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.

I yawned when I read your comment.

Me too but I also wonder how much I'm influenced by knowing that that is supposed to happen.

I want to yawn, but I'm fighting it. Not all heros wear capes.

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 without the need to block & blow your nose, 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.

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.

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.

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.

It is detrimental though. It is socially impolite to yawn in public.

Edit: why am I being downvoted for this?

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)?

Cats certainly do.

Strangely, dogs sneeze to show deference.

Interesting you went in the opposite direction of my assumption, which was "another member is tired, perhaps we should all pack it it"

got me also

same here

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.