The contagious nature of yawning is so weird. It has to be evolutionarily advantageous because it's so wide spread, but it's also non-obvious.
clscott•Feb 4, 2026
A trait doesn’t have to be advantageous to persist just non-detrimental.
rtkwe•Feb 4, 2026
Yeah that's (to me) a more accurate framing, also evolution is bad at revisions so even if there are minor disadvantages to a setup so long as it's not affecting your ability to have and raise kids it's basically completely absent as far as evolution is concerned. For example there are some wild inefficiencies in body layout left over from fish body patterns where the nerve from the brain to the voice box wraps down around your aortic arch because the relative position of the throat, brain, and heart were very different in fish so the path it took then was more direct. It happens in humans and most hilariously in giraffes where it goes all the day down their enormous necks.
cyanydeez•Feb 4, 2026
If Giraffe could speak, would they then be perceptibly delayed compared to humans?
seszett•Feb 4, 2026
Well they make no sound, so that might be related. Maybe it's just really impossible because of this.
samus•Feb 4, 2026
That remains as it is because it's very difficult to evolve away from. Evolution is very good at chasing and sticking around local optima. Big changes are risky.
EA-3167•Feb 4, 2026
They can be detrimental too, especially if they're linked to beneficial traits. The test is ultimately whether or not the harm done is sufficiently disadvantageous that it interferes with reproductive fitness. Baldness is arguably detrimental, but it's linked to a bunch of recessive genes that function in other ways, and it doesn't impact us until we're likely to have already reproduced.
That's a simplification, but you get the idea.
TheGRS•Feb 4, 2026
Peacocks with their giant tail feathers are my favorite example. They make flying really difficult, but they make attracting female mates much easier. The reproduction need wins.
awesome_dude•Feb 4, 2026
And that, my friends, is why I bought a Pontiac...
AngryData•Feb 4, 2026
I don't know if I would consider it especially difficult for them. It is obviously not convenient but when I had peacocks they would still fly way up in some tall pine trees to roost even with a full tail without too much trouble. That said these were domestic peacocks so they didn't have to fly very far at all for everything they ever wanted, wild peacocks might have to go farther.
CGMthrowaway•Feb 4, 2026
It is detrimental though. It is socially impolite to yawn in public.
Edit: why am I being downvoted for this?
frisbm•Feb 4, 2026
is it so detrimental that it leads to a person never finding a mate and reproducing? Maybe for a totally extreme outlier, but probably not
CGMthrowaway•Feb 4, 2026
Is that the right criteria? A trait must be completely, 100% disqualifying as a mate or else it sticks around?
Our ancestors used to have tails. We no longer have tails. Plenty of people wear artificial tails today and get laid, it's not a 100% disqualifying trait
vizzier•Feb 4, 2026
Natural selection doesn't require 100% disqualifying, it just needs a slight preference and a shit load of time.
CGMthrowaway•Feb 4, 2026
Yes that is more along the lines I was thinking
kace91•Feb 4, 2026
>Plenty of people wear artificial tails today and get laid
…Do they? What did I miss?
samus•Feb 4, 2026
[delayed]
bc569a80a344f9c•Feb 4, 2026
Even if yawning in public affected sexual fitness: how long has it been socially impolite to yawn in public? Evolution takes a rather long time in species with long reproductive cycles. Almost all mammals yawn, it would take significant genetic changes to breed that out of us. That doesn't happen overnight.
CGMthrowaway•Feb 4, 2026
400-500 years minimum (15-20 generations), although point taken
victorbjorklund•Feb 4, 2026
I wonder if that has always been the case or if it is a modern thing (modern in the sense of our evolutionary history).
JoshTriplett•Feb 4, 2026
> It is socially impolite to yawn in public.
No, it isn't. It can be socially impolite to yawn unexcused, when someone is talking to you, as it has come to be interpreted as boredom rather than tiredness or similar. But it isn't inherently impolite to, for instance, yawn when walking down the street, or in a setting where someone isn't talking to you.
avazhi•Feb 4, 2026
> why am I being downvoted for this?
Because you don’t know what detrimental means in this context and clearly don’t understand evolutionary timescales?
frisbm•Feb 4, 2026
and not even that, I'd narrow it further to not detrimental before and during the prime reproductive periods of a species. After that period, detrimental traits are totally fair game and more dependent on technology, culture, and family care dynamics. Heart disease later in life caused by genetic predisposition to high cholesterol isn't something people generally select for or against in a partner, but its effects happen later in life well after people have children so it passes on.
toasterlovin•Feb 4, 2026
> Heart disease later in life caused by genetic predisposition to high cholesterol isn't something people generally select for or against in a partner, but its effects happen later in life well after people have children so it passes on.
That depends. It can still affect genetic fitness if it affects an individual's ability to confer benefits on their descendants. Of note: most of the most wealthy and influential people in our society are beyond their reproductive years (not technically true for men, but mostly true in practice).
samus•Feb 4, 2026
Parents must also be alive for long enough to care for their children until they can sustain themselves.
kasabali•Feb 4, 2026
just reading the title made me yawn for real.
mannycalavera42•Feb 4, 2026
same here
marcelbundle•Feb 4, 2026
got me also
nickthegreek•Feb 4, 2026
I literally yawned as I clicked on this article from my RSS reader. The contagious nature at the mere idea of a yawn is wild.
davidw•Feb 4, 2026
Me too but I also wonder how much I'm influenced by knowing that that is supposed to happen.
embedding-shape•Feb 4, 2026
I yawned as I read the title on the frontpage. Smiled a bit when I read the rest of the comments. Contagious beyond physical proximity sure is wild.
carlmr•Feb 4, 2026
I yawned when I read your comment.
InsideOutSanta•Feb 4, 2026
I want to yawn, but I'm fighting it. Not all heros wear capes.
kgwxd•Feb 4, 2026
Just about all our behaviors are contagious. Scratching, deep breath, emotion, looking in a certain direction, sudden alertness. If yawning were different, that would be weird.
nickthegreek•Feb 4, 2026
Most of those can also be done consciously though. Yawning is different. It is more inline with flatulence, crying, or vomiting. Actions that are in many ways, outside of our direct control.
kobalsky•Feb 4, 2026
I can yawn on command. Rumbling my ears and edging swallowing it triggers a yawn 100% of the time
_factor•Feb 4, 2026
I can yawn on command continuously every few seconds just by thinking about how it feels.
HPsquared•Feb 4, 2026
It's a bit like laughing. Synchronise the mood of the group. I assume other mammals have contagious yawns too?
My cat always responds when I yawn regardless of what room either of us are in.
wjb3•Feb 4, 2026
I think you're onto something here. Does anyone know if there are examples of very non-social species yawning (i.e., something that has a brief mating period with no prolonged pair bonding, and then it lays eggs and takes off)?
wjb3•Feb 4, 2026
So, I tried to track down an answer. And, apparently, there’s currently no well-replicated study showing true contagious yawning in a species that is otherwise non-social and non-bonding.
B-Con•Feb 4, 2026
Yawing seems like it must be adventurous, the contagious part not so much.
Even the mention of a yawn can trigger it.
Perhaps we are almost always in a state of needing a yawn, but the trigger is seldom met, and seeing or hearing about it is enough to make our brain go "oh yeah I forgot about that".
Perhaps yawning is actually underdeveloped and an ideal human would yawn at regular intervals without any prompting.
kakacik•Feb 4, 2026
Not so much if you think about if from security point of view of our ancestors. Those 1-2s if we talk about proper yaw you are defenseless and clueless, its actually pretty dangerous during say high speed drive on tightly packed highway (as in every single car in all lanes goes too fast to handle any major driver's mistake). But its great for equalizing pressure in ear via eustach tube, something both mountaineers/paragliders and divers are well aware of.
Same goes for sneezing, actually that's even worse for driving, I literally don't see anything for a second at least. Sometimes can be blocked, sometimes not so much.
baggy_trough•Feb 4, 2026
It is strange how well yawning is conserved, even as far back as in reptiles, since it doesn't really seem to do anything.
angst_ridden•Feb 4, 2026
contagi-yawn
Terr_•Feb 4, 2026
I assumed it was a kind of warning system: "Another member of the tribe detected impairment/fatigue and took measures to become more alert, perhaps you should raise alertness also."
rhcom2•Feb 4, 2026
Interesting you went in the opposite direction of my assumption, which was "another member is tired, perhaps we should all pack it it"
adrianmonk•Feb 4, 2026
There's probably a strong survival advantage in convincing whoever is leading a meeting that it's time to adjourn.
> “Each individual seems to have what looks like an individual yawning signature”
I’m looking forward to “yawn to unlock”.
Also, what’s the deal with that article image?
yread•Feb 4, 2026
> yawning is not simply an intensified breath but a distinct cardiorespiratory manoeuvre that reorganizes neurofluid flow
Brilliant, I'll use that next time I yawn somewhere inappropriately.
cyanydeez•Feb 4, 2026
I've just reorganized my neurofluid flow, that's how I feel about this.
rustyhancock•Feb 4, 2026
Yawning is so baffling, I woke in the night to yawn yesterday. I was turning over in bed and suddenly found myself yawning enough to perk my sleepy awareness.
Distinctly remember being outraged.
Makes more sense I suppose if yawning isn't just signalling sleepiness to do it even while asleep!
tetris11•Feb 4, 2026
> If an animal is drowsy or bored, it will be less alert than when fully awake and less prepared to spring into action. "Contagious" yawning could be an instinctual signal between group members to stay alert.
> Anecdotal evidence suggests that yawning helps increase a person's alertness.
> Paratroopers have been noted to yawn during the moments before
they exit their aircraft.
Reminds me of a recent finding that attention lapses in a sleep-deprived brain correlate with flushing of cerebrospinal fluid (almost a garbage collection pause).
There was an article posted recently about a new discovery around CSF flows during sleep too. It sounds like yawning causes similar flows, which could maybe explain why you yawn more when tired? It could be a compensation mechanism to provide a bit of the same effect you normally get when sleeping.
You know how yawning is also a social function, and seeing someone yawn makes you yawn?
I just got forced into a good neurofluid flow reorganization session just by reading the title.
ljsprague•Feb 4, 2026
Why do I yawn more when I'm cold?
whalesalad•Feb 4, 2026
cold = contracted vessels etc = less fluid movement = yawn required.
happens to me a lot when i am on shrooms too
ncr100•Feb 4, 2026
"To tire, perchance to yawn."
zb3•Feb 4, 2026
I did not read the article. But my question is - does it mean yawning (like trying to yawn on purpose which in my case will make me "really" yawn soon) influences those fluids inside my brain?
14 Comments
That's a simplification, but you get the idea.
Edit: why am I being downvoted for this?
Our ancestors used to have tails. We no longer have tails. Plenty of people wear artificial tails today and get laid, it's not a 100% disqualifying trait
…Do they? What did I miss?
No, it isn't. It can be socially impolite to yawn unexcused, when someone is talking to you, as it has come to be interpreted as boredom rather than tiredness or similar. But it isn't inherently impolite to, for instance, yawn when walking down the street, or in a setting where someone isn't talking to you.
Because you don’t know what detrimental means in this context and clearly don’t understand evolutionary timescales?
That depends. It can still affect genetic fitness if it affects an individual's ability to confer benefits on their descendants. Of note: most of the most wealthy and influential people in our society are beyond their reproductive years (not technically true for men, but mostly true in practice).
Strangely, dogs sneeze to show deference.
Even the mention of a yawn can trigger it.
Perhaps we are almost always in a state of needing a yawn, but the trigger is seldom met, and seeing or hearing about it is enough to make our brain go "oh yeah I forgot about that".
Perhaps yawning is actually underdeveloped and an ideal human would yawn at regular intervals without any prompting.
Same goes for sneezing, actually that's even worse for driving, I literally don't see anything for a second at least. Sometimes can be blocked, sometimes not so much.
Is that the paper in question?
I’m looking forward to “yawn to unlock”.
Also, what’s the deal with that article image?
Brilliant, I'll use that next time I yawn somewhere inappropriately.
Distinctly remember being outraged.
Makes more sense I suppose if yawning isn't just signalling sleepiness to do it even while asleep!
> Anecdotal evidence suggests that yawning helps increase a person's alertness.
> Paratroopers have been noted to yawn during the moments before they exit their aircraft.
https://en.wikipedia.org/wiki/Yawn
https://news.ycombinator.com/item?id=45771636
https://news.ycombinator.com/item?id=45771636
happens to me a lot when i am on shrooms too
Or - a change in those fluids makes me yawn?