Jenny Dobson, of Dunedin, asks :-
Why, when one person starts yawning, does everyone else around them appear to do the same?
Rodger Pack, a physiologist at Massey University's Institute of Food, Nutrition and Human Health, responded.
This is a very interesting question and one I have been asked a number of times over the years. Let us establish what it is not. Unlike the sigh, which we all do more frequently than we realise (normally about every two minutes), and the cough, which occurs when our airways are irritated, it does not alter our breathing or the way in which our respiratory system is working.
Yawning is a brainstem reflex that is not under conscious control. However, it results from changes in our conscious mind. These include various emotions, such as stress or boredom, but particularly tiredness. Although we occasionally yawn when we are on our own, we most frequently yawn in company. This gives us a clue as to its role. It is very important in our body language. Yawning in company roughly translates as "I am tired and I want to be left alone". To yawn back, which is also a sub-conscious reflex, translates as "me too - I will not disturb you". It follows that the answer to your question is that when someone yawns at you in company and you do not feel the need to disturb them, you will sub-consciously yawn back (both actions are body language).
Yawning seems to occur in all mammalian species. It is sometimes used for communication between species. If you disturb a dog or cat that is snoozing it will frequently lift its head and yawn at you. If you simulate a yawn back you can, sometimes, get it to put its head down and go back to sleep.
There is a little experiment you can do. When with a group that might be tired simulate a yawn. Most people responding will yawn back. However, some may get up to do something other than relax.