species. While its precise function remains mysterious—some evidence points to brain cooling—the contagiousness of yawning is strongly tied to our social brains and ability to empathize and imitate. In short, seeing someone yawn is a subtle neurological nudge of our social nature.

Bonus: Left-handed listeners, you're seen and appreciated—machinery and dental tools notwithstanding.

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Transcript

[Narrator]

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[Norman Swan]

No.

[Sandy]

Stop it. No. I am so suggestible. I need you to stop. I'm so suggestible that looking at the

[Norman Swan]

topic for today's WhatsApp rash, I started yawning without even thinking about it.

[Dr. Norman Swan]

I'm seriously yawning, actually.

[Norman Swan]

It's not preemptive boredom.

[Sandy]

It's actually fascinating. But we are of course talking about why you yawning is contagious.

[Mandy]

Cause you're listening to what's that Rash.

[Sandy]

It's the show where we answer the health questions everyone is asking. And this is a question that was asked at our recent live show at

[Norman Swan]

World Science Festival, Brisbane. This question's from Claire. What is yawning?

[Dr. Norman Swan]

Well, you can pretend to be Claire now.

[Norman Swan]

My name's Claire. What is yawning?

[Sandy]

And why is it contagious, even between different species? Species?

[Norman Swan]

I'm barely awake after watching a pine marten yawn. We're all yawning because of the pine Martin. So I would like for us to do a little bit of research throughout this chat. If you yawn at any point, can you just keep a tally? Just keep a tally of yawns. I will be keeping a tally of my own yawns as well. Even saying the word is making you yawn.

[Dr. Norman Swan]

I can see just starting you're trying to stop yourself.

[Norman Swan]

I see your yawn, sir. I see your yawn. What is yawning?

[Dr. Norman Swan]

Are we so boring?

[Norman Swan]

Yeah, exactly.

[Dr. Norman Swan]

So yawning. The actual process is that it's an inhalation followed by a forceful stretching. They call it mandibular gaping. And then an exhalation. A forceful exhalation. And the technical term here is plesiomorphic.

[Mandy]

In other words, it.

[Dr. Norman Swan]

It crosses. Just like handedness, it crosses species.

[Norman Swan]

It crosses species as we'll get to

[Sandy]

in a little bit.

[Norman Swan]

But obviously, as evidenced by the pine martin there, the science of yawning is called chasmology, as in a yawning chasm. And I was like, okay, which came first, the chasm or the yawn? And I'm still not really? Sure. The word chasm actually comes from the Latin word for yawn and gaping. So I think maybe the yawn came first and then we named like cat chasms after it. And it comes from the same root as the word for chaos, as in the void, which means. Yawning is very existential. It's very meta. In fact, it's something that happens to us even before we're born. The baby isn't even born yet. It's already bored of you, Norman.

[Dr. Norman Swan]

Yeah, what can I do for those listening? What we were showing, there was a video of a baby in the womb,

[Norman Swan]

in the womb yawning because Norman couldn't stop talking about the Mediterranean diet. And it wasn't just random mouth movements either. So that was part of a. Well, there has been studies done where they looked and they compared the random kind of mouth movements of babies in the womb and that sort of thing, and that's a real yawn. So why? Why do we yawn?

[Dr. Norman Swan]

Well, an early theory was that this is a way of increasing the oxygenation of your bloodstream.

[Norman Swan]

That's what I always thought it was.

[Dr. Norman Swan]

Out it goes. And you've actually expanded your lungs and. Or your carbon dioxide in your blood is getting too high. And when you want to get rid of carbon dioxide, you over breathe, so you try and ventilate more. And when they've studied this and artificially raised the carbon dioxide in the blood, in the air, for example, you don't yawn more. So it doesn't seem to be related to oxygenation. The weird theory that seems to have lasted is brain cooling.

[Norman Swan]

Brain cool. That sounds fake. Brain cooling.

[Dr. Norman Swan]

So brain cooling. So it looks as though that the process. I know. Go with me on this. I'm so sure I believe it either. But they have done research into this that in some sense that because you're doing this in the head and because you've got this rapid exhalation, that the brain gets cooled by the process of yawning. And they've cooled the brain and the animals stop yawning. And so if you actually look at animals, the bigger their brain, the longer their yawns. For example, okay, mammals yawn more than birds.

[Norman Swan]

So this is what I wanted to ask. How we know that a pine marten can yawn? We know that humans yawn. It can be contagious in humans. How far back do you reckon yawning goes? Just throw me a species that you don't think yawns or not. A species like a. Whales, whales and mammals. I think whales yawn. Actually, let's go to an aquatic setting. Let's have a look. Fish yawn. This is a vertebrate thing. That's how ancient it is. And it's been passed down to all of us from all the way back there. It's really, really, really old. And I still don't know why. And I don't know about that. Fish's brain.

[Dr. Norman Swan]

Brain overheating, cooling.

[Norman Swan]

Does that mean that we yawn less in cold weather than in hot weather?

[Mandy]

Very good question.

[Norman Swan]

I don't know. Science. This doesn't feel right to me.

[Dr. Norman Swan]

No. So, okay, and animals seem to. When they look at animal behavior and they look at. When they yawn, they tend to yawn more when they're tense. You know, you don't want to be anthropomorphic about it. So when they're in a tense situation, when aggression is being expressed, there's yawning in one or other animal.

[Norman Swan]

Okay, so why is it contagious then? So if we don't even know what causes it, why is there such a strong relationship between seeing someone else yawn and needing to yawn? I have been holding back yawns ever since we started talking about this.

[Dr. Norman Swan]

So this is a fascinating area. And what it may be a symptom of is that we tend to mirror other people. We are a social species. And part of this is called the theory of mind. Now, theory of mind is about. It's about social cognition and it's about us recognizing ourselves as self and others as other. And there's a process in the brain called the default mode network, which goes up and down.

[Norman Swan]

So I've got my Mediterranean diet bell, as you know. I've got my pleiotropy xylophone that I never use anymore. I've got my fine particulate air pollution harmonica that again, I don't use anymore because you stop talking about it now. I feel like I need a default mode network.

[Dr. Norman Swan]

That thing, something like.

[Norman Swan]

That's your favourite thing at the moment.

[Narrator]

You're talking constantly.

[Norman Swan]

But for a recap for people who don't know what it is.

[Dr. Norman Swan]

So this is the part of the brain that becomes active when you think your brain's resting. So your brain never rests. So parts of your brain go quiet. Other parts of your brain become active and they start talking to each other and looks as though. Thank you for your yawn. There are parts of your brain where, when you're looking at somebody or an animal is looking at another animal. There are parts of your brain where the neurons in that part of your brain light up. And they particularly light up when this default mode network is active. And it's part of this empathy and connection and community that I want to be like you, or I want to imitate you, or I want to learn from you. So learning from other people happens in these particular areas of the brain, and they're called mirror neurons, where we look and we act accordingly. And it looks as though yawning. The contagion of yawning, is those neurons in our brains where we learn how to be social beings, we learn how to respond to others, we recognize other as other, and we want to be empathic. Those are fired up with yawning, and we imitate it.

[Norman Swan]

It's funny. So I said, like so many species yawn. We saw it in fish, we saw it in all sorts of different creatures. Contagious yawning doesn't seem to be as common as spontaneous yawning. So more social species have been observed catching yawns, like chimpanzees, baboons, and dogs, but not necessarily a fish. So there's something about the socialness of a species that seems to come into play here. Yeah, it's actually really funny. So there's this guy who's done all of the yawning research. I like to call him professor yawn. His name is actually Andrew Gallop. He's an evolutionary biologist at State University of New York Polytechnic Institute. And he says that when he first. Because he's been studying this for years and years. And when he first started studying yawning, he was yawning all the time. So he's like, I was reading literature and writing notes and writing papers and found I was yawning all the time. But over time, I became habituated to the effects. I still yawn contagiously during social interactions, but seeing the stimuli that I use in the lab no longer produces the effect. So you can get, like, yawning tolerance,

[Dr. Norman Swan]

I guess, or yawning boredom.

[Norman Swan]

Yawning boredom. So to summarise for Claire, why is a yawn contagious?

[Dr. Norman Swan]

Because we're mirroring other people and we want to copy you. We want to learn from you. It's part of you being a social being.

[Norman Swan]

Well, big yawn and stretch to celebrate that one. Oh, come on, everyone. You can do it. All right, well, how many yawns did we get across the room? Can you. Chuck? How do we do this? If you yawned once during the discussion. Once or more during the discussion. Chuck your hand up. My God, that's like two thirds of the room easily. If you yawned more than twice, keep your hand up. Someone put their hand.

[Dr. Norman Swan]

Almost a thin number.

[Norman Swan]

Anyone who yawned once or more. So we've got a greater than one yawn. Yes. All right. Put your hand down. If you only yawned once. Put your hand down. If you only yawned twice. Three times, people still got their hands in the air four times. Okay, like. All right, we're kind of tapering off now. We've got a nice little bell curve happening. Five times, six times. Who's asleep? I saw

[Dr. Norman Swan]

nine.

[Norman Swan]

Nine yawns. Who can do better than nine? How many yawns? Stop it. Twelve. Oh, my gosh. Twelve.

[Dr. Norman Swan]

God, we got some social beings in this room.

[Norman Swan]

I'm sorry. I guess it feels like an indictment on us, Norman. Did anyone yawn zero times? Well, cooled brains in the house.

[Mandy]

That's right.

[Dr. Norman Swan]

We weren't hot enough.

[Norman Swan]

Well, as promised, it's mailbag time. Now, normally people would go to all the trouble of sending us an email asking their questions. Shelby would copy it over for us and we'd answer it. It's much, much easier today. All you have to do is stick your hand in the air. Someone will come around to you with a microphone. We would love to answer your questions live this morning. And when I say we, I mean Norman. We'd love to answer your questions this afternoon. Please put your hand in the air if you have a question you would like Norman to answer.

[Dr. Norman Swan]

Sorry, I don't know.

[Norman Swan]

All right, here's the microphone, Norman.

[Audience Member 1]

I read a study about grip strength and dementia, and I think it's. Those that have poor grip strength can have increased incidence of dementia, and I became interested in that study. And one of you knew of that study or anything? We've got a friend who's. She's Greek, she's 88. Her grip strength is amazing and she's bloody sharp as. And. Yeah. Anyway, there's a life study right there.

[Dr. Norman Swan]

Yes. It's not just one study, it's multiple studies showing. And so people use grip strength. They use it now, actually, as a proxy for measuring your risk of dementia or your risk of frailty, probably more than your risk of dementia. And it's still out for debate as to. So does that mean then you don't need to go and exercise and you just exercise your grip strength and there's no evidence that just exercising your forearm. It'd be great if you could. It changes something in your brain. It's a proxy for your general fitness and well being. Almost certainly. Now people argue about this. There are people who think, not mad people, people who research this area, they think there is something about grip strength itself, but it's just hard. It doesn't make sense really. I mean, I suppose pickle juice at the back of your throat doesn't make sense either. But it's a proxy for your general frail, for your risk of general frailty and your general physical and muscle well being that if you've got good strong muscles in your forearm, it's likely you've got good strong muscles elsewhere. And if it means that you go off and do chin ups at the gym when you're 85 years old, good on you.

[Sandy]

So we actually got an in real time follow up to that question in the audience from someone who'd had a heart attack and was told to improve

[Audience Member 2]

his grip strength about 10 years ago. One of the things that they always said was important was you had to improve your grip strength because of the heart attack and that's going to improve your heart muscle and everything like that. Are you basically saying that could be not right? In looking at from that aspect, I

[Dr. Norman Swan]

would say it'd be insufficient. Yeah.

[Audience Member 2]

Is this really interesting because it came from a cardiologist of all people?

[Dr. Norman Swan]

Yeah, I, I remember doing a session with a few hundred cardiologists in the room about cardiac rehab and what proportion of people sent people off for cardiac rehab and it was very low. It's changed, but it's very low. I mean cardiac rehab is not about grip strength. Cardiac rehab is getting on the bike. It's about changing your diet. No, I'm not going to say it. And losing a bit of weight and so on. Toning your body up. It's not about grip strength.

[Norman Swan]

We are fresh out of time. Thank you all so much for coming along. Today has been an absolute delight.

[Sandy]

So we had even more responses to our right versus left handedness episode that we just have to share. Alex says I was born Left handed in 1946 in South India. Had I grown up in the South, I probably would have remained left handed because South Indians were pretty relaxed about these things. But as my dad was in the Air force he was transferred all over the country and most of his postings during my early childhood were in North India where left handedness was frowned upon. Alex says I was often beaten at school, although by those who looked after me. As a small child I was forced to become a right handed writer. However, I do everything else with my left hand. Combing my hair, brushing my teeth, using tools. I'm also left handed at sports. I bat left Handed at cricket and I kick balls with my left foot.

[Mandy]

Isn't that interesting?

[Sandy]

So I thought that too. I thought this is really interesting. But Alex goes on to say about engineering, so this is really interesting. Alex says, I had some awful experiences while studying engineering. Have you noticed? I think this is directed at me

[Norman Swan]

as a fellow left hander.

[Sandy]

Nearly all machine tools, lathes, milling machines, drill presses, et cetera, have controls positioned for the convenience of right handers. It's quite difficult for a left handed person to safely operate most machine tools. It takes a lot of practice and effort. I nearly failed my engineering workshop practicals because I was so slow. It is interesting like so many machines are built for safety.

[Mandy]

That's right. That was exactly what I was thinking.

[Dr. Norman Swan]

You know, the inherent danger.

[Sandy]

Yeah, I'm thinking about, I'm not super into building stuff with heavy machinery, but I'm thinking about where the handles are on the.

[Norman Swan]

I'm moving my hands as I say

[Sandy]

this on, on the different machines that I used when I was doing like

[Norman Swan]

shop classes at school and stuff.

[Sandy]

And yeah, my memory is my, I'm.

[Norman Swan]

I'm holding my right hand above my head. I'm pretty sure they were right handed tools.

[Mandy]

And then Mandy has written in on this.

[Sandy]

So Mandy. So I did some etymology in our left handed, right handed chat on a previous WhatsApp rash. Anyway, Mandy is giving us a Russian vocabulary lesson and watch me mispronounce these words. Mandy says in Russian it is Pravi and Levi. Pravi is part of a big family. Pravo is a right.

[Mandy]

Pravda is truth named after your famous newspaper in the Soviet Union.

[Norman Swan]

Ah, okay.

[Sandy]

And Pravilny is correct. So these are all right. And then in Lyevy, if you do or obtain anything now on the left, it is definitely dodgy. So the bias persists.

[Mandy]

So Paul writes, it reminded our discussion, reminded him of his first day as a dental student at the university when one of the lecturers asked the left handers to present their hand and there were seven out of 50. And then he proceeded to tell them to consider picking up the dental handpiece with their right hand and resist the urge to use their left hand right from the start. Because the dental world is generally right handed. Dental chairs are designed for right handed dentists and dental assistants are trained to sit on the left side of the chair. Of the seven, only three were successful in changing to the right and four couldn't so remained left handed dentists. Interesting. A bit unfair for the lefties.

[Norman Swan]

I've never thought about that.

[Sandy]

Of course dental chairs are very. You're really forced to use one hand. And some dent surgeries, the way they're set up, you can't really access the other side of the chair even if you wanted to.

[Norman Swan]

It's a rough world out there for

[Sandy]

us, left handed Norman.

[Mandy]

It is well rough world for these patients of left handed dentists. I'm going to take a closer look next time. And next time is next week. See you then.

[Norman Swan]

See you then.