I just yawned after reading all these posts about yawning!!!
I wonder if it’s an evolutionary/survival thing. Maybe one person back in the day yawned to get some extra oxygen to the brain, due to poor air quality or something. Those around him/her subconsciously picked up on the message and yawned as well to get their brains some extra oxygen, thus ensuring their continued survival with healthy brains. Now we don’t have the poor air quality threatening our survival, but we have the residual reactionary yawning. Kind of like how we evolved to have allergies to pollen (runny noses, watery eyes) because those allergens could threaten our systems once upon a time, so we evolved allergic reactions to flush out the allergen. Now pollens and such are not a threat anymore, but we still have the reaction. Or so it’s been explained to me when I am going through a box of Kleenex an hour and crying, “Why, why, WHY?”