From Mercedes Rodriguez Escud:

Re: Why is yawning contagious? (March 5, 2005) I myself have also an interest in yawning and I have a different, possibly original idea which I would like to share with other researchers, in order to see if with the help of everyone we can enlighten such a mysterious biological function.

Yawning could be a way of getting rid of volatile substances, either from internal origin such as nitric oxide (?) or from outside origin. The jungle of chemicals that we breath all the time are supposed to be detoxyfied by healthy airways by means of fluids lining the mucosae, the antioxidant enzimes and other measures. However sometimes this function might be faulty and too many volatile chemicals might go deep into the airways and lungs.

A powerful blowing out during the yawning would discharge the airways of volatile chemicals and send them away, cleaning the organism from certain unnecessary, perhaps noxious chemical compounds.

Yawning would not be due to sleepiness, boredom and so on. While we yawn we lose for a moment the awareness of our environment, eyes fill with tears, etc. That is inconvenient for a predator or for a prey. What would happen is that the creature would wait until it was relaxed, (before sleeping, bored, etc) in order to exhale more a powerful yawn more at rest. It would be contagious because it would serve to remind animals that it is good to take a moment of time to clean their organism from unwanted volatile chemicals.

If I am correct it would be most interesting to analyze with precision what gases are exhaled by people and animals during spontaneous yawning (they does not have to be the same, biochemistry is different between species). It would be necessary to avoid obvious “psychological” yawning, those of people who just yawn as a tic.

If you find this an interesting idea I could comment it further. An email contact for answers: lo dmer @ xs 4all .com (remove spaces).