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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.
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.
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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
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
> 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.
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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.
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.
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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…
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.
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A trait doesn’t have to be advantageous to persist just non-detrimental.
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…
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A trait doesn’t have to be advantageous to persist just non-detrimental.
It is detrimental though. It is socially impolite to yawn in public. Edit: why am I being downvoted for this?
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.
https://www.biorxiv.org/content/10.64898/2025.12.17.695005v1 Is that the paper in question?